Why Do Hamstring Injuries Occur?

The biceps femoris is particularly vulnerable, being involved in 80% of hamstring injuries. This is likely due to the muscle’s role during the swing phase of running, where it contracts eccentrically just before heel contact. This phase is critical, as the muscle is maximally tensed and stretched while it works to decelerate knee extension and counter hip flexion. Additionally, the biceps femoris is a biarticular muscle, which makes it more prone to fiber tears. Contributing risk factors include age, previous injuries, core instability, and weak gluteal muscles. Limited mobility, such as poor flexibility in the hip flexors (e.g., iliopsoas) or short muscle fascia in the hamstrings, especially in the biceps femoris, can also be influential. Finally, an imbalance between the front and back thigh muscles and poor neuromuscular control significantly raise the risk of hamstring injuries. 

Muscular Inhibition – A Target for EMG

When overload, fiber rupture, or similar muscular damage occurs, it results in a natural protective inhibition of the tissue. This should only persist until the tissue has regenerated. After that, it is essential for the muscle to relearn how to activate properly and to let go of any compensation strategies. Typical compensations involve the gluteal muscles, the semimembranosus and semitendinosus (semigroup), and the lower back. These compensations can create muscular imbalances and secondary inhibitions. EMG (electromyography) helps visualize muscle activity and detect such imbalances and compensations. Based on this data, EMG biofeedback can guide targeted exercises that support the breakdown of faulty compensation patterns and restore proper muscle function.

EMG Mapping for Early Detection and Prevention

EMG mapping is a standardized analysis of muscle activity lasting about 3 minutes. The process is guided by the myoact app through predefined exercises tailored for 36 surface-accessible muscles. The result is a personalised report including a balance score, visualised using a traffic-light system to highlight imbalances and abnormal activation patterns. This makes it possible to detect dysfunctions early on and address them immediately with targeted EMG biofeedback training.

EMG Mapping of the Hamstrings

When mapping the hamstrings, the resting position is first tested in a standing position, during which the hamstring muscles should not yet be working. Six further tests are then carried out. First, the toe touch with straight knees to check the counter-tension: does the muscle relax in this position and is the upward movement biceps-dominant or at least balanced with the semi-group? Active neck flexion tests the neurodynamics – if the tension in the dorsal chain increases with the head movement, there is a tonic protective reaction of the nervous system. While knee flexion exercises recruit the semimembranosus and semitendinosus muscles in particular, hip extension targets the biceps femoris. Therefore, both exercises are part of standardised EMG mapping to check whether this is actually the case for the athlete. Finally, single-leg bridging with the knee almost fully extended is used to test the hamstrings under functional conditions.

Practical Example: The Role of Hamstring Training

Take the case of a professional footballer who had suffered multiple hamstring injuries on both legs. EMG mapping and EMG biofeedback were used to integrate tailored exercises into his training routine, successfully preventing further relapses. At the end of the season, a screening showed good symmetry in leg extension strength, with excellent values on the right and average values on the left. However, after transferring to a new club with a different training philosophy, shifting from high-load to high-repetition training, he developed significantly poorer activation patterns. During single-leg bridging, compensation by the semigroup for the biceps femoris and frequent cramping under load were observed.

Crucial: Reducing Compensations

Since the athlete was still able to perform hip extension with external rotation correctly, therapy could build on this movement. The goal was to transfer this isolated activation into loaded functional movement. A follow-up EMG mapping revealed that the gluteus medius, which should act only as a stabilizer, was just as active as the biceps femoris, indicating a compensation. To resolve this, the activations of the gluteus medius and biceps femoris had to be separated. EMG biofeedback displayed each muscle’s activity with a separate bar. It showed that although the biceps femoris initially activated correctly, even slight movement adjustments caused the gluteus medius to take over. By specifically training this targeted activation and only increasing the load once the coordination was mastered, compensation could be reduced and proper movement restored.

3 Steps to Hamstring Assessment

Overall, there are three points that should always be included in an assessment and targeted prevention of hamstring injuries. The first step is to assess the basic tone and muscle activity during neck flexion. If the biceps femoris is working here, this indicates inefficient muscle activity. The second step is to test whether the semigroup works more dominantly in knee flexion and the biceps femoris in hip extension. A reverse pattern is a sign of compensation. The third step then involves learning targeted control to counteract compensation. Once this has been mastered, the load can be slowly increased without compensation occurring again. An additional tip is to also screen surrounding structures to uncover further compensations, such as those caused by the gluteus medius, and to ensure that these are sufficiently trained (e.g. the transversus or foot mobility).

Conclusion

These three steps offer a clear roadmap to proactively prevent hamstring injuries. EMG mapping identifies hidden compensation patterns that often go unnoticed and contribute to injury risk. EMG biofeedback enables precise muscle targeting and coordination training, resulting in more efficient movement and reduced injury vulnerability for athletes.