Twenty-eight days of exposure to 3,454 m increases mitochondrial volume density in human skeletal muscle

• The role of hypoxia on skeletal muscle mitochondria is controversial. Studies superimposing exercise training with hypoxic exposure demonstrate an increase in skeletal muscle mitochondrial volume density (MitoVD ) over equivalent normoxic training. In contrast, a reduction in both skeletal muscle mass and MitoVD have been reported following mountaineering expeditions. These observations may however be confounded by negative energy balance, which may obscure the results. Accordingly we sought to examine the effects of high altitude hypoxic exposure on mitochondrial characteristics, with emphasis on MitoVD , while minimizing changes in energy balance. For this purpose, skeletal muscle biopsies were obtained from 9 lowlanders at sea level (Pre) and following 7 (7 Days) and 28 (28 Days) days of exposure to 3454 m. Maximal ergometer power output, whole-body weight and composition, leg lean mass, and skeletal muscle fibre area all remained unchanged following the altitude exposure. Transmission electron microscopy determined intermyofibrillar (IMF) MitoVD was augmented (P = 0.028) by 11.5 ± 9.2% from Pre (5.05 ± 0.9%) to Day 28 (5.61 ± 0.04%). On the contrary, there was no change in subsarcolemmal (SS) MitoVD . As a result total MitoVD (IMF + SS) was increased (P = 0.031) from 6.20 ± 1.5% at Pre to 6.62 ± 1.4% on Day 28 (7.8 ± 9.3%). At the same time no changes in mass-specific respiratory capacities, mitochondrial protein or antioxidant content were found. This study demonstrates that skeletal muscle MitoVD may increase with 28 days acclimation to 3454 m.

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MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

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