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The use of cycle ergometers with strain gauges bonded on to the cranks enables the evaluation of strength, velocity and power.
However, the torque measured at the end of downstroke is higher at high velocity than at medium velocity in contradiction
with the force–velocity relationship. Kinematic data were collected with a camera during sprints on a Lode ergometer with
strain gauges. Leg mechanical energy (E
Leg) and its derivative (dE
Leg/dt) were calculated from the sum of the kinetic and potential energies. The opposition of P
ext (output at crank level) and dE
Leg/dt before bottom dead centre suggested a transformation of E
Leg into external work, explaining the higher torque at the end of downstroke at peak velocity. Another explanation is that the
leg muscles worked on different parts of their torque–angle relationships as the phase between knee and ankle angles was different
at low and high cycling frequencies. Musculo-skeletal net power output (algebraic sum of P
ext and dE
Leg/dt) indicated that musculo-skeletal structures participated in the upward movement, whereas P
ext was negative. 相似文献
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Tarak Driss Tarak Driss Henry Vandewalle Jacques Quièvre Christian Miller Hugues Monod 《Journal of sports sciences》2013,31(2):99-105
The aim of this study was to determine the effects of external loading on power output during a squat jump on a force platform in athletes specializing in strength and power events (6 elite weight-lifters and 16 volleyball players) and in 20 sedentary individuals. Instantaneous power was computed from time-force curves during vertical jumps with and without an external load (0, 5 or 10 kg worn in a special vest). The jumps were performed from a squat position, without lower limb counter-movement or an arm swing. Peak instantaneous power corresponded to the highest value of instantaneous power during jumping. Average power throughout the push phase of the jump was also calculated. A two‐way analysis of variance showed significant interactions between the load and group effects for peak instantaneous power ( P < 0.01) and average power ( P < 0.001). Peak instantaneous power decreased significantly in sedentary individuals when moderate external loads were added. The peak instantaneous power at 0 kg was greater than that at 5 and 10 kg in the sedentary individuals. In contrast, peak instantaneous power was independent of load in the strength and power athletes. Mean power at 0 kg was significantly lower than at 5 kg in the athletes; at 0 kg it was significantly higher than at 10 kg in the sedentary males and at 5 and 10 kg in the sedentary females. In all groups, the force corresponding to peak instantaneous power increased and the velocity corresponding to peak instantaneous power decreased with external loading. The present results suggest that the effects of external loading on peak instantaneous power are not significant in strength and power athletes provided that the loads do not prevent peak velocity from being higher than the velocity that is optimal for maximal power output. 相似文献
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Tarak Driss Virgile Serrau David George Behm Ethelle Lesne-Chabran Armande Le Pellec-Muller Henry Vandewalle 《Journal of sports sciences》2013,31(1):60-69
AbstractThe present investigation verified that strength is improved by a training programme consisting of repetitions of maximal isometric voluntary co-contractions without increasing co-activations during contractions against external resistances. Ten participants performed 12 training sessions (four sets of 6 × 4 second maximal isometric co-contraction of the elbow flexor and extensors, 3 days a week for 4 weeks). Surface electromyograms of triceps and biceps brachii were collected during maximal voluntary isometric elbow flexion and extension against a force transducer. Maximal voluntary isometric force increased significantly after training, by 13.8 ± 6.0% (extension) and 9.6 ± 9.5% (flexion), but the observed increases in EMG of agonist muscles during maximal voluntary contraction were not significant. No significant changes in the levels of co-activation of the elbow flexors and extensors were observed. No significant change was observed for all the parameters in a control group of ten participants. These results indicated that the strength improvements after co-contraction training occur without increases in co-activation level. 相似文献
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The aim of this study was to determine the effects of external loading on power output during a squat jump on a force platform in athletes specializing in strength and power events (6 elite weight-lifters and 16 volleyball players) and in 20 sedentary individuals. Instantaneous power was computed from time-force curves during vertical jumps with and without an external load (0, 5 or 10 kg worn in a special vest). The jumps were performed from a squat position, without lower limb counter-movement or an arm swing. Peak instantaneous power corresponded to the highest value of instantaneous power during jumping. Average power throughout the push phase of the jump was also calculated. A two-way analysis of variance showed significant interactions between the load and group effects for peak instantaneous power (P< 0.01) and average power (P< 0.001). Peak instantaneous power decreased significantly in sedentary individuals when moderate external loads were added. The peak instantaneous power at 0 kg was greater than that at 5 and 10 kg in the sedentary individuals. In contrast, peak instantaneous power was independent of load in the strength and power athletes. Mean power at 0 kg was significantly lower than at 5 kg in the athletes; at 0 kg it was significantly higher than at 10 kg in the sedentary males and at 5 and 10 kg in the sedentary females. In all groups, the force corresponding to peak instantaneous power increased and the velocity corresponding to peak instantaneous power decreased with external loading. The present results suggest that the effects of external loading on peak instantaneous power are not significant in strength and power athletes provided that the loads do not prevent peak velocity from being higher than the velocity that is optimal for maximal power output. 相似文献
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The effect of maternal nutritional supplementation during pregnancy and lactation on the mental and motor development of infants was studied in a rural population in Taiwan. Women were randomly assigned to 2 treatment groups: 1 received a high-calorie and protein supplement ("supplement" group); the other received a placebo ("control" group). Infants received no direct supplementation. At approximately 8 months of age, the mental and motor development of the infants was assessed using a research to maternal supplementation in either scale, nor were the mental scale scores of infants of supplement mothers significantly higher than infants of control mothers. However, the motor scores of supplement infants were higher than those of control infants, which is consistent with the findings of 2 other large-scale nutritional supplementation studies. 相似文献
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Loyal W. Joos 《Journal of Experimental Education》2013,81(4):357-358
In this paper, the use of several measurement models for the analysis of data arising from learning hierarchies is discussed, and the results of an empirical investigation of the application of an Item Response Theory (IRT) model to a learning hierarchy in subtraction are examined. The analysis confronts the test developer’s original intentions with empirical data through the use of the IRT model, and three ways that the model can be useful in explicating the patterns of empirical results from a learning hierarchy are described. 相似文献
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