Monitoring recovery from muscle damage in Rugby Union

Abstract

INTRODUCTION Acute and long-term decreases in athletic performance as a result of muscle damage from participating in rugby union, are well documented. To date, research designed to measure recovery from muscle damage using jump performance has adopted a wide range of methodologies, often in experimental settings. The purpose of this study was to investigate performance decrements of rugby union players in a variety of jump activities after experiencing muscle damage in an experimental (study 1) and applied (study 2) environment. METHODS In both studies subjects recorded a baseline squat jump (SJ), countermovement jump (CMJ), drop jump from 30cm (DJ) and submaximal hop (SH) during which the force (F), power (P), velocity (V), ground contact time (tc) and flight time (tf) were measured alongside baseline creatine kinase (CK) levels. Peak force, peak power output, leg stiffness, reactive strength index (RSI), peak velocity and jump height were recorded for each of the given jumps. All jumps were then retested 4min, 1d, 2d, 3d and 7d post a stimulus designed to cause muscle damage with CK recorded at all intervals excluding the 4min interval. In study one subjects completed five sets of ten repetitions of the lowering portion of a back squat at 95% of their back squat 1- RM with a five second eccentric contraction. In study two subjects participated in a full competitive rugby union match. In both studies jump variables were analysed using separate single-factor repeated-measures analyses of variance and correlation analysis between CK and jump variables was carried out using a Pearson’s correlation. The effect size of the change between intervals was also recorded for each variable measured. RESULTS In study one, a very large (ES = 3.53) increase in CK was recorded from 256+158 U/I to 813.8+577 U/I, which although not significant (p>0.05), remained elevated until returning to below baseline levels at 7d post intervention. All jump activities experienced significant decreases in performance (p<0.05) across various intervals with DJ RSI displaying the highest correlation with changes in CK over the seven-day period (r=-.61, p<0.01). In study two a very large, but non-significant (p>0.05, ES = 1.93) peak from baseline CK (257.9+91.2 U/I) was recorded at 24hrs post-competition (434+207.8 U/I), which remained elevated before returning to below baseline levels 7d post competition. No jump activities experienced significant decreases in performance. CONCLUSION The results suggest that while jump activities can be used to identify the state of recovery from muscle damage, particularly the RSI of a 30cm DJ, this is dependent on the stimulus used to instigate muscle damage. It can also be concluded that results obtained from an experimental setting may not be applicable to an applied ‘real world’ environment. Strength and conditioning practitioners therefore must assess whether or not the chosen jump method is suitable to the mechanism of muscle damage experienced by their athletes before implementing a monitoring programme using athletic performance measures.