Journal of Gerontology: BIOLOGICAL SCIENCES 1990. Vol. 45. No. 4. B125-128
Copyright I WO by The Geronlological Society of America
Eccentric Knee Strength of Elderly Females Anthony A. Vandervoort, John F. Kramer, and Evelin R. Wharram Department of Physical Therapy, University of Western Ontario.
between groups of young and old adults COMPARISONS have shown that isometric strength of a variety of limb muscles is decreased in the elderly population (see review by Vandervoort et al., 1986). Healthy individuals in their seventh and eighth decades score on average about 20 to 40% less during strength tests than young adults (Fisher and Birren, 1947; Larsson et al., 1979; Clarkson et al., 1981; Murray etal., 1980, 1985; Young etal., 1984, 1985;Davies et al., 1986; Clarkson and Dedrick, 1988) and the very old show even greater (50% or more) reduction (Mathiowetz et al., 1985; Vandervoort and McComas, 1986). Such trends have been found in studies of muscles in both the upper and lower limb from proximal and distal locations (Vandervoort et al., 1986), although the size of the age effect appears to vary from muscle to muscle (Grimby, 1988). Strength testing of concentric exercise (i.e., during which muscles shorten as the joint moves) has shown similar age differences to isometric contractions. For the knee extensors, strength decrements during isokinetic (constant angular velocity) testing of elderly versus young subjects were approximately 25% in males aged 60-69 (Larsson et al., 1979), 45% in males aged 70-86 (Murray et al., 1980), and 35% in women aged 70-86 (Murray et al., 1985). The latter two values agree with isometric strength levels reported in the studies by Young et al. (1984, 1985). A longitudinal investigation of 23 males ranging in age from 73 to 83 years found isometric and concentric knee strength decreased 1022% over a seven-year period, depending on the test velocity (Aniansson et al., 1986). Limb muscles also perform many common movements in a manner which has been referred to as "eccentric" exercise, i.e., the muscles are lengthened while actively trying to resist an external force such as body weight (see Chapman, 1985, for a review). Functional examples include using the knee extensors to control body weight while one sits down or descends stairs, and during certain phases of the gait cycle when muscles exert braking forces by resisting lengthening. Despite the physiological importance of this type of muscle action, the strength of elderly muscle for eccentric exercise has yet to be examined. It was thought to be of particular interest to study elderly females, in whom muscle mass and
absolute strength are considerably decreased at the same time as body weight is usually the same or greater than young adults (Novak, 1972; Lexell etal., 1988; Vandervoort and Hayes, 1989). Thus, the purpose of this study was to compare knee extension and flexion voluntary strength during eccentric versus concentric exercise in groups of young and elderly women. Two angular velocities of knee joint rotation were studied, 45° and 90°/s. A preliminary report of this research has been given by Vandervoort et al., 1988. METHODS
Subjects. — Groups of 26 young and elderly female volunteers (20-29 and 66-89 years, respectively) completed testing of the knee extensors and flexors of one leg (Table 1). The sample of elderly women had a shorter mean height {p < .01), but a slightly heavier mean weight than the young group. All subjects were mentally competent to give informed consent for participation in the study. To be included, they had to be without any injury or deformity to their tested leg, able to walk independently without limping, and have at minimum a habitual activity level of daily walking. Each subject was asked about medication use and potential volunteers with a history of diagnosed disease which restricted exercise capacity (e.g., cardiac, thyroid or Parkinson's disease, osteoporosis), were excluded. Young women were drawn mainly from the university setting; the elderly were all living independently in their own home or apartment. Test procedures. — All testing was completed using the Kinetic-Communicator (KinCom, Med*Ex Diagnostics of Canada, Coquitlam, British Columbia), a hydraulically driven, computer-controlled dynamometer. With this machine the velocity of the lever arm attached to the subject's leg is accurately controlled (see Farrell and Richards, 1986) in either "concentric" mode, where the subject pushes the lever arm at a preset velocity as strongly as possible, or "eccentric" mode, in which the motor rotates the lever arm and the individual tries to resist. Two knee motions, extenB125
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This study compared the strength of the knee extension and flexion muscles in groups of young and elderly women under two conditions: eccentric exercise in which the muscles were lengthened while subjects tried to resist an external force, versus concentric contractions in which the muscles shortened. Twenty-six females, aged 20 to 29 (Mean 25 ± 3 SD), and 26 elderly women, aged 66 to 89 (Mean 73 ± 6 SD), were tested at two angular velocities of movement, 45° and 90"ls, on a KinCom isokinetic dynamometer. Elderly women had significantly lower peak and average torque values in all comparisons with the young female group (25 to 54% lower, p < .01). However, differences between the age groups were consistently smallerfor the eccentric type of muscle action than the concentric, in both knee extensors and flexors.
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Table 1. Subject Characteristics Age Group Elderly Young
Age Group (years) 73 ± 6° 25 ± 3**
Height (m) 1.59 ± .05 1.67 ± .07**
Weight (Kg)
Table 2. Peak and Average Torque Values for Concentric and Eccentric Exercise of the Knee Extensors in Young and Elderly Women Angular Velocity
63.6 ± 7.3 59.6 ± 7.5
"Values are Mean ± SD, N = 26. **p< .01.
Data analysis. — Strength patterns of individual subjects were analyzed using the KinCom's Torque vs Angle computer program (see Tredinnick and Duncan, 1988). The boundaries of the range of motion included in the analysis were set at 90° to 10° of knee flexion, thereby allowing about 10° movement before entering and after leaving the data acquisition zone. The two trials (of the three) with the highest peak torques were averaged to provide the criterion scores. Four separate three-way analysis of variance (ANOVA) procedures (two age groups by two velocities by
Concentric
90°/s Eccentric
Concentric
Eccentric
61 i 16 131 ± 26
100 ± 27 152 ± 52
45 ± 12 97 ± 18
66 ± 22 100 ± 37
Peak Torque Elderly Young
72 ± 19137 ± 33
Elderly Young
52 ± 14 97 ± 20
94 ± 27 151 ± 51 Average Torque 63 ± 22 97 ± 36
"Values are Mean ± SD, in N-m, N = 26. All differences between elderly and young women are significant (p < .01).
two contraction types), with repeated measures on the last two factors, were used to examine the peak and average torques during knee extension and flexion for statistically significant differences. Any significant interaction effects were analyzed further with the Newman-Keuls technique to compare selected pairs of means (Winer, 1971). Peak torque is a commonly reported isokinetic measure that indicates maximal capability within a specific range of motion. Average torque reflects mean capability across the range of motion tested and is related to muscular power and work done (Sale and Norman, 1982). RESULTS
Knee extension. — The age and the contraction type main effects were statistically significant on both ANOVAs of peak torque and average torque values [p < .01). As shown in Table 2, the young women had consistently higher values in all comparisons, and values for the eccentric exercise were greater than concentric. The latter values showed a trend to decrease between the lower and higher velocity, while torques during eccentric exercise showed the opposite trend. Knee flexion. — The age and the contraction type main effects were statistically significant on both ANOVAs of peak torque and average torque values {p < .01). As shown in Table 3, the young women had consistently higher values in all comparisons, and values for the eccentric exercise were again greater than concentric. Velocity had only a minor effect on peak and average torque values. Means of the peak torque scores for the elderly group (from Tables 2 and 3) were divided into the corresponding means for the young women in order to compare the effect of age on strength in the concentric versus eccentric exercise. The resultant percentage values ranged from 46 to 75%, as illustrated in Figure 1. In each case, the relative strength during eccentric exercise was higher than in the concentric. DISCUSSION
Lower strength values for concentric exercise in the el-
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sion and flexion, at two angular velocities of knee joint rotation, 45° and 907s, were tested during a single session of about 45 minutes duration. These slow velocities are comparable to many functional movements and were easy to learn to perform. Fast velocities were avoided due to the potential for injury when the muscle is lengthened at high rates (McCully and Faulkner, 1986). The subjects were positioned sitting against a back support, keeping the hip angle at approximately 80°. Stabilizing belts were secured over the lap and across the thigh of the test leg, which was usually their dominant one (defined regarding preference for kicking a ball). Each type of knee motion, extension or flexion, was completed at the 45° or 907s velocity in a random testing order. Foam padding was placed under the subject's popliteal fossa in order to minimize any discomfort arising from compression of the tissues against the seat of the KinCom. The rotational axis of the dynamometer's lever arm was positioned such that it lay at the level of the lateral epicondyle of the subject's knee during contraction efforts. The resistance pad was located at the distal end of the lower leg, just above the ankle where it did not restrict dorsiflexion. Standardization procedures included only allowing subjects to grasp the lap seat belt, but not the edge of the testing table, and correcting all torque measures for the effects of gravity on the lower leg and the dynamometer's resistance pad. The range of movement consisted of from 100° of knee flexion to as far as the individual could comfortably extend the knee. Each muscle group was assessed using three reciprocal concentric-eccentric cycles, without a pause between the two phases of activation. Subjects completed at least three submaximal and one maximal practice routines. They were then asked if they believed they could perform the test motion maximally; any subjects requesting additional practice were allowed to do so. Verbal encouragement was given during the recorded trials, and a 2-minute rest period was always inserted between the different conditions of velocity and muscle group.
45°/s Age Group
AGE AND ECCENTRIC STRENGTH
Table 3. Peak and Average Torque Values for Concentric and Eccentric Exercise of the Knee Flexors in Young and Elderly Women
Age Group
Concentric
PERCENT OF YOUNG MEAN
60
Angular Velocity 45'7s
80
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90°/s Eccentric
Concentric
Eccentric
40
36 ± 10 64 ± 14
64 ± 20 85 ± 24
20
25 ± 7 49 ± 11
43 ± 18 61 ± 23
Peak Torque Elderly Young
37 ± 8" 68 ± 17
60 ± 20 85 ± 23 Average Torque
Elderly Young
27 ± 6 51 ± 12
39 ± 19 63 ± 19
derly females in comparison to the young were again confirmed by this study. Such results had previously been reported for the knee extensor muscles by Murray et al. (1985). In our comparisons of this variable between young and elderly females the differences were quite marked, amounting to approximately 50% reduction in strength for both knee extension and knee flexion. The age-related difference in strength may be attributable to a failure of descending drive from the motor cortex during volitional efforts of the elderly group, or the result of smaller (atrophied) muscles. The first factor was assessed in a previous study by Vandervoort and McComas (1986) using the twitch interpolation technique (a brief electrical shock is applied to the motor nerve during a maximal voluntary contraction, cf. Belanger and McComas, 1981). Results indicated that the sample of healthy elderly people, ranging in age from 60 to 100, had the ability to activate their ankle muscles maximally, because a superimposed twitch stimulus had little additional effect on their volitional force output. Decreases in strength found in those elderly subjects were thus attributed to a decreased excitable muscle mass. It seems reasonable to extrapolate these results to the knee musculature, in which other investigators have shown that well-motivated subjects can achieve high levels of voluntary muscle excitation (Jones and Rutherford, 1987). Our testing procedures included considerable learning and practice trials, and then encouragement to the subjects throughout their maximal efforts. Additional analysis of the test records indicated performance was stable, because they had low deviations among the three trials with little evidence of a learning effect. A number of different investigators have examined the relationship between age and size of muscles. Young et al. (1984) used a technique of ultrasound scanning to measure cross-sectional areas of the quadriceps muscles in young (21-28 yr) and old (70-79 yr) women and found a 33% decrease in the latter group. Significant reductions of this magnitude have also been reported when comparisons of the size of the isolated vastus lateralis muscle were made between young and elderly autopsy cases, using systematic morphometric techniques (Lexcll et al., 1988). In vivo
KNEE FLEX
45 degrees/s •
CONCENTRIC
KNEE EXT
KNEE FLEX
90 degrees/s M ECCENTRIC
Figure 1. Relative peak torque values for knee strength of elderly women, expressed as percentage of the corresponding young adult mean (derived from Tables 2 and 3). Note the consistent pattern of higher values for the eccentric type of muscle exercise in both knee extension (EXT) and knee flexion (FLEX).
studies that measured cross-sectional area of the ankle plantarfiexors have also confirmed this difference in muscle size between young and old adults (Vandervoort and McComas, 1986; Rice etal., 1989). Actual fiber size in samples of quadriceps muscle from elderly subjects has also been investigated by removing some tissue and examining it microscopically (Aniansson et al., 1986; Essen-Gustavsson and Borges, 1986; Oertel, 1986; Lexell et al., 1988). Fiber atrophy is most evident for the Type II fast-twitch glycolytic fibers (see review by Rice et al. (1988) re: fiber type classifications), and not observed in the Type I slow-twitch fibers (Essen-Gustavsson and Borges, 1986; Oertel, 1986; Lexell et al., 1988; Grimby, 1988). Observations have also been made that the number of functional motor units is lower in the elderly (Campbell et al., 1973; Vandervoort and McComas, 1986; Brown et al., 1988). However, the shape and exterior girth of limbs may appear to be maintained, because increased amounts of fat and connective tissue have replaced the disappearing contractile component of muscle (Borkan et al., 1983; Lexell et al., 1988; Rice etal., 1989). As noted in Table 1, the group of elderly females in this study had a slightly higher mean weight than the young group, despite being significantly shorter in stature. Research with aged rodents has not indicated significant losses in fiber number (Daw et al., 1988), or a decrease in the velocity of shortening (Brooks and Faulkner, 1988). Our new observations on the strength of elderly women revealed a consistent finding that values obtained under conditions of eccentric exercise were less affected by the age factor than concentric. This characteristic is illustrated in the figure contrasting the relative strength of the elderly subjects for the two types of muscle exercise; they clearly did better when the muscle was lengthening. Viewed another way, the greater force development during the eccentric type of exercise, which was expected (see review by Chapman, 1985), became accentuated in the aged muscle. This accentuation does not appear to have been reported previously, and we do
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"Values are Mean ± SD, in N-m, N = 26. All differences between elderly and young women are significant (p < .01).
KNEE EXT
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VANDERVOORT ET AL.
ACKNOWLEDGMENTS
This research was funded by the Gerontology Research Council of Ontario and Employment and Immigration Canada's summer experience program. Address correspondence to Dr. Anthony A. Vandervoort, Department of Physical Therapy, Faculty of Applied Health Sciences, University of Western Ontario, London, Ontario, Canada N6G 1H1. REFERENCES
Aniansson, A.; Hedberg, M.; Henning, G.; Grimby, G. Muscle morphology, enzymatic activity and muscle strength in elderly men: A followup study. Muscle Nerve 9:585-591; 1986. Belanger, A. Y.; McComas, A. J. Extent of motor unit activation during effort. J.Appl. Physiol. 51:1131-1135; 1981. Borkan, G. A.; Hults, D. E.; Gerzof, S. G.; Robbins, A. H.; Silbert, C. K. Age changes in body composition revealed by computed tomography. J. Gerontol. 38:673-677; 1983. Brooks, S. V.; Faulkner, J. A. Contractile properties of skeletal muscles from young, adult and aged mice. J. Physiol. (Lond.) 404:71-82; 1988. Brown, W. F.; Strong, M. J.; Snow, R. Methods for estimating numbers of motor units in biceps-brachialis muscles and losses of motor units with aging. Muscle Nerve 11:423-432; 1988. Campbell, M. J.; McComas, A. J.; Petito, F. Physiological changes in ageing muscles. J. Neurol. Neurosurg. Psychiatry 36:174-182; 1973. Chapman, A. E. The mechanical properties of human muscle. Exerc. Sport Sci. Rev. 13:443-501; 1985. Clarkson. P. M.; Dedrick, M. E. Exercise-induced muscle damage, repair, and adaptation in old and young subjects. J. Gerontol. Med. Sci. 43:M91-96; 1988. Clarkson, P. M.; Kroll, W.; Melchionda, A. M. Age, isometric strength, rate of tension development and fiber type composition. J. Gerontol. 36:648-653; 1981. Davies, C. T. M.; Thomas, D. O.; White, M. J. Mechanical properties of young and elderly human muscle. Acta Med. Scand. (Suppl.) 711: 219-226; 1986. Daw, C. K.; Starnes, J. W.; White, T. P. Muscle atrophy and hypoplasia with aging: impact of training and food restriction. J. Appl. Physiol. 64:2428-2432; 1988. Essen-Gustavsson, B.; Borges, O. Histochemical and metabolic characteristics of human skeletal muscle in relation to age. Acta Physiol. Scand. 126:107-114; 1986.
Farrell, M.; Richards, J. G.: Analysis of the reliability and validity of the kinetic communicator exercise device. Med. Sci. Sports Exerc. 18: 44-49;1986. Fisher, M. B.; Birren, J. E.: Age and strength. J. Appl. Psychol. 31: 490-497; 1947. Grimby, G. Physical activity and the effects of muscle training in the elderly. Ann. Clin. Res. 20:62-66; 1988. Jones, D. A.; Newham, D. J.; Round, J. M.;ToIfree, S. E. J. Experimental human muscle damage: morphological changes in relation to other indices of damage. J. Physiol. (Lond.) 375:435-448, 1986. Jones, D. A.; Rutherford, O. M. Human muscle strength training: The effects of three different regimes and the nature of the resultant changes. J. Physiol. (Lond.) 391:1-11; 1987. Larsson, L.; Grimby, G.; Karlsson, J. Muscle strength and speed of movement in relation to age and muscle morphology. J. Appl. Physiol. 46:451^56: 1979. Lexell, J.; Taylor, C. C ; Sjostrom, M. What is the cause of the ageing atrophy? Total number, size and proportion of different fiber types studied in whole vastus lateralis muscle from 15- to 83-year-old men. J. Neurol. Sci. 84:275-294; 1988. Mathiowetz, V.; Kashman, N.; Volland, G.; Weber, K.; Dowe, M.; Rogers, S. Grip and pinch strength: Normative data for adults. Arch. Phys. Med. Rehabil. 66:69-72; 1985. McCully, K. K.; Faulkner, J. A. Characteristics of lengthening contractions associated with injury to skeletal muscle fibers. J. Appl. Physiol. 61:293-299; 1986. Murray, M. P.; Gardner, G. M.; Mollinger, L. A.; Sepic, S. B. Strength of isometric contractions. Knee muscles of men aged 20 to 86. Phys. Ther. 60:412-419; 1980. Murray, M. P.; Duthie, E. H.; Gambert, S. R.; Sepic, S. B.; Mollinger, L. A. Age-related differences in knee muscle strength in normal women. J. Gerontol. 40:275-280; 1985. Novak, L. P. Aging, total body potassium, fat-free mass, and cell mass in males and females between ages 18 and 85 years. J. Gerontol. 27: 438-443; 1972. Oertel, G. Changes in human skeletal muscles due to aging. Acta Neuropathol. 69:309-313; 1986. Rice, C. L.; Pettigrew. F. P.; Noble, E. G.; Taylor, A. W. The fibre composition of skeletal muscle. In: Poortmans, J. R., ed. Principles of exercise biochemistry. Vol. 27 of Med. and Sport Sci. series. Basel: Karger; 1988:22-39. Rice, C. L.; Cunningham, D. A.; Paterson, D. H.; Lefcoe, M. S. Arm and leg composition determined by computed tomography in young and elderly men. Clin. Physiol. 9:207-220; 1989. Sale, D. G.; Norman, R. W. Testing strength and power. In: MacDougall, J. D.; Wenger, H. A.;Green, H. J., ed. Physiological testing of the elite athlete. Ottawa: Can. Assoc. Sport Sci.; 1982. Tredinnick, J. T.; Duncan, P. W. Reliability of measurements of concentric and eccentric isokinetic loading. Phys. Ther. 68:656-659; 1988. Vandervoort, A. A.; Hayes, K. C. Plantarfiexor muscle function in young and elderly women. Eur. J. Appl. Physiol. 58:389-394; 1989. Vandervoort, A. A.; McComas, A. J. Contractile changes in opposing muscles of the human ankle joint with aging. J. Appl. Physiol. 61:361-367; 1986. Vandervoort, A. A . ; Hayes. K. C ; Belanger, A. Y. Strength and endurance
of skeletal muscle in the elderly. Physiother. Can. 38:167-173; 1986. Vandervoort, A. A.; Kramer, J. F.; Reidl, E. R. Eccentric knee strength of elderly females. Proceedings of the 17th annual meeting of the Canadian Association on Gerontology. Halifax; October 1988. Winer, B. J. Statistical principles in experimental design. Second Edition. Toronto: McGraw-Hill; 1971. Young, A.; Stokes, M.; Crowe, M. Size and strength of the quadriceps muscles of old and young women. Eur. J. Clin. Invest. 14:282-287; 1984. Young, A.; Stokes. M.; Crowe, M. The size and strength of the quadriceps muscles of old and young men. Clin. Physiol. 5:145-154; 1985.
Received January 18, 1989 Accepted July 17, 1989
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not know the mechanism conferring this relative advantage to the eccentric condition. Measurement of muscle strength in elderly females during both shortening and lengthening types of action has shown that age-related differences in strength would have less influence on their ability to perform activities involving eccentric exercise (e.g., with body weight). A functional example is that while lowering oneself into a sitting position the quadriceps muscles are lengthening, but while rising out of a chair the same muscles must shorten and work at a greater percentage of their total capacity. Thus, the phase when the muscles are controlling a given velocity of movement while lengthening may feel like much less effort than if the required forces had to be developed by shortening the muscle. However, it is important that the lengthening muscle not be contracting at its maximal tension-generating level, where damage and soreness will occur (McCully and Faulkner, 1986; Jones et al., 1986; Clarkson and Dedrick, 1988). Thus, before eccentric exercise can be recommended as a movement pattern for the elderly, detailed comparisons of its strength and safety should be made in an animal model.
Copyright I WO by The Geronlological Society of America
Eccentric Knee Strength of Elderly Females Anthony A. Vandervoort, John F. Kramer, and Evelin R. Wharram Department of Physical Therapy, University of Western Ontario.
between groups of young and old adults COMPARISONS have shown that isometric strength of a variety of limb muscles is decreased in the elderly population (see review by Vandervoort et al., 1986). Healthy individuals in their seventh and eighth decades score on average about 20 to 40% less during strength tests than young adults (Fisher and Birren, 1947; Larsson et al., 1979; Clarkson et al., 1981; Murray etal., 1980, 1985; Young etal., 1984, 1985;Davies et al., 1986; Clarkson and Dedrick, 1988) and the very old show even greater (50% or more) reduction (Mathiowetz et al., 1985; Vandervoort and McComas, 1986). Such trends have been found in studies of muscles in both the upper and lower limb from proximal and distal locations (Vandervoort et al., 1986), although the size of the age effect appears to vary from muscle to muscle (Grimby, 1988). Strength testing of concentric exercise (i.e., during which muscles shorten as the joint moves) has shown similar age differences to isometric contractions. For the knee extensors, strength decrements during isokinetic (constant angular velocity) testing of elderly versus young subjects were approximately 25% in males aged 60-69 (Larsson et al., 1979), 45% in males aged 70-86 (Murray et al., 1980), and 35% in women aged 70-86 (Murray et al., 1985). The latter two values agree with isometric strength levels reported in the studies by Young et al. (1984, 1985). A longitudinal investigation of 23 males ranging in age from 73 to 83 years found isometric and concentric knee strength decreased 1022% over a seven-year period, depending on the test velocity (Aniansson et al., 1986). Limb muscles also perform many common movements in a manner which has been referred to as "eccentric" exercise, i.e., the muscles are lengthened while actively trying to resist an external force such as body weight (see Chapman, 1985, for a review). Functional examples include using the knee extensors to control body weight while one sits down or descends stairs, and during certain phases of the gait cycle when muscles exert braking forces by resisting lengthening. Despite the physiological importance of this type of muscle action, the strength of elderly muscle for eccentric exercise has yet to be examined. It was thought to be of particular interest to study elderly females, in whom muscle mass and
absolute strength are considerably decreased at the same time as body weight is usually the same or greater than young adults (Novak, 1972; Lexell etal., 1988; Vandervoort and Hayes, 1989). Thus, the purpose of this study was to compare knee extension and flexion voluntary strength during eccentric versus concentric exercise in groups of young and elderly women. Two angular velocities of knee joint rotation were studied, 45° and 90°/s. A preliminary report of this research has been given by Vandervoort et al., 1988. METHODS
Subjects. — Groups of 26 young and elderly female volunteers (20-29 and 66-89 years, respectively) completed testing of the knee extensors and flexors of one leg (Table 1). The sample of elderly women had a shorter mean height {p < .01), but a slightly heavier mean weight than the young group. All subjects were mentally competent to give informed consent for participation in the study. To be included, they had to be without any injury or deformity to their tested leg, able to walk independently without limping, and have at minimum a habitual activity level of daily walking. Each subject was asked about medication use and potential volunteers with a history of diagnosed disease which restricted exercise capacity (e.g., cardiac, thyroid or Parkinson's disease, osteoporosis), were excluded. Young women were drawn mainly from the university setting; the elderly were all living independently in their own home or apartment. Test procedures. — All testing was completed using the Kinetic-Communicator (KinCom, Med*Ex Diagnostics of Canada, Coquitlam, British Columbia), a hydraulically driven, computer-controlled dynamometer. With this machine the velocity of the lever arm attached to the subject's leg is accurately controlled (see Farrell and Richards, 1986) in either "concentric" mode, where the subject pushes the lever arm at a preset velocity as strongly as possible, or "eccentric" mode, in which the motor rotates the lever arm and the individual tries to resist. Two knee motions, extenB125
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This study compared the strength of the knee extension and flexion muscles in groups of young and elderly women under two conditions: eccentric exercise in which the muscles were lengthened while subjects tried to resist an external force, versus concentric contractions in which the muscles shortened. Twenty-six females, aged 20 to 29 (Mean 25 ± 3 SD), and 26 elderly women, aged 66 to 89 (Mean 73 ± 6 SD), were tested at two angular velocities of movement, 45° and 90"ls, on a KinCom isokinetic dynamometer. Elderly women had significantly lower peak and average torque values in all comparisons with the young female group (25 to 54% lower, p < .01). However, differences between the age groups were consistently smallerfor the eccentric type of muscle action than the concentric, in both knee extensors and flexors.
VANDERVOORT ET AL.
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Table 1. Subject Characteristics Age Group Elderly Young
Age Group (years) 73 ± 6° 25 ± 3**
Height (m) 1.59 ± .05 1.67 ± .07**
Weight (Kg)
Table 2. Peak and Average Torque Values for Concentric and Eccentric Exercise of the Knee Extensors in Young and Elderly Women Angular Velocity
63.6 ± 7.3 59.6 ± 7.5
"Values are Mean ± SD, N = 26. **p< .01.
Data analysis. — Strength patterns of individual subjects were analyzed using the KinCom's Torque vs Angle computer program (see Tredinnick and Duncan, 1988). The boundaries of the range of motion included in the analysis were set at 90° to 10° of knee flexion, thereby allowing about 10° movement before entering and after leaving the data acquisition zone. The two trials (of the three) with the highest peak torques were averaged to provide the criterion scores. Four separate three-way analysis of variance (ANOVA) procedures (two age groups by two velocities by
Concentric
90°/s Eccentric
Concentric
Eccentric
61 i 16 131 ± 26
100 ± 27 152 ± 52
45 ± 12 97 ± 18
66 ± 22 100 ± 37
Peak Torque Elderly Young
72 ± 19137 ± 33
Elderly Young
52 ± 14 97 ± 20
94 ± 27 151 ± 51 Average Torque 63 ± 22 97 ± 36
"Values are Mean ± SD, in N-m, N = 26. All differences between elderly and young women are significant (p < .01).
two contraction types), with repeated measures on the last two factors, were used to examine the peak and average torques during knee extension and flexion for statistically significant differences. Any significant interaction effects were analyzed further with the Newman-Keuls technique to compare selected pairs of means (Winer, 1971). Peak torque is a commonly reported isokinetic measure that indicates maximal capability within a specific range of motion. Average torque reflects mean capability across the range of motion tested and is related to muscular power and work done (Sale and Norman, 1982). RESULTS
Knee extension. — The age and the contraction type main effects were statistically significant on both ANOVAs of peak torque and average torque values [p < .01). As shown in Table 2, the young women had consistently higher values in all comparisons, and values for the eccentric exercise were greater than concentric. The latter values showed a trend to decrease between the lower and higher velocity, while torques during eccentric exercise showed the opposite trend. Knee flexion. — The age and the contraction type main effects were statistically significant on both ANOVAs of peak torque and average torque values {p < .01). As shown in Table 3, the young women had consistently higher values in all comparisons, and values for the eccentric exercise were again greater than concentric. Velocity had only a minor effect on peak and average torque values. Means of the peak torque scores for the elderly group (from Tables 2 and 3) were divided into the corresponding means for the young women in order to compare the effect of age on strength in the concentric versus eccentric exercise. The resultant percentage values ranged from 46 to 75%, as illustrated in Figure 1. In each case, the relative strength during eccentric exercise was higher than in the concentric. DISCUSSION
Lower strength values for concentric exercise in the el-
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sion and flexion, at two angular velocities of knee joint rotation, 45° and 907s, were tested during a single session of about 45 minutes duration. These slow velocities are comparable to many functional movements and were easy to learn to perform. Fast velocities were avoided due to the potential for injury when the muscle is lengthened at high rates (McCully and Faulkner, 1986). The subjects were positioned sitting against a back support, keeping the hip angle at approximately 80°. Stabilizing belts were secured over the lap and across the thigh of the test leg, which was usually their dominant one (defined regarding preference for kicking a ball). Each type of knee motion, extension or flexion, was completed at the 45° or 907s velocity in a random testing order. Foam padding was placed under the subject's popliteal fossa in order to minimize any discomfort arising from compression of the tissues against the seat of the KinCom. The rotational axis of the dynamometer's lever arm was positioned such that it lay at the level of the lateral epicondyle of the subject's knee during contraction efforts. The resistance pad was located at the distal end of the lower leg, just above the ankle where it did not restrict dorsiflexion. Standardization procedures included only allowing subjects to grasp the lap seat belt, but not the edge of the testing table, and correcting all torque measures for the effects of gravity on the lower leg and the dynamometer's resistance pad. The range of movement consisted of from 100° of knee flexion to as far as the individual could comfortably extend the knee. Each muscle group was assessed using three reciprocal concentric-eccentric cycles, without a pause between the two phases of activation. Subjects completed at least three submaximal and one maximal practice routines. They were then asked if they believed they could perform the test motion maximally; any subjects requesting additional practice were allowed to do so. Verbal encouragement was given during the recorded trials, and a 2-minute rest period was always inserted between the different conditions of velocity and muscle group.
45°/s Age Group
AGE AND ECCENTRIC STRENGTH
Table 3. Peak and Average Torque Values for Concentric and Eccentric Exercise of the Knee Flexors in Young and Elderly Women
Age Group
Concentric
PERCENT OF YOUNG MEAN
60
Angular Velocity 45'7s
80
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90°/s Eccentric
Concentric
Eccentric
40
36 ± 10 64 ± 14
64 ± 20 85 ± 24
20
25 ± 7 49 ± 11
43 ± 18 61 ± 23
Peak Torque Elderly Young
37 ± 8" 68 ± 17
60 ± 20 85 ± 23 Average Torque
Elderly Young
27 ± 6 51 ± 12
39 ± 19 63 ± 19
derly females in comparison to the young were again confirmed by this study. Such results had previously been reported for the knee extensor muscles by Murray et al. (1985). In our comparisons of this variable between young and elderly females the differences were quite marked, amounting to approximately 50% reduction in strength for both knee extension and knee flexion. The age-related difference in strength may be attributable to a failure of descending drive from the motor cortex during volitional efforts of the elderly group, or the result of smaller (atrophied) muscles. The first factor was assessed in a previous study by Vandervoort and McComas (1986) using the twitch interpolation technique (a brief electrical shock is applied to the motor nerve during a maximal voluntary contraction, cf. Belanger and McComas, 1981). Results indicated that the sample of healthy elderly people, ranging in age from 60 to 100, had the ability to activate their ankle muscles maximally, because a superimposed twitch stimulus had little additional effect on their volitional force output. Decreases in strength found in those elderly subjects were thus attributed to a decreased excitable muscle mass. It seems reasonable to extrapolate these results to the knee musculature, in which other investigators have shown that well-motivated subjects can achieve high levels of voluntary muscle excitation (Jones and Rutherford, 1987). Our testing procedures included considerable learning and practice trials, and then encouragement to the subjects throughout their maximal efforts. Additional analysis of the test records indicated performance was stable, because they had low deviations among the three trials with little evidence of a learning effect. A number of different investigators have examined the relationship between age and size of muscles. Young et al. (1984) used a technique of ultrasound scanning to measure cross-sectional areas of the quadriceps muscles in young (21-28 yr) and old (70-79 yr) women and found a 33% decrease in the latter group. Significant reductions of this magnitude have also been reported when comparisons of the size of the isolated vastus lateralis muscle were made between young and elderly autopsy cases, using systematic morphometric techniques (Lexcll et al., 1988). In vivo
KNEE FLEX
45 degrees/s •
CONCENTRIC
KNEE EXT
KNEE FLEX
90 degrees/s M ECCENTRIC
Figure 1. Relative peak torque values for knee strength of elderly women, expressed as percentage of the corresponding young adult mean (derived from Tables 2 and 3). Note the consistent pattern of higher values for the eccentric type of muscle exercise in both knee extension (EXT) and knee flexion (FLEX).
studies that measured cross-sectional area of the ankle plantarfiexors have also confirmed this difference in muscle size between young and old adults (Vandervoort and McComas, 1986; Rice etal., 1989). Actual fiber size in samples of quadriceps muscle from elderly subjects has also been investigated by removing some tissue and examining it microscopically (Aniansson et al., 1986; Essen-Gustavsson and Borges, 1986; Oertel, 1986; Lexell et al., 1988). Fiber atrophy is most evident for the Type II fast-twitch glycolytic fibers (see review by Rice et al. (1988) re: fiber type classifications), and not observed in the Type I slow-twitch fibers (Essen-Gustavsson and Borges, 1986; Oertel, 1986; Lexell et al., 1988; Grimby, 1988). Observations have also been made that the number of functional motor units is lower in the elderly (Campbell et al., 1973; Vandervoort and McComas, 1986; Brown et al., 1988). However, the shape and exterior girth of limbs may appear to be maintained, because increased amounts of fat and connective tissue have replaced the disappearing contractile component of muscle (Borkan et al., 1983; Lexell et al., 1988; Rice etal., 1989). As noted in Table 1, the group of elderly females in this study had a slightly higher mean weight than the young group, despite being significantly shorter in stature. Research with aged rodents has not indicated significant losses in fiber number (Daw et al., 1988), or a decrease in the velocity of shortening (Brooks and Faulkner, 1988). Our new observations on the strength of elderly women revealed a consistent finding that values obtained under conditions of eccentric exercise were less affected by the age factor than concentric. This characteristic is illustrated in the figure contrasting the relative strength of the elderly subjects for the two types of muscle exercise; they clearly did better when the muscle was lengthening. Viewed another way, the greater force development during the eccentric type of exercise, which was expected (see review by Chapman, 1985), became accentuated in the aged muscle. This accentuation does not appear to have been reported previously, and we do
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"Values are Mean ± SD, in N-m, N = 26. All differences between elderly and young women are significant (p < .01).
KNEE EXT
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VANDERVOORT ET AL.
ACKNOWLEDGMENTS
This research was funded by the Gerontology Research Council of Ontario and Employment and Immigration Canada's summer experience program. Address correspondence to Dr. Anthony A. Vandervoort, Department of Physical Therapy, Faculty of Applied Health Sciences, University of Western Ontario, London, Ontario, Canada N6G 1H1. REFERENCES
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Received January 18, 1989 Accepted July 17, 1989
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not know the mechanism conferring this relative advantage to the eccentric condition. Measurement of muscle strength in elderly females during both shortening and lengthening types of action has shown that age-related differences in strength would have less influence on their ability to perform activities involving eccentric exercise (e.g., with body weight). A functional example is that while lowering oneself into a sitting position the quadriceps muscles are lengthening, but while rising out of a chair the same muscles must shorten and work at a greater percentage of their total capacity. Thus, the phase when the muscles are controlling a given velocity of movement while lengthening may feel like much less effort than if the required forces had to be developed by shortening the muscle. However, it is important that the lengthening muscle not be contracting at its maximal tension-generating level, where damage and soreness will occur (McCully and Faulkner, 1986; Jones et al., 1986; Clarkson and Dedrick, 1988). Thus, before eccentric exercise can be recommended as a movement pattern for the elderly, detailed comparisons of its strength and safety should be made in an animal model.
