Human skeletal muscle fibre types and force: velocity properties

It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3–8 rad · s^–1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force: velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad · s^–1. Measurements of torque: angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r > 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters.     

Leg and calf press training modes and their impact on jump performance adaptations

To examine the effects of resistance exercise (REX) mode on jump performance, subjects were assigned to one of three groups over a 6-week period with no cross-over. Subjects were assigned to leg and calf press REX on either a standard (n = 10) or ergometer (n = 9) device while a third group (n = 9) served as controls (CTRL). REX subjects worked out twice per week, which consisted of a three-set, 10-repetition paradigm for leg and calf press exercises. Immediately before and after the 6-week period, subjects performed tests that assessed jump (standing vertical jump, four-jump test protocol, depth jump) ability, while a fourth estimated knee extensor fast-twitch percentage (FT%) from fatigue incurred through a 50-repetition isokinetic protocol. Data analyses utilized 3 x 2 (group x time) repeated-measures ANCOVAs. Several dependent variables showed effects by group (standard REX, ergometer REX > CTRL) and time (post > pre). An interaction occurred for explosive leg power factor, a four-jump test variable, with standard REX post-test values as the interaction source. A trend for an interaction occurred for depth jump hang time, as ergometer REX values improved over time. Results suggest that mode-specific adaptations occur with REX training. Thus, athletes are best served with the selection of a REX device that is most specific to the demands of their jump performance task.     

Age differences in knee extension power, contractile velocity, and fatigability.

The purposes of this study were to examine age and gender differences in knee extensor strength, power, and fatigue using open- and closed-chain testing procedures. We tested the hypothesis that specific strength (strength/unit muscle mass) would not differ by age, whereas age differences in specific power and fatigue would remain consequent to blunted maximal contractile velocity. Skeletal muscle performance was examined in 28 young (26.9 +/- 0.7 yr) and 24 older (63.6 +/- 0.8 yr) men and women. Assessments included one-repetition maximum strength for knee extension, leg press, and squat; concentric knee extensor peak power, velocity, and fatigability; and sit-to-stand power, fatigability, and relative neural activation (electromyograph activity during sit-to-stand movement normalized to electromyograph activity during isometric maximum voluntary contraction). Thigh lean mass (TLM; kg) was assessed by dual-energy X-ray absorptiometry. Specific strength (N/kg TLM) and specific power (W/kg TLM) were estimated by dividing absolute values by TLM. Age differences in specific strength were observed for knee extension only (young, 41.2 +/- 1.0 N/kg TLM; older, 32.4 +/- 1.0 N/kg TLM; P < 0.05). Adjustment for TLM did not negate age differences in knee extension specific power (25-41% lower in older; P < 0.05) across loads tested. Older adults experienced fatigue across 10 repetitions of knee extension as peak velocity fell by 24% (P < 0.05). Deficits in concentric power persist after adjustment for TLM as maximum contractile velocity falls markedly with aging. Older adults are less capable of sustaining maximum concentric velocity during repetitive contractions. These findings suggest that velocity impairments are a possible contributor to mobility loss and falls risk among older adults. Interventions for improving contractile velocity should be pursued.     

A comparison of isoload and isoinertial leg press training on bone and muscle outcomes

The subjects of this study (n = 20; 16 women, 4 men) performed 10 weeks of leg press training using one of two exercise modes (isoload or isotonic) with no crossover. Their workouts, which were performed 3 times per week, involved 4 sets of 8 repetitions with maximal voluntary effort. Testing was performed pre- and posttraining to examine bone and muscle changes. Posttraining, both groups incurred significant concentric knee extensor strength and leg muscle mass gains, while the percentage of body fat and total body fat mass each decreased. Leg and total body bone mineral densities showed group-by-time interactions, as isoload exercise caused posttraining gains, while isoinertial values were unchanged. Bone resorption assays showed insignificant changes. Isoload training likely involved greater strain magnitudes and rates to evoke higher peak forces and osteogenesis. Transduction of the training stimulus may have involved (a) formation in response to microdamage, and (b) piezoelectric-induced potentials that stimulated site-specific osteoblast activity and osteogenesis.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Muscle strength assessment from functional performance tests: role of body size

The aim of the study was to test the hypothesis that the body size plays an important role in assessment of muscle ability to exert force by standard functional performance tests. Twenty-one male students were tested on maximal isometric lift, one leg rising, vertical jump, and box lift tests, and the maximal isokinetic strength of hip and knee extensors was also recorded. When indices of the 4 functional performance tests were related to the strength of each of the 2 leg extensor muscle groups, only maximal isometric lift demonstrated positive correlation with knee extensors strength. When muscle strength was corrected for body mass, however, the aforementioned relationship became insignificant, but the 1 leg rising performance demonstrated a positive relationship with knee extensor strength. In addition, maximal isometric lift and 1 leg rising test performance provided positive and negative correlation, respectively, with body mass. The obtained findings were in line with the effects of scale applied on the tested performance. We generally conclude that the assessment of muscle capability to exert force based on some standard functional performance tests could be confounded by the body size effect.     

Jump peak power assessment through power prediction equations in different samples

The aim of this study was to describe the characteristics of jump capacity in a group of secondary school students and to develop 2 specific equations-applied to boys and girls, respectively, to estimate the jump power of secondary school students. Four hundred and fifty-six boys (age, 14.1 ± 0.8 years; mass, 61.9 ± 15.7 kg; height, 1.64 ± 0.10 m) and 465 girls (age, 14.1 ± 0.9 years; mass, 55.1 ± 10.0 kg; height, 1.58 ± 0.07 m), all of them secondary school students, volunteered to participate in this study. They performed a vertical jump test (Abalakov) on a force platform, and jump height and peak power were measured. Most importantly, peak power was also estimated through a series of previously established power equations. For the purpose of establishing statistically significant differences, a p value ≤ 0.05 was fixed. The equations proposed by Canavan and Vesconvi, and Harman were the most precise with respect to actual power, reaching a percentage of 1.9-2.1 and 3.6-4.1%, respectively. The equations by Sayers and Lara showed a greater difference in percentage (9.9-12.4 and 22.4-24.2%, respectively) with that of actual power. Similar results were not obtained in other studies, which means that a specific equation will be required according to the characteristics of the assessed sample. Two equations specifically addressed to secondary school students will be established in this article: boys: ([61.8 jump height (cm)] + [37.1 body mass (kg)] - 1,941.6); girls: ([31 jump height (cm)] + [45 body mass (kg)] - 1,045.4). Crossvalidation tests that were done to prove the validity of said equations showed positive results. Practical applications: Those teachers who wish to estimate the jump power of their pupils can use these equations and thereby calculate jump power by the indirect method from jump height and body mass index, without any need to use any expensive tools.     

Force-velocity relations and fiber composition in human knee extensor muscles.

Standardized measurements of dynamic strength of the kneee extensor muscles were performed in 25 healthy male subjects (17-37 yr) by means of isokinetic contractions, i.e., knee extensions with constant angular velocities. Overall variation between double determinations of maximal torque throughout the 90 degrees arc of motion (0 degrees = fully extended leg) averaged 10% for the different constant velocities chosen. At any given angle of the knee the torque produced was higher for isometric than for dynamic contractions. Dynamic torque decreased gradually with increased speed of shortening. Peak dynamic torque was reached at knee angles in the range: 55-66 degrees, with a displacement toward smaller knee angles with higher angular velocities. Correlations were demonstrated between peak torque produced at the highest speed of muscle shortening and percent as well as relative area of fast twitch fibers in the contracting muscle. In addition muscles with a high percentage of fast twitch fibers had the highest maximal contraction speeds. These observations on intact human skeletal muscle are consistent with earlier findings in animal skeletal muscle preparations.     

Power and work produced in different leg muscle groups when rising from a chair

The aim of this study was to determine the power output and work done by different muscle groups at the hip and knee joints during a rising movement, to be able to tell the degree of activation of the muscle groups and the relationship between concentric and eccentric work. Nine healthy male subjects rose from a chair with the seat at knee level. The moments of force about the hip and knee joints were calculated semidynamically. The power output (P) and work in the different muscle groups surrounding the joints was calculated as moment of force times joint angular velocity. Work was calculated as: work = f Pdt. The mean peak concentric power output was for the hip extensors 49.9 W, hip flexors 7.9 W and knee extensor 89.5 W. This power output corresponded to a net concentric work of 20.7 J, 1.0 J and 55.6 J, respectively. There was no concentric power output from the knee flexor muscles. Energy absorption through eccentric muscle action was produced by the hip extensors and hip flexors with a mean peak power output of 4.8 W and 7.4 W, respectively. It was concluded that during rising, the hip and knee muscles mainly worked concentrically and that the greatest power output and work were produced during concentric contraction of the knee and hip extensor muscles. There was however also a demand for eccentric work by the hip extensors as well as both concentric and eccentric work by the hip flexors. The knee flexor muscles were unloaded.     

Predicting lower body power from vertical jump prediction equations for loaded jump squats at different intensities in men and women

The purpose of this study was to determine the efficacy of estimating peak lower body power from a maximal jump squat using 3 different vertical jump prediction equations. Sixty physically active college students (30 men, 30 women) performed jump squats with a weighted bar's applied load of 20, 40, and 60% of body mass across the shoulders. Each jump squat was simultaneously monitored using a force plate and a contact mat. Peak power (PP) was calculated using vertical ground reaction force from the force plate data. Commonly used equations requiring body mass and vertical jump height to estimate PP were applied such that the system mass (mass of body + applied load) was substituted for body mass. Jump height was determined from flight time as measured with a contact mat during a maximal jump squat. Estimations of PP (PP(est)) for each load and for each prediction equation were compared with criterion PP values from a force plate (PP(FP)). The PP(est) values had high test-retest reliability and were strongly correlated to PP(FP) in both men and women at all relative loads. However, only the Harman equation accurately predicted PP(FP) at all relative loads. It can therefore be concluded that the Harman equation may be used to estimate PP of a loaded jump squat knowing the system mass and peak jump height when more precise (and expensive) measurement equipment is unavailable. Further, high reliability and correlation with criterion values suggest that serial assessment of power production across training periods could be used for relative assessment of change by either of the prediction equations used in this study.     

Predicting a 10 repetition maximum for the free weight parallel squat using the 45 degrees angled leg press

The purpose of this research was to devise prediction equations whereby a 10 repetition maximum (10RM) for the free weight parallel squat could be predicted using the following predictor variables: 10RM for the 45 degrees angled leg press, body mass, and limb length. Sixty men were tested over a 3-week period, with 1 testing session each week. During each testing session, subjects performed a 10RM for the free weight parallel squat and 45 degrees angled leg press. Stepwise multiple regression analysis showed leg press mass lifted to be a significant predictor of squat mass lifted for both the advanced and the novice groups (p < 0.05). Leg press mass lifted accounted for approximately 25% of the variance in squat mass lifted for the novice group and 55% of the variance in squat mass lifted for the advanced group. Limb length and body mass were not significant predictors of squat mass lifted for either group. The following prediction equations were devised: (a) novice group squat mass = leg press mass (0.210) + 36.244 kg, (b) advanced group squat mass = leg press mass (0.310) + 19.438 kg, and (c) subject pool squat mass = leg press mass (0.354) + 2.235 kg. These prediction equations may save time and reduce the risk of injury when switching from the leg press to the squat exercise.     

Effects of 8-week in-season upper and lower limb heavy resistance training on the peak power, throwing velocity, and sprint performance of elite male handball players

The aims of this study were to test the potential of in-season heavy upper and lower limb strength training to enhance peak power output (Wpeak), vertical jump, and handball related field performance in elite male handball players who were apparently already well trained, and to assess any adverse effects on sprint velocity. Twenty-four competitors were divided randomly between a heavy resistance (HR) group (age 20 ± 0.7 years) and a control group (C; age 20 ± 0.1 years). Resistance training sessions were performed twice a week for 8 weeks. Performance was assessed before and after conditioning. Peak power (W(peak)) was determined by cycle ergometer; vertical squat jump (SJ) and countermovement jump (CMJ); video analyses assessed velocities during the first step (V(1S)), the first 5 m (V(5m)), and between 25 and 30 m (V(peak)) of a 30-m sprint. Upper limb bench press and pull-over exercises and lower limb back half squats were performed to 1-repetition maximum (1RM). Upper limb, leg, and thigh muscle volumes and mean thigh cross-sectional area (CSA) were assessed by anthropometry. W(peak) (W) for both limbs (p < 0.001), vertical jump height (p < 0.01 for both SJ and CMJ), 1RM (p < 0.001 for both upper and lower limbs) and sprint velocities (p < 0.01 for V(1S) and V(5m); p < 0.001 for V(peak)) improved in the HR group. Upper body, leg, and thigh muscle volumes and thigh CSA also increased significantly after strength training. We conclude that in-season biweekly heavy back half-squat, pull-over, and bench-press exercises can be commended to elite male handball players as improving many measures of handball-related performance without adverse effects upon speed of movement.     

Why is the force-velocity relationship in leg press tasks quasi-linear rather than hyperbolic?

Force-velocity relationships reported in the literature for functional tasks involving a combination of joint rotations tend to be quasi-linear. The purpose of this study was to explain why they are not hyperbolic, like Hill's relationship. For this purpose, a leg press task was simulated with a musculoskeletal model of the human leg, which had stimulation of knee extensor muscles as only independent input. In the task the ankles moved linearly, away from the hips, against an imposed external force that was reduced over contractions from 95 to 5% of the maximum isometric value. Contractions started at 70% of leg length, and force and velocity values were extracted when 80% of leg length was reached. It was shown that the relationship between leg extension velocity and external force was quasi-linear, while the relationship between leg extension velocity and muscle force was hyperbolic. The discrepancy was explained by the fact that segmental dynamics canceled more and more of the muscle force as the external force was further reduced and velocity became higher. External power output peaked when the imposed external force was ～50% of maximum, while muscle power output peaked when the imposed force was only ～15% of maximum; in the latter case ～70% of muscle power was buffered by the leg segments. According to the results of this study, there is no need to appeal to neural mechanisms to explain why, in leg press tasks, the force-velocity relationship is quasi-linear rather than hyperbolic.     

Assessment of the effectiveness of nontransdermal energy patches on muscle endurance and power

Claims of recently developed energy patches suggest that organic nanoscale biomolecular "antennas" produced by L and D-stereoisomers resonate at frequencies in unison with molecules in the cells inducing electron flow to assists in recruiting calcium ions, allowing greater muscle fiber recruitment during muscle contraction. The purpose of the study was to assess the efficacy of energy patches in the performance of selected muscle power and endurance measures. After a 5-minute warm-up and stretch, 41 college varsity football players (age, 20.37 +/- 1.24 years; height, 169.91 +/- 7.44 cm; weight, 109.45 +/- 19.85 kg) were pre-tested on 102-kg maximal bench press repetitions, standing vertical jump, grip strength, peak torque, torque to body weight, total work, average power, and average torque as measured by 50 repetitions of leg extensions at 180 degrees .s. The following week, the players were randomly assigned the experimental or placebo patches. After placement of the patches, the participants again completed a 5-minute warm-up, followed by the identical pre-test protocol. Repeated-measures ANOVAs were used to compare resultant data. No significant group interaction effects were found between experimental and placebo patches for maximal bench press repetitions (p = 0.48), vertical jump distance (p = 0.39), grip strength (p = 0.29), total work (p = 0.26), torque to body weight (p = 0.05), average peak torque (p = 0.08), and average power (p = 0.05). A significant increase occurred in the experimental group for peak torque (p = 0.04). It was concluded that the energy patches significantly improved performance over placebo patches in one of the eight variables tested and registered near significance in two additional variables. However, inconsistency in overall results demands further studies to determine the reliability in improvement of performance in the presence of energy patches.     

The energetics of the jump of the locust Schistocerca gregaria.

The anatomy of the metathoracic leg is redescribed with particular reference to storage of energy in cuticular elements and the way in which the stored energy is used in jumping. The jump of adult male locusts requires an energy of 9 mJ and that of the female requires 11 mJ. The semilunar processes of each metafemur store 4 mJ at a stress of 15 N, and the extensor tibiae apodeme stores a further 3 mJ at the same stress. The total stored energy in both metathoracic legs is 14 mJ. The extensor tibiae muscle produces a maximum isometric force of over 15 N at 30 degrees C and, when loaded with the extensor apodeme and semilunar processes, attains this force in 0.3 sec with a strain of 0.8 mm. The peak power output is 36 mW or 0.45 W.g-1. The peak isometric force is attained when the tibia is fully flexed and the force falls as the tibia extends. The extensor tibiae muscle A band is 5.5 mum long and the peak force is over 0.75 N.m-2. The peak velocity of shortening is 7 mm.sec-1 or about 1.75 lengths/sec at 30 degrees C. The tensile strength of the extensor apodeme is 0.6 kN.mm-2 and Young's modulus is 19 kN.mm-2. The safety factor does not exceed 1.2 and the safety factor of the semilunar processes and tibial cuticle is little higher. The jump impulse lasts 25-30 msec. A velocity of 3.2 m.sec-1 is reached after a peak acceleration of 180 m.sec-2. The peak power output is 0.75 W at close to maximum velocity. Energy losses in rotating the femur and tibia are small and it is shown that the leg is able to extend at 7 times the normal rate with losses of about 20%. Most of the stored energy is converted to kinetic energy as the animal jumps. A model is based on the relaxation of a spring that has the properties of the elastic elements of the locust leg into a lever with the same kinematics as the locust leg produces a force-distance curve similar to that measured for locust jumps. The major part of the jump energy is stored before the jump.     

The relation between anthropometric and physiological variables and bat velocity of high-school baseball players before and after 12 weeks of training

The purpose of this article was to investigate the relation between anthropometric and physiological variables to linear bat swing velocity (BV) of 2 groups of high-school baseball players before and after completing a 12-week periodized resistance exercise program. Participants were randomly assigned to 1 of 2 training groups using a stratified sampling technique. Group 1 (n = 24) and group 2 (n = 25) both performed a stepwise periodized resistance exercise program and took 100 swings a day, 3 d·wk-1, for 12 weeks with their normal game bat. Group 2 performed additional rotational and full-body medicine ball exercises 3 d·wk-1 for 12 weeks. Fourteen variables were measured or calculated before and after 12 weeks of training. Anthropometric and physiological variables tested were height, body mass, percent body fat, lean body mass (LBM), dominant torso rotational strength (DTRS) and nondominant torso rotational strength (NDTRS), sequential hip-torso-arm rotational strength measured by a medicine ball hitter's throw (MBHT), estimated 1 repetition maximum parallel squat (PS) and bench press (BP), vertical jump (VJ), estimated peak power, angular hip velocity (AHV), and angular shoulder velocity (ASV). The baseball-specific skill of linear BV was also measured. Statistical analysis indicated a significant moderately high positive relationship (p ≤ 0.05) between prelinear BV and pre-NDTRS for group 1, pre-LBM, DTRS, NDTRS, peak power, and ASV for group 2; moderate positive relationship between prelinear BV and preheight, LBM, DTRS, peak power, BP, PS, and ASV for group 1, preheight, body mass, MBHT, BP, and PS for group 2. Significantly high positive relationships were indicated between postlinear BV and post-NDTRS for group 1, post-DTRS and NDTRS for group 2; moderately high positive relationships between postlinear BV and post-LBM, DTRS, peak power, BP, and PS for group 1, postheight, LBM, VJ, peak power for group 2; moderate positive relationships between postlinear BV and postheight, body mass, MBHT, and VJ for group 1, postbody mass, MBHT, BP, PS, and ASV for group 2. Significantly low positive relationships were indicated between prelinear BV and prebody mass, MBHT, and VJ for group 1, pre-VJ and AHV for group 2; postlinear BV and post-AHV for group 2. These data show that significant relationships do exist between height, body mass, LBM, rotational power, rotational strength, lower body power, upper and lower body strength, AHV, and ASV to linear BV of high-school baseball players. Strength coaches may want to consider using this information when designing a resistance training program for high-school baseball players. Those recruiting or scouting baseball players may want to use this information to further develop ways of identifying talented players. However, one should be cautious when interpreting this information when designing strength training programs for high-school baseball players to increase linear BV.     

Evaluation of peak power prediction equations in male basketball players

This study compared peak power estimated using 4 commonly used regression equations with actual peak power derived from force platform data in a group of adolescent basketball players. Twenty-five elite junior male basketball players (age, 16.5 +/- 0.5 years; mass, 74.2 +/- 11.8 kg; height, 181.8 +/- 8.1 cm) volunteered to participate in the study. Actual peak power was determined using a countermovement vertical jump on a force platform. Estimated peak power was determined using countermovement jump height and body mass. All 4 prediction equations were significantly related to actual peak power (all p < 0.01). Repeated-measures analysis of variance indicated significant differences between actual peak power and estimate peak power from all 4 prediction equations (p < 0.001). Bonferroni post hoc tests indicated that estimated peak power was significantly lower than actual peak power for all 4 prediction equations. Ratio limits of agreement for actual peak power and estimated peak power were 8% for the Harman et al. and Sayers squat jump prediction equations, 12% for the Canavan and Vescovi equation, and 6% for the Sayers countermovement jump equation. In all cases peak power was underestimated.     

Torque-velocity characteristics and muscle fiber type in human vastus lateralis

The relationship between torque-velocity characteristics of the knee extensors during isokinetic contractions and muscle fiber type of the vastus lateralis, determined from two muscle biopsy samples, was investigated in 12 male and 18 female subjects. Peak torque, corrected for the effect of gravity and impact artifact, was classified as corrected peak torque. The torque measured 30 degrees from full extension and, corrected for gravity, was classified as corrected torque at 30 degrees. No significant correlations were found between the percentage of fast-twitch fibers (%FT) or the relative area of FT fibers (%FTA) and corrected peak torque values for any of the velocities tested or the knee angles where corrected peak torques were measured. However, significant inverse relationships were determined for corrected torque at 30 degrees at all but the fastest velocity (270 degrees/s) and both %FT and %FTA for the male subjects. These results reveal that muscle fiber type of the vastus lateralis, based on duplicate muscle samples, is not related to the peak torque actually generated by the knee extensors but may influence the shape of the torque output for maximal contractions sustained over the entire range of motion.     

Relative net vertical impulse determines jumping performance

The purpose of this investigation was to determine the relationship between relative net vertical impulse and jump height in a countermovement jump and static jump performed to varying squat depths. Ten college-aged males with 2 years of jumping experience participated in this investigation (age: 23.3 ± 1.5 years; height: 176.7 ± 4.5 cm; body mass: 84.4 ± 10.1 kg). Subjects performed a series of static jumps and countermovement jumps in a randomized fashion to a depth of 0.15, 0.30, 0.45, 0.60, and 0.75 m and a self-selected depth (static jump depth = 0.38 ± 0.08 m, countermovement jump depth = 0.49 ± 0.06 m). During the concentric phase of each jump, peak force, peak velocity, peak power, jump height, and net vertical impulse were recorded and analyzed. Net vertical impulse was divided by body mass to produce relative net vertical impulse. Increasing squat depth corresponded to a decrease in peak force and an increase in jump height and relative net vertical impulse for both static jump and countermovement jump. Across all depths, relative net vertical impulse was statistically significantly correlated to jump height in the static jump (r = .9337, p < .0001, power = 1.000) and countermovement jump (r = .925, p < .0001, power = 1.000). Across all depths, peak force was negatively correlated to jump height in the static jump (r = -0.3947, p = .0018, power = 0.8831) and countermovement jump (r = -0.4080, p = .0012, power = 0.9050). These results indicate that relative net vertical impulse can be used to assess vertical jump performance, regardless of initial squat depth, and that peak force may not be the best measure to assess vertical jump performance.     

Functional torque-velocity and power-velocity characteristics of elite athletes

Technical limitations of some isokinetic dynamometers have called into question the validity of some data on human muscle mechanics. The Biodex dynamometer has been shown to minimize the impact artefact while permitting automatic gravity correction. This dynamometer was used to study quadriceps muscle torque and power generation in elite power (n = 6) and elite endurance (n = 7) athletes over 12 randomly assigned isokinetic velocities from 30 degrees.s-1 to 300 degrees.s-1. The angle at peak torque varied as a negative, linear function of angular velocity, with the average angle across test velocities being 59.5 degrees (SD 10.2 degrees). Power athletes developed greater peak torque at each angular velocity (P less than 0.05) and experienced a 39.7% decrement in torque over the velocity range tested. Endurance athletes encountered a 38.8% decline in peak torque. Torques measured at 60 degrees of knee flexion followed a similar trend in both groups; however the greatest torques were recorded at 60 degrees.s-1 rather than at 30 degrees.s-1. Leg extensor muscle power increased monotonically with angular velocity in both power (r2 = 0.728) and endurance athletes (r2 = 0.839); however these curves diverged significantly so that the power athletes produced progressively more power with each velocity increment. These inter group differences probably reflected a combination of natural selection and training adaptation.