Comparing pain perception and muscle swelling between skeletal muscle microbiopsy and eccentric leg press: preliminary results

Background Skeletal muscle tissue swelling is a common indicator of muscle damage. The microbiopsy (MB) method is considered a less invasive muscle biopsy procedure and may reduce participant burden. However, the swelling and perception of pain associated with MB could discourage participation, while the swelling and pain resulting from exercise may be more socially accepted and less likely to deter participation. This study aims to compare the pain response and muscle swelling following an eccentric leg press (ELP) protocol and MB to better understand tolerability and physiological responses to each condition.Methods Participants, (n = 13; age: 21.0 ± 2.1 years; height: 168.5 ± 10.7 cm; weight: 73.6 ± 14.3 kg; BMI: 26.0 ± 4.9 kg/m2; Sex: ♂: 3 ♀: 10) completed both experimental conditions (MB and ELP) separated by one week. Ultrasound imaging was used to assess swelling (muscle thickness; MT) of the m. vastus lateralis (VL) at four standardized sites (40, 50, 60, and 75% of femur length). Images were captured at baseline (BL), immediately post (IP), and 24-, 48-, and 72-h post-condition to evaluate changes in MT analyzed with NIH Image J. Pain pressure threshold (PPT) was assessed at each time point using a pressure algometer applied to the skin over the VL locations until volitional discomfort. Visual analog scale (VAS) ratings were also collected to measure subjective pain intensity. A RMANOVA was used to determine the effects of condition, location, and time on PPT, VAS, and MT measures.Results PPT values showed no significant main effects for condition (p > .05, η2 = .279), time (p > .05, η2 = .260), condition×location interaction (p > .05, η2 = .083), location×time interaction (p > .05, η2 = .136), or condition×location×time interaction (p > .05, η2 = .086). A significant main effect was observed for location (p = .026, η2 = .279), with higher PPT values at 75% VL compared to 60% VL (p = .044). VAS data showed no significant main effects. MT showed no significant differences between VL locations. At 40% of the VL, there were no significant main effects for time (p > .05, η2 = .124), condition, or the time × condition interaction. At 50% VL, no significant difference was observed for condition (p > .05, η2 = .247); significant main effects were found for time (p < .001, η2 = .473) and the time × condition interaction (p = .049, η2 = .252). At 60% VL, there was a significant main effect for time (p = .008, η2 = .343) and a significant time × condition interaction (p = .044, η2 = .257), with no significant effect of condition. At 75% VL, no significant differences were found for time (p > .05, η2 = .141), condition, or the time × condition interaction.Conclusions Currently, no differences were found in PPT, VAS, and MT measures of the VL between conditions. PPT-assessed location differences were found (75% vs. 60% of VL), which may be explained by fat mass deposition (i.e. “padding”). There were notable and expected time differences for regional MT measures (50 and 60%); the more proximal and distal ends of the VL were unaffected. Pain perception and muscle swelling results seem to be similar when comparing ELP and MB.