Eur J Appl Physiol (1992) 65:475-479

,oum.,"'°A '"o,p p l i e d Physiology and Occupational Physiology © Springer-Vedag1992

The effect of shuttle test protocol and the resulting lactacidaemia on maximal velocity and maximal oxygen uptake during the shuttle exercise test Said Ahmaidi, Katia Collomp, and Christian Pr6faut Laboratoire d'Exploration Fonctionnelle Respiratoire, H6pital Aiguelongue, Avenue du Major Flandre, Montpellier, F:34059 Cedex, France Accepted June 30, 1992

Summary. The purpose of this study was to investigate the influence of the shuttle test protocol (20-MST) and the resulting lactacidaemia on maximal velocity (Vmax) and maximal oxygen uptake (I2Oam~x). Firstly, three randomly assigned tests to exhaustion were performed by 12 subjects: the treadmill test, the 20-MST, and a continuous running track test using the same prerecorded 1-min protocol as in the 20-MST (T1). One week later, subjects performed another track test, which was conducted up to the same level of effort as attained during the 20-MST (T2). For each test, Vmax, ~rO 2 . . . . lactate concentration at rest and during recovery, maximal heart rate, and distance covered were determined. The results indicated that the 20-MST underestimated Vm~x; only T1 satisfactorily assessed Vma~ (F= 15.49, P < 0 . 0 0 1 ) . At the same level of effort, the peak blood lactate concentration ( t = 2 . 7 , P < 0 . 0 2 ) and 1202m,x (t= 11.35, P < 0 . 0 0 1 ) values were higher for the shuttle than for the continuous protocol. It was concluded that Vmax was limited by the running backwards and forwards in the protocol of the shuttle test. The higher values of peak blood lactate concentration and its earlier appearance obtained for the shuttle may have been one of the limiting factors of Vm~. However, the higher values of 1202m~x obtained for the 20-MST were most likely due to a combination of the relative hyperlactacidaemia and the biomechanical complexities required for this type of protocol. Key words: Lactacidaemia - Maximal velocity - Maximal oxygen uptake - Shuttle test - Track test

test with 1-min stages (20-MST) has been shown to correspond to these criteria (L6ger et al. 1983). This test has been based on the linear relationship which links the increase of running velocity to the rise in oxygen consumption (Menier and Pugh 1968; Falls and Humphrey 1976) and, when conducted to exhaustion, can be used to determine maximal oxygen uptake (1202max) and maximal velocity (Vmax). From a practical point of view, Vmax is more important for coaches and athletes than I202 . . . . T h e Vmax, in addition of assessing the aerobic effect of training programmes, can also be used to suggest exercise regimens. The validity of the test for 12Ozmax assessment has been satisfactorily demonstrated (Poortmans et al. 1986; Gadoury and L6ger 1986; Van Mechelen et al. 1986; Paliczka et al. 1987; L6ger et al. 1988; Ahmaidi et al. 1990); however, a previous study concerning the assessment of Vmax has shown values consistently lower for the 20-MST than for the treadmill test at the same level of metabolic and cardiorespiratory requirement (Ahmaidi et al. 1992). We have hypothesized that the running backwards and forwards in the course of the 20-MST caused more lactic acidosis, which limited Vm~xand thus influenced 1202 . . . . The purpose of the present study was twofold: 1. To see whether a change of protocol for the shuttle test, such as conducting the test on a circular track, would result in an increase of the Vmax attained 2. To investigate the influence of the 20-MST protocol on lactacidaemia and 12Ozma~in comparison to a continuous running test

Methods Introduction Graded aerobic exercise testing is interesting in that it costs relatively little and allows the assessment of both functional capability and the oxygen transport system with its aerobic energy process. The 20-m shuttle run Correspondence to: S. Ahmaidi

Subjects. The study was conducted with 12 healthy male volun-

teers after obtaining their informed consent. The subjects, aged from 18 to 26 years, were physical education students with differing levels of physical fitness. None of them were competitive athletes, nor had they had prior experience with the tests used in this study. The anthropometric characteristics are summarized in Table 1. Each subject underwent a medical examination, including an electrocardiogram and complete medical history. No electrocar-

476 Table 1. The anthropometric characteristics of subjects (n = 12) Age (years) Mean 23.9

Height (cm) SEM 0.8

Mean 175.8

Body mass (kg) SEM 2.1

Mean 76.4

SEM 1.6

diogram abnormalities at rest were detected. During the entire period of the tests, the subjects received no medication. Just prior to the initial test session, details of experimental procedures were provided. Protocol. Incremental tests to exhaustion were used for the measurement of Vm,x, 12Osm,x, maximal heart rate (fo.m~), postexercise peak blood lactate concentration ([la-]b ...... ise), and distance covered. Three tests were performed by the subjects in random order: the treadmill test, the 20-MST, and the continuous running-track test using the same prerecorded 1-min protocol as in the 20-MST (T1). The tests were performed on separate days to eliminate any possible fatigue effects. One week later, subjects again performed the continuous running track test, which was conducted up to the same level of effort as that attained in the 20-MST (T2). During this test, the same variables as for the previous tests were calculated. All tests were carried out in the afternoon, well after the consumption of standard meals, to avoid variations due to circadian and digestive factors. Heart rate was monitored continuously during the entire study using a cardiofrequency meter (Sport Tester TM PE 3000, Polar Electro, Kemple, Finland) which averaged heart rate and stored it every 5 s. For each test capillary blood was taken from the fingertip for lactate concentration analysis at rest ([la-]b.rest) and then every min for 5 minutes of the recovery period to determine peak concentration. Treadmill measurements. Procedures. The Vm~ and l~rO2maxwere determined on a motor-driven treadmill (Gymrol Control 1800, Roche la Moli~re, France) using an incremental progressive protocol. The subjects warmed up by jogging at 8 k m ' h -1 on a 3% gradient for 3 rain. Following the warm-up period the gradient was maintained at 3% and the velocity was increased by 0.5 km. h-1 every minute. The increases in velocity were reduced to 0.25 k m . h -1 for the last stages of effort to obtain the best determinations of the true values of Vmax and [~rO2rnax. The 12Os was determined using an open circuit technique. The subject breathed through a rubber mouthpiece attached to a one-way valve (Warren E. Collins, Inc., Mass., USA) with low resistance and small dead space. Inspiratory airflow was measured continuously during exercise through a pneumotachograph (Fleish no. 4) and a Validyne MP 45 pressure transducer with a measuring range of + 2 cm H20 (Engineering Corp., Calif., USA). The pneumotachograph was placed on the inspiratory tubing to avoid problems due to condensation of water vapour. The calibration on the flow module was accomplished by introducing a calibrated volume of" air at several flow rates. Metabolic parameters. Expired gases were sampled in a mixing chamber (5 1) through a flexible hose, dried with CaCI2, and analysed for Os with a polarographic analyser (Godard Capnographe, Statham, The Netherlands) and for COs with an infrared analyser (Godard Rapox, Statham, The Netherlands). Each gas analyser was calibrated before and after each test with a standard certified commercial gas preparation. The inspiratory air flows and the fraction of expired Os and COs were calculated by computer (Apple IIe) from the last ten breath cycles of every minute. Averages were then established for minute ventilation (12nl'min -1, body temperature and pressure, saturated), 12Os [l'min -1, standard temperature and pressure, dry (STPD)], CO2 production (12COz 1. rain-a STPD), respiratory exchange ratio (R), ventilatory equi-

valent for Os (12~. 120£1) and COs (12E"12CO£1), and breathing frequency (fb). During the test, the subject's electrocardiogram was followed continuously on a cardioscope (Diascope, Simonsen and Weel, Denmark). Electrodes were placed in the CM5 lead position. In addition, the heart rate was assessed with a Sport Tester. The test ended when the subject could no longer continue despite verbal encouragement. The 12Oz was considered maximal if two of the following criteria were achieved: levelling off of l;'Os despite an increase in velocity; R equal to or greater than 1.1; and heart rate no less than 10% below predicted fo . . . . The Vm~ was considered to be the velocity attained during the last stage of effort. Before and after each test the accuracy of the treadmill speed was verified by a stopwatch recording of 15 treadmill belt revolutions. Field measurements. The 20-m shuttle run test. The 20-MST was performed according to the l-rain protocol of L6ger et ai. (1983). In this test subjects run backwards and forwards between two lines placed 20 m apart, the running pace being set by audio signals emitted at fixed intervals from a prerecorded cassette tape. The continuous running tests. Two continuous running tests, T1 and T2, were performed by each subject. These tests were conducted on a 400 m track with inclined curves. Markers were placed every 20 m along the track. The subjects were paced using the same prerecorded tape as in the l-rain protocol used for the 20MST. The T1 was performed until exhaustion, while the T2 was performed up to the same stage of effort as that attained during the 20-MST. For all track tests, the running speed was 8 k m . h - I at the start and this was increased by 0.5 k m ' h -1 every minute thereafter. The subjects ran in groups of no more than three to stimulate competition and to ensure maximal effort. They were instructed to complete as many stages as possible while performing the 20-MST and the T1. During the tests the subjects were informed of their progress every 30 s by audio signal to help them decide whether they should attempt to complete the stage. The test was ended when the subject was unable to maintain the pace. At each stage, velocity was verified by measurement of the distance covered in 30 s. During the last stage, the assessed velocity was adjusted in terms of the length of time it was maintained. This adjusted velocity was calculated by using the equation proposed by Kuipers et al. (1985):

Vm~ (kin. h - 1) = v + 0.5 x (n/60) where v is the velocity maintained during the next to last stage; 0.5 is the value of the increase in velocity in km" h-1 from one stage to another; n is the number of seconds for which the last stage was maintained; and 60 is the number of seconds in the stage. The adjusted velocity was considered as Vm,~. The VO2maxvalues were calculated from the adjusted Vm~, obtained in the 20MST using the regression equation provided by L6ger et al. (1988) for individuals aged 18 years: 1202max (ml" kg - 1. min - 1) = 6 v - 27.44 where v is the adjusted Vm,~ in k m ' h -1 obtained in the last stage. The adjusted velocity attained during the T1 and T2 was converted to VO2max using the equation of L6ger and Mercier (1983) for continuous running: I?O2max (ml" k g - 1.min-1) = 1.353 + (3.163 x v) + 0.0122586 x v 2 where v is the adjusted Vm~x in k m . h - I attained in the last stage. The running speed of the cassette recorder was checked prior to the start of each test to ensure that any deviation was less than 1 s-min-1 (L~ger and Ruillard 1983). Blood lactate measurements. Blood lactate concentration was measured first at rest and then on completion of each field and laboratory test. The subjects remained seated during the recovery

477 Table 2. The physiological and metabolic variables determined following the treadmill test, the shuttle test (20-MST) and the continuous running test conducted to exhaustion (T1) and up to the same level of effort as the 20-MST (T2)

Treadmill Mean SEM 20-MST Mean SEM T1 Mean SEM T2 Mean SEM

[la - ]b,rest (raM. 1- 1)

Vmax (km. h - 1)

WOzlrlax (ml. kg - i. min - 1)

fc . . . . (beats. m i n - 1)

[la - ]b...... ise (mM. 1- ~)

Distance (m)

1.41 0.18

15.66 0.43

55.55 1.42

188 1.72

1.52 0.18

13.38*** 0.20

53.07 1.31

193 2.46

10.93 0.27

1699"** 42

1.60 0.18

15.75 0.33

53.40 1.17

191 2.3

10.38 0.54

2519 190

1.44 0.17

13.45 0.19

44.43 °°0 0.56

186°° 1.84

10.20° 0.14

1788 128

8.96* 0.38

2288 127

* P 0 . 0 5 ) , a n d [ l a - ] b .... t ( F = 0 . 2 5 , P > 0 . 0 5 ) a m o n g the treadmill test, 20-MST, a n d T1. Tests conducted up to the same level o f effort. The m e a n s of [ l a - ] b ...... i~e ( t = 2 . 7 , P < 0 . 0 2 ) , VO2max ( t = 11.35, P < 0.001) a n d f c . . . . ( t = 3.26, P < 0.01) determ i n e d for the 20-MST showed significantly higher values t h a n for those of T2. However, n o difference was n o t e d in [la-]b,rest ( t = 0 . 8 4 , P > 0 . 0 5 ) , Vmax ( t = l . 0 1 , P > 0 . 0 5 ) a n d distance covered ( t = 1.17, P > 0 . 0 5 ) . The a d d i t i o n a l l a c t a c i d a e m i a o b t a i n e d d u r i n g the 20-MST

478 explained 24.8% of the difference in the two tests:

3.3

~rO2maxbetween

([la - ]b, exercise- - [la - ]b, rest)20-MST- ([la - ]b...... ise-- [la - ]b.... t)T2 ~r02 ....

20-MST-

~r02 ....

T2

Discussion

The results of this study clearly indicated that the 20MST protocol involving running backwards and forwards limited Vm~, and that its assessment depended in part on the capacity of the subject to sustain his effort in an anaerobic condition. The 20-MST was developed to evaluate maximal functional aerobic power (MFAP), which is a combined index of 12Ozmaxand mechanical efficiency. The MFAP is thus more useful to the athlete and trainer than 12Oim~x alone. In practice, MFAP is considered to be the Vm~xobtained during the 20-MST and can be used for advising on training regimens as well as for evaluating the aerobic effect of training programmes. Our results, however, showed that the 20-MST underestimated Vmaxand thus could not be recommended for these purposes. Only the continuous track protocol allows one to determine Vm~xwith reasonable accuracy. The similar 1202m~x values obtained for the three tests to exhaustion clearly indicated that the two equations satisfactorily evaluated TkOzmax during maximal effort, as has been shown in earlier studies (Poortmans et al. 1986; Gadoury and L6ger 1986; Paliczka et al. 1987; Van Mechelen et al. 1986; L6ger et al. 1988; Ahmaidi et al. 1990). However, the significant difference in blood lactate concentration measured after the treadmill test, the T1, and the 20-MST would suggest that the contribution of anaerobic glycolysis was greater in the field tests. Indeed, the measurement of peak blood lactate concentration is the most commonly used indicator of the involvement of the anaerobic pathway (He r manssen 1969; Astrand and Rodahl 1986; Di Prampero 1981). It is assumed that the higher the peak blood lactate, the higher the anaerobic contribution. The lower values of lactate concentration following the laboratory test were accompanied by slightly lower heart rate values. This also indicated greater reliance on anaerobic energy in the field tests, possibly because of the high motivation during these tests. Environmental factors such as wind resistance have been shown to be additional factors in energy expenditure (Pugh 1970, 1971; Davies 1980a, b) and may also be identified with anaerobic process. The highest lactate concentration obtained for the 20-MST corresponded to the lowest velocity. This indicated that the 20-MST was less economical than the other tests. However, in order to link the decreased velocity to the effect of lactacidaemia, it would be necessary to know the lactacidaemia level for an equivalent effort. Indeed, for the same level of effort there was a difference in blood lactate concentration between the 20MST and T2. This clearly showed that for an equivalent

velocity, the shuttle test resulted in hyperlactacidaemia. Moreover, peak blood lactate concentration occurred earlier with the shuttle test. Blood lactate concentration only indirectly reflected the muscle lactate level, but it seems probable that, during the 20-MST, the higher blood lactate level and its earlier appearance (Fig. 1) was due to an earlier glycogenolysis participation, which induced greater blood lactate production. Indeed, it is known that high lactate concentration in muscles induces a decrease in muscle pH. This decrease in pH has been found to induce a perturbation of muscle contractile properties, i.e. a decrease in the contraction speed (Di Prampero et al. 1981; Donaldsson and Hermanssen 1978; Mainwood and Renaud 1985), and a decrease in enzymatic activity, particularly that of lactate dehydrogenase in adenosine 5'-triphosphate (ATP) production (Triverdi and Danforth 1966; Bertocci and Gollnick 1985). Although the difference in the lactate concentrations in our investigation appeared small, it was statistically significant. In addition, it has been shown that lactate measured in the blood is always lower than that directly measured in muscle (Jorfeldt et al. 1978). Indeed, lactate was measured in whole blood in our study, and Foxdal et al. (1990) have shown that venous blood lactate concentration is 40% lower than in plasma. Thus the Vmaxmeasured during the 20-MST may have been limited by a greater muscle lactate concentration. Although the two tests were conducted to the same level of effort, the 12Ogmaxvalues obtained for the 20MST were higher than for T2, as shown by the difference in the regression coefficients for the two equations used to determine 1202. . . . The correction factor used by the equation of L6ger et al. (1983) to determine 12Ogmax during the shuttle test was thus satisfactory. The anaerobic energy expenditure estimated in this study was calculated from the peak blood lactate concentration determined during the post-test recovery period. The estimate of Margaria et al. (1971) that we used is currently the one most accepted: to an increase in lactate concentration of 1 mM.1-1 in relation to its resting value, this estimate corresponds to an energy expenditure equal to a 1202 of 3.3 ml.kg -~. The difference in VO2 uptake may be attributed to the higher blood lactate concentrations obtained during T2, but this does not explain the total difference. The lactic anaerobic energy expenditure represents only 24.8% of the difference in IkO2max. The difference in 1202max may thus also be attributed to other factors of a biomechanical nature. The energy expenditure depends on the style of running: the best motion is the most economical. A number of studies have shown a strong correlation between success in distance running and the economy of running, i.e. the less energy used to cover a given distance, the better the performance (Costill and Fox 1969; Costill and Winrow 1970; Gregor and Kirkendall 1978). Indeed, for the same velocity, if a subject is asked to increase or decrease the stride length he has spontaneously adopted, he will in both cases increase his VO2. It is probable that the lower 1202maxvalue in the continuous track test was due to the fact that subjects modified their running style in such a way as to improve economy of movement.

479 D u r i n g the 2 0 - M S T , the subjects were u n a b l e to a d a p t their stride length to be the m o s t e c o n o m i c a l . T h e difference in ~rOzmaxlevel c o u l d also be a t t r i b u t e d to the app a r e n t d i f f e r e n c e in the vertical lift w o r k o f the b o d y . I n d e e d , the vertical lift w o r k in the c o n t i n u o u s r u n a p p e a r e d m o r e e c o n o m i c a l t h a n d u r i n g the shuttle run. M o r e o v e r , the r a p i d r h y t h m changes o f the 2 0 - M S T c r e a t e d a d i s e q u i l i b r i u m f o r which the subject h a d to c o m p e n s a t e c o n t i n u a l l y b y the use o f muscles n o t directly i m p l i c a t e d in r u n n i n g . I n c o n c l u s i o n , the'Vmax o b t a i n e d with the 2 0 - M S T was highly d e p e n d e n t o n the p r o t o c o l used. T h e m a j o r f i n d i n g o f this s t u d y is the significantly higher level o f l a c t a c i d a e m i a d u r i n g the shuttle p r o t o c o l c o m p a r e d to the c o n t i n u o u s p r o t o c o l . This relative h y p e r l a c t a c i d a e m ia m a y be c o n s i d e r e d as one o f the limiting f a c t o r s o f Vmax. H o w e v e r , the higher values o f ~rOzmaxo b t a i n e d f o r the 2 0 - M S T at the s a m e level o f e f f o r t as T2 c a n n o t be entirely e x p l a i n e d b y this h y p e r l a c t a c i d a e m i a , b u t are m o s t likely due to the c u m u l a t i v e effect o f b o t h m e t a bolic a n d b i o m e c h a n i c a l c o m p o n e n t s .

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