Surface EMG Amplitudes of Back Muscles Are Largely Unaffected by Individual Factors

Although surface electromyography (SEMG) is widely used in research, it remains unclear whether systematic differences in SEMG amplitudes are sensitive to sex, age, or individual force capacity. To address this issue, the present study conducted a re-evaluation of SEMG amplitude values of back muscles in a total of 239 healthy participants (115 women) aged 18–52 years. SEMG data were obtained during static submaximal and maximal (MVC) tasks. Across the subgroups defined by sex, age, BMI, and force capacity, no relevant differences in amplitude were identified, with the following exceptions M. iliocostalis: young > older and all muscles low BMI > high BMI. In contrast, during MVC, amplitude differences were consistently detected: men > women, young > older, low BMI > high BMI, and strong > weaker. Analysis of the amplitude-force relationship using values normalized to MVC revealed nearly perfectly linear relation-ships across all subgroups. Although the data points were in different positions along the range of origin, the slopes were nearly identical. These findings suggest that, within the submaximal range, SEMG amplitudes of the back muscles may be analyzed jointly without adjustment for sex, age, or force capacity. By contrast, SEMG data obtained during MVC should be evaluated separately for the respective subgroups.