The impact of an eccentric or isometric exercise intervention on hamstring strength, muscle architecture and sprint performance across an Australian Rules Football season.

Introduction: Hamstring strain injuries (HSIs) remain the most common cause of time lost from competition in team sports. Including the Nordic hamstring exercise (NHE) as part of a training program reduces HSI risk. Despite these benefits, the NHE is not widely implemented in team sports. The lack of NHE implementation may be due to fear of muscle soreness caused by this high-intensity eccentric stimulus, which has led to interest in isometric hamstring exercises interventions. Despite interest in isometric hamstring exercises, there has been limited research into the potential benefits of these interventions on HSI risk factors and sprint performance. Therefore we aimed to investigate the impact of an isometric (ISO) or NHE intervention, alongside a sprint training program on hamstring strength, architecture and sprinting performance in Australian Footballers Methods: Twenty-five male athletes undertook NHE (n = 13) or ISO (n = 12) training across a 38-week period. Biceps femoris long head (BFlh) architecture, isometric and eccentric knee flexor strength were assessed at baseline, end of pre-season and following the intervention. Sprint times and force-velocity profiles were determined at baseline and at the end of pre-season Results: Following the intervention both groups had significant improvements in BFlh fascicle length (NHE: 1.16cm, 95%CI 0.68 to 1.63cm, d=1.88, p<0.001; ISO: 0.82cm, 95%CI 0.57 to 1.06cm, d=1.70, p<0.001), muscle thickness (NHE: 0.11cm, 95%CI 0.01 to 0.21cm, d=0.51, p=0.032; ISO: 0.21cm, 95%CI 0.10 to 0.32cm, d=0.86, p=0.002) and eccentric strength (NHE: 83N, 95%CI 53 to 114N, d=1.79, p<0.001; ISO: 83N, 95%CI 17 to 151N, d=1.17, p=0.018). Both groups also finished the intervention weaker isometrically than they started (NHE: -45N, 95%CI -81 to -8N, d=-1.03, p=0.022; ISO: -80N, 95%CI -104 to -56N, d=-3.35, p<0.001). At the end of pre-season the NHE group had improved their 5m sprint time by 3.3% (±2.0%) and their maximum horizontal velocity was 3% (±2.1) greater than the ISO group who saw no changes. Discussion: Both ISO and NHE training with a periodized sprinting program can increase BFlh fascicle length, thickness, and eccentric strength in Australian Footballers. NHE training also improves 5m sprint time and maximum velocity. Both interventions may reduce isometric strength. Impact/Application to the field: This is the first study to investigate the impact of a 38-week NHE or isometric knee flexor training intervention, alongside a periodised sprinting program, on BFlh architecture, strength and sprinting performance in Australian Football athletes. The key inclusion of the periodised sprinting program alongside a single-mode hamstring specific exercise intervention allows for a more holistic and translatable set of findings as it shows the outcomes when both are prescribed together, which is commonplace in applied settings. It also suggests that completing a NHE or ISO intervention alongside a periodised sprinting program may have beneficial effect on HSI risk mitigation which can have direct impact on practice and application. The improvement in a performance metric such as 5m split time may also assist the “buy-in” and implementation of an exercise-based injury prevention strategy in a high-performance setting where the balance between performance and prevention is a key component of the role Declaration: Ryan Timmins is a SMA Conference Committee Member. A/Prof David Opar is listed as a co-inventor on a patent, filed by the Queensland University of Technology (QUT), for a field-testing device of eccentric hamstring strength, which is now known commercially as the NordBord. A/Prof Opar has received revenue distributions from QUT based on revenue that QUT has generated through the commercialisation of his intellectual property. A/Prof Opar is a minority shareholder in Vald Performance Pty Ltd, the company responsible for commercialization of the NordBord, among other devices. A/Prof Opar has received research funding from Vald Performance, for work unrelated to the current manuscript. A/Prof Opar was previously the Chair of the Vald Performance Research Committee, a role that was unpaid. A/Prof Opar has family members who are minor shareholders and/or employees of Vald Performance. Co-authors of this paper, Christopher Pollard and Joshua Ruddy, were previously employed with Vald Performance who manufacture the Nordbord and ForceDecks used in this study. However, neither were employed by Vald Performance at the time of completing this study.