Muscle contractile properties of professional soccer players according to playing position and limb dominance

This study aimed to characterise selected lower-limb muscle contractile properties in a sample of male professional soccer players, and to investigate if muscle contractile properties differed according to playing position or limb dominance. One hundred and ninety-three male professional soccer players (mean ± SD: age=21.6yrs±4.4; height=181.1cm±10.0; body mass=77.4kg±8.5) had bilateral measurements of muscle contractile properties taken during the pre-season period (June-July) of the 2016-17, 2017-18 and 2018-19 seasons using Tensiomyography. The following muscles were measured: Adductor Magnus (AM), Bicep Femoris (BF), Gastrocnemius Lateralis (GL), Gastrocnemius Medialis (GM), Gluteus Maximus (GT) and Rectus Femoris (RF). Participants were sub-categorised by playing position and limb dominance. Data were analysed using Kruskal Wallis H tests or Mann-Whitney U tests. The left GM muscle produced the shortest delay time (Td) (19.5 ms ± 1.9) and contraction time (Tc) (21.3 ms±14.3) whilst the right BF had the longest sustain time (Ts) (196.9ms±83.9). Relaxation time (Tr) was shortest in the right GL (39.3ms±22.7) and the right GT the largest maximal displacement (Dm) value (10.2mm±3.6). Small differences were present between the left AM Td in Forwards (p=0.005, η2=0.05) and Midfielders and in the left GM Ts between Forwards and Goalkeepers (p=0.04, η2=0.02). The right RF Tc measurement was lower in the right dominant participants (p=0.04, η2=0.35). No other differences were detected between playing positions or limb dominance (p>0.05). The findings from this study provide a profile of lower limb muscle contractile properties in a sample of male professional soccer players. The lack of consistent differences reported between sub-categories suggest that soccer players are homogeneous, regardless of playing position or limb dominance. The data generated from this study may be used to monitor soccer players following periods of inactivity, fixture congestion, long-term injury or acute changes in professional status.