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The characteristics of simple muscle power by gripping: gender differences and reliability of parameters using various loads.

AIM
There are few studies on muscle power during local muscle contractions with a small range of motion such as in gripping. The purposes of this study were to clarify the properties of the developmental phase based on time series of muscle power output, the reliability of the parameters, their relationships and the load intensity derived peak power by gender differences, and to examine the possibility of evaluating muscle power using gripping.


METHODS
Fifteen young males and 15 females participated in this study. Based on a crossover experimental design, each subject carried out 2 explosive grips at 20%, 30%, 40% and 50% loads of maximal using a voluntary grip contraction (MVC). The grip contraction velocities, sampled at 100 Hz, were measured accurately using a power instrument with an accelerometer. Muscle power curves were drawn from the product of the velocity and the set-up load.


RESULTS
The cross-correlation coefficients between the trials for the average curve of the time-series moving distance, the velocity, and the power in any load were very high (over 0.95) in both genders. The reliability of each parameter was mostly good in both genders (intraclass correlation coefficient, ICC>0.75). The peak power curve differed between genders, and the curve around the peak value in females was irregular.


CONCLUSIONS
A gender difference was found in the maximal power and the properties of the power curve. The maximal muscle power appeared at 30-50% MVC in males, and at 20-40% MVC in females. The peak power during the whole contraction, and the time to peak may reflect the conditions throughout the whole of the contraction. The new device used in this study to evaluate local regional muscle power (grip) is a very reliable and useful tool.