Seasonal variation of physical performance, bilateral deficit and inter-limb asymmetry in elite academy soccer players: which metrics are sensitive to change?
Bishop, Chris, Abbott, Will, Brashill, Calum, Loturco, Irineu, Beato, Marco, Turner, Anthony N.
Abstract
This study aimed to report seasonal variations for: 1) physical performance, 2) inter-limb asymmetry and, 3) BLD data over the course of a competitive soccer season, and determine which metrics are sensitive to change. This study used a repeated measures observational design for 19 under-20 elite academy soccer players (age: 17.58 ± 0.61 years; height: 1.81 ± 0.09 m; body mass: 74.36 ± 7.58 kg), who conducted bilateral and single leg countermovement jumps (CMJ and SLCMJ), linear speed (5, 10, 20 and 30-m) and 505 change of direction (COD) speed tests, at pre, mid and end of season time points. For jump tests, jump height, reactive strength index modified (RSI-Mod), time to take-off and countermovement depth metrics were monitored, with inter-limb asymmetry and the bilateral deficit (BLD) also calculated for each. Significant improvements (p < 0.05) in performance were evident in all fitness tests: CMJ (ES: 0.61 to 1.03), SLCMJ (ES: 0.60 to 2.25), linear speed (ES: -0.54 to -1.96) and COD speed (ES: -0.68 to -1.14). Significant reductions in asymmetry (ES: -0.68 to -1.07) and significant increases in the BLD (ES: 1.15 to 1.57) were also evident throughout the season. Additionally, Kappa coefficients were used to determine consistency in limb dominance throughout the season, but only poor to fair levels of agreement (K: -0.17 to 0.37) were evident, highlighting the fluctuating nature of limb dominance throughout the season. Despite all tests exhibiting meaningful change, the SLCMJ and linear speed showed the most frequent and largest differences in performance, highlighting their usefulness in the ongoing monitoring process of physical capacities in elite male academy players across a competitive soccer season.