Rapid isometric hamstring strength scores from professional soccer players at pre-season: Positional differences and relationship to peak force

The assessment of rapid force within a single joint assessment is becoming common practice within elite sport environments. Recent observations have highlighted that rapid force maybe more sensitive to fatigue than peak force within the hamstrings. Yet limited information exists on rapid force production in elite male soccer players. Eighty-nine senior professional men's soccer players (age; 24.2 ± 5.1 years, height; 1.83 ± 0.05 m, mass; 78.95 ± 7.53 kg) participated within the present study they performed two isometric assessments at joint angles of 30° and 90° of hip flexion and knee. They performed three trials with mean and standard deviation determined differences between soccer positions (defender, midfielder and strikers) and differences between limbs were determined via two-way ANOVA with post-hoc analysis. A small overall effect was observed between positions was observed for both the 90:90 (p = 0.709, η2P = 0.17), and 30:30 isometric assessments (p = 0.604, η2P = 0.02), with trivial pairwise positional differences (d = 0.00-0.03) observed for relative force at 100 ms and 200 ms. Pearson's correlation coefficients revealed moderate relationships (r = 0.34-0.48) between rapid force and peak force. Positional differences were only observed when rapid force was made relative to peak force, with midfielders producing greater relative force within 100 ms in comparison to both defenders and forwards, which could be a result of match demands for high-speed running. Using both peak and rapid force would enable accurate reflection of changes through training or fatigue, which could be used to monitor the risk of hamstring injury.