Impact of repeated bouts of eccentric exercise on sarcolemma disruption in human skeletal muscle.

In animal models, unaccustomed eccentric exercise (EE) has been widely related to muscle fiber membrane (sarcolemma) damage. On the contrary, studies in humans reported that sarcolemma was not susceptible to damage following a single bout of EE. We hypothesized that the single bout of EE used by those studies was not sufficient to induce sarcolemma damage, in humans. In this study we examined muscle biopsies from untrained males who either performed six sets of 15 reps of maximum voluntary eccentric contractions (n=9), for six consecutive days, or served as control-group (n=6). Blood and biopsy samples were obtained one week prior to exercise, immediately after bout 3, and 24h after the last training session. In addition to standard haematoxylin-eosin staining, all biopsies were stained immunohistochemically using antibodies specific for fibronectin and desmin antigens. In the exercise-group, no biopsies taken at pre-exercise or post-exercise level showed evidence of sarcolemma damage as stained by anti-fibronectin antibody in eight of nine subjects. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities increased significantly throughout the study despite the lack of sarcolemma damage.We suggest that in humans, repeated bouts of EE do not cause gross sarcolemma damage in the mid-belly of Vastus Lateralis.

The effect of exercise and oxidant-antioxidant intervention on the levels of neurotrophins and free radicals in spinal cord of rats.

STUDY DESIGN: This study was designed to investigate the effects of oxidant and antioxidant treatment, as well as regular exercise, on neurotrophin levels in the spinal cord of rats. OBJECTIVES: Reactive oxygen species (ROS) play a role in neurodegenerative diseases, but ROS at moderate levels could stimulate biochemical processes through redox-sensitive transcription. METHODS: Exercised or sedentary animals were injected subcutaneously with hydrogen peroxide (H(2)O(2)), N-tert butyl-alpha-phenyl nitrone (PBN) or saline for the last 2 weeks of a 10-week experimental period to challenge redox balance. Free radical (FR) concentration was evaluated in the spinal cord by electron spin resonance, protein carbonyls, brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) levels and the mRNA expression of BDNF receptor and tyrosine kinase receptor B (TrKB). SETTING: Research Institute of Sport Science, Semmelweis University, Budapest, Hungary. RESULTS: Exercise or PBN decreased the concentration of FR, whereas the carbonyl content did not change. BDNF was significantly decreased in exercised sham and sedentary PBN-treated groups, and its content correlated with the level of FR. GDNF was significantly increased in sedentary H(2)O(2)-treated groups. No differences were observed in TrkB mRNA expression among groups. CONCLUSIONS: Results suggest that regular exercise alone and PBN in sedentary animals can successfully decrease FR levels in the spinal cord. Redox alteration seems to affect the levels of GDNF and BDNF, which might have clinical consequences, as neurotrophins play an important role in cellular resistance and regeneration.