Standing Up to Dysglycemia: Textile Electromyography Identifies Hamstring Muscle Activity Benefits

Standing shows inconsistent associations with glycemic profiles. This study examined whether thigh muscle activity during standing modifies the association between standing time and glycemic profiles under free-living conditions. Thirty physically inactive young women contributed 52 participant-days while wearing a continuous glucose monitor, thigh-worn accelerometer, and textile electromyography (EMG) shorts. Waking behavior was classified into sitting, standing, and moving and expressed as a three-part compositional time-use variable. During standing, quadriceps and hamstring EMG were summarized as average normalized amplitude and active duration. Outcomes were mean glucose, coefficient of variation (CV), time in range (TIR), time above range (TAR), and time below range (TBR). Regression models tested whether standing-specific EMG metrics moderated associations between behavior composition and glycemic outcomes. Standing was not independently associated with glycemic outcomes. Hamstring EMG active duration moderated the association between standing and TIR (β = 0.473, 95% CI [0.277, 0.668], p < 0.001, Cohen's f² = 0.15) and TBR (β = -0.467, 95% CI [-0.653, -0.282], p < 0.001, Cohen's f² = 0.153), but not TAR, CV, or mean glucose after multiple testing correction. A higher standing proportion was associated with higher TIR when hamstring EMG active duration exceeded 38.8% and lower TBR when it exceeded 29.7%; below 16.8%, a higher standing proportion was associated with lower TIR. These findings suggest that the potential glycemic benefits of standing may depend on hamstring muscle engagement, highlighting EMG-derived muscle engagement as a marker for distinguishing physiologically heterogeneous forms of standing.