How Can Sprinting Prevent Hamstring Injuries?

The late swing phase of the sprint cycle has been identified as the most likely moment to sustain a hamstring strain (Bramah et al., 2024; Danielsson et al., 2020). During this phase, the hamstring undergo rapid eccentric lengthening and reach maximal length as the knee reaches full extension just before the foot strike, while simultaneously producing high forces (Bramah et al., 2024; Danielsson et al., 2020). This leads to peak muscle activation, the highest lengthening velocity, and greatest negative work performed by the hamstrings at the same time. As a result, the risk of a hamstring strain increases, especially when the muscle is in a fatigued state (Bramah et al., 2024; Danielsson et al., 2020).

Hamstring injuries in football can be influenced by both non-modifiable and modifiable risk factors. Non-modifiable factors, which cannot be changed or controlled, include a history of previous injury and age (Green et al., 2020). Modifiable factors, such as eccentric knee flexor strength, can be changed or controlled, for example, by targeted training (Green et al., 2020; Petersen et al., 2011; Timmins et al., 2016). Stronger eccentric muscle contractions allow the hamstring to absorb greater force and potentially lead to a reduced strain on the hamstring (Petersen et al., 2011). Additionally, a shorter fascicle length in the biceps femoris long head (BFLH) increases susceptibility to hamstring strains (Green et al., 2020; Timmins et al., 2016). Shorter fascicles make the hamstring more prone to overstretching during powerful eccentric contractions, as in high-speed running (Timmins et al., 2016). The Nordic Hamstring Curl (NHC) has proven to be an effective exercise for reducing hamstring injuries by specifically addressing these modifiable risk factors (Bramah et al., 2024; Petersen et al., 2011). Petersen et al. (2011) found that a NHC protocol could reduce new hamstring injuries by 60% and recurrent injuries by 85% among football players.

Sprinting has also been identified as a risk factor, but it can potentially also help to lower the risk of sustaining a hamstring injury (Bramah et al., 2024; Green et al., 2020; Mendiguchia et al., 2022). Sprinting mechanics can play a big role in the mechanical strain placed on the hamstrings (Bramah et al., 2024; Mendiguchia et al., 2022). Instead of a single biomechanical factor causing hamstring injuries, a combination of multiple kinematic and kinetic factors, often related to movement quality and technical aspects, can influence the strain on the hamstrings and can cause an injury (Bramah et al., 2024; Mendiguchia et al., 2022). By including sprint training with a focus on refining sprint mechanics, athletes can improve their running technique, which may prevent them from hamstring injuries (Mendiguchia et al., 2022). 

Back-side mechanics describes the degree of lower-limb movements occurring behind the centre of mass during sprinting (Bramah et al., 2024). Running with poor back-side mechanics results in longer stance phase and shorter flight times during sprinting. This gives the lower limb less time to reposition for the next foot contact, making faster limb switching more necessary (Bramah et al., 2024). These changes can lead to several compensatory mechanics, such as an increased forward trunk lean, anterior pelvic tilt, and overstriding. Such compensations can potentially elongate the hamstring strain and increase eccentric workload, which may raise injury risk (Bramah et al., 2024; Mendiguchia et al., 2022).

For athletes showing a poor back-side mechanics, focusing on front-side mechanics can help improve sprinting technique and decrease the chance of hamstring injuries (Bramah et al., 2024; Mendiguchia et al., 2022). Front-side mechanics refer to the actions and positions of the legs when they are in front of the body during a sprint (Haralabidis et al., 2022; Mendiguchia et al., 2022). Key aspects of good front-side mechanics include a high knee drive, bringing the knee to hip level. This prepares the foot to land closer to the centre of mass at initial ground contact (Haralabidis et al., 2022; Mendiguchia et al., 2022). This results in short, elastic ground contacts, allowing the leg to quickly transition back up for the next stride, which limits excessive backward leg movement and time spent during back-side mechanics (Haralabidis et al., 2022; Mendiguchia et al., 2022). This leads to a more neutral pelvic position and an upright posture, which decreases strain on the hamstring (Bramah et al., 2024; Mendiguchia et al., 2022). Placing the foot closer to the centre of mass at ground contact reduces the chance of overstriding (Haralabidis et al., 2022). Overstriding, where the foot is placed in front of the centre of mass, increases breaking forces and requires greater hamstring effort to reaccelerate the centre of mass during HSR (Bramah et al., 2024; Haralabidis et al., 2022). Repeated sprints can lead to early fatigue, weakening the hamstring’s capacity to resist strain and increasing the risk for a fatigue-related injury (Bramah et al., 2024; Malone et al., 2018). Improving an athlete’s sprint mechanics takes time and ask for consistent practice (Mendiguchia et al., 2022).