Reliability and sensitivity of a simple isometric posterior lower limb muscle test in professional football players

This study aimed (1) to determine the reliability of a simple and quick test to assess isometric posterior lower limb muscle force in professional football players and (2) verify its sensitivity to detect reductions in force following a competitive match. Twenty-nine professional football players performed a 3-s maximal isometric contraction of the posterior lower limb muscles for both legs with players lying supine. Both legs were tested using a knee angle of 90 degrees and 30 degrees measured on a force plate. Players were tested twice with one week between sessions to verify reliability. Sensitivity was tested following a full competitive football match. The test showed high reliability for dominant leg at 90 degrees (CV=4.3%, ICC=0.95, ES=0.15), non-dominant leg at 90 degrees (CV=5.4%, ICC=0.95, ES=0.14), and non-dominant leg at 30 degrees (CV=4.8%, ICC=0.93, ES=0.30) and good reliability for dominant leg at 30 degrees (CV=6.3%, ICC=0.86, ES=0.05). The measure was sensitive enough to detect reductions in force for dominant leg at 90 degrees (P=0.0006, ES > 1), non-dominant leg at 90 degrees (P=0.0142, ES=1), and non-dominant leg at 30 degrees (P=0.0064, ES>1) and for dominant leg at 30 degrees (P=0.0016, ES>1). In conclusion, the present test represents a useful and practical field tool to determine the magnitude of match-induced fatigue of the posterior lower limb muscles and potentially to track their recovery.