Abstract
Recently, it has been shown that the extramuscular connective tissue (ECT) is likely involved in delayed onset muscle soreness (DOMS). Therefore, the aim of the present study was to investigate the effects of maximal trunk extension eccentric exercise (EE) on ECT thickness, self-reported DOMS, ECT stiffness, skin temperature, and possible correlations between these outcomes. Healthy adults (n = 16, 29.34 ± 9.87 years) performed fatiguing EE of the trunk. A group of highly active individuals (TR, n = 8, > 14 h of sport per week) was compared with a group of less active individuals (UTR, n = 8, < 2 h of sport per week). Ultrasound measurements of ECT thickness, stiffness with MyotonPro and IndentoPro, skin temperature with infrared thermography, and pain on palpation (100 mm visual analog scale, VAS) as a surrogate for DOMS were recorded before (t(0)), immediately (t(1)), 24 h (t(24)), and 48 h (t(48)) after EE. ECT thickness increased after EE from t(0) to t(24) (5.96 mm to 7.10 mm, p = 0.007) and from t(0) to t(48) (5.96 mm to 7.21 mm, p < 0.001). VAS also increased from t(0) to t(24) (15.6 mm to 23.8 mm, p < 0.001) and from t(0) to t(48) (15.6 mm to 22.8 mm, p < 0.001). Skin temperature increased from t(1) to t(24) (31.6° Celsius to 32.7° Celsius, p = 0.032) and t(1) to t(48) (31.6° Celsius to 32.9° Celsius, p = 0.003), while stiffness remained unchanged (p > 0.05). Correlation analysis revealed no linear relationship between the outcomes within the 48-hour measurement period. The results may confirm previous findings of possible ECT involvement in the genesis of DOMS in the extremities also for the paraspinal ECT of trunk extensors. Subsequent work should focus on possible interventions targeting the ECT to prevent or reduce DOMS after strenuous muscle EE.