First of all, here is a general distinction between the different applications of EMG depending on the area of use. The use case described here addresses use cases A and B: (Bild) An EMG mapping compares three activity states. The “Resting tone” is measured while standing and should not exceed a maximum activity of 15 µV. If abnormalities are found, detonic measuresor an intensive activation can help. “Voluntary activation”, or the ability to intentionally activate a muscle, enhances an athlete’s control over their strength. “Involuntary activation” visualises the muscle economy during movement. High activity values in this test are not necessarily “good” as they may indicate weakness compensated by high effort (high activity). Therefore all three activity states as well as a balance score should be considered when identifying inter- & intramuscular differences. Mapping results should lead to biofeedback training to improve both voluntary and involuntary activation. Dynamic training exercises help to ensure targeted and rapid muscle activation ability in sport-specific movement. This is here illustrated using the selected use case for the gluteus medius of a professional football player.

The Importance of Gluteus medius (GM)

The GM is crucial for stabilising the pelvis and supporting the lower back, leading to improved posture (pelvic control and hip stability) and movement efficiency. Its proper function can help prevent injuries in unilateral loading situations. The analysis of EMG scree­nings of 48 male football players from Germany’s top three leagues revealed significant variability in the voluntary activation (average: 430 µV [± 215 µV], range: 140 – 1133 µV) as well as in involuntary activation (average: 449 µV [± 168 µV], range: 219 – 1116 µV), with the highest averages found among players in the first Bundesliga.

Case: exertion-dependent hip pain

The following case study illustrates the interplay of mappings and biofeedback training sessions of the GM based on an athlete with exertion-dependent hip pain. In football, especially in the supporting leg, sagittal stability is crucial to ensure optimal performance and economy. Evaluating the neuromuscular function of the gluteus medius serves as an important para­meter in this regard.

Initial gluteus medius mapping (Fig. 2 a)

The standardised mapping of the GM consists of 6 exercises and always starts with the rest position, which in this case showed good results far below the guideline of 20 µV. The second exercise is squeezing both glutes (voluntary activation) in which the player reached a balance score of 74 % ending up slightly below the symmetry goal of 80 %. A significant difference showed up in the unilaterally isolated activation exercises: The left gluteus reached 119 µV (balance score of 89 %) while the right gluteus only reached 62 µV (55 % balance score) as the left gluteus compensates when the athlete is asked to individually squeeze his right muscle. The last exercise “one leg stands left and right” aims at the involuntary activation and was unremarkable as they almost reached the 400 µV guideline each side.

Biofeedback Training

In biofeedback training mode the player sees the muscle activity values of the EMG sensors on a tablet screen (external focus), which is the basis to improve voluntary and “isolated” voluntary activation. Body awareness, motivation and compliance increase. To transfer learnings to involuntary movements, single-leg standing with external rotation of the raised leg were introduced. If activity decreases or stagnates, it indicates compensation by other muscles. Improvements should be noticeable with the first training session, at the latest after a few days of active practice.

Continuous use in Athletic Training

After adding GM exercises to the individual training plan, measuring activation during strength exercises enhanced execution and exercise efficiency. For example, during a side plank, complete pelvic thrusting often increases activation by up to 200 µV, highlighting the importance of small execution adjustments. EMG also aids in identifying compensatory patterns by monitoring the activity of muscles such as the tensor fasciae latae and biceps femoris, allowing trainers/therapists to make appropriate corrections.

First phase results (Fig. 2 b)

After three weeks of intervention, the resting tone remained stable, and voluntary activation (Squeeze Your Glutes) has been significantly improved from 100 µV to 600 µV both sides. Since strength training is limited in the competition phase, this increase is less attributed to strength gains but rather to a considerably better voluntary activation. This is also evident in isolated voluntary activation (Squeeze Your Left/Right Glute) with higher µV values and better balance scores. The involuntary exercises (One Leg Stand) also recorded higher values but an asymmetry of 69% balance score occurred, which was addressed in the next training phase.

Re-Test in Mid-Season Screening (Fig. 2 c)

After a period without intensive EMG supervision and mapping, the team’s mid-season screening showed a left-dominant imbalance and slightly increased activity of the passive muscle on each side during voluntary activation.
Remarkably, there was a significant decrease in the involuntary activation of the gluteus medius during the One Leg Stand on the right, returning to the value of the initial mapping. This highlights the importance of regular training.
But this can also be rapidly improved again by targeted biofeedback training. Figure 3 shows the athlete´s development over three different measurements for the exercise Squeeze Your Right Glute. It shows the increase after 3 weeks intervention and a slight decrease after 6 months.

Conclusion

EMG screenings provide deep insights into muscle activity and support indivi­dual analyses. Biofeedback training improves the muscle activation ability and assists the athlete intuitively with the efficient execution of exercises. Even if there is a lack of engagement or motivation, biofeedback training can have a supportive effect with its direct visual feedback and the display of positive changes. Successful integration of EMG into athletic routines requires user-friendly, intuitive, preferably wireless systems for flexible and effective use. The opportunity to rapidly collect and interpret data is crucial in professional sports.