Muscle characteristics in career breath-hold divers: Effect of water temperature

Introduction: In a previous study we reported that Korean female breath-hold divers (BHD) with life-long experience of diving in cold water (10-12°C in winter and 25-27°C in summer) had reduced muscle fiber size and increased capillary density. The hypothesis tested in the present study was whether prolonged habitual diving at a moderate water temperature (MWT, 29-30°C all year round) similarly caused a reduction in muscle fiber size. Methods: The subjects were 14 Indonesian BHDs with long experience of diving at MWT, and a control group of 10 age-matched non-diving Indonesian men (CON), selected from the same tribe among which the BHDs lived. Muscle samples obtained from the middle portion of the vastus lateralis muscle were analyzed for muscle morphology by histochemical analysis and the levels of vascular endothelial growth factor (VECF) protein by Western blotting. Results: Muscle fiber type composition was identical in both groups, and no difference in cross-sectional area (CSA), VECF protein, or capillarity between the BHD and the CON was observed. Conclusion: The present study demonstrated that prolonged habitual breath-hold diving at MWT does not cause any alteration in muscle fiber composition, fiber size, or capillarity.