Effect of fatigue on hamstring reflex responses and posterior-anterior tibial translation in men and women

Abstract

Anterior cruciate ligament (ACL) rupture ranks among the most common injuries in sports. The incidence of ACL injuries is considerably higher in females than in males and the underlying mechanisms are still under debate. Furthermore, it has been suggested that muscle fatigue can be a risk factor for ACL injuries. We investigated gender differences in hamstring reflex responses and posterior-anterior tibial translation (TT) before and after fatiguing exercise. We assessed the isolated movement of the tibia relative to the femur in the sagittal plane as a consequence of mechanically induced TT in standing subjects. The muscle activity of the hamstrings was evaluated. Furthermore, isometric maximum voluntary torque (iMVT) and rate of torque development (RTD) of the hamstrings (H) and quadriceps (Q) were measured and the MVT H/Q as well as the RTD H/Q ratios were calculated. After fatigue, reflex onset latencies were enhanced in women. A reduction of reflex responses associated with an increased TT was observed in females. Men showed no differences in these parameters. Correlation analysis revealed no significant associations between parameters for TT and MVT H/Q as well as RTD H/Q. The results of the present study revealed that the fatigue protocol used in this study altered the latency and magnitude of reflex responses of the hamstrings as well as TT in women. These changes were not found in men. Based on our results, it is conceivable that the fatigue-induced decrease in neuromuscular function with a corresponding increase in TT probably contributes to the higher incidence of ACL injuries in women.

Figure 1. Schematic drawing of the experimental setup.

A: Experimental setup, B: Measurement system | 1: stopper, 2: falling weight, 3: pulley, 4: steel rope, 5: force transducer, 6: force plate, 7: visual cover, 8: linear potentiometer. Arrows indicate the direction of the force. Posterior-anterior tibial translation was assessed by two linear potentiometers (8) placed on the patella and the tibial tuberosity. A force transducer (5) was used to measure the force transmitted to the shank.

Figure 2. EMG and tibial translation data from one representative subject.

EMG activity of biceps femoris and semitendinosus/semimembranosus as well as posterior-anterior tibial translation of one subject. In the figure, EMG data is rectified in order to visualize the different parts of the hamstring stretch reflex. The vertical bold line indicates the onset of posterior-anterior tibial translation. Three different time intervals were analyzed (20–40, 40–60 and 60–95 ms).

Figure 3. Effect of fatigue on tibial translation (left) and reflex responses (middle and right).

Filled bars: Pre, open bars: Post, BF: biceps femoris, ST: semitendinosus/semimembranosus. Data are displayed as means ± standard error of the mean. * denotes a significant difference compared to the pre-measurement, * P≤0.05; ** P≤0.01.