Energy expenditure, aerodynamics and medical problems in cycling. An update.

REVIEW ARTICLE

Sports Medicine 14 (I): 43-63, 1992 0112-1642/92/0007-0043/$10.50/0 © Adis International Limited. All rights reserved. SPOl146

Energy Expenditure, Aerodynamics and Medical Problems in Cycling

An Update

Irvin E. Faria Human Performance Laboratory, Department of Health and Physical Education, California State University, Sacramento, California, USA

Contents 43 44 45 46 47 48 48 49 5J 5J

53 55 55 58 58 59 59 60

Summary

Summary I. Energy Expenditure 2. Oxygen Cost and Economy During Cycling 3. Indices of Cycling Performance 3.1 Power Output 3.2 Measurement of Technique 3.3 Muscle Fibre Type and Recruitment 3.4 Shoes and Pedal Design 3.5 Crank Length 3.6 Pedalling Rate 3.7 Muscle Involvement 3.8 Saddle Height 4. Aerodynamics of Cycling 5. Medical Problems 5.1 Overtraining 5.2 Overuse Injuries 5.3 Shoes 6. Conclusions and Directions for the Future

The cyclist's ability to maintain an extremely high rate of energy expenditure for long durations at a high economy of effort is dependent upon such factors as the individual's anaerobic threshold, muscle fibre type, muscle myoglobin concentration, muscle capillary density and certain anthropometric dimensions. Although laboratory tests have had some success predicting cycling potential, their validity has yet to be established for trained cyclists. Even in analysing the forces producing propulsive torque, cycling effectiveness cannot be based solely on the orientation of applied forces. Innovations of shoe and pedal design continue to have a positive influence on the biomechanics of pedalling. Although muscle involvement during a complete pedal revolutio~ may be similar, economical pedalling rate appears to differ significantly between the novice and racing cyclist. This difference emanates, perhaps, from long term adaptation. Air resistance is by far the greatest retarding force affectingcycling. The aerodynamics of the

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Sports Medicine 14 (1) 1992

rider and the bicycle and its components are major contributors to cycling economy. Correct body posture and spacing between riders can significantly enhance speed and efficiency. Acute and chronic responses to cycling and training are complex. To protect the safety and health of the cyclist there must be close monitoring and cooperation between the cyclist, coach, exercise scientist and physician.

The physiological and biomechanical parameters of the sport of bicycling have intrigued researchers for nearly 9 decades. The advent of new materials for the construction of lighter, more durable and streamlined bicycles and components and modern technology have enhanced cycling performance. To optimise cycling performance requires bridging the gap between .the engineer, exercise physiologist and biomechanist. In addition, the human power component must be coupled with an aerodynamically efficient bicycle. The bicycle ergometer has been the most utilised modality in the investigation of physiological and biomechanical parameters in cycling. Reasons for its use include the ease of adaptation to various body size, the cycling experience of subjects and its ease of calibration (Ericson et al. 1985). Modifying the bicycle ergometer, e.g. with drop handlebars and racing pedals, more closely replicates road racing in the laboratory (Cast & Welch 1985; Faria et al. 1978). Other researchers (Bolourchi & Hull 1985; Davis & Hull 1981; Hull & Jorge 1985; Redfield & Hull 1986) have used bicycle rollers during testing procedures. Wind trainers, calibrated for research conditions, have been explored as testing instruments (Firth 1981). In order to replicate road racing cycling conditions in the laboratory, subjects have ridden their own racing bicycles on a treadmill (Despires 1974; Faria et al. 1982). Wind tunnel and coast-down testing methods are other effective modes of testing (Kyle 1979). Cycling efficiency, power output and joint moments have been measured using dynamometer pedal force systems and potentiometer crank and pedal position indicators. This review examines the study of cycling as approached from perspectives of biochemistry, electromyography, cinematography and computer graphics, ergometry, biomechanical application and

aerodynamic analysis. The unique approach of each research tool will become evident. The physiological and anatomical determinants of cycling are briefly examined. Aerodynamics of cycling is considered with particular reference to the rider, equipment and bicycle. Finally, the impact of cycling on acute and chronic medical problems is reviewed.

1. Energy Expenditure Energy can be defined as mechanical work; a force moving through a distance. When energy is expended by the human body in performing work, fuel (food) reacts with oxygen to produce mechanical energy and heat. During exercise energy expenditure is measured by oxygen use or uptake; approximately 5 kcal of energy are generated per litre of oxygen consumed. A metabolic equivalent T (MET) which is equal to 3.5ml of oxygen consumed per kilogram of bodyweight per minute (ml/kg/rnin) serves as a convenient expression of energy expenditure. For example: assume a 150lb (68kg) cyclist works at 82% of his/her maximal oxygen uptake of 80 ml/ kg/min for 4 hours. The oxygen uptake would be: 80 nil/kg/min x 0.82 (= 65.6 nil/kg/min) x 68kg = 4.5 Lzmin. Energy expenditure would be: 4.5 L/ min x 5 kcal/L = 22.5 kcal/min, The total energy expenditure becomes: 22.5 kcal/min x 240 minutes = 5400 kcal or 1350 kcal/h, An equivalent MET cost is: 65.6 nil/kg/min + 3.5 nil/kg/min = 18.7 MET. The cyclist's ability to maintain an extremely high rate of energy expenditure for 2 hours or more is impressive (Faria 1978). In order to cycle at speeds common to road racing, the endurance cyclist must increase the rate of muscular energy production to approximately 20 times that of rest. The

Aerodynamics and Medical Problems in Cycling

elite racing cyclist uses 30.7 kcal/min at 25 mph (40 km/h) at an energy use efficiency of approximately 19 to 29% (Asmussen 1953; Asmussen & Bonde-Petersen 1974; Banister & Jackson 1967; Dickinson 1929; Faria et al. 1982;Gaesser & Brooks 1975; Garry & Wishart 1931; Hagberg et a1. 1974; Jordan & Merrill 1974; Seabury et a1. 1976).

2. Oxygen Cost and Economy During Cycling Maximal oxygen uptake ('V02max) is defined as the maximum amount of oxygen an individual can use during physical work while breathing air at sea level. Oxygen uptake during cycling consists of 3 components: (a) that necessary to maintain the body in position on the bicycle and the physiological maintenance work; (b) that required to move the legs at zero load through the prescribed pattern of movement; and (c) that necessary to overcome the resistive load. Data for elite cyclists suggest that moderately high oxygen uptake capacities are required for successful competition at the national and international levels. Table I summarises the oxygen uptake values of several national cycling teams. These data lend support to the contention that V02max is an important determinant of endurance performance. However, regardless of the cyclist's V02max, the lower the submaximal oxygen uptake for a given workload the better. Individuals vary considerably in the amount of energy expended to perform the same submaximal task, such as cycling at a particular speed. The question is whether the differences in energy cost are due to differences in cycling efficiency. For example, a cyclist with a high V02max at a given speed may very well be performing more mechanical work than one with a lower oxygen cost, but both may be operating at precisely the same muscular efficiency. Endurance cycling performance is highly related to energy cost. The submaximal oxygen uptake per unit bodyweight (V02submax) required to perform a given task (i.e. cycling a certain speed) is important for success. It may be thought of as the economy of

45

Table I. Comparison of anaerobic power among elite athletes (from Faria et al. 1989) Team

Oxygen uptake (ml/kg/ min)

Cyclists GB Olympic team (White et al. 1982) E. German national team (Israel & Weber 1972) Plymouth-Reebok (Faria et al. 1989) Indian team (Malhotra et al. 1984) US national team (Burke et al. 1982) Norwegian team (Hermansen 1973) French team (Joussellin et al. 1984) Australian national team (Hahn et al. 1986) US class I, II (Lopatequi et al. 1986) US elite (Strernrne et al. 1977) Swedish national team (stremme et al. 1977) Swedish team (Burke 1982) Danish team (Faria et al. 1968) Elite Dutch national team (Bonjer, 1979)

77.4 75.5 75.5 75.1 74.0 73.0 71.1 70.0 69.6 69.1 69.1 69.0 68.0 67.6

Runners US middle-long distance (Pollock 1977) US marathon (Pollock 1977)

78.8 74.1

Rowers US elite (Strernrne et al. 1977) French team (Joussellin et al. 1984)

65.7 64.7

Cross-country skiers US elite (stremme et al. 1977)

72.8

Track (10 OOOm) French team (Joussellin et al. 1984)

81.3

Track (3000-5000m) French team (Joussellin et al. 1984)

75.9

Track (800-1500m) French team (Joussellin et al. 1984)

71.8

Modern pentathalon French team (Joussellin et al. 1984)

73.0

Elite triathletes American (O'Toole et al. 1987)

76.0

the effort or as the physiological criterion for the efficient cycling performance. Successful performance in endurance events is highly related to the energy cost (Conley & Krahensbuhl 1980) and is independent of the work done. Because of its practical significance and because of the difficulty in obtaining accurate esti-

46

Sports Medicine 14 (J) 1992

mates of work done, Cavanagh and Kram (1985) prefer the term 'economy' rather than 'muscle efficiency'. Economy is defined as the submaximal oxygen uptake per unit of bodyweight (VOzsubmax) required to perform a given task. Economy, then, is the physiological criterion for 'efficient' performance. From both a technical and practical point of view 'economy' (VOZsubmax for a given task) offers a conceptually clear and useful measure for the evaluation of cycling performance. Two factors influence cycling economy: (a) the cyclist's maximal capacity to consume oxygen as reflected by VOZmax; and (b) the maximal level for steady rate cycling as indicated by the cycling intensity at the anaerobic threshold. However, VOz max is not an independent determinant of endurance cycling success (Bradley et al. 1986; Pollock et al. 1980; Sjodin & Svedenhag 1985). Fractional utilisation of VOz max is an important determinant of endurance performance (Costill 1986). The anaerobic threshold, the fractional utilisation of oxygen and economy of effort are of vital importance (Wasserman et al. 1973). Van Handel et al. (1988) have reported anaerobic thresholds for men and women athletes as high as 88.6 and 88.8% VOZmax, respectively. Faria et al. (1989) reported an anaerobic threshold for young elite cyclists at 83% of V02max. Coyle et al. (1991) have shown that l-hour power output is highly related (r = 0.93) to the cyclist's VOz at the lactate threshold. The cyclist who has the highest VO Zmax plus the highest lactate/ventilatory threshold plus the greatest cycling economy plus the greatest ability to tolerate metabolic acidosis has the greatest potential for winning. The combination of hereditary endowment and training emphasis determine which of these variables will prevail in the cyclist.

3. Indices of Cycling Performance The highest average workrate that a cyclist can perform on a Monark ergometer appears to depend on 5 factors: (a) VOz at blood lactate threshold (L/ min), rZ = 0.86; (b) percentage of slow twitch oxidative muscle fibres, r Z = 0.91; (c) calfcircumference, rZ = 0.92; (d) mid-thigh circumference, r 2 =

0.95; and (e) muscle myoglobin concentration, rZ = 0.97 (Coyle et al. 1991). As a corollary to the latter, Coyle et al. (1991) found 5 factors which best predict time-trial performance to include: (a) average absolute work rate for l-hour performance, rZ = 0.78; (b) muscle capillary density (capillaries per mm-) r 2 = 0.94; (c) muscle phosphofructose kinase activity, rZ = 0.97; (d) lean bodyweight, rZ = 0.98; and (e) VOz max at lactate threshold (L/ min), rZ = 0.99. The average absolute workrate maintained during a l-hour laboratory cycling test using a Monark ergometer may be used to predict (r = 0.88) a 40km time-trial performance (Coyle et al. 1991). Timetrial performance demonstrated a high correlation to the average VOz (Lzmin) maintained during a l-hour laboratory cycling ergometer test. The important implication is that the power required to cycle at racing velocities is not proportional to bodyweight (Marion & Leger 1988; Swain et al. 1987;Coyle et al. 1991). Although elite cyclists have been found capable of generating more power output during a l-hour performance test than less experienced cyclists, the effectiveness of force application to the pedal was not found to predict performance (Coyle et al. 1991). Elite national-class cyclists are capable of cycling at 90 ± 1% VOZmax for I hour (Coyle et al. 1990). The authors found the factors which distinguish the elite class from the 'good cyclist' include: (a) %VOZ max at lactate threshold; and (b) higher absolute VOz (Lzmin) at lactate threshold. The lactate threshold may, therefore, be an effective means for predicting performance. Muscle fibre type and specific enzyme presence contribute to the lactate threshold. The high muscle capillary density possibly contributes to augmented lactate removal from the muscle. The reliability and validity of heart rate monitors has improved. Knowing the heart rate will allow the prediction, with reasonable accuracy, of the oxygen cost of a cycling effort. Heart rate and oxygen consumption tend to be linearly related throughout a large portion of the aerobic range. Therefore, the exercise heart rate can be used to estimate oxygen consumption during cycling on the


road when oxygen consumption cannot practically be measured. This estimate is determined using a cycle ergometer graded exercise test while oxygen uptake is measured and heart rate is recorded to derive the heart rate-oxygen consumption relationship, which may then be applied to the cycling heart rate. Although the technique offers ease of use, its validity has yet to be established for trained cyclists. If only an estimation of the cyclist's aerobic power is required a cycle ergometer may be employed. When gas analysis is not possible the following formula is used to estimate the oxygen uptake (American College of Sports Medicine 1991): ml/rnin =

(kg.m min

x~) + kg- min

(3.5 ml/kg/rnin x kg bodyweight)

3.1 Power Output Maximal human power output may be measured using several methods of ergometry (Gross et al. 1983; Kyle & Edelman 1974). These methods include standard and modified bicycle ergometers, treadmill and stair climbing. The modified bicycle ergometer provides a reliable method of predicting rider performance when combined with data from coast-down tests. Average time-trial speed may be predicted with a ± 2.3% average error. The term 'force effectiveness' is often used in cycling to quantify the relationship between the force 'applied' (Fr) by the rider and the force 'used' (Fe) in propulsion (force applied perpendicular to the crank). Force effectiveness is expressed by: Fe/Fr. Direct measurement of these quantities using a force-measuring pedal has shown that the index of effectiveness during the propulsive phase of cycling in elite riders is only 76% (Lafortune & Cavanagh 1983). This fact suggests that 24% of the applied force, during cycling, is used to deform the cranks and other parts of the bicycle. Thus, the conven-

47

tional method of applying force to the bicycle transmission is an inefficient process. However, increased force effectiveness has not been found to account for higher power output. High power output is attributed to higher peak vertical forces and torque during the cycling downstroke (Coyle et al. 1991). For a single thrust of one leg and pull with the other for 0.1 second, the power output has been measured at 3095W (Kyle & Caiozzo 1986). This effort occurs during less than one-half rotation of the crank. The standard cycling position has been found to be clearly superior to prone and supine positions for power development. When arm and leg cycling are combined the power output may be increased by 17%. The most efficient mode is bilateral arm movement or arms moving opposite to legs as in walking (Kyle & Caiozzo 1986). Using only legs for 30 seconds and leg and arms combined for 30 seconds was found to be even more effective. The authors point out, however, this mode may not be best if the subject were arm trained. A tandem receiving an input of slightly more than I horsepower from each rider can attain a speed of about 62 mph (100 krn/h). For a lone cyclist on a standard bicycle that speed would require more than 6 horsepower, which is clearly impossible from a human rider. The question raised is how may a lone rider produce maximum power output? Cycle power output is often determined by measuring forces exerted on the bicycle pedal and crank. The power output appears to be positively related to lean body mass {Coyle et al. 1991). Elite cyclists have been shown to generate more power than 'good-class' cyclists by producing higher peak vertical forces and crank torque during the downstroke (Coyle et al. 1991). This greater magnitude of vertical force results in more work per revolution; at equal cadence this means a larger power output.vlt might be concluded that effective vertical force is essential for superior performance, but Coyle et al. (1991) demonstrated that this is not necessarily the case. The authors observed that the proportion of the resultant force applied to the pedal is not necessarily correlated to propulsive

48


torque. Clearly, a measure of cycling effectiveness cannot be based solely on the orientation of applied pedal forces. Previous studies have concluded that cyclists do not pull up on the pedal during the upstroke, except Coyle et al. (1991) who found that cyclists reduce the negative torque during the upstroke by pulling up on the pedal. However, at high power outputs, increased peak torque during the downstroke is more responsible for increased power output than is reduced negative torque during the upstroke. Pursuit cyclists have registered power outputs ranging from 331 to 449W with cadences between 103 and 126 revs/min (Buke et al. 1990). Competitive cyclists can maintain a power output of more than 300W for 1 hour. Eddy Merckx has registered the highest power output of 440W for 1 hour. Greg LeMond's 1989 unforgettable Versailles-Paris time-trial defeat of Laurent Fignon was accomplished using a 55 X 12 gear ratio [a gear of almost 120 inches (300cm)] for 26:57 minutes [an astounding average speed of 54.545 km/h (33.89 mph)]. 3.2 Measurement of Technique Poor cycling performance may be a matter of cycling technique including ineffective muscle fibre recruitment. Another determinant may be the lactate threshold. Coyle et al. (1983) found that cyclists whose blood lactate threshold was markedly lower when cycling than when running uphill on a treadmill were characterised by less than 3 years' cycling experience. Years of training and racing possibly have an influence on the percentage ofslow twitch oxidative fibres in the vastus lateralis and other major cycling muscles. Long term chronic overloading of these muscles possibly increases the number of slow twitch oxidative fibres (Pette et al. 1973). Tesch and Karlsson (1985) observed that endurance athletes possess higher percentage of slow twitch oxidative fibres in their trained muscle, but a normal percentage of slow twitch oxidative fibres in their untrained muscles.

3.3 Muscle Fibre Type and Recruitment Both genetic and training factors influence muscle fibre type. Human skeletal muscles differ widely in their speed of contraction, fatiguability, and response to different rates of stimulation. Three distinct fibre types have been identified. Slow twitch oxidative (SO) fibres possess a greater quantity of mitochondria and contain correspondingly greater amounts of Krebs cycle and electron transport system enzymes than other types. When oxygen is provided, these fibres can produce large amounts of ATP. These fibres have a greater ability for fatty acid and ketone body utilisation than do less oxidative fibres. In contrast, fast twitch glycolytic (FG) fibres possess high levels of myofibrillar ATPase and have a lesser oxidative potential, but exhibit a greater anaerobic capacity to produce ATP than the slow twitch fibres. These fibres rely heavily on carbohydrates in the form of glycogen as a substrate. Fast twitch oxidative-glycolytic (FOG) fibres are considered to be intermediate in character, in that their fast contraction ability is combined with a moderately well developed potential for both aerobic and anaerobic energy transfer. Muscle fibre type is initially established by its nerve innervation, but foreign reinnervation, i.e. a fast muscle with a nerve normally supplying a slow muscle or vice versa, leads to a transformation of the muscle phenotype. Fast to slow transitions can also be brought about by increased contractile activity such as endurance cycling (Jansson 1978). Chronic endurance training leads to a transformation of the muscle's structural, functional and molecular properties. Cycling speed or intensity is related to the recruitment of different categories of muscle fibre types. Elite road race cyclists exhibit higher percentages of FOG and FG fibres (Sjegaard et al. 1985). Sjegaard (1984) found some elite road cyclists' leg muscles to be composed of more than 70% SO fibres. Burke et al. (1977) found no significant differences in proportions muscle fibre types between elite competitive and nonelite cyclists. Leg muscles of world-class sprint cyclists, however, may show a predominance of FOG and FG fibres (Burke

49


et al. 1977;Segaard et al. 1985). The extent to which such dominance is due to training or natural endowment remains unanswered. Likewise, while a high percentage of one fibre type may suggest potential for a specific mode of cycling, fibre type dominance has not been shown to be a determinant of success At 60 revs/min the peak tension per pedal thrust has to be developed in less than 300 msec, a time too short for slow twitch fibres to develop sufficient tension. Therefore, fast twitch fibres with their shorter contraction times are recruited with pedalling speeds over 60 revs/min. Successful distance (road) cyclists exhibit relatively more SO muscle fibres than FOG and FG fibres (Burke et al. 1977; Segaard 1984). The leg muscles of some elite road cyclists are more than 70% SO fibres (Sjogaard 1984). The vastus lateralis of elite road racers is composed of a high percentage of slow twitch oxidative muscle fibres (Coyle et al. 1991). These attributes include a higher percentage of slow twitch oxidative fibres and higher muscle capillary density (Coyle et al. 1991). Additionally, they displaya propensity for higher citrate synthase activity and lower lactate dehydrogenase activity. Worldclass sprint cyclists, in contrast, have leg muscles composed predominantly of FOG and FG fibres (Burke et al. 1977; Sjegaard et al. 1985). 3.4 Shoes and Pedal Design The design of cycling shoes is a direct consequence of the nature of forces applied by the cyclists to the pedal-crank system of the bicycle. Effective pedalling requires that the rider apply forces to the pedals that are transferred via crank, front chain rings and chain to the rear sprocket and wheel. The objective is to overcome friction and air resistance. Pedalling is a circular motion with a repetitive pattern of force application. Force application is not constant throughout the stroke cycle. Figure 1 illustrates the changes in force application during 1 rotation of the pedal-crank pedalling at 100 revs/min at a power output of about 200W (Sanderson 1990). The pedal forces vary

Direction of rotation

TDC

,J Fig.1. The pattern offorce application throughout the pedal rotation beginning at top dead centre (TDC). Pedal position is illustrated at 18°.

continuously both in magnitude and orientation throughout the pedal-crank rotation. Crank rotation is dependent upon forces applied perpendicular to the crank, the 'effective component' (Lafortune & Cavanagh 1983). The torque is the product of the effective force and the crank arm length. At the bottom of the stroke the total force is quite large, but it is applied almost parallel to the crank arm, representing wasted force. However, at 90· after top dead centre (TDC) the force is applied approximately perpendicular to the crank. At this point the effective component is much larger. When the force is not perpendicular to the crank, it is wasted. The objective, then, is to make it possible to apply forces which would always result in a positive, effective component. Pedal-crank motion throughout the second 180· of rotation often results in force applied opposite to the desired direction. During this 'recovery phase' the goal is to introduce as much positive effective force as possible, i.e. to retain the propulsive phase as long as possible. To do so requires that shoe and pedal design as well as cycling technique be given special attention. Not only must shoe ensure comfort and safety but its interface be-


50

tween the cyclist's foot and bicycle pedal must provide effective transmission of force. Negative peak torque has been described by Bolourchi and Hull (1985) as the foot being lifted during the recovery phase by the opposite pedal. Evidence suggests that cyclists do not significantly pull up on the pedal during the upstroke (Coyle et al. 1991). The larger peak torque often observed during high power output may be attributable to recruitment of relatively larger quantity of muscle per crank revolution. Davis and Hull (1981) reported that for cleated cyclingshoes with hard soles negative torque was produced past 200 in the revolution, which resulted in an arc of 5SO of negative torque. Cooper (1990) found that negative torque lies within the range of 241 to 295 in the recovery phase of pedalling. When comparing torque curves for the 'Look' pedal system and the conventional pedal system there was virtually no difference. The competitive cyclist's shoe contains a midsole made of plastic designed to facilitate the application of force to the pedal while distributing the force over a large area of the foot. To date, there has been little published research in the area of pressure distribution in cycling shoes. Sanderson and Cavanagh (1987) using a specially designed insole with 256 discrete force measuring elements and computer acquisition software, measured the variations in the pressure distribution throughout the pedal cycle (fig. 2). It was observed that the major pressures were recorded in the forefoot where major contact is made with the pedal. The first metatarsal head region and the hallux were primary load-bearing areas (fig. 2). A significant finding was that peak pressures in the forefoot region were higher for the cycling shoe than for the running shoe. The distribution of pressure in the forefoot regions was more even in the running shoe than in the cycling shoe. Apparently, the midsole of the running shoe was deforming and distributing the pressure over a broader area. Effective loading of the pedal was not altered by the running shoe. The running shoe simply changed the distribution among the regions. These data indicate that, during steady speed cycling, the most important interaction of the pedal 0

0

~~~~~~~!11J~M~ean peak pressure

Fig. 2. A 3-dimensional representation of the distribution of the peak pressures over the plantar surface of the foot during normal cycling. Height is proportional to the pressure applied (from Sanderson 1990).

with the foot occurs at the first metatarsal head, the lesser metatarsal heads and the hallux. The traditional hard-sole cycling shoe does not appear to result in a dramatic increase in the distribution of foot to pedal pressure. Recently developed clip-on pedal systems are designed to be more comfortable and more effective in terms of force transmission. Positive peak torque has been found to occur within the range of 90 to 110 of the power phase of pedalling (Bolourchi & Hull 1985). A study comparing torque produced at 2 workloads during submaximal cycling, at 90 revs/min, using 'clip-in' pedals (Look) and conventional toe clips and cleats revealed neither pedal system to produce more torque on the crank arm than the other (Cooper 1990). A posterior instead of an anterior foot position decreases the dorsiflexing ankle load moment and increases the gluteus medius and rectus femoris activity. At the same time, there is a decrease in soleus muscle activity but the hip and knee moments are not changed (Ericson 1986). Jorge and Hull (1986) found that muscular activity levels of the quadriceps are influenced by the type of shoes worn. Muscle activity increases with soft sole shoes as opposed to cycling shoes with cleats and toe clips. 0


3.5 Crank Length Conrad and Thomas (1983) examined crank lengths between 165 and 180mm at 2.5mm increments. At a constant work load of 79% of the cyclist's V02max there were significant differences among the 7 crank lengths in respect to oxygen cost. The authors concluded that for trained cyclists during work at approximately 80% of their aerobic power, different crank arm lengths within the range tested do not influence cycling efficiency. The findings of Carmichael et al. (1982) disagree with those of Conrad and Thomas (19833). Employing 6 crank lengths (150, 160, 170, 180, 190 and 200mm) the authors found crank length correlated significantly with aerobic power. Variations in crank arm length and cadence are found to increase the minimum cost function. Cost function increases with size because a taller cyclist requires greater kinematic joint moments than others to move the crank due to the increased mass and the moments of inertia of the larger lower limb segments increase the cost. Optimal crank arm lengths increase with increased body size, which supports Borysewics's (1985) recommendation that a taller rider requires a longer crank arm than a shorter or average cyclist. The data also indicate that as the rider's size increases and crank arm length increases, cadence decreases. The longer crank length requires low pedal forces, resulting in a decrease in static moments. However, a longer crank arm demands. more motion from leg segments. Thus, crank arm length and pedalling rate effects are inversely related. 3.6 Pedalling Rate A number of variables affect the intersegmental loads of the leg during pedalling when the power output is constant. The 4 variables include crank length, seat height, seat tube angle and longitudinal foot position on the pedal. A fifth biomechanical variable is pedalling rate (Gonzalez & Hull 1998). These variables influence the linkage kinematics and thus the intersegmental loads. Previous research has examined the effect of these variables

51

on cycling performance measures. It appears that the trained cyclist is more effective than the recreational rider at directing the pedal forces perpendicular to the crank arm, and can thereby pedal at high cadence without power or efficiency decrements. The vast amount of published research regarding pedal rate is conflicting. Disagreement stems from those factors which influence the efficiency of pedalling. Factors include crank length, body position, linear and angular displacements, velocities and accelerations of body segments and forces in joints and muscles. Cycling experience also influences the effect of various pedal speeds and efficiency. Racing cyclists tend to acquire the skill to ride at a cadence above 90 revs/min, whereas recreational or novice cyclists tend to prefer lower pedal rates (Garnevale & Gaesser 1991). At 120 revs/min the duration of a crank cycle is 500 msec; half of the crank cycle is 250 msec. The duration of twitch response of the quadriceps muscle is about 250 msec (Edwards et al. 1977). The relaxation time of the quadriceps muscle after electrical stimulation is 103 msec. When pedalling at 120 revs/min the relaxation time would represent a crank rotation of 72°. The inability of the muscle to contract and relax more rapidly could explain why the force continues further into the crank cycle than is desirable. The trained cyclist appears to have the ability to apply forces by bringing into play other muscle groups. This timing improves the direction and magnitude of the resultant force and reduces the overall muscle response time. Patterson and Person (1983) suggest that the forces applied to the pedals become less optimally directed as the pedalling rate increases. The average for the effectiveness index, the ratio of the force applied perpendicular to the crank arm to the force applied to the pedals, decreases from 0.5 to 0.35 as the pedalling rate changes from 40 to 90 revs/ min at 60% of V02max (Lafortune & Cavanagh 1980). The relationship between the velocity (speed) of muscle shortening and the tension it is able to generate is an important constraint or limiting factor

52

in the performance of rapid pedalling rates. Cyclists typically spin at about 90 revs/min when cruising at the 200W power level (Whitt & WIlson 1982). The force that a muscle can exert is inversely related to the speed of shortening. This force-velocity relationship is noteworthy when trying to apply large forces to rapidly turning bicycle pedals. Speed of limb movement has a marked effect on the gross efficiency of work output. Efficiencies of 19.6 to 28.8% have been reported in the literature (Asmussen 1953; Asmussen & Bonde-Petersen 1974; Banister & Jackson 1967; Dickinson 1929; Faria et al. 1982; Gaesser & Brooks 1975; Garry & Wishart 1931; Hagberg et al. 1974;Merrill & White 1984;Seabury et al. 1976). Faria et al. (1982) found that at high power output a decrease in efficiency was not evident when pedal rate was increased while holding power ouput constant. It was concluded that there appears to be a significant advantage in employing a high pedalling rate at high power output. Even at a pedal rate of 130 revs/ min the efficiency was rated at 22%. Gonzalez and Hull (1989), using a biornechanical model of the lower limb, applied optimisation analysis to 5 variables that influence the cost function of cycling. Pedalling rate was found to be the most sensitive, followed by the crank arm length, seat tube angle, seat height and longitudinal foot position on the pedal. The optimal crank arm length, seat height, and longitudinal foot position on the pedal were found to increase as the size of the rider increased. Optimal cadence and seat tube angle decreased as the rider's size increased. Table II presents the optimum variable values for anthropometric varitions. These data imply that a cyclist may minimise the cost function of cycling by setting the biomechanical variable values to the optimal variable values listed in the table. Optimum seat tube angie decreasesas cyclist size increases. A decreased tube angle shifts the hip axis backward relative to the crank axis. Consequently, the taller cyclist, with larger leg segments, will benefit from shifting her/his position rearward. Conversely, the shorter cyclist whose leg segments


are smaller will benefit from shifting her/his position forward. Optimum longitudinal foot position increases with cyclist size (Gonzalez & Hull, 1989). Cyclists will benefit from placing their foot further back on the pedal. The seat angle should be adjusted to the cyclist to realise minimum joint moments. These data emphasise the importance of tailoring the bicycle and components to the anthropometry of the cyclist. An important point here is that the peak force generated per pedal thrust decreases when a constant power output is performed with increasing pedal frequency (Sjegaard 1977). This finding lends support to the belief that high pedal frequencies are preferred at high power outputs. These data also support the hypothesis that a reduced strain on the mechanoreceptors is the reason for preferring high pedal frequencies when performing high power outputs. Ratings of perceived exertion are reported to be minimal around 80 revs/min for a constant power output, despite oxygen uptake, ventilation, and heart rate being lowest at 40 to 60 revs/min (Pandolf & Noble 1973; Stamford & Noble 1974). Redfield and Hull (1986) found that the optimal pedal rate was 90 to 105 revs/min at a power output level of 200W using a crank length of 0.170m. This is the range typically selected by cyclists generating such a power output. The claim has been made that a pedalling rate of 90 to 100 revs/min minimises peripheral forces and therefore pheripheral muscle fatigue compared to 40, 50 and 120 revs/min at a power output of 100W (Patterson & Moreno 1990). These findings agree with those of Hull and Gonzalez (1988) who found a cadence of 100 revs/min using a crank arm of 170mm to correspond to the cost function minimum. In addition, at increased power output, the high pedalling rates correspond to the minimum exercise cost. Boning et al. (1984) investigated pedal rates of 40, 60, 70, 80 and 100 revs/min at workloads of 50, 100 and 200W. Oxygen uptake, ventilation, heart rate, and lactate concentration were used to determine the most efficient pedal rate associated with workload. No single pedal rate was found to be the most efficient. Coast and Welch (1985) ex-


53

Table II. Optimal crank arm length, seat tube angle, seat height and foot position at given cadences and anthropometric variations Parameter

Short man

Average man

Tall man

Given cadence (revs/min) Crank arm length (rn) Seat tube angle (0) Seat height (m) Foot position (m) Moment cost function value (N2m2)

95 0.193 81.6 0.696 0.130 41481

90 0.191 78.4 0.773 0.143 48053

85 0.185 74.9 0.858 0.156 58442

Given cadence (revs/min) Crank arm length (m) Seat tube angle (0) Seat height (m) Foot position (m) Moment cost function value (N2 m2)

100 0.182 80.7 0.705 0.130 40560

95 0.178 77.6 0.784 0.143 47982

90 0.173 74.5 0.868 0.156 57176

Given cadence (revs/min) Crank arm length (m) Seat tube angle (0) Seat height (m) Foot position (rn) Moment cost function value (N2 m2)

105 0.171 80.0 0.714 0.130 39766

100 0.167 77.0 0.793 0.143 47095

95 0.161 74.0 0.876 0.156 56262

Given cadence (revs/min) Crank arm length (m) Seat tube angle (0) Seat height (m) Foot position (m) Moment cost function value (N2 m2)

110 0.161 79.3 0.722 0.130 39090

105 0.157 76.5 0.801 0.143 46405

100 0.151 73.4 0.876 0.156 55819

amined pedal rates of 40, 60, 80, 100 and 120 revs/ min at varying power outputs. However, findings for optimal pedal rate were variable due to the skill level of test subjects. In a follow-up study Coast et al. (1986) found efficiency was low at 60 or 80 revs/ min. Merrill and White (1984) tested highly trained cyclists working at a constant power output (75% V02max) at pedal rates of approximately 70, 95 and 126 revs/min. The authors found that gross and net muscular efficiency were significantly lower at the high pedal rate. Hagberg et al. (1981), studying well trained competitive cyclists, found 91 revs/ min to be most economical with a preferred range of70 to 102 revs/min. At 80% ofV02max the most economical pedalling rate was slightly below 90 revs/min (Hagberg et al. 1981) Coast et al. (1986) reported that for trained bicycle racers riding for 20 to 30 minutes at 85% of V02max the most economical pedalling rate was between 60 and 80 rpm. Patterson and Moreno (1990) suggest that pedal-

ling at 90 to 100 revs/min may minimise peripheral forces and therefore peripheral muscle fatigue, even though such a rate may result in a higher oxygen uptake. It appears that road speed is gained by experienced cyclists by high pedal rates at additional physiological cost which for some may adversely affect muscular efficiency. Pedalling at 90 to 100 revs/min may minimise peripheral muscle fatigue (Patterson & Moreno 1990). Both hip and knee joints show an average moment which is minimum near 105 revs/min for cruising cycling (Redfield & Hull 1986). 3.7 Muscle Involvement Electromyographic (EMG) studies have been used to identify the specific muscle involvement during the power and recovery phase of pedalling (Faria & Cavanagh 1978). The muscles which are

54

Fig. 3. The major muscle groups of the lower limb used in cycling. I = gluteus maxim us; 2 = hamstrings; 3 = semitendinosus; 4 = iliopsoas; 5 = vastus medialis; 6 = vastus lateralis; 7 = gastrocnemius; 8 = soleus; 9 = extensor digitorum longus; 10 = tibialis anterior.

employed in cycling include the rectus femoris, vastus lateralis and medialis, semimembranosus, biceps femoris, tibialis anterior, gluteus maximus and gastrocnemius. Figure 3 depicts the general anatomy of these muscles. The tibialis anterior (labelled 10 on fig. 3) dorsiflexes the foot. The extensor digitorum longis (labelled 9 on fig. 3) dorsiflexes the ankle. The gastrocnemius (labelled 7 on fig. 3) both plantar flexes the foot and flexes the knee, as does the soleus (labelled 8 on fig. 3). The gluteus maximus (labelled I on fig. 3) extends the hip. The iliopsoas (labelled 4 on fig. 3) like the rectus femoris, is partly responsible for the motion of the leg during the recovery phase of the pedal path.


The vastus medialis (labelled 5 on fig. 3) and lateralis (labelled 6 on fig. 3) form the quadriceps group which extends the knee. The rectus femoris (not shown), part of the quadriceps group, crosses both the hip and knee joints. Thus, it both flexes the hip and extends the knee. A section of the semitendinosus (labelled 3 on fig. 3) flexes the knee. The biceps femoris long head (labelled 2 on fig. 3), part of the hamstring group, crosses the 2 joints, and by doing so serves to extend the hip and flex the knee. The semimembranosus (not shown) also crosses 2 joints, the hip and knee, and thereby functions to both extend the hip and flex the knee. Lying in front of the knee joint is a small, flat and triangular shape bone, the patella or knee cap, which slides along in a groove at the end of the femur. The efficiency of the knee extensors is radicallyimproved by the presenceof the patella. These muscles, the I-joint vastii group and the 2-joint rectus femoris, make up the quadriceps; all of these muscles terminate in the same tendon, which may be felt just above the knee cap when tensing the quadriceps. If the patella were absent this tendon would itself ride in the groove at the end of the femur on its way to insertion in the top of the tibia. The patella increases the turning effect of the quadriceps by moving the line of action of their force further from the centre of rotation of the joint. An EMG analysis of muscle involvement during a complete rotation of the crank and pedal reveals several interesting muscle interrelationships. Muscle activity is seen to increase with increased pedal speed. However, gastrocnemius activity does not increase at higher pedal loads and a lack of a marked decrease throughout the maximum activity regions in quadriceps is seen at lower pedal loads. The onset of muscle activity for all muscles in the quadriceps group occurs well before O· or top dead centre (TOC). The rectus femoris begins its activity close to the middle of the recovery phase (200· to TOC) and terminates contraction at about 120 to 130·. Its greatest activity is observed prior to TOC, where it is greater than 50% maximum, for a brief period between 30· before TOC to 30 after. The onset of activity of the vastii appears later than that of the rectus femoris. Both vastii


muscles exhibit greatest activity between 340° and 100°. The vastii muscles are activated about 40 to 50° later than the rectus femoris. Quadriceps group activity terminates at about the same angle. The biceps femoris exhibits greatest activity between 80° and bottom dead centre (BDC), while the greatest activity for the other hamstring occurs in the region from 60 to 240°. The gluteus maximus is active from TDC to about 130°, which is within the region of the power stroke (25 to 160°). Its greatest activity (>50%) has been observed between 10 and 100°, which represents the power stroke when the hip is being extended. The biceps femoris and semimembranosus exhibit the largest region of activity, from just after TDC to the middle of the recovery phase. In the lower leg, the tibialis anterior muscle is active in the second half of the recovery phase from about 280° to just past TDe. At about 30° the gastrocnemius begins to contract and terminates at about 270°. Activity of the gastrocnemius begins a few degrees after termination of the tibialis anterior, and terminates a few degrees prior to the onset of the tibialis anterior. It is interesting to observe that the gastrocnemius, a knee flexor, is active when the quadriceps are extending the knee (45 to 110°). Consequently, there is little cocontraction of agonist/antagonist muscles. Different muscles are active during different times in the crank cycle (fig. 4). Three regions of the crank cycle can be identified. From TDC to 90° the active muscles include the gluteus maxim us, the muscles of the quadriceps group, and gastrocnemius. From 90 to 270° the active muscles are limited to the gastrocnemius and the hamstrings. Active muscles in the third region, from 270° to TDC, are tibialis anterior and rectus femoris. In the first region, even though all 3 quadriceps muscles are active, only the 2-joint muscle rectus femoris crosses the hip. During pedalling, the hip and knee are very different in their actions. Hip movement is extensor. Knee movement is first extensor and then flexor. There appears to be dominance of knee extensors over hip extensors in the first quadrant of the pedal revolution (Gregor et al. 1985). In the second

55

quadrant of pedal revolution a substantial reduction of knee extensor activity is observed. Gregor et al. (1985), observing muscle activity during pedalling, found that the general activity picture at all 3 joints, hip, knee and ankle, is characterised by little cocontraction of agonist/antagonist muscles. This is especially true for the gastrocnemius/tibialis anterior at the ankle and the hamstrings/quadriceps at the knee. If the knee extensor muscles were to develop moments in excess of the flexor moment generated at the knee by the 2-joint extensors it would be metabolically uneconomical. 3.8 Saddle Height Seat height is the distance from the top of the seat to the top surface of the pedal platform, measured along the seat tube with the crank arm in the down position but parallel to the seat tube. Evidence suggests that saddle height should be 97 to 100% of the distance measured from the greater trochanter to the floor with the subject standing straight-legged on bare feet (Gonzalez & Hull 1989; Hamley & Thomas 1967) and 109% of the symphysis pubis height (Hamley & Thomas 1967;Nordeen-Synder 1977). These heights result in the most efficient oxygen consumption. A lower seat results in higher quadriceps force and thus higher muscle activity (Hull & Butler 1981). When the seat is set at 95% of the trochanter length there is an increase in muscle activity levels for both the quadriceps and hamstrings (Jorge & Hull 1986). Increased saddle height decreases the maximum flexing knee load moment, but does not significantly change the flexing hip or dorsiflexing ankle load moment (Ericson 1986).

4. Aerodynamics of Cycling Air resistance is by far the greatest retarding force affecting cycling. Drag is a major impediment to riding speed only when it exceeds 10 mph (16 km/ h). Wind forces at the bicycle-racing speed offrom 20 to 30 mph (32 to 48 km/h) are enormous. A cyclist travelling at 20 mph (32 krn/h) typically displaces approximately 1000lb (450kg) of air per

Sports Medicine J4 (1) 1992

56

Ql

-a'" e OJ

Ql

:-

8CIl ex:

BOC Fig. 4. The activity periods of 6 muscle groups during the revolution of the pedals. TDe (BDC) = top (bottom) dead centre.

minute. At that speed about 70% of the power is used to overcome the air resistance to the rider and 30% for the air resistance to the bicycle. Obviously, the first concern is improving the aerodynamics of the rider. When the cyclist bends her/his elbows and crouches with the torso nearly parallel to the ground , the wind resistance is lowered by about 20%. If the rider assumes the hill descent position, hands on centre of upper handlebars, chin resting on the hands, crank parallel to ground , the wind resistance is lowered by about 28%. A crouched rider on a conventional racing bicycle could reach a maximum velocity of about 34 mph (54 km/h) with a power input of I horsepower. On an aerodynamic bicycle the same rider making the same effort could achieve 38 mph (61 km/h). When the bicycle and rider are not aerodynamically prepared , they produce a significant wake and demand a high energy cost. Two forms of aerodynamic drag affect the eye-

list and bicycle. When the flow of air fails to follow the contours of the moving body, pressure drag is created. This separation of air from the body changes the distribution of air pressure. When this separation occurs toward the rear of the body, the air pressure there becomes lower than it is on the forward surface, resulting in drag. The second form, skin-friction drag, results from the viscosity of the air. I~ is caused by the layer of air immediately next to the body. Thus, any object projecting from the bicycle frame or cyclist causes airflow to separate from the surfaces. Low pressure regions form behind the projections, resulting in pressure drag. However, air flows smoothly around a streamlined shape, closing in behind as the body passes. Head winds, tail winds, and cross-winds can significantly change both aerodynamic drag and the power requirements. A cyclist travelling at 18 mph (29 krn/h) in still air must increase his/her power output by 100% to maintain that speed against a


head wind of 10 mph (16 km/h), Of course, a tail wind makes the bicycle go faster. At speeds over 18 to 20 mph (29 to 32 km/h) wind drag comprises over 90% of the total mechanical resistance to motion against a bicycle (Kyle & Edelman 1975). A pure tail wind or head wind will speed up or slow down the rider slightly more than half the wind speeds. A rider going 20 mph (32 km/h) with a 10 mph (16 krn/h) tail wind is capable of travelling about 26 mph (42 km/h), A 10 mph (16 km/h) head wind will slow the same rider to about 14 mph (22 km/h). When drafting in the wake of another rider the power requirements of the drafting rider are reduced by about 30%; tandem riders use 20% less power per rider than 2 separate cyclists. An ordinary bicycle and its rider will have an effective frontal area of from 0.3 to 0.55m 2 . Aerodynamic drag increases as the square of the velocity. Power is proportional to the product of the drag force and velocity, so that the power needed to drive an object through the air increases as the cube of the velocity. Therefore, a small increase in speed requires an enormous increase in power. The rider who suddenly doubles his/her output of power while travelling at 20 mph (32 km/h) will increase his/her speed to only 26 mph (42 krn/h), Consequently, high speeds require extremely high aerodynamic efficiency. Numerous investigators have addressed the issue of wind and rolling resistance of racing and touring cyclists. Wind resistance is responsible for most of the metabolic cost of cycling (80 to 90%) [Kyle, 1979]. Kyle and Burke (1984) suggest 4 methods effective in decreasing the wind resistance of bicycling: (a) reducing the frontal area of the rider and bicycle; (b) improving airflow around the shoe by eliminating straps and toe clips. A cleaner shoe profile reduces drag by about 0.08 pounds at 30 mph (48 km/h). A Spandex shoe cover reduces drag by 0.12 pound. With streamlined shoes, drag may be reduced by 0.25 to 0.40 pounds; (c) reducing air turbulence caused by the bicycle. Aero tubing reacts better in cross-wind than standard tubing. Smaller wheels, fewer spokes, narrower tyres, narrow hubs, aero rims, covered wheels and aero spokes all lower

57

drag; and (d) streamlining the accessories. Even an inefficiently streamlined water bottle adds almost 0.2 pounds of drag to the bicycle at 30 mph (48 km/h), Sheathed cable adds about 0.03 pound per foot of drag, much more than bare wire. A faired wheel has a much lower drag, about one-quarter that of the plain wheel (Kyle & Burke 1984). Clothing can make a difference. A l-piece, fulllength suit of 'Lycra Spandex' material with an aerohood will reduce overall wind drag by about 11 %. The worst possible condition is not wearing a helmet. Covering long hair with a streamlined helmet reduces drag by 7% and can cut as much as 1 minute from a 40km time trial (Kyle 1988). It has been estimated that leMond was able to reduce his 1989 Tour de France winning time-trial by at least 10 seconds by wearing an aerodynamic helmet. A helmet with smooth contours, rather than cavities and sharp edges, can lower air drag from 10 to 15% (Swart 1989). From a practical view point, a 0.002 pound decrease will lower the time for a 4000m pursuit by about 0.3 seconds. The maximum drag decrease possible, using traditional equipment as standard, is about 1 pound at 30 mph (48 km/h), which will reduce the 4000m time by 13 seconds. Nontraditional equipment allows further gains. For example, clip-on handlebars, and other models such as 'Scott HD' bars, trim 1 pound from a rider's drag at 30 mph (48km/h) compared with using normal time-trial bars (Kyle 1989). In groups of cyclists, riders behind the leader consume less energy, being partially shielded from the wind. By travelling in a group, cyclists can increase their speed by about 2 to 4 mph (3.2 to 6.4 km/h), The use of pace lines in cycle racing is an important race tactic. Touring cyclists of equal ability riding in a group can travel from 1 to 3 mph (1.6 to 4.8 krn/h) faster than any lone rider. This is accomplished by taking advantage of an artificial tail wind, i.e. the air is already moving forward when they reach it. When 2 cyclists are in a pace line at 25 mph (40 km/h) the front cyclist consumes the same energy as if riding alone, but the cyclist following requires about 33% less power output. At this speed, reduction in wind resistance

58

is about 38%. However, since rolling resistance is unaffected by slipstreaming, the decrease in external power required is smaller. When a third cyclist joins in a slipstream, the power required by the first 2 remains the same as before. There appears to be no measurable advantage between positions in the pace line, as long as a rider is following at least I person. Spacing between riders is important. The closer one cyclist follows another, the greater the drag reduction. The total wind resistance decline averages 44% at 1.7m between riders or a zero wheel gap, and only about 27% at 3.7m between riders or a 2m wheel gap. It is better to ride directly behind another cyclist using safe wheel spacing than to overlap wheels. An upright body position provides better shelter for following riders in the racing position, but total drag and energy consumption are greater under all circumstances for the rider in the upright position. The larger the body size and frontal area of the leading rider, the greater the advantage to those following. Cyclists at the rear of a pace line consume less energy than the front rider. Thus, a group can travel much faster than a single rider if they rotate turns at the front, assuming near equal ability. While in front or dropping back, cyclists may go into increasing oxygen debt. However, while in the shelter of the pace line they are conserving energy reserves for their next turn at the front. In a pace line it is necessary that riders be of nearly equal ability, in order that the pace line speed be greater than that of the best rider. The pace line can increase its speed about 3 to 4 mph (4.8 to 6.4 krn/h) over what they are capable of ordinarily, providing there is a steady pace, level course, and little wind. Conversely, when riders are not equally matched, the group can actually be slower than the fastest rider. However, if the stronger person takes a longer lead, then the group speed can still be higher than any individual in the group. For the team pursuit, a pace line wheel clearance of 15cm will reduce wind resistance of the following riders by an additional 2% over a clearance of 30cm. This results in a 1.5 to 2-second advantage in 4000m.

Sports Medicine 14 (l) 1992

5. Medical Problems 5.1 Overtraining While no definitive markers of overtraining have yet been identified, changes in certain physiological, biochemical and psychological factors appear to be associated with the overtraining syndrome. increased morning heart rate and T-wave changes in the electrocardiogram have been associated with overtraining (Dressendorfer et al. 1985; Wolf 1961). Other markers are decreased muscular strength, decreased V02max, increased V02max during standard submaximal exercise, decreased oxygen pulse, and increased blood lactate during submaximal work (Costill 1986; Costill et al. 1985; Houston et al. 1979; Maron et al. 1977; Mellerwowicz & Barron 1971; Sherman et al. 1984; Wolf 1961). Overtraining has been associated with several blood chemistry changes. A rise in serum creatine phosphokinase is often a marker of skeletal muscle damage and an increase of this enzyme in serum may be associated with overtraining (Dressendorfer et al. 1985; Pate et al. 1978). Symptoms of overtraining may be caused by altered endocrine and immune functions. Endocrine factors which may be helpful in identifying and predicting the onset of overtraining are response of catecholamines (Costill 1986; Galbo 1983; Prokop 1963), ACTH and cortisol (Barron et al. 1985; Galbo 1983; Prokop 1963) to submaximal and maximal exercise. The ratio between resting levels of plasma testosterone and cortisol may serve as an index of overall metabolic state, e.g. anabolic vs catabolic (Galbo 1983; Hakkinen et al. 1985; Wheller et al. 1984). Markers of immune function helpful in assessing development of overtraining include lymphocyte subpopulations and T lymphocyte function (Eskola et al. 1978; Hanson & Flaherty 1981; Hedfors et al. 1976; Makinodan et al. 1984; Monjan & Collector 1977; Simon 1984; Tomasi et al. 1982). Physiological markers such as apathy, lack of appetite, irritability and sleep disturbances have been shown to suggest a state of overtraining (Brown et al. 1983; Mellerwowicz 1971; Morgan 1985). An instrument which has been proven a


helpful indicator of the overtrained state is the Profile of Mood Status (McNair et al. 1971). 5.2 Overuse Injuries Cycling is generally not considered an 'impact' sport. However, during cycling the ankle joint compressive force and Achilles tendon force have been reported as 1.4 and 1.1 times bodyweight, respectively (Ericson et al. 1985). Forces of 3 times bodyweight are applied to the pedals during intermittent bursts of hill climbing and short sprints (Leadbetter & Schneider 1982; Soden & Adeyefa 1979). During steady cycling forces are often equal to bodyweight (Davis & Hull 1981; Sargeant et al. 1981; Soden & Adeyefa 1979). Extremely rapid flexion-extension of the knee occurs when cycling at typical pedalling frequencies of 80 to 100 revs/ min. A 4-minute running pace, by comparison, causes an angular velocity at the knee equal to only 40 revs/min (Nordeen & Cavanagh 1976). Acute and chronic knee pain is the most common overuse syndrome in cycling (Gaston 1978, 1979; Leadbetter & Schneider 1982; Rhodes 1978). Typical overuse knee problems include: infrapatellar tendon strain and/or bursitis, chondromalacia patellae, retropatellar tendon bursitis, infrapatellar fat pad syndrome, prepatellar bursitis, quadriceps insertion pain on the patella, pes anserinus bursitis, iliotibial band syndrome and medial or lateral collateral ligament strain (Gaston 1979; Leadbetter & Schneider 1982). In the articular cartilage, such as the knee, repetitive microtrauma often results in a pattern of injury starting with softening and progressing to shredding and thinning of the articular surface. It becomes clear that the combination of high velocity muscular and joint movement compounded with high repetitive forces can precipitate overuse injuries. Healthy muscle can exert a force of approximately 289.59 kPa (42 lb/in-') of cross-sectional area. The quadriceps can exert a maximum force of approximately 317.5kg (700lb). This means that large forces are applied directly to the cartilagecovered surfaces of the patella and femoral con-

59

dyles as they slide upon each other during each rotation of the crank. Chondromalacia, a degeneration of knee cartilages, is often the result of such constant irritating force. Pedalling in low gears reduces the force necessary to tum the crank and appears to be important in preventing the injury. Experience suggests that pedalling in low gears also prevents aggravation of the condition once it has begun (Faria 1984). A successful approach to the treatment of overuse cycling injuries is pedal, shoe or orthotic modifications (Davis & Hull 1981;Gaston 1978; Hlavac 1977; Leadbetter & Schneider 1982; Rhodes 1978; Schubert 1980; Smith 1980; Weaver 1979). Many knee symptoms can be relieved through neutral orthotics, cleat adjustment or pedal canting. Adjustment in foot/pedal position can effect immediate changes in the knee position during the pedalling stroke. The consequence is enhancement of function with a decrease in overuse knee injuries. 5.3 Shoes The hard-sole cycling shoe, through its application of high pressures, has been associated with localised paraesthesia in long-distance cycling. This condition is often exacerbated by the traditional cage pedal with one or more straps over the foot. The combination of the traditional hard-sole shoe and strapped pedal may lead to injury and subsequent reduction in cyclingefficiency.The new clipon pedal systems remove the old straps that contributed to the increased pressure on the foot. When the foot is bearing a large load during steady-statecycling, the foot structures respond with a pronatory action at the subtalar joint with the concomitant internal rotation of the tibia. This leads to an internal torsion of tibia which, in tum, can precipitate injuries of the knee joint. Ericson et al. (1985) have shown that normal frontal plane knee joint moment is in varus. The magnitude of this movement, while being dependent upon the magnitude and orientation of the vertical and medial-lateral pedal reaction forces, is also dependent upon position of the knee with respect to the pedal. Francis (1986) reported that wedgingthe foot or

60

rotating its position on the pedal can affect the position and path of motion of the knee joint. He believes that these changes could lead to a more healthy loading pattern of the tissues within and around the knee joint. Yet to be verified is whether force reduction in the cruciate ligaments is possible from such action. Toe clip position can prevent cleat or cant adjustment if it does not allow the foot to properly position itself on the pedal platform. The toe clip, pressing on the shoe, can nullify any positional adjustments made elsewhere and prevent the shoe from assuming its properly aligned position with the metatarsal heads directly over the pedal axle. Alterations, using spacers for sagittal plane elevation or size changes, may be necessary (Hannaford et al. 1985). It is important that when the pedal is fully loaded the forefoot (beneath the metatarsal heads) is parallel with the ground, the reason being that force of pedalling is applied through the metatarsal heads to the shoe onto the cleat and finally to the pedal. Hannaford et al. (1985) point out that in the rigid soled cycling shoes worn by competitive cyclists, simple longitudinal arch support in the overthe-counter orthotics or rear foot-only types of orthotics cannot prevent abnormal knee motion at higher forces. If the knee alignment problems are due to an imbalance originating in the rear foot only then traditional support may resolve the problem. Likewise, during light to moderate cycling, the rearfoot type of support or rigid orthoses, placed in the cycling shoe may be adequate to prevent excessive transverse/frontal knee motion. However, with high power output accompanied by large forces placed directly on the metatarsal heads the foot will collapse in the direction that allows the forefoot to become parallel with the cleat or pedal platform. Consequently, the knee deviates from vertical and loses its stability. An attempt to prevent such motion by overcorrecting and longitudinal arch or turning the cleat inwardly or outwardly can precipitate injury. Muscle or ligament strain may be the result. Often the knee will move away from its optimum linear sagittal motion. Video film analysis and treatment methods described by Hannaford et al. (1985) have been shown

Sports Medicine 14 (J) 1992

to be effective in evaluating and treating overuse knee problems in cyclists. For an indepth presentation on overtraining in athletes, the reader is referred to the comprehensive review by Fry et al. (1991).

6. Conclusions and Directions for the Future This review attempts to synthesise the scientific knowledge pertaining to cycling. The physiological demands on, and the characteristics of, cyclists are identified and discussed. A review of research contributions that modern technology has made to the sport of cycling is presented. Evidence is given which shows how the exercise physiologist, biomechanist and engineer, through shared knowledge and professional expertise, and with the best interest of the athlete in mind, have advanced the sport to new levels, and how the superior performance of contemporary cyclists is the result of a complex blend of research from the areas of physiology, biochemistry, electromyography, cinematography and computer graphics, ergonometry, biomechanical application and aerodynamic analysis. The findings ofresearch into enhancing cycling performance include: (a) to be successful at the national and international level of competition, a moderately high oxygen uptake is required; (b) for maximum performance, cycling economy (as represented by VOZ max and anaerobic threshold) is essential; (c) to assure maximum force transmission to the bicycle pedal the cyclist should attempt to achieve maximum interaction between the pedal and first metatarsal head, the lesser metatarsal head and the hallux; (d) emphasis on downward thrust with the range of 90 to 110° of the power phase of pedalling at a recommended 90 to 100 revs/min; (e) to achieve top cycling speed both the cyclist and the bicycle must display aerodynamic qualities; (f) extremely high aerodynamic efficiency and a close draft riding position will best serve to complement the physiological capabilities of the cyclist; (g) the importance of minimising drag for greater speed with less effort cannot be overem-


phasised; (h) overtraining is evidenced by the cyclist's inability to perform to her/his previous personal best despite continued training. Signs of overtraining include indicators of muscle damage, suppressed immunity and related symptoms. Future cycling research should demand a sportspecific approach. There needs to be greater focus towards sport-specific experimental design, methodology, protocol, equipment and subject selection. Experienced racing cyclists performing on a bicycle designed for racing should constitute a minimal acceptable standard. Various experimental designs are needed for optimising training protocols to enhance the cyclist's anaerobic threshold. There is a need for further research on the value of the lactate threshold for predicting both short and long term cycling performance. The validity of heart rate during cycling as an indicator of lactate threshold needs further examination. The conventional method of applying force to the bicycle transmission should be examined more closely with concern specifically on vertical forces and torque during the cycling down-stroke. Additional attention should be given to cycling shoe design as it relates to force application. The cycling

shoe's interface between the cyclist's foot and bicycle pedal requires further research. A more comprehensive and indepth inquiry is needed into different muscle activation and percentage involvement per crank revolution, as related to change in saddle position both forward and backward on the frame. Experimentation and wind tunnel tests should continue to be directed towards aerodynamic bicycle frame and component design, helmet design, clothing material and rider position.

Acknowledgements The author wishes to express his sincere gratitude and appreciation to those fellow researchers whose works are discussed and cited in this paper.

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Correspondence and reprints: Dr Irvin E. Faria, 3731 Dell Road, Carmichael, CA95608, USA.

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