Power is required for any kind of physical activity,

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1 Journal of Strength and Conditioning Research, 2007, 21(3), National Strength & Conditioning Association RELATIONS BETWEEN FORCE-VELOCITY CHARACTERISTICS OF THE KNEE-HIP EXTENSION MOVEMENT AND VERTICAL JUMP PERFORMANCE JUNICHIRO YAMAUCHI 1 AND NAOKATA ISHII 2 1 Department of Orthopaedics, University of California, San Diego, California 92103; 2 Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo, Japan. ABSTRACT. Yamauchi, J., and N. Ishii. Relations between forcevelocity characteristics of the knee-hip extension movement and vertical jump performance. J. Strength Cond. Res. 21(3): Relations between force-velocity characteristics of the multijoint movement of the lower limbs and vertical jump performance were investigated. A total of 67 untrained subjects (age: years; height: cm; body mass: kg, mean SD) performed isometric and isotonic knee-hip extension movements on a servo-controlled dynamometer, and the force-velocity relations were determined. Also, vertical jump (VJ) performance was measured with a jump gauge. The force-velocity relation was described with a linear function so that the maximum isometric force (Fmax) and the maximum unloaded velocity (Vmax) for the knee-hip extension movement were estimated by extrapolation. Maximum isometric force coincided with maximum isometric force, F 0 (F 0 /Fmax ). Maximum isometric force, Vmax, and maximum power output (Pmax) were positively correlated with VJ (r 0.48, 0.68, and 0.76, respectively; p 0.001). However, when Fmax, Vmax, and Pmax were normalized with body mass (BM), leg length (LL), and BM, respectively, no correlation was seen between Fmax/BM and VJ (r 0.24, p 0.05), and significant correlations were seen between Vmax/LL and VJ (r 0.56, p 0.001) and between Pmax/BM and VJ (r 0.65, p 0.001). On the other hand, Fmax and Vmax (r 0.12, p 0.05) and Fmax/BM and Vmax/LL (r 0.05, p 0.05) were not significantly correlated, indicating that Fmax and Vmax were independent variables. The present estimates of Fmax, Vmax, and Pmax can be useful for evaluating the actual performance of multijoint movement of the lower limbs. It is suggested that, although in untrained individuals the speed of movement might be a more important determinant of jump performance, jump performance ability has a potential to improve with increases in strength of the lower limb. KEY WORDS. multijoint movement, force-velocity relation, maximum isometric force, maximum unloaded velocity, maximum power INTRODUCTION Power is required for any kind of physical activity, including sports. It has also been reported that the ability to produce explosive force or power in the knee extensor muscles declines with age in both men and women, in association with a decline in neuromuscular function of fasttwitch (FT) motor units (16, 17). Because mechanical power is the product of force and velocity, the force-velocity characteristic of muscle is one of the critical factors in determining physical performance. Thus, appropriate evaluation of force-velocity characteristics is essential to quantify the mechanical performance of muscle in vivo. Up to now, a number of studies have been conducted on the dynamic properties of single-joint movements, including knee extension. It has been reported that the characteristics of force-velocity and the power of knee extension movements, as determined by force-velocity relations and the maximum isometric force-time curve, are related to muscle fiber types (35, 36) and vertical jump performance (14), respectively. However, the evaluation of muscular dynamic properties in the multijoint movements is more important in many aspects, including activity for daily living compared with monoarticular movements. The vertical jump test has been used as one of the instantaneous methods to evaluate the peak mechanical power of the leg extensor muscles, which simply measures the height of the vertical jump (5, 12, 13, 30) or further calculate the product of the vertical velocity and the vertical ground reaction force (44). On the other hand, some studies on the force-velocity relation of multijoint exercises have shown that velocity is a function of force and maximum power is developed at a particular force (3, 10, 11, 29, 38). However, the correlation between vertical jump performance and the force-velocity-power characteristics of multijoint movements in the lower limbs remains unclear. The dynamometer with a high time resolution servo system was recently developed to obtain the isotonic force-velocity relation of knee-hip extension movements (42). Thus, in this study, we investigated the force-velocity relation of the knee-hip extension movement under precisely controlled isotonic conditions and examined correlations between the force-velocity-power characteristics and vertical jump performance. It was hypothesized that the force and velocity characteristics of the knee-hip extension movements would be independently related to jump performance. METHODS Experimental Approach to the Problem This study was designed to investigate the relations between force-velocity characteristics of the knee-hip extension movements and vertical jump performance. To address this issue, the newly developed dynamometer, in which force was controlled by the servo system, was used to examine the force-velocity relation of the knee-hip extension movements. A relatively large number of untrained subjects were chosen to minimize the influence of training so that intuitive characteristics of muscle functions could be determined with a wide range of individual differences. Subjects A total of 67 young untrained men and women (age: years; height: cm; body mass: kg, mean SD) volunteered for the study. Before 703

2 704 YAMAUCHI AND ISHII FIGURE 1. Experimental setup. the experiment, subjects warmed up for a few minutes by stretching the quadriceps, hamstrings, and triceps surae muscles. The methods and all procedures used during these experiments accorded with current local guidelines and the Declaration of Helsinki. All of the subjects were informed about the experimental procedure and the purpose of the study before study onset. Written informed consent was obtained from all participants. Measurements of Muscle Function of Knee-Hip Extension Movements Lower limb muscle function in terms of maximum isometric force (F 0 ), and extrapolated maximum isometric force (Fmax), maximum unloaded velocity (Vmax), and maximum power output (Pmax) were measured from the force-velocity relation determined with the servo-controlled, knee-hip extension dynamometer which was developed in collaboration with Matsushita Electric Works Ltd. (Osaka, Japan) for precisely controlling force and displacement during the movement. Details of the apparatus and methodology for the measurements have been described elsewhere (41). Briefly, the system consisted of a vertically placed triaxial force plate (MC3A-X-500; AMTI Inc., Watertown, MA), a servomotor (MSM352A1G; Matsushita Inc., Osaka, Japan), and a computer-assisted control unit to produce a servo loop (Figure 1). The force plate was connected to a servomotor, the position of which was detected with a rotary encoder placed coaxially with the servomotor. The force clamp, which keeps the force constant during the shortening of muscles (isotonic contraction), was established with the servo feedback control of displacement. In this study, displacement of the force plate was controlled with a function of force (force command) so as to keep the force relative to the maximum isometric force constant at any position. The force command was generated by a personal computer (SL2-A50K; Epson Inc., Nagano, Japan) and sent to a servoamplifier (MSD353A1V; Matsushita Inc.). The output from the force plate was introduced to the computer and fed back to the servoamplifier, which then generated a signal for controlling the servomotor so as to cancel the difference between the force command and measured force. Oscillation frequency of the whole mechanical system was about 5 khz, the time resolution of a servo-controlled system was 2 ms, and the controlled range of force was 150 to 3,000 N. During the measurement on the dynamometer, the subjects sat on a reclining seat with their feet on the plate and their legs flexed at 70% of leg length (LL) as a starting position, and they performed horizontally bilateral knee-hip extension movements against the force plate, from which force was controlled by the servo system. The LL was referred to as the longitudinal distance between the sole of foot and the hip joint (greater trochanter of the femur), and 100% LL means a full extension of legs in a seated position. The controlled force function was determined according to the LL-force relation. It was shown that the maximum isometric force progressively increased with increasing LL up to 80 90% and then declined rapidly. Accordingly, the force command for 70 90% LL applied the same force relative to the isometric force consistently, regardless of LL (isotonic in terms of relative force). In the tests, the subjects were secured by pelvis and trunk with straps and by shoulders with adjustable pads and were instructed to move without raising their hip from the seat. In the maximum isometric force (F 0 ) measurement, the subjects exerted force as explosively as possible for 3 seconds to retain a force plateau. Measurement was repeated 3 times with at least 2-minute rest period between bouts, and the largest value among the measurements was chosen for F 0. In the isotonic force measurements, the subjects performed 3 5 trials at a force level close to their body weight to familiarize themselves with the testing apparatus and procedure. They were asked to extend their legs as fast as possible after a signal. Three trials were completed under each load, and the best trial among them at each relative force was chosen for analysis. To determine the force-velocity relations, the measurements were made in a low-to-high force order 8 times; then, measurements of lower forces were repeated to eliminate the effect of fatigue. The maximum isometric force (F 0 ), force (F), and velocity (V) were determined at 80% LL. In addition, with some of the subjects, the time required for force development (TFD) from 30 to 60% of the maximum isometric force of the knee-hip extension movements was determined from the maximum isometric force-time curve, and the reproducibility of the force-velocity measurement was also examined by means of a test-retest procedure separated by a week. Measurement of Vertical Jump Performance Vertical jump (VJ) ability was assessed with a countermovement jump. The subjects performed the vertical jump on a jump gauge (Takei Scientific Instruments Co. Ltd., Niigata, Japan). They were instructed to jump vertically so as to land in the same position and at the same place from takeoff to avoid lateral or horizontal displacement. The subjects placed their hands on their sides throughout the entire jump and kept their torso in an upright position to emphasize the use of the leg extensor muscles (4). The subjects were to attempt to jump as high as possible and performed 3 trials with sufficient time for recovery between attempts. The highest trial was recorded. Statistical Analyses Data are presented as means SD. Differences between Fmax and F 0 and gender differences in all parameters were examined with the paired and unpaired t-test, respectively. Regression analysis was made for the relationships between parameters. Reproducibility of Fmax and Vmax was evaluated with intraclass correlation coefficients (ICCs), and paired a t-test was used to examine differences between test-retest data. The level of statis-

3 FORCE-VELOCITY RELATION AND VERTICAL JUMP 705 RESULTS The force-velocity relation of the knee-hip extension movements was well described with a linear function as shown in Figure 2. The Fmax and Vmax were estimated by extrapolating the linear regressions of the force-velocity relation onto both axes. Because the force-power relation was obtained as a simple quadratic function, Pmax was calculated by 0.5Fmax 0.5Vmax. The Fmax, Vmax, Pmax, and VJ were 1, N, m s 1, 1, W, and cm, respectively. In men (n 42), these values were 2, N, m s 1, 1, W, and cm, respectively, whereas in women (n 13), these values were 1, N, m s 1, W, and cm, respectively. All values were significantly larger in men than women. However, precise comparison between men and women was difficult in this study because of the large difference in the sampling number. Maximum isometric force coincided with F 0 (F 0 /Fmax ) and was not significantly different (p 0.05) from F 0 (n 28, Fmax 1, N vs. F 0 1, N). The ICC values between the first and second measurements for Fmax and Vmax (n 6) were 0.91 and 0.97, respectively, and no significant differences between test-retest data were seen. As shown in Figure 3, Fmax, Vmax, and Pmax were positively correlated with VJ (r 0.48, 0.68, and 0.76, respectively, p 0.001). However, when Fmax, Vmax, and Pmax were normalized with body mass (BM), LL, and BM, respectively, no correlation was found between Fmax/BM and VJ (r 0.24, p 0.05), and significant correlations were found between Vmax/LL and VJ (r 0.56, p 0.001) and between Pmax/BM and VJ (r 0.65, p 0.001). When men and women were analyzed separately, Vmax, Vmax/LL, Pmax, and Pmax/BM in men were significantly correlated with VJ (r 0.52, 0.40, 0.47, and 0.37, respectively). For data from women, no significant correlations were seen, possibly because of the small n. Time required for force development (n 6) was negatively correlated with Fmax (r 0.98, p 0.001), Pmax (r 0.94, p 0.01), and VJ (r 0.97, p 0.01), whereas it was not significantly correlated with Vmax (r 0.77, p 0.05). There were no significant correlations between Fmax and Vmax (r 0.12, p 0.05) and between Fmax/BM and Vmax/LL (r 0.05, p 0.05), as shown in Figure 4, indicating that Fmax and Vmax were independent variables. FIGURE 2. Representative force-velocity and force-power relations of the knee-hip extension movement. Circles velocity; squares power; lines regressions (r 0.99). Maximum isometric force (Fmax) and maximum unloaded velocity (Vmax) were obtained by extrapolating the linear regression. tical significance was set at p 0.05 unless otherwise noted. DISCUSSION Measurements of the force-velocity relation of the kneehip extension movements with the servo-controlled dynamometer could safely and precisely evaluate force, speed, and power. It showed that Fmax coincided with the measured F 0 and that each value of Fmax and Vmax were well correlated between test-retest data in terms of reproducibility, so that they can be adequately estimated by extrapolation. There is no generality of muscle function (2), so measurements of muscle functions should be specific to the movement. Therefore, it was useful to evaluate the relations between the dynamic characteristics of knee-hip extension movements and vertical jump performance compared with isolated joint movements. It was shown that Pmax of knee-hip extension movements was highly correlated with vertical jump performance. The results confirmed the hypothesis that, although both Fmax and Vmax were correlated with VJ, each of Fmax and Vmax was related to VJ independently because Fmax and Vmax were not correlated. Furthermore, when Fmax and Vmax were normalized with body mass and leg length, respectively, only relative Vmax was correlated with VJ; thus, the maximum speed of the knee-hip extension movements was more significantly related to the vertical jump performance in untrained individuals. The methods of this study could estimate most appropriately Pmax because the optimum force for power generation could only be found in the force-velocity relation (11, 22). Pmax was positively correlated with VJ, which has often been used for evaluation of leg muscular power (5, 12, 13, 30). This is consistent with others (11, 18, 38) who have shown a positive correlation between maximum power from the force-velocity relations measured on a cycle ergometer and vertical jump performance. However, it should be noted that body mass used for the vertical jump was not necessarily close to optimum load (50% of Fmax) for Pmax, so that it might be on the ascending phase or descending phase of the parabolic force-power relation. Such a discordance of actual load with optimal load for maximum power in the vertical jump is also present in other studies in which the peak power was measured in a single bout (11, 22). Therefore, it is difficult to predict with accuracy the value of Pmax from the height of the vertical jump (38). The correlation between Pmax and VJ might largely depend on the correlation between Vmax and VJ, although Fmax was also correlated with VJ (Figure 3). On the other hand, Driss et al. (11) have reported that the correlation between maximum power output and VJ is mainly due to the correlation between maximum force and VJ. This difference can be explained with the state of subjects and mode of exercise tests used. Untrained individuals were used in this study as subjects, whereas

4 706 YAMAUCHI AND ISHII FIGURE 3. Relations between vertical jump height and maximum isometric force (Fmax) (a), maximum unloaded velocity (Vmax) (b), maximum power output (Pmax) (c), Fmax/body mass (BM) (d), Vmax/leg length (LL) (e), and Pmax/BM (f ) of the knee-hip extension movement. Squares men; circles women; lines least squares regressions for both men and women. Significant correlations (p 0.001) were found between all 3 parameters except Fmax/BM (d) and vertical jump height.

5 FORCE-VELOCITY RELATION AND VERTICAL JUMP 707 FIGURE 4. Relations between maximum isometric force (Fmax) and maximum unloaded velocity (Vmax) (a) and Fmax/body mass (BM) and Vmax/leg length (LL) (b) of the knee-hip extension movement. Squares men; circles women. No significant correlation (p 0.05) was seen between the 2 variables. Driss et al. (11) used trained volleyball players. It is well known that the muscle fiber composition is influenced by genetic (8) and environmental factors (19) (e.g., slowtwitch fibers are predominant in long-distance runners, whereas FT fibers are predominant in sprinters and jumpers). Another interesting study has compared the vertical jump ability between a moderately trained subject with 70% FT and an Olympic 100-m freestyle swimmer with 60% FT but larger muscle cross-sectional area by 12% (27). Both subjects showed the same vertical jump performance, suggesting that vertical jump ability depended not only on the percentage of FT muscle fibers but also on the muscle mass. It has also been shown that maximum leg extension force correlates significantly with the vertical jumping height in basketball players (14). Therefore, in well-trained athletes with a large proportion of FT fibers, strength might be a more important determinant of jump performance than speed. It can be assumed that the maximum unloaded velocity estimated by extrapolating the force-velocity relation could reflect muscle fiber composition, although physiologic means of Vmax in the knee-hip extension movement remain unclear. It has been reported that individuals with a high percentage of FT muscle fibers in the vastus lateralis muscle have a higher maximum contraction velocities in knee extension movements under isokinetic (35) and isotonic afterloaded (36) conditions. In addition, a proportion of type II fiber in the vastus lateralis muscle is related to the optimal velocity for maximum power generation in the pedaling exercise and in jumping (18). Thus, for untrained subjects used in this study, muscle fiber composition could be a primary determinant of vertical jump performance. The coordination of agonist-antagonist muscle activation cannot be excluded for one of the factors to determine by the velocity of multijoint movements because contractions of many muscles are involved at the same time. Our preliminary electromyographic measurements during knee-hip extension movements showed that activity of the hip extensor muscle declined as the load decreased, whereas activity of the knee extensor declined as the load increased up to the maximum isometric force (42). This suggests that the mechanisms underlying the linear appearance of the force-velocity relation involve, at least partially, the coordination of muscle activity. It is suggested that the coordination of muscle activities are required to manage the proper movement (43). Thus, in this study, we further suggest that an improvement of muscular coordination can give rise to an increase in Vmax and an improvement in jump performance. Furthermore, the significant correlations between TFD and vertical jump performance suggest that the ability of the neuromuscular system to develop the greatest force in the shortest time is required for recruitment of the greatest number of motor units at the beginning of contractions and for the development of the high vertical force. It has been argued that peak power generation during the vertical jump performance with countermovement is not pure maximum muscle power but is also a combination with elastic energy. A rapid stretching of muscle during an eccentric action and following concentric action would produce a forceful movement in a short period of time (9). This stretch-shortening cycle (SSC), as a natural type of muscle function, is able to the make final action more powerful than is a concentric action alone (19, 31, 34, 39, 40) or a concentric action subsequent to an isometric action (33). Therefore, our measurement of VJ might also be influenced by the efficacy of SSC, which can be determined by an effective generation of eccentric force during the stretching phase. Individuals with a larger proportion of FT fibers might have a higher ability to generate large eccentric force rapidly because FT fibers are predominantly recruited during the eccentric action, irrespective of the Size Principle (6, 20, 23, 25, 26). Differences between men and women in the jump performance might exist in force-velocity characteristics of the knee-hip extension movement (Figure 3), although it was difficult to discuss in detail because only small numbers of female subjects participated. In line with our results in untrained individuals, Häkkinen (14) has reported that male basketball players record higher maximum forces of the knee-hip extensor and hip flexor muscles, shorter times required to produce maximum isometric force, and higher maximum vertical jumping heights than female basketball players. It has also been suggested that in the SSC movement, men have a greater utilization of

6 708 YAMAUCHI AND ISHII stored elastic energy at high prestretch velocities, whereas women have a better utilization of stored elastic energy at slow prestretch velocities (1). This could indicate that men, especially young men, require higher speed movements for maximum use of the stored elastic energy in the SSC movement (32). Such gender differences in neuromuscular power of the lower limb could occur during puberty because boys increase their vertical jump height at that time, whereas girls do not increase it but also decrease the takeoff force (28). Also, the elderly men can produce greater muscular power than elderly women during a countermovement jump (7). An age-related decline in the neuromuscular function, both during dynamic and isometric force productions (16, 17), seems to be dependent on the type of muscular contraction and gender: a decline in concentric strength starts earlier in both men and women than eccentric strength, which also starts earlier in men than in women (21), whereas lower velocity during the concentric phase of a countermovement jump is seen in elderly women (7). The methodology used to estimate muscular functions such as Fmax, Vmax, and Pmax of knee-hip extension movements can be useful for evaluating the actual performance of multijoint movement of the lower limbs. Evaluation of dynamic properties from measurements with relatively low loads is advantageous for untrained individuals because the rapid development of a large force during jump performance could stress the body excessively. Also, it was suggested that, in untrained individuals, the speed of movement might be a more important determinant of jump performance, although both strength and velocity were correlated with vertical jump performance independently. PRACTICAL APPLICATIONS From a practical point of view, to improve vertical jump performance, moderate resistance with high-speed multijoint movement techniques can be useful for speed and strength development so as to maximize mechanical power. Although it seems that jump performance ability is primarily determined by genetic factors, such as maximum shortening velocity or muscle fiber type of the lower limb muscles, it still has a higher potential to develop with increases in strength, especially for untrained individuals. The training program for untrained individuals might not be so important as long as training volume and intensity are of sufficient levels (15); however, to continuously gain strength, training intensity should be increased progressively as training proceeds. The maximum power can be developed with a combination of various loads with maximum effort (37). Such high-intensity stimulus during the forced development of dynamic movement is necessary for activation of the FT motor units, which are required for speed and strength enhancement; thus, the movement must be executed at maximum speed within any range of training intensity. Also, it is known that the effects of training can be greatest when the muscle action type used for training is similar to the specific movements (24). Therefore, to improve maximum power related to vertical jump performance, speed-strength training with knee-hip extension movements is best. REFERENCES 1. AURA, O., AND P.V. KOMI. The mechanical efficiency of locomotion in men and women with special emphasis on stretch-shortening cycle exercises. Eur. J. Appl. Physiol. 55: BAKER, D., G. WILSON, AND B. CARLYON. Generality versus specificity: A comparison of dynamic and isometric measures of strength and speedstrength. Eur. J. Appl. Physiol. 68: BOSCO, C., A. BELLI, M. ASTRUA, J. TIHANYI, R. POZZO, S. KELLIS, O. TSARPELA, C. FOTI, R. MANNO, AND C. TRANQUILLI. A dynamometer for evaluation of dynamic muscle work. Eur. J. Appl. Physiol. 70: BOSCO, C., AND P.V. KOMI. Influence of aging on the mechanical behavior of leg extensor muscles. Eur. J. Appl. Physiol. 45: BOSCO, C., P. LUHTANEN, AND P.V. KOMI. A simple method for measurement of mechanical power in jumping. Eur. J. Appl. Physiol. 50: BURKE, R.E. Motor unit properties and selective involvement in movement. Exerc. Sport Sci. Rev. 3: CASEROTTI, P., P. AAGAARD, E.B. SIMONSEN, AND L. PUGGAARD. Contraction-specific differences in maximal muscle power during stretch shortening cycle movements in elderly males and females. Eur. J. Appl. Physiol. 84: CLAMANN, H.P. Motor unit recruitment and the gradation of muscle force. Phys. Ther. 73: CLUTCH, D., M. WILTON, C.MCGOWN, AND G.R. BRYCE. Effect of depth jumps and weight training on leg strength and vertical jump. Res. Q. Exerc. Sport 54: DRISS, T., H. VANDEWALLE, J.M. LE CHEVALIER, AND H. MONOD. Force velocity relationship on a cycle ergometer and knee-extensor strength indices. Can. J. Appl. Physiol. 27: DRISS, T., H. VANDEWALLE, AND H. MONOD. Maximal power and force velocity relationships during cycling and cranking exercises in volleyball players. Correlation with the vertical jump test. J. Sports Med. Phys. Fitness 38: GLENCROSS, D.J. The nature of the vertical jump test and the standing broad jump. Res. Q. 37: GRAY, R.K. A test of leg power. Res. Q. 33: HÄKKINEN, K. Force production characteristics of leg extensor, trunk flexor and extensor muscles in male and female basketball players. J. Sports. Med. Phys. Fitness 31: HÄKKINEN, K., P.V. KOMI, M. ALÉN, AND H. KAUHANEN. EMG, muscle fibre and force production characteristics during a 1 year training period in elite weight-lifters. Eur. J. Appl. Physiol. 56: HÄKKINEN, K., W.J. KRAEMER, AND R.U. NEWTON. Muscle activation and force production during bilateral and unilateral concentric and isometric contractions of the knee extensors in men and women at different ages. Electromyogr. Clin. Neurophysiol. 37: HÄKKINEN, K., U.M. PASTINEN, R. KARSIKAS, AND V. LINNAMO. Neuromuscular performance in voluntary bilateral and unilateral contraction and during electrical stimulation in men at different ages. Eur. J. Appl. Physiol. 70: HAUTIER, C.A., M.T. LINOSSIER, A. BELLI, J.R. LACOUR, AND L.M. ARSAC. Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition. Eur. J. Appl. Physiol. 74: KOMI, P.V. Physiological and biomechanical correlates of muscle function: Effects of muscle structure and stretch-shortening cycle on force and speed. Exerc. Sport Sci. Rev. 12: KRAEMER, W.J., S.J. FLECK, AND W.J. EVANS. Strength and power training: Physiological mechanisms of adaptation. Exerc. Sport Sci. Rev. 24: LINDLE, R.S., E.J. METTER, N.A. LYNCH, J.L. FLEG, J.L. FOZARD, J.TO- BIN, T.A. ROY, AND B.F. HURLEY. Age and gender comparisons of muscle strength in 654 women and men aged yr. J. Appl. Physiol. 83: LINOSSIER, M.T., D. DORMOIS, R. FOUQUET, A. GEYSSANT, AND C. DENIS. Use of the force velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer. Eur. J. Appl. Physiol. 74: MORITANI, T. Neuromuscular adaptations during the acquisition of muscle strength, power and motor tasks. J. Biomech. 26(Suppl. 1): MORRISSEY, M.C., E.A. HARMAN, AND M.J. JOHNSON. Resistance training modes: Specificity and effectiveness. Med. Sci. Sports Exerc. 27: NARDONE, A., C. ROMANÒ, AND M. SCHIEPPATI. Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles. J. Physiol. (Lond.) 409: NARDONE, A., AND M. SCHIEPPATI. Shift of activity from slow to fast muscle during voluntary lengthening contractions of the triceps surae muscles in humans. J. Physiol. (Lond.) 395: PRINS, J. Physiological review of leg extensor power and jumping ability. Swimming World 21: QUATMAN, C.E., K.R. FORD, G.D. MYER, AND T.E. HEWETT. Maturation leads to gender differences in landing force and vertical jump performance: A longitudinal study. Am. J. Sports Med. 34:

7 FORCE-VELOCITY RELATION AND VERTICAL JUMP RAHMANI, A., F. VIALE, G.DALLEAU, AND J.R. LACOUR. Force/velocity and power/velocity relationships in squat exercise. Eur. J. Appl. Physiol. 84: SARGENT, D.A. The physical test of a man. Am. Phys. Educ. Rev. 26: SVANTESSON, U., B. ERNSTOFF, P.BERGH, AND G. GRIMBY. Use of a Kin- Com dynamometer to study the stretch shortening cycle during plantar flexion. Eur. J. Appl. Physiol. 62: SVANTESSON, U., AND G. GRIMBY. Stretch shortening cycle during plantar flexion in young and elderly women and men. Eur. J. Appl. Physiol. 71: SVANTESSON, U., G. GRIMBY, AND R. THOMEÉ. Potentiation of concentric plantar flexion torque following eccentric and isometric muscle actions. Acta Physiol. Scand. 152: SVANTESSON, U., AND K.S. SUNNERHAGEN. Stretch shortening cycle in patients with upper motor neuron lesions due to stroke. Eur.J.Appl. Physiol. 75: THORSTENSSON, A., G. GRIMBY, AND J. KARLSSON. Force velocity relations and fiber composition in human knee extensor muscles. J. Appl. Physiol. 40: TIHANYI, J., P. APOR, AND G. FEKETE. Force-velocity-power characteristics and fiber composition in human knee extensor muscles. Eur. J. Appl. Physiol. 48: TOJI, H., AND M. KANEKO. Effect of multiple-load training on the force velocity relationship. J. Strength Cond. Res. 18: VANDEWALLE, H., G. PERES, J.HELLER, J.PANEL, AND H. MONOD. Force velocity relationship and maximal power on a cycle ergometer. Correlation with the height of a vertical jump. Eur. J. Appl. Physiol. 56: WILSON, G.J., B.C. ELLIOTT, AND G.A. WOOD. The effect on performance of imposing a delay during a stretch shorten cycle movement. Med. Sci. Sports Exerc. 23: WILSON, G.J., G.A. WOOD, AND B.C. ELLIOTT. The performance augmentation achieved from use of the stretch shorten cycle: The neuromuscular contribution. Aust. J. Sci. Med. Sport 23: YAMAUCHI, J., C. MISHIMA, M. FUJIWARA, S. NAKAYAMA, AND N. ISHII. Steady-state force velocity relation of human multi-joint movement determined with force clamp analysis. J. Biomech. 40: YAMAUCHI, J., C. MISHIMA, S.NAKAYAMA, AND N. ISHII. The force velocity relation of human multi-joint movement: A study with force clamp analysis. J. Physiol. (Lond.) 555P:PC ZAJAC, F.E. Muscle coordination of movement: A perspective. J. Biomech. 26(Suppl. 1): ZAMPARO, P., G. ANTONUTTO, C. CAPELLI, M. GIRARDIS, L. SEPULCRI, AND P.E. DI PRAMPERO. Effects of elastic recoil on maximal explosive power of the lower limbs. Eur. J. Appl. Physiol. 75: Address correspondence to Junichiro Yamauchi, Ph.D., juyamauchi@ucsd.edu.