Purpose: This study investigated responses of single-leg balance and landing and countermovement jump (CMJ) following rugby union training and the specific components of training load associated with test decrement. Methods: Twenty-seven Professional rugby union players performed CMJ, single-leg balance and landing tests on a 1000 Hz force plate at the beginning and end of training days. Training load was described by session RPE, Banister's TRIMP, GPS total distance, high-speed running distance (>5.5 m s"1), relative speed and body load. Results: CMJ eccentric rate of force development (EccRFD) demonstrated moderate impairment post-training (ES ± 90%CL = -0.79 ± 0.29, MBI = almost certainly). CMJ height (-0.21 ± 0.16, possible), concentric impulse (ConIMP) (-0.35 ± 0.17, likely) and single-leg balance sway velocity on the non-dominant leg (0.30 ± 0.26, possible) were also impaired. Regression analyses identified the strongest relationship between sRPE and impaired ConIMP (r = -0.68 ± 21, ß = -0.68) whilst other load measures explained 27-50% of the variance in balance and CMJ changes. Condusions: CMJ variables representing altered movement strategy (EccRFD and IMP) may be useful for assessing acute neuromuscular fatigue in rugby union, though single-leg balance sway velocity may be an alternative when maximal tests are impractical.
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