THE EFFICIENCY OF ECCENTRIC AND CONCENTRIC MUSCLE CONTRACTIONS
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This study examined the mechanical efficiencies of eccentric and concentric muscle contractions, as well as their relative efficiency. Twenty subjects were tested isokinetically eight times during two testing sessions. The subjects performed twenty repetitions of either all eccentric or all concentric work with the knee extensor/flexor musculature. The KIN/COM dynamometer was used to measure the total work output during each test. The efficiency of two types of contractions (eccentric and concentric) were examined at two speeds of movement (60 deg./s and 120 deg./s) and the two intensities of work (low and medium). During each test, the oxygen consumption was measured using a MMC Horizon metabolic cart. The total work performed during these tests was divided by the calculated metabolic cost of the work to obtain the efficiency for each test. The relative efficiency of each protocol was calculated as the ratio between the eccentric efficiency and the concentric efficiency (d) at similar velocities and intensities. Analysis of variance with repeated measures was used to examine the effects of the independent variables contractions type, exercise speed, and the exercise intensity on the dependent variable mechanical efficiency. The statistical results revealed that: (a) there was an overall decrease in the efficiency for both concentric and eccentric contractions with an increase in exercise intensity; (b) the efficiency of eccentric contractions were more efficient than concentric muscle contractions for any of the conditions tested; and (c) the efficiency of eccentric contractions increased with exercise speed whereas the efficiency of concentric contractions showed no change with an increase in exercise speed. The relative efficiency (d) was dependent only on speed. Intensity had no effect on d. The results of this study indicate that muscular contraction efficiency values are dependent on contraction type, exercise speed, and exercise intensity. As such, it is inappropriate to report muscular efficiency without also specifying the level of these three factors.