Isokinetic Strength of Icelandic Football Players

Abstract

A growing body of evidence indicates the that the Nordic Hamstring exercise (NHE) can reduce the risk of Hamstrings injury yet Hamstrings injuries remain the most common injury in all football. Despite its utility, elite-level athletes seem to have difficulties adhering to high volume NHE programs. Recent research further suggest that activation patterns of the Hamstrings muscles can be altered with Tibial rotation in isometric contraction but similar results have not been confirmed definitively with eccentric contractions. The purpose of this study was to determine the efficacy of a 4-week NHE with internal vs. external Tibial rotation intervention on Hamstrings strength in elite-level football athletes. Isokinetic strength outputs of Hamstrings and Quadriceps were assessed pre- and post-intervention. Participants were 19 male football players of Leiknir Reykjavík FC and were randomized into two groups, performing NHE with internal or external rotation of the tibia. Strength output variables were obtained with isokinetic dynamometry KINCOM and analyzed with mixed model statistical analysis.A significant interaction of ‘contraction by time’ (p=0.028) was found for peak Hamstring strength outputs where strength increases were only of eccentric, not of concentric contraction. A significant interaction of ‘speed by contraction type’ was also found, as although concentric peaks were similar across speeds, eccentric peaks of 180°/s were higher compared to 30°/s. As for peak strength, significant interactions for ‘contraction type by time’ (p=0.006) and ‘contraction type by speed’ (p=<.001) were found for average strength output for the range of motion tested. Results for angles of peaks of Hamstrings indicated a three-way interaction of speed by contraction over time (p=0.029), as small changes were seen at 30°/s while changes in different directions were seen for knee angles seen at peak eccentric vs. concentric values at 180°/s. Overall, there were no significant changes in Quadriceps strength after the 4-week intervention. No statistical differences were found between intervention groups and no statistical differences were found in Hamstrings to Quadriceps (H/Q) ratio in post-intervention measurements. Low compliance rate and small sample-size may have influenced results. Results of this study suggest that the NHE selectively improves eccentric muscle strength of the Hamstrings, regardless of Tibial rotation. Further research is needed to determine effects of coupling Tibial rotation with eccentric exercise on Hamstrings strength and activation.