THE EFFECTS OF SERIAL STRETCH LOADING ON STRETCH WORK AND STRETCH-SHORTEN CYCLE PERFORMANCE IN THE KNEE MUSCULATURE

Training methods to optimize stretch-shorten cycle performance and an active muscle's ability to resist a sudden stretch (stretch work) and the relationship between the two have not been fully explored. The pur pose oi this study was to examine the effects oi an 8-week strengtheni ng program oi serial stretch loading on stretch work and stretch-short en cycle performance in the quadriceps and hamstring muscles. Thirty-o ne asymptomatic subjects participated in pre- and post-tests oi maximu m voluntary isometric contractions, stretch work and stretch-shorten c ycle trials, and single-leg vertical jumps. The training portion consi sted of progressively resisted isotonic single-leg squats. One leg exe rcised against an isotonic load with serial stretch loading, while the other leg exercised against isotonic load alone. Training resulted in strength gains in both legs indicated by the increase in weight lifte d during training but not by maximum voluntary isometric contractions. Vertical jump height increased in both legs. In the hamstring, stretc h work decreased and stretch-shorten cycle performance increased in bo th legs. In the quadriceps, serial stretch loading intervention result ed in increased stretch-shorten cycle performance and no significant c hange in stretch work. The correlation between stretch-shorten cycle a nd stretch work was weak but significant. These findings suggest that the use oi serial stretch loading could improve muscular performance a nd enhance a muscle's potential for dynamic stabilization.