Ultrasound and EMG Combined Track Biceps Fatigue in Trained and Novice Lifters

Combining ultrasound imaging with surface electromyography can distinguish between different stages of localized muscle fatigue in the biceps brachii, according to a new study published in BMC Sports Science, Medicine and Rehabilitation. Researchers assessed forty healthy men performing seated right-arm 10-kg dumbbell curls until voluntary exhaustion and found that advanced resistance trainees completed more repetitions and showed smaller fatigue-related changes in muscle thickness than novices. When stage-matched ultrasound video and electromyography recordings were fed into a classification model, participant-level internal cross-validation yielded an exploratory three-class accuracy of 86.23% and a macro-F1 score of 86.32%, suggesting that multimodal recordings may hold value for objective fatigue-state recognition.

The study allocated participants to an advanced resistance-training group of twenty men or a novice group of twenty men. Each volunteer curled a 10-kg dumbbell until he could no longer continue. The authors emphasized an important caveat: because the same absolute load represented different relative intensities across individuals and groups, comparisons of training status had to be interpreted accordingly. Four measures were recorded at three time points—baseline, moderate fatigue, and exhaustion: biceps brachii muscle thickness on B-mode ultrasound, peak systolic velocity in the anterior circumflex humeral artery on Doppler ultrasonography, surface electromyography root mean square amplitude, and median frequency.

The behavioral difference between groups was clear. Advanced trainees completed 16.3 ± 2.7 repetitions before exhaustion, compared with 13.3 ± 2.3 repetitions in novices, a difference that was statistically significant (p < 0.001). Morphological adaptation also differed. The increase in muscle thickness from baseline to exhaustion was smaller in the advanced group—12.69 ± 4.67% versus 18.14 ± 5.87% in novices, a mean difference of −5.44 percentage points (95% CI −8.84 to −2.04; p = 0.003). This suggests that trained muscle swelled less under the same absolute load, although the differing relative intensity of that load limits how strongly training status itself can be credited.

The vascular and electrical signals followed their own patterns. Peak systolic velocity in the anterior circumflex humeral artery increased as fatigue developed, but the exhaustion value did not differ between the trained and novice groups (mean difference −1.35 cm/s, 95% CI −7.78 to 5.07; p = 0.672). On the electromyography side, the root mean square amplitude rose with fatigue, while the median frequency traced an inverted-U trajectory across the exercise bout. Together, the authors note, these measures captured complementary morphological, hemodynamic, and electrophysiological associations during localized biceps brachii fatigue—information that neither modality alone would provide.

The classification result comes with explicit limits. The 86.23% accuracy and 86.32% macro-F1 were obtained through participant-level five-fold internal cross-validation on ultrasound video and electromyography recordings from the 35 participants whose data were free of artifacts. The authors describe these findings as exploratory: they suggest potential value for multimodal fatigue-state recognition but do not establish deployment readiness. Confirming the approach, they write, will require individualized loading, larger and more diverse samples, and external validation. If those steps succeed, objective assessment of localized muscle fatigue could eventually support exercise prescription, rehabilitation monitoring, and sports performance management—applications the researchers identify as the motivation for developing such measurement tools in the first place.

Subject of Research: Multimodal ultrasound and surface electromyography assessment of biceps brachii fatigue during resistance exercise in trained and novice men

Article Title: Multimodal ultrasound and surface electromyography assessment of training-dependent biceps brachii fatigue during resistance exercise

Article References: Xie, S., Pan, W., Wang, Y., Huang, J., Xu, R., & Zhao, J. (2026). Multimodal ultrasound and surface electromyography assessment of training-dependent biceps brachii fatigue during resistance exercise. BMC Sports Science, Medicine and Rehabilitation. https://doi.org/10.1186/s13102-026-02188-5

Image Credits: AI Generated

DOI: 10.1186/s13102-026-02188-5

Keywords: muscle fatigue, biceps brachii, ultrasound, surface electromyography, resistance training, Doppler ultrasonography, muscle thickness, peak systolic velocity, exercise prescription, cross-validation, Multimodal, surface