The effects of fatigue caused by soccer-specific treadmill simulation on balance, strength and angle of peak torque in adolescent male soccer players

Our study was designed to examine the effects of fatigue, obtained by soccer-specific treadmill simulation, on balance and strength (peak torque of knee flexors and angle of peak torque) performance in adolescent soccer players (n=17). Postural stability test (Biodex Balance System SD), knee flexor concentric-eccentric muscle strength in prone position on isokinetic dynamometer (Cybex Humac NORM) and angle of peak torque test values were recorded for dominant and non-dominant legs, respectively. These tests were performed 6 times in total; before the simulation (t0), at the end of the half-time break (t40+15) and at the end of every 20 minutes (t20, t40, t60 and t80). Statistical analyses were done by ''IBM SPSS 22'' software program. Wilcoxon Signed-Rank test was used to evaluate the data and 0,05 was determined as a significance level (p<0.05). In the range of t40 - t40+15, there were significant decreases in general stability index and medial-lateral stability index for non-dominant leg; and also in anterior-posterior stability index for dominant leg. There were significant decreases in concentric peak torque at 60°/s in the range of t20 - t40, at 120°/s in the range of t60 - t80; and also in eccentric peak torque at 60°/s in the range of t20 - t40, at 120°/s in the range of t60 - t80 for dominant leg. There were significant decreases in concentric peak torque at 60°/s in the ranges of t20 - t40 and t40 - t40+15; and also in eccentric peak torque at 60°/s in the range of t20 - t40, at 120°/s in the ranges of t20 - t40 and t40+15 - t60 for non-dominant leg. Angle of peak torque for concentric knee flexors at 60°/s showed a significant decrease only in the range of t40+15 - t60 for non-dominant leg. None of the measurements about angle of peak torque changes out of this range were statistically significant. As a result, 15 minutes halftime break may be sufficient time for the balance performance to return to pre-match levels. Supporting the negative effects of fatigue on strength, there were decreases in strength in our study, especially at the end of the first and second half. These findings are consistent with the hamstring injury times in the literature. In order to prevent potential injuries due to fatigue and to determine the intervention methods, it has been predicted that simulation studies performed by following the strength and balance values in fatigue situations may be beneficial, especially in pre-season periods. Considering the low level of evidence in the literature and the non-significant results in our study, future studies might question the use of angle of peak torque, which is a marker of hamstring injury risk.