Fatigue-induced alterations in the spatial distribution of lumbar erector spinae activity in older versus young adults

Purpose: This study examined differences in the spatial distribution of lumbar erector spinae (LES) muscle activity during a submaximal isometric trunk extension contraction between older and younger adults. Methods: Thirteen older adults (OLDER) and thirteen young adults (YOUNG) participated. High-density surface electromyography signals were recorded from the LES muscle during an isometric trunk extension task at 30% of maximal voluntary isometric force until failure. The spatial distribution of muscle activity was assessed via the x and y coordinates of the centroid of the root mean square map. Muscle fibre conduction velocity (MFCV) was calculated as a physiological index of local muscle fatigue. Force steadiness was quantified using the coefficient of variation (CoV) of force. Results: MFCV values significantly decreased during the fatiguing task (p < 0.001), with the two groups showing a similar rate of decline. Significant "Time*Group" interactions were found for the centroid displacement along both the y axis (p = 0.017) and the x axis (p = 0.006), with OLDER showing a cranial shift of muscle activity and YOUNG a lateral shift. Endurance time was similar between groups (p = 0.749). The CoV was consistently higher in OLDER throughout the task (p = 0.001). Conclusion: This study highlights age-related differences in LES activity adaptations to muscle fatigue, with older adults showing potentially protective, but less efficient recruitment strategies. In addition, older participants demonstrated poorer trunk force control during the task.