CONTRACTILE VELOCITY IS MORE IMPORTANT THAN FORCE APPLICATION IN THE DEVELOPMENT OF POWER

Clark, D. J., Patten, C., Reid, K. F., Phillips, E. M., & Fielding, R. A. (2007). Does force or velocity contribute more to maximal muscle power in older adults? ACSM Annual Meeting New Orleans, Presentation Number, 1646.

[This study involves older persons. However, it is likely that its implications will applicable to younger persons, at least until contradictory studies are produced.]

"Muscle power, the product of force and velocity, has been found to be more sensitive than strength for predicting functional status in older adults. Some investigators therefore advocate the use of high velocity contractions during resistance training to target power. However, the relative contributions of force and velocity to power remain unclear and are critical to explaining age-related decline in motor performance".

This study investigated how age-related decrements in force and velocity contributed to muscle power. Ss included 13 healthy middle-aged adults (M = 5; F = 8), 12 healthy older adults (M = 9; F = 3), and five older adults at risk for mobility disability (M = 2; F = 3). EMG was acquired during five maximal effort knee extensions of the dominant leg under three conditions: 1) power measured against a resistance of 25 Nm, 2) isometric maximum voluntary contraction torque at 60 of knee flexion, 3) velocity at 40% 1 RM. Torque, velocity and EMG were averaged for each dynamic trial between 40 and 60 of knee flexion. Isometric maximum voluntary contraction torque was averaged over a 500 ms window surrounding peak torque. For all data, the mean of trials 2-4 was used for analysis.

Power, maximum voluntary contractions, and velocity were similar between middle-aged and older healthy groups, but the older at-risk group demonstrated a significant impairment of power (52% less), maximum voluntary contractions (28% less), and velocity (39% less). Despite similar group means for all variables in the middle-aged and older healthy groups, a stepwise regression analysis revealed that velocity explained more of the variance in power, especially for the older adults, than any other variable. While maximum voluntary contraction predicted 50% of the variability in power for the middle-aged group, it explained only 37% in the older group. Adding velocity to the model explained an additional 33% of the variability in the young group (83% total), and 54% in the older group (90% total). Evaluated across all Ss, agonist muscle activation was significantly correlated with velocity (r = .62), while antagonist co-contraction was not (r = .24).

Implication. Peak muscle power in older adults is dominated by movement velocity rather than force. This finding on older adults is in agreement with what is known about the development in power in younger, active individuals. Age-related declines in muscle velocity are strongly associated with deficits in agonist muscle activation. [For sports that require speed of movement, the speed with which specific training occurs is most important.]

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