A mixed methods approach to training for the mitigation of modifiable risk factors for hamstring strain injury and the development of athletic performance.

Ross, Steven

Abstract

Hamstring strain injuries (HSIs) are the most common non-contact injuries in various sports, including soccer, American football, rugby union, Australian rules football, cricket, and sprinting. Epidemiological studies have highlighted the significant loss of training and competition time associated with HSIs, with a typical 25-player soccer squad experiencing 5-6 hamstring injuries per season, each resulting in approximately 14 days of absence. Despite extensive research into injury risk factors, rehabilitation, and mitigation techniques, the incidence of hamstring injuries continues to rise, particularly in men's elite European professional soccer. Research has indicated that exercises like the Nordic hamstring exercise (NHE) can reduce HSI incidence, though this claim has been debated due to methodological discrepancies. Compliance with injury prevention programmes is crucial, with higher compliance rates leading to greater success in reducing HSI rates. Despite the potential benefits of evidence-based prevention programmes, adherence remains a challenge, particularly with high-volume training. The results of recent studies indicate that lower volume NHE programmes can be effective, indicating the feasibility of incorporating such exercises into athletic training schedules. Given the limitations of single-exercise interventions, there is a need for research into more comprehensive training programmes that combine resistance training with high-speed running (HSR) to effectively reduce HSI risk and enhance athletic performance. The overarching aim of this thesis was to inform exercise selection, athlete assessment, and training practices to mitigate HSI risk and improve athletic performance, reflecting the applied practices of strength and conditioning, injury rehabilitation and sport science practitioners.

This research investigated hamstring training practices and perceptions for injury prevention and athletic performance enhancement through both quantitative and qualitative analyses. Chapter 3 utilised a mixed-methods survey to gather data from sport and exercise practitioners across various sports, exploring their training methods, including HSR and approaches to resistance training. The survey revealed significant disparities in training practices, highlighting the influence of educational background, professional role, and multi-disciplinary team (MDT) dynamics. It emphasised the importance of practitioner education, effective communication within MDTs, and developing evidence-informed training practices tailored to sport-specific demands and athlete characteristics.
Building on these findings, Chapter 4 expanded through semi-structured interviews with twelve practitioners, providing a deeper qualitative understanding of nuanced approaches to hamstring training. It explored the rationale behind training decisions, the challenges practitioners faced, and strategies employed to enhance athlete compliance and engagement. Key themes included micro-dosing of the NHE, integrating hip hinge exercises like Romanian deadlifts (RDL), and applying isometric training during congested fixture periods. The study highlighted the critical role of MDT dynamics and continuous athlete education in effective training interventions.
Together, these chapters highlighted the need for more ecologically valid research including concurrent resistance training with HSR, rather than single exercise interventions. The insights aimed to bridge the gap between research and real-world application, providing a robust foundation for developing effective training strategies to reduce hamstring injury incidence and enhance athletic performance.

Chapter 5 focused on establishing the most appropriate normalisation method for electromyography (EMG) based on within-session reliability and variability of various maximal voluntary isometric contraction (MVIC) methods. The study concluded that the manual resistance method (hip extension) provided a reliable and time-efficient means of normalising EMG data for the hamstring and gluteal muscles, which was then utilised in the exercise comparisons conducted in Chapter 6.
Chapter 6 compared the kinetic and EMG characteristics of the RDL and good morning (GM) exercises. Utilising the established EMG normalisation method from Chapter 5, this chapter aimed to develop a biomechanically robust basis for exercise selection decisions. The findings indicated that while higher absolute loads were lifted during the RDL, both exercises produced comparable joint moments and muscle excitations, indicating that the GM could serve as an alternative hip-hinge exercise requiring lower absolute loads yet potentially yielding similar training adaptations.
Together, these chapters provided a comprehensive understanding of hamstring training practices and the reliability of EMG normalisation methods, informing evidence-based decisions in exercise selection for reducing hamstring injury risk and enhancing athletic performance.
Chapter 7 investigated the reliability and bilateral force asymmetry during the NHE using a NordBord device. The study aimed to quantify knee flexor strength, assess bilateral force asymmetry, and determine the reliability of peak force (PF) and mean force (MF) measures. Nineteen strength-trained male participants performed three maximal NHE trials. Data collection focused on PF, MF, and instantaneous force (IF) throughout the exercise. The study found moderate to excellent reliability for PF across trials, with improved reliability and reduced variability when excluding the first trial. MF, while also showing improvements, demonstrated slightly lower reliability and higher variability than PF. The analysis revealed significant between-limb differences in MF, favouring the right limb, and higher IF in the right limb for most of the exercise duration. These findings indicate that relying solely on PF might mask underlying bilateral force asymmetries, highlighting the importance of including MF and IF measures in assessments. This chapter concluded that monitoring multiple force metrics during the NHE was crucial for accurately identifying bilateral asymmetries and informing targeted training interventions. The insights gained were applied in future exercise comparison and training intervention studies within this thesis.
Finally, Chapter 8 examined the effects of integrating knee flexor-biased (NHE) and hip hinge-biased (RDL) resistance training programmes with concurrent HSR on hamstring strength, sprint performance, jump performance, and lower body strength in academy soccer players. The study addressed the lack of ecological validity in previous research, which often focused on single exercise interventions, by employing a more comprehensive training approach. Thirty-seven participants from a football academy were randomly assigned to one of three groups: NHE, RDL, or control. Over six weeks, all groups engaged in a standardised resistance and HSR training programme, with only the RDL, NHE or reverse lunge (control) differing between programmes. The training aimed to progressively increase load while maintaining consistent volume, with sessions held twice weekly. Pre- and post-intervention assessments included countermovement jumps (CMJ), countermovement rebound jumps (CMJ-R), isometric mid-thigh pull (IMTP), and 20 m sprints.
Results indicated significant improvements in all groups, with the NHE group showing the greatest increase in eccentric knee flexor strength, likely due to the specificity and supramaximal nature of the NHE. Both training interventions experienced significant improvement in 20 m sprint performance. However, both intervention groups and the control group experienced significant improvements in 5 m sprint performance, indicating that the sprint intervention was sufficient to improve 5 m acceleration performance, but addition of either the NHE or RDL is required to significantly improve 20 m sprint performance. The study concluded that combining resistance training with HSR enhanced athletic performance and reduced hamstring injury risk, with each training focus providing distinct benefits. The findings supported the integration of varied resistance training strategies in athlete conditioning programs to optimise performance and injury prevention.

• Thesis Type: Thesis
• Acceptance Date: Feb 13, 2025
• Online Publication Date: Mar 27, 2025
• Deposit Date: Feb 14, 2025
• Publicly Available Date: Apr 28, 2025
• Award Date: Mar 27, 2025