Acute effects of whole-body vibration exercise on musculotendinous stiffness and reactive strength index of the triceps surae

Whole-body vibration (WBV) has been shown to improve performance in stretch-shortening cycle (SSC) activities; this is dependent on musculotendinous stiffness prior to the concentric phase of movement (Anderson, 1996, Sports Medicine, 22, 76-89). This study aimed to examine acute effects of WBV on musculotendinous stiffness (KTS) and reactive strength index (RSITS) of the triceps surae. Following institutional ethical approval, seven trained males (mean age 22.1, s = 1.4 yrs; mean height 1.84, s = 0.06 m; mean weight 87.0, s = 7.5 kg) volunteered for this study. Pre-tests were conducted on each leg immediately prior to vibration of the dominant leg. Subjects lay on a bench with the tested leg and thigh secured. A sledge device was dropped from 30 cm above the foot and pushed back up the sledge rails as quickly and rhythmically as possible using the test limb, for two trials of four rebounds per limb. WBV consisted of 10 vibrations at 30 Hz ± 4 mm with 60 seconds rest between each exposure on a Vibrogym platform (Vibrogym Inc., The Netherlands). The knee of the dominant leg was flexed to 110° and knee of the control leg held flexed away from the vibration plate. Post-tests (identical to pre-tests) were conducted immediately, 5, 10, 15, 20, 30 and 40 minutes following WBV. A 3D motion analysis system operating at 100 Hz (Motion Analysis Corporation, CA, USA) was used to calculate sledge displacement, acceleration, contact time, flight time and for calculation of KTS (McMahon and Cheng, 1990, Journal of Biomechanics, 23, 65-78) and RSITS. ANOVA with repeated measures indicate maximum KTS (vibrated limb) and RSITS (vibrated and control limbs) post-WBV was significantly different to pre-WBV scores (Table 1). Table 1. Effect of WBV on KTS and RSITS of vibrated and control limbs KTS (N/mm) RSITS Limb Pre-WBV Post-WBV maximum P Pre-WBV Post-WBV maximum P Vibrated 9.45 ± 0.981 10.48 ± 0.887 0.012 1.80 ± 0.418 2.49 ± 0.554 0.020 Control 9.45 ±1.370 10.80 ± 0.628 0.071 1.57 ± 0.419 2.22 ± 0.421 0.020 Enhanced performance in SSC activities following WBV may be due to increased musculotendinous stiffness, as a result of enhanced contractile activity (post-activation potentiation). Future work should isolate WBV effects on muscle and tendon stiffness to determine which structures are particularly affected.