Changes in tibialis anterior architecture affect the amplitude of surface electromyograms.
Taian M Vieira, Maria Cristina Bisi, Rita Stagni and 1 others
PMID 28807025WHAT IT FOUND
Surface EMG amplitude from tibialis anterior changed with ankle position even when nerve stimulation was held constant.
For therapists, EMG amplitude shifts during movement may reflect muscle shape, not just activation.
Key findings
01In 10 healthy subjects, tibialis anterior M-wave amplitude was significantly smaller in plantar flexion than in neutral and dorsiflexion at both stimulation intensities.
02Pennation angle and muscle width were greater in dorsiflexion than plantar flexion, with values of 15.3 degrees and 67.8 mm versus 8.0 degrees and 58.1 mm.
03Greater pennation angle and width were associated with larger M-wave amplitude, including when signals were recorded with the conventional bipolar montage.
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How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only 10 healthy adults were studied, and none reported a neuromuscular disorder, so the result may not apply to people with neuromuscular disorders. The study tested tibialis anterior only, and the authors state the effect may not generalise to other muscles or other pennate muscles. M waves were measured with nerve stimulation while the muscle was relaxed, not during voluntary contractions or gait, so real movement EMG may also include changes in neural drive. The study did not show how to correct EMG amplitude for ankle position during dynamic tasks.
The easy way to misread this
Do not read a lower surface EMG amplitude in plantar flexion as proof that tibialis anterior activation is lower. The nerve stimulation was held constant, and amplitude changed with ankle position and muscle architecture.