Changes in nerve growth factor in vastus lateralis muscle after the first versus second bout of one-leg eccentric cycling.

Delayed onset muscle soreness (DOMS) develops after performing unaccustomed eccentric exercises. Animal studies have shown that DOMS is mechanical hyperalgesia through nociceptor sensitization induced by nerve growth factor (NGF) and glial cell line-derived neurotrophic factor (GDNF) upregulated by cyclooxygenase-2 (COX-2). However, no previous study has investigated these in relation to DOMS in humans. This study compared the first and second bouts of one-leg eccentric cycling (ECC) for changes in NGF, GDNF, and COX-2 mRNA in the vastus lateralis (VL). Seven healthy adults (18-40 years) performed two bouts of ECC (10 sets of 50 contractions) with 80% maximal voluntary concentric peak torque separated by 2 weeks (ECC1, ECC2). Muscle soreness that was assessed by a visual analog scale and maximal voluntary isometric contraction (MVC) torque of the knee extensors were measured before, immediately after (MVC only), 24 and 48 h post-exercise. Muscle biopsy was taken from the VL before the first bout from nonexercised leg (control) and 24 h after each bout from the exercised leg, and analyzed for NGF, GDNF, and COX-2 mRNA. Peak DOMS was more than two times greater and MVC torque at 48 h post-exercise was approximately 20% smaller after ECC1 than ECC2 (p < 0.05), suggesting the repeated bout effect. NGF mRNA level was higher (p < 0.05) post-ECC1 (0.79 ± 0.68 arbitrary unit) than control (0.06 ± 0.07) and post-ECC2 (0.08 ± 0.10). GDNF and COX-2 mRNA did not show significant differences between control, post-ECC1, and post-ECC2. These results suggest that an increase in NGF is associated with the development of DOMS in humans.