Stretch shorten cycle as compared to isometric preload: contributions to enhanced muscular performance

To isolate any difference muscular contraction history may have on co ncentric work output, 40 trained male subjects performed three separa te isokinetic concentric squats that involved differing contrac-tion histories: 1) a concentric-only (CO) squat, 2) a concentric squat pre ceded by an isometric preload (IS), and 3) a stretch-shorten cycle (S SC) squat. Over the first 300 ms of the concentric movement, work out put for both the SSC and IS conditions was significantly greater (154 .8 639.8 and 147.9 6 34.7 J, respectively; P , 0.001) compared with t he CO squat (129.7 6 34.4 J). In addition, work output after the SSC test over the first 300 ms was also significantly larger than that fo r the corresponding period after the IS protocol (P , 0.05). There wa s no difference in normalized, integrated electromyo-gram among any o f the conditions. It was concluded that concentric performance enhanc ement derived from a preced-ing stretch of the muscle-tendon complex was largely due to the attainment of a higher active muscle state bef ore the start of the concentric movement. However, it was also hypoth -esized that contractile element potentiation was a significant contr ibutor to stretch-induced muscular performance under these conditions .