Abstract
BACKGROUND: The last phases of a competitive game are when shoulder injuries most commonly happen, and fatigue is thought to be a major contributing factor, perhaps because of reduced proprioception and motor control. The purpose of this study was to investigate the effect of concentric fatigue on proprioception, motor control, and performance of the upper limb in handball players. METHODS: Forty-six right-handed handball players (all males, age 26.1 ± 5.54 years) were included in this test-retest laboratory experiment. Proprioception was assessed using joint reposition sense (JRS), threshold to detection of passive movement (TTDPM), muscle onset latency (MOL), motor control using Y balance test upper quarter (YBT-UQ) and performance using the athletic shoulder test (ASH) before and immediately after fatigue intervention. The fatigue protocol consisted of concentric, maximal effort, isokinetic contractions at 900/sec with sets of 30 repetitions of the shoulder external and internal rotator muscles. Fatigue was determined by a 40% decline in the peak torque over three consecutive contractions despite reinforcing feedback and encouragement. RESULTS: A significant increase in absolute angular error (AAE) was observed in all target angles in both external rotation (ER) and internal rotation (IR) directions (p < 0.01). In addition, there was a significant increase in TTDPM in internal rotation after fatigue intervention (p = 0.020. Variable changes were found in YBT-UQ and ASH tests. Specifically, statistically significant differences were found in anteromedial (AM) (p = 0.041), superolateral (SL) reach directions (p = 0.005), composite score (p = 0.009) in the right hand and inferolateral (IL) reach direction in the left hand (p = 0.020) in the YBT-UQ. In addition, there was a significant reduction in isometric strength (ASH test) in the I position of the right hand (p = 0.010) and all positions of the left hand (p<0.05). Furthermore, there was an increase in MOL scores after fatigue but the increase was not significant (p > 0.05). CONCLUSIONS: Concentric fatigue of the rotator cuff muscles induces notable deficits in joint position awareness, kinesthesia, motor control, and performance of the upper extremity in elite male handball players. Although fatigue reduces reflex reaction time the effect is only marginal.