Improving Estimates of Maximum Voluntary Isometric Contractions: Exploring the Utility of Feedback Manipulations

Pelvic floor dysfunction (PFD), often resulting from weakened pelvic floor muscles (PFM), significantly impacts quality of life and increases health risks, particularly among the elderly. Strengthening PFMs through exercise is effective, yet invasive treatment protocols deter adherence. Non-invasive surface electromyography (sEMG) provides a promising alternative for assessing PFM strength. This study evaluates a reinforcement-based strategy (R-MVIC) against standard verbal encouragement (SVE) for estimating the maximal voluntary isometric contraction strength (MVIC) of PFMs. Using a single-case reversal design (ABAB), we compared peak amplitudes across experimental and control conditions. All experimental sessions occurred in a small examination room at a major University. Using an (AB)^k single-case research design power analysis to determine our N, we recruited ten participants who performed isolated PFM contractions. The R-MVIC condition involved pre-training, task-specific instructions, criterion-based feedback, and an extinction burst manipulation. To determine the strength of muscle contraction, we used sEMG, placed over the transverse abdominis/internal oblique (TrA/IO) site, to measure muscle activity in microvolts (mV). Results indicated R-MVIC produced significantly higher peak amplitudes compared to SVE, with a mean difference of 746 mV, representing a 52% increase. The R-MVIC condition consistently evoked stronger contractions, demonstrating the efficacy of feedback and extinction bursts in enhancing MVIC estimates. These findings suggest that R-MVIC is a valuable strategy for improving estimates of PFM strength. Overall, the results suggest that sEMG-based biofeedback provides a non-invasive technology for improving treatment protocols.