Philippou, A., Bogdanis, G. C., & Maridaki, M. (2009). Changes in the rate of force development measured at different muscle lengths following eccentric and isometric exercise. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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This study examined the effects of isometric exercise at long muscle length on the rate of force development -- length relationship and to compare them with those presented after eccentric exercise. Male volunteers (N = 14) were randomly divided into an eccentric (N = 7) or the isometric (N = 7) exercise group. Ss performed 50 maximal voluntary eccentric or isometric contractions at a long length of the elbow flexors of the non-dominant arm on an isokinetic dynamometer. Peak isometric force (PIF) and time to peak force (TPIF) were measured at five different elbow angles (50, 70, 90, 140, 160), before and for four consecutive days post-exercise. Maximum rate of force development was determined as the PIF/TPIF ratio. Flexed and relaxed elbow angles and muscle soreness (DOMS) were also assessed at the same time points.

Both exercise protocols induced significant changes in the indirect markers of muscle damage post-exercise (DOMS, flexed elbow angle, and relaxed elbow angle) when compared to baseline. Maximum rate of force development before exercise was higher at the 140 angle compared to 50 and 70. A similar rate of force development -- length relationship was found in both groups. Maximum rate of force development was significantly decreased in both groups at all the angles tested in the days after the exercise regimens. The percent changes in rate of force development (i.e., normalized to pre-exercise values) were also significant in each group over time, but not between angles in any group or between groups.

Implication. The rate of force development -- angle relationship was found to be similarly affected after both eccentric and isometric exercise at a long muscle length. The decreased rate of force development following muscle damaging exercise has been attributed to changes in cytoskeletal integrity and to an increase in the compliance of some muscle fibers. However, the similar decreases in rate of force development at various muscle lengths found in the present study imply that other factors such as neuromuscular disturbances following muscle damage may also play an important role.

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