Lower limb muscle fatigue on grass and artificial turf playing surfaces among elite soccer players
Greyling, J. A. T.
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INTRODUCTION: Fatigue and hard playing surfaces have been indicated as risk factors for injury in soccer players. Recent literature, however, has found contradictory results on the prevalence of injuries on different playing surfaces, as well as regarding the interaction between fatigue and the type of playing surface. This raises the question as to the true mechanisms underlying the cause of injury on different playing surfaces. AIM: The aim was therefore to compare lower limb muscle fatigue on grass and artificial surfaces in elite soccer players. METHODS: Twenty two elite soccer players (mean age 24.8 years) were included in a cross-over study design. The players were randomly allocated to two conditions. It involved exposure to the same soccer-specific fatigue protocol on a grass and artificial surface respectively. A force plate was used for pre-test and post-fatigue measurements on force generation, force rates and jump height. The Pearson correlation coefficient was used to determine associations between baseline variables and interpreted by means of effect sizes and p-values. The Wilcoxon signed-ranks test was used to determine statistical significant changes from pre-test to post-test for each condition while the Chi-square test was used to compare the findings between the two conditions. RESULTS: Statistical significant correlations were found at baseline between propulsion and concentric forces (r=0.66, p<0.001); propulsion force and body mass (r=0.78, p<0.001); propulsion force and BMI (r=0.645, p<0.01); landing force and body mass (r=0.82, p<0.001); landing and eccentric forces (r=-0.75, p<0.001); jump height and concentric force (r=0.84, p<0.001); and body mass and concentric force (r=0.76, p<0.05). Propulsion and concentric forces increased statistical significance after fatigue on the grass surface (p=0.026 and 0.005 respectively). On the artificial surface there was a statistical significant increase in propulsion force and propulsion force rate post-fatigue (p=0.0001 and 0.0153 respectively). Comparison of the changes from baseline to fatigue between the two conditions yielded no significant differences (p>0.05). CONCLUSION: Limited significant differences were found comparing forces after fatigue on artificial and grass surfaces. The inconsistency in the behaviour of forces in response to fatigue indicate the possible variability in adaptation strategies to cope with a speculated fatigue state. Surface-specific training could therefore be recommended in order for muscle and sport/surface-specific adaptation to take place, thereby decreasing the risk for injury