STRETCH-SHORTEN CYCLE COMPARED WITH ISOMETRIC PRELOAD - CONTRIBUTIONSTO ENHANCED MUSCULAR PERFORMANCE

To isolate any difference muscular contraction history may have on con centric work output, 40 trained male subjects performed three separate isokinetic concentric squats that involved differing contraction hist ories: 1) a concentric-only (CO) squat, 2) a concentric squat preceded by an isometric preload (IS), and 3) a stretch-shorten cycle (SSC) sq uat. Over the first 300 ms of the concentric movement, work output for both the SSC and IS conditions was significantly greater (154.8 +/- 3 9.8 and 147.9 +/- 34.7 J, respectively; P < 0.001) compared with the C O squat (129.7 +/- 34.4 J). In addition, work output after the SSC tes t over the first 300 ms was also significantly larger than that for th e corresponding period after the IS protocol (P < 0.05). There was no difference in normalized, integrated electromyogram among any of the c onditions. It was concluded that concentric performance enhancement de rived from a preceding stretch of the muscle-tendon complex was largel y due to the attainment of a higher active muscle state before the sta rt of the concentric movement. However, it was also hypothesized that contractile element potentiation was a significant contributor to stre tch-induced muscular performance under these conditions.