Electromyography (EMG) For Hamstring Screening

Hamstring injuries remain a major concern affecting athletes in running sports, accounting for approximately 10% of all injuries in field sports. Within the hamstring group, the long head of the biceps femoris is the most frequently injured muscle. During sprinting, the hamstrings extend the hip and flex the knee, but in the late swing phase they shift to an eccentric role, decelerating the forward motion of the leg just before ground contact — the phase when hamstring injuries most typically occur.

The tendency of hamstring injuries to recur (typically around 15–30%, with rates as high as 63% in some studies) is equally troubling. With the frequency and intensity of sport ever increasing and player unavailability costly for clubs, the need for better tools to monitor, screen, and understand athletes’ neuromuscular function is growing more pressing. Electromyography (EMG) is one tool that can provide additional insights by investigating asymmetries, compensations, and more.

How Can EMG Help in Applied Sport?

In applied sport, jump and strength tests are often used to monitor rehabilitation after injury. While these tests provide useful values, they can’t reveal how those results were achieved. Compensations following hamstring injury mean that similar performance values can be achieved through different activation strategies. EMG exposes these compensations — such as asymmetries in activation between medial and lateral hamstrings — which may increase reinjury risk.

By measuring activity from the biceps femoris and semitendinosus on both legs, practitioners can see the relative contributions of each muscle during specific exercises. When used in this context, EMG helps practitioners use common exercises as a screening tool, revealing which muscles are most optimally recruited and what needs to change to allow an athlete to progress or reduce injury risk.

Data Collection and Method

In this case study, one healthy male participant completed a range of hamstring rehabilitation exercises. Four Trigno Avanti sensors were paired with a Trigno Lite receiver and placed on the left biceps femoris, left semitendinosus, right biceps femoris, and right semitendinosus — following SENIAM guidelines. Each sensor was normalized to a Maximum Voluntary Contraction (MVC) to allow comparisons between muscles, athletes, and sessions.

Six exercises were performed in a randomized order: Nordic hamstring curl, bridges (90° knee flexion), single leg bridge (90° knee flexion), long lever bridge (30° knee flexion), Romanian deadlift (with 30 kg barbell), and Roman chair (45° hip extension).

Results and Interpretation

Across the session, the right hamstrings typically showed higher activation levels than the left. The standout finding was the under-recruitment of the left biceps femoris (left BF) across most tasks alongside comparatively high activity in the other muscles measured. Symmetry reports highlighted a large asymmetry between left BF and left semitendinosus activation — a common theme throughout the exercises.

The only exception was during Nordic Hamstring Curls, where the left BF did reach high activation levels. This suggests the muscle may be under-recruited during other exercises due to task or technique issues.

Potential Next Steps

• Technique changes to bias BF — Alter exercise execution (e.g., hip or foot rotation) to increase left BF activation.
• EMG-guided biofeedback — Use real-time biofeedback to help the athlete focus on left BF activation and visualize the effect of any alterations.
• Incorporate single leg exercises — Asymmetry decreased during single leg bridges, so these can help reinforce correct technique and reduce right leg input.
• Transfer to sprinting — EMG during running and sprinting can identify if a similar asymmetry is apparent in sport-specific movement.

Take-Home Points

EMG adds a crucial extra layer to athlete monitoring through hamstring screening. It shows how the hamstrings contribute, not just the performance outcome, allowing the right muscle to be targeted with the right exercise. EMG complements strength and jump tests rather than replacing them, by giving practitioners the missing neuromuscular context behind those numbers — enabling better decisions with the goal of increased player availability and reduced costly days missed.