Muscle activation during maximum voluntary contraction and m-wave related in healthy but not in injured conditions: Implications when normalizing electromyography

Background: Electromyography signal amplitude is influenced by a variety of factors. Normalization strategies aimed at decreasing signal variability include using peak electromyography signal during a maximum voluntary contraction and peak-to-peak M-wave amplitude. However, whether these normalization methods are comparable has not been investigated in injured populations. This study investigated the relationship between peak signal during maximum voluntary contraction and M-wave amplitude in individuals with a unilateral Achilles tendon rupture. Secondarily, we observed whether the two normalizations strategies would yield similar results when evaluating between limb differences in muscle activity during a jump task. Methods: Eleven individuals 1–3 years after a unilateral Achilles tendon rupture were included in this study. Surface electromyography was used on the medial and lateral gastrocnemii bilaterally. Peak maximum voluntary contraction, M-wave amplitude, and electromyography during a jumping task were collected. Findings: A strong relationship was observed between peak maximum voluntary contraction and M-wave amplitude on the uninjured (r = 0.71–0.88, P < 0.05) but not on the ruptured side (r = 0.41–0.44, P > 0.05). The two normalization techniques did not produce different results when comparing the uninjured and ruptured sides. Interpretation: The findings of this study suggest that M-wave normalization yields similar results as peak maximum voluntary contraction-normalized electromyography in uninjured conditions. M-wave normalization may be a useful strategy in an injured population where a maximal muscle contraction is unsafe or impaired.