Power produced by maximal velocity elbow flexion

An analysis of horizontal elbow flexion at maximal velocity was made to determine how different loads affected power output. Twenty male subjects operated a specially constructed dynamometer initially performing a maximal effort isometric trial with the elbow fully extended and then three dynamic trials at each of three loads equal to 75, 50, and 25 per cent of the maximal isometric strength. Angular acceleration was used to calculate forearm torque, and power was obtained by taking the product of torque and angular velocity. Power was found to be a cubic function of time and a fourth-order polynomial function of angular displacement reaching a peak early in the movement. The 50 per cent load resulted in a higher peak level of power than either the 25 or 75 per cent loads.     

Differences in performance between trained and untrained subjects during a 30-s sprint test in a wheelchair ergometer

To compare physiological responses and propulsion technique of able bodied subjects with no prior experience of wheelchairs (AB) and wheelchair dependent subjects (WD), ten AB and nine WD performed a 30-s sprint test in a wheelchair ergometer. The WD had spinal cord injuries with a lesion at T8 or lower. The WD and AB did not show significantly different physiological responses. The power values averaged for the right wheel over the 30 s of the test were 50.2 (SD 14.7) W and 48.0 (SD 4.4) W for WD and AB, respectively. No significant differences in torque application could be discerned, although WD subjects seemed to have a more flattened torque curve with a smaller negative deflection at the beginning of the push. The WD applied a significantly higher horizontal propulsive force to the handrims but did not apply force more effectively. The percentages of effective force to total propulsive force were 61 (SD 16)% for WD and 57 (SD 4)% for AB. With regard to the kinematic parameters, AB followed the handrims significantly longer than WD (end angle AB 65°, WD 44°), started the push phase with their arms more in retroflexion and flexed their trunks further forward. The AB did however show a movement pattern comparable to that of wheelchair athletes measured in a comparable experiment. It could not be decided conclusively that inexperience in wheelchair propulsion led to a less effective propulsion technique. Despite the selection of WD with respect to lesion level, interindividual differences in terms of level of training may have been responsible for the absence of significant results.     

A simple method for measurement of maximal downstroke power on friction-loaded cycle ergometer

The aim of this study was to propose and validate a post-hoc correction method to obtain maximal power values taking into account inertia of the flywheel during sprints on friction-loaded cycle ergometers. This correction method was obtained from a basic postulate of linear deceleration-time evolution during the initial phase (until maximal power) of a sprint and included simple parameters as flywheel inertia, maximal velocity, time to reach maximal velocity and friction force. The validity of this model was tested by comparing measured and calculated maximal power values for 19 sprint bouts performed by five subjects against 0.6-1 N kg(-1) friction loads. Non-significant differences between measured and calculated maximal power (1151+/-169 vs. 1148+/-170 W) and a mean error index of 1.31+/-1.20% (ranging from 0.09% to 4.20%) showed the validity of this method. Furthermore, the differences between measured maximal power and power neglecting inertia (20.4+/-7.6%, ranging from 9.5% to 33.2%) emphasized the usefulness of power correcting in studies about anaerobic power which do not include inertia, and also the interest of this simple post-hoc method.     

Determining the Optimum Power Load in Jump Squat Using the Mean Propulsive Velocity

The jump squat is one of the exercises most frequently used to improve lower body power production, which influences sports performance. However, the traditional determination of the specific workload at which power production is maximized (i.e., optimum power load) is time-consuming and requires one-repetition maximum tests. Therefore, the aim of this study was to verify whether elite athletes from different sports would produce maximum mean propulsive power values at a narrow range of mean propulsive velocities, resulting in similar jump heights. One hundred and nine elite athletes from several individual/team sport disciplines underwent repetitions at maximal velocity with progressive loads, starting at 40% of their body mass with increments of 10% to determine the individual optimum power zone. Results indicated that regardless of sport discipline, the athletes’ optimum mean propulsive power was achieved at a mean propulsive velocity close to 1.0 m.s⁻¹ (1.01 ± 0.07 m.s⁻¹) and at a jump height close to 20 cm (20.47 ± 1.42 cm). Data were narrowly scattered around these values. Therefore, jump squat optimum power load can be determined simply by means of mean propulsive velocity or jump height determination in training/testing settings, allowing it to be implemented quickly in strength/power training.     

Electrically evoked isokinetic plantar flexor torque in males

The involuntary angle-specific isokinetic plantar flexor torques of seven male subjects aged 18-21 yr were measured using a Cybex II dynamometer (Lumex) modified by the addition of a strain-gauge load cell to improve the dynamic response of the instrument. Supramaximal electrical stimuli were used to evoke a maximal tetanic response from the triceps surae and ensure constant muscle activation at each angular velocity studied. Angle-specific torques were measured over a range (0.5-5.0 rad/s) of preset velocities, torque decreasing in a nonlinear manner with increasing angular velocity. The torque-velocity data was adequately described by an exponential equation of the form: V = a(e-1/b - e-Po/b) where V = velocity (rad/s), P = torque (N.m), Po = isometric torque (N.m), and a and b are constants. The mean intrasubject coefficient of variation of torque over the range of velocities studies was 7.9 +/- 1.88% (SD).     

A dynamometer for the measurement of force, velocity, work and power during an explosive leg extension

A dynamometer for measurement under static and dynamic conditions is presented. At different load levels, force, velocity, work and power can be measured in explosive leg extensions. Measurements on 53 subjects at different load levels (0-125.5 kg) were carried out. Peak power ranged from 2611 to 1746 W, force from 1351 to 1899 N, velocity from 1.61 to 0.89 m X s-1 and work from 329 to 605 J. Between trial correlation coefficients ranged from 0.72 to 0.95. The dynamometer is compared with others, and it is concluded that data obtained by this dynamometer have a greater practical validity.     

Predicting maximum eccentric strength from surface EMG measurements

The origin of the well-documented discrepancy between maximum voluntary and in vitro tetanic eccentric strength has yet to be fully understood. This study aimed to determine whether surface EMG measurements can be used to reproduce the in vitro tetanic force–velocity relationship from maximum voluntary contractions. Five subjects performed maximal knee extensions over a range of eccentric and concentric velocities on an isovelocity dynamometer whilst EMG from the quadriceps were recorded. Maximum voluntary (MVC) force–length–velocity data were estimated from the dynamometer measurements and a muscle model. Normalised amplitude–length–velocity data were obtained from the EMG signals. Dividing the MVC forces by the normalised amplitudes generated EMG corrected force–length–velocity data. The goodness of fit of the in vitro tetanic force–velocity function to the MVC and EMG corrected forces was assessed. Based on a number of comparative scores the in vitro tetanic force–velocity function provided a significantly better fit to the EMG corrected forces compared to the MVC forces (p?0.05), Furthermore, the EMG corrected forces generated realistic in vitro tetanic force–velocity profiles. A 58±19% increase in maximum eccentric strength is theoretically achievable through eliminating neural factors. In conclusion, EMG amplitude can be used to estimate in vitro tetanic forces from maximal in vivo force measurements, supporting neural factors as the major contributor to the difference between in vitro and in vivo maximal force.     

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.     

Isometric torque–angle relationships of the elbow flexors and extensors in the transverse plane

Maximal voluntary isometric torque–angle relationships of elbow extensors and flexors in the transverse plane (humerus elevation angle of 90°) were measured at two different horizontal adduction angles of the humerus compared to thorax: 20° and 45°. For both elbow flexors and extensors, the torque–angle relationship was insensitive to this 25° horizontal adduction of the humerus. The peak in torque–angle relationship of elbow extensors was found at 55° (0° is full extension). This is closer to full elbow extension than reported by researchers who investigated this relationship in the sagittal plane. Using actual elbow angles during contraction, as we did in this study, instead of angles set by the dynamometer, as others have done, can partly explain this difference.We also measured electromyographic activity of the biceps and triceps muscles with pairs of surface electrodes and found that electromyographic activity level of the agonistic muscles was correlated to measured net torque (elbow flexion torque: Pearson’s r = 0.21 and extension torque: Pearson’s r = 0.53). We conclude that the isometric torque–angle relationship of the elbow extensors found in this study provides a good representation of the force–length relationship and the moment arm–angle relationship of the elbow extensors, but angle dependency of neural input gives an overestimation of the steepness.     

Comparison of forces developed by the leg of the rock lobster when walking free or on a treadmill

Summary In the free walking rock lobster the forces developed by legs 4 and 5 were investigated during the power stroke. Two orthogonal force components lying in the horizontal plane were measured. Based on these results the diffent tasks of the two legs during walking are discussed. The forces developed by leg 4 were compared when the animal walked freely and on a treadmill. In these two situations the results differ qualitatively as in driven walking the forces are nearly identical in a long series of consecutive steps whereas in free walking the forces can vary greatly from step to step. However, similar mean values of force were measured with those on the treadmill being somewhat higher. This shows that, although the treadmill is driven by a motor, the animal does perform active walking movements. In the treadmill situation the forces increase as the speed of treadmill motor is decreased.Supported by DAAD and DFG (Cr 58) for H. Cruse and by ATP (80 119.112) INSERM for F. Clarac     

Evidence of residual force enhancement for multi-joint leg extension

Force enhancement is a well accepted property of skeletal muscle and has been observed at all structural levels ranging from single myofibrils to voluntarily activated m. quadriceps femoris in vivo. However, force enhancement has not been studied for multi-joint movements like human leg extension; therefore knowledge about its relevance in daily living remains limited. The purpose of this study was to determine whether there is force enhancement during maximal voluntary multi-joint leg extension. Human leg extension was studied (n=22) on a motor driven leg press dynamometer where external reaction forces under the feet as well as activity of 8 lower extremity muscles were measured. In addition, torque in the ankle and knee joints was calculated using inverse dynamics. The steady-state isometric force, joint torques, and muscle activation after active stretch (20° stretch amplitude at 60°/s) were compared with the corresponding values obtained during isometric reference contractions. There was consistent force enhancement during and following stretch for both forces and joint torques. Potentiation during stretch reached values between 26% and 30%, while a significant force enhancement of 10.5–12.3% and 4.3–7.4% remained 0.5–1 and 2.5–3 s after stretch, respectively. During stretch, EMG signals of m. gastrocnemius medialis and lateralis were significantly increased, while following stretch all analyzed muscles showed the same activity as during the reference contractions. We conclude from these results that force enhancement exists in everyday movements and should be accounted for when analyzing or modelling human movement.     

Relationship between traditional and ballistic squat exercise with vertical jumping and maximal sprinting

The purpose of this study was to quantify the magnitude of the relationship between vertical jumping and maximal sprinting at different distances with performance in the traditional and ballistic concentric squat exercise in well-trained sprinters. Twenty-one men performed 2 types of barbell squats (ballistic and traditional) across different loads with the aim of determining the maximal peak and average power outputs and 1 repetition maximum (1RM) values. Moreover, vertical jumping (countermovement jump test [CMJ]) and maximal sprints over 10, 20, 30, 40, 60, and 80 m were also assessed. In respect to 1RM in traditional squat, (a) no significant correlation was found with CMJ performance; (b) positive strong relationships (p < 0.01) were obtained with all the power measures obtained during both ballistic and traditional squat exercises (r = 0.53-0.90); (c) negative significant correlations (r = -0.49 to -0.59, p < 0.05) were found with sprint times in all the sprint distances measured when squat strength was expressed as a relative value; however, in the absolute mode, no significant relationships were observed with 10- and 20-m sprint times. No significant relationship was found between 10-m sprint time and relative or absolute power outputs using either ballistic or traditional squat exercises. Sprint time at 20 m was only related to ballistic and traditional squat performance when power values were expressed in relative terms. Moderate significant correlations (r = -0.39 to -0.56, p < 0.05) were observed between sprint times at 30 and 40 m and the absolute/relative power measures attained in both ballistic and traditional squat exercises. Sprint times at 60 and 80 m were mainly related to ballistic squat power outputs. Although correlations can only give insights into associations and not into cause and effect, from this investigation, it can be seen that traditional squat strength has little in common with CMJ performance and that relative 1RM and power outputs for both squat exercises are statistically correlated to most sprint distances underlying the importance of strength and power to sprinting.     

Time-of-day effect on patella tendon stiffness alters vastus lateralis fascicle length but not the quadriceps force-angle relationship

AIM: To examine the time-of-day (TOD) effect on torque-force/angle, fibre length (FL), tendon stiffness (K), stress, and strain using the quadriceps muscle-tendon complex as a model. METHODS: Twelve healthy young men (aged 27+/-2.0 years) were studied at AM (7h45) and PM (5h45). Maximal isometric contractions were carried out on an isokinetic dynamometer, with real-time recordings of vastus lateralis (VL) FL and patella tendon K using B-mode ultrasonography. Percutaneous electrical twitch doublets superimposed on maximal torque were used to test for muscle activation capacity (AC). RESULTS: At PM, torque and force increased by 16+/-3.0% (P<0.01) over 30-90 degrees knee angles. Where the load was standardised (at 250N) in order to discriminate between torque generation capacity and tendon K changes, PM relative to AM, there were 8% and 13% (P<0.01) reductions in relaxed and contracted FL, respectively. Average K decreased by 21% (P<0.001) and the maximal stress and strain were increased at PM by 11% and 16%, respectively (P<0.01). No TOD effect on AC was seen. CONCLUSION: The quadriceps torque or force-angle relationships shift upwards at PM vs. AM, with no shift in the position of the optimal knee angle. This torque or force increase appears not to be centrally modulated. Although K decreases with TOD thereby potentially shortening the working length of the sarcomeres, these changes overall do not affect the ability of the muscle to produce greater torque in the evening.     

Force–velocity,force–power relationships of bilateral and unilateral leg multi-joint movements in young and elderly women

The present study investigated force–velocity and force–power relationships of bilateral and unilateral knee-hip extension movement in young and elderly women. Twelve healthy young (age, 19–31 yr) and 12 healthy elderly (age, 60–82 yr) women performed bilateral and unilateral knee-hip extension movements on the dynamometer against loads controlled by the servo system. Under the isotonic force condition, force–velocity relationships were measured. The maximum isometric force (F_max), unloaded velocity (V_max) and power output (P_max) of the movements were calculated from extrapolating force–velocity and force–power relationships. F_max and P_max of bilateral and unilateral knee-hip extension movements were 20–30% lower in elderly than in young women. On the other hand, there were no significant differences in V_max between young and elderly women and between bilateral and unilateral movements. Bilateral deficit was larger as the generation of force was larger in both young and elderly women. Also, bilateral deficit of F_max and P_max were not different between young and elderly women. The results were that lower maximum power output of bilateral and unilateral leg multi-joint movements in elderly women did not depend on the intrinsic shortening velocity of muscle action, but largely on reduction in force generating capacity. This suggests the importance of preventing a loss of force generating capacity of muscles during leg multi-joint movements in elderly women.     

Supramaximal test results of male and female speed skaters with particular reference to methodological problems

Six male and six female elite speed skaters were tested during two bicycle ergometer tests: a 30 s sprint test and a 2.5 min supra maximal test. During the 2.5 min test oxygen consumption was measured every 30 s. The males showed 30-31% higher mean power output values both during the sprint test (1103 versus 769 Watt) and during the 2.5 min test (570 versus 390 Watt). Maximal oxygen consumption was 31% higher for the males than for the females (5.10 versus 3.50 1.min-1). However, when expressed per kilogram lean body weight (LBM), power output and oxygen consumption was equal for both sexes. Differences between present and previous results are most likely due to methodological problems with the estimation of load during the supra maximal test. Subjects appear to experience difficulties in distributing their power output over the 2.5 min if they are tested for the first time. For experienced skaters and cyclists, fixed levels of 19 W.kgLBM-1 as initial load setting for the sprint test and 8 W.kg LBM-1 for the 2.5 min test are recommended.     

Ground reaction force values in cosmonauts during locomotor exercises on board the International Space Station

Optimal methods for the prevention of negative impact of weightlessness have been developed based on the concept of Kozlovskaya, which states that support afferentation plays a trigger role in the development of the hypogravity motor syndrome. In this study, the maximal vertical ground reaction force (GRF) values were analyzed when locomotor training was performed on a BD-2 treadmill in long-term spaceflights. The study involved 12 cosmonauts. Recorded segments of the locomotor training (4554) performed in active (motor-driven) and passive (non-motor-driven) modes of BD-2 belt motion were analyzed. The data were analyzed by the methods of correlation and regression analysis and the nonparametric Mann–Whitney test. It was found that when running, regardless of the treadmill modes, an increase in the axial load by 1 kg was associated with a more than 1-kg increase in GRF; during walking an increase in GRF was less than 1 kg. As the speed increased, the GRF values increased most quickly when running in a passive mode and most slowly when walking in a passive mode. The GRF values in different BD-2 modes depended on both individual parameters of cosmonauts and locomotion types (walking or running). Our data can be the basis for the individualization of locomotor training onboard the ISS.     

Importance of upper-limb inertia in calculating concentric bench press force

The purpose of this study was to investigate the influence of upper-limb inertia on the force-velocity relationship and maximal power during concentric bench press exercise. Reference peak force values (Fpeakp) measured with a force plate positioned below the bench were compared to those measured simultaneously with a kinematic device fixed on the barbell by taking (Fpeakt) or not taking (Fpeakb) upper-limb inertia into account. Thirteen men (27.8 +/- 4.1 years, 184.6 +/- 5.5 cm, 99.5 +/- 18.6 kg) performed all-out concentric bench press exercise against 8 loads ranging between 7 and 74 kg. The results showed that for each load, Fpeakb was significantly less than Fpeakp (P < 0.0001), whereas no significant difference was found between Fpeakp and Fpeakt. The values of maximal force (F0), maximal velocity (V0), optimal velocity (Vopt), and maximal power (Pmax), extrapolated from the force- and power-velocity relationships determined with the kinematic device, were significantly underestimated when upper-limb inertia was ignored. The results underline the importance of taking account of the total inertia of the moving system to ensure precise evaluation of upper-limb muscular characteristics in all-out concentric bench press exercise with a kinematic device. A major application of this study would be to develop precise upper-limb muscular characteristic evaluation in laboratory and field conditions by using a simple and cheap kinematic device.     

Active drag related to velocity in male and female swimmers

Propulsive arm forces of 32 male and 9 female swimmers were measured during front crawl swimming using arms only, in a velocity range between 1.0 m s-1 and 1.8 m s-1. At constant velocity, the measured mean propulsive force Fp equals the mean active drag force (Fd). It was found that Fd is related to the swimming velocity v raised to the power 2.12 +/- 0.20 (males) or 2.28 +/- 0.35 (females). Although many subjects showed rather constant values of Fd/v2, 12 subjects gave significantly (p less than 0.01) stronger or weaker quadratic relationships. Differences in drag force and coefficient of drag between males and females (drag: 28.9 +/- 5.1 N, 20.4 +/- 1.9 N, drag coefficient: 0.64 +/- 0.09, 0.54 +/- 0.07 respectively) are especially apparent at the lowest swimming velocity (1 m s-1), which become less at higher swimming velocities. Possible explanations for the deviation of the power of the velocity from the ideal quadratic dependency are discussed.     

Force-velocity relationship and stretch-shortening cycle function in sprint and endurance athletes

This study examined the torque-velocity and power-velocity relationships of quadriceps muscle function, stretch shortening cycle function, and leg-spring stiffness in sprint and endurance athletes. Isokinetic maximal knee extension torque was obtained from 7 sprinters and 7 endurance athletes using a Con-trex isokinetic dynamometer. Torque and power measures were corrected for lean-thigh cross-sectional area and lean-thigh volume, respectively. Stretch-shortening cycle function and muscle stiffness measurements were obtained while subjects performed single-legged squat, countermovement, and drop-rebound jumps on an inclined sledge and force-plate apparatus. The results indicated that sprinters generated, on average, 0.15 +/- 0.05 N.m.cm(-2) more torque across all velocities compared with endurance athletes. Significant differences were also found in the power-velocity relationships between the 2 groups. The sprinters performed significantly better than the endurance athletes on all jumps, but there were no differences in prestretch augmentation between the groups. The average vertical leg stiffness during drop jumps was significantly higher for sprinters (5.86 N.m(-1)) compared with endurance runners (3.38 N.m(-1)). The findings reinforce the need for power training to be carried out at fast contraction speeds but also show that SSC function remains important in endurance running.     

The intra-push velocity profile of the over-ground racing wheelchair sprint start

The aim of this study was to analyse the first six pushes of a sprint start in over-ground racing wheelchair propulsion. One international male wheelchair athlete (age=28 years; body mass=60.6 kg; racing classification=T4) performed maximal over-ground sprint trials, over approximately 10 m, in his own racing wheelchair fitted with a velocometer. Each trial was filmed at 200 Hz using a "Pan and Tilt" system. Eight trials were manually digitised at 100 Hz. Raw co-ordinate data were smoothed and differentiated using a quintic spline routine. Across the period from pushes one to six the duration of each push cycle decreased (0.82+/-0.02-0.45+/-0.01 s) with the mean duration of the propulsive phase decreasing from 0.62+/-0.02 to 0.21+/-0.01 s and the recovery phase increasing from 0.20+/-0.01 to 0.24+/-0.02 s. The push-rim was contacted progressively closer to top dead centre and released progressively closer to bottom dead centre with each push. The data indicate that peak velocity occurred after release. The main findings of this study support the observation that racing wheelchair sprint propulsion is a complex form of locomotion and cannot be described accurately by using just the established definitions of a propulsive and a recovery phase.