Abstract
INTRODUCTION: The purpose of this study was to explore the relationship between human fiber type specific mitochondria volume density and VO2max. METHODS: Eleven recreational active subjects (VO2max mean 4.54±0.58 L/min) reported to lab for a progressive ergometer cycle test to estimate VO2max. Ten muscle fibers were obtained in each 9 biopsies in vastus lateralis from each of the 11 subjects. In each fibers, 24 images where obtained in a randomized systematic order, thus 528 fibers and 13968 images were analyzed. Point counting was used to estimate imtermyofibrillar (IMF) mitochondrial content as a volume density and subsarcolemmal (SS) mitochondrial content as a volume per fiber surface. Total mitochondrial content were obtained by recalculating the SS subfraction to myofibrillar volume density. Fibre type was determined by z-disk widths. Lean body mass(LBM) was determined by DXA. All data are presented are means ± SD. Associations was evaluated using Pearson´s correlation coefficient. RESULTS: The total, IMF and SS mitochondrial content in type1 are 0.087±0.021 μm3·μm-3, 0.065±0.014 μm3·μm-3, 0.451±0.159 μm3·μm-2, respectively, and in type2 are 0.059±0.018 μm3·μm-3, 0.046±0.012 μm3·μm-3, 0.271±0.129μm3·μm-2, respectively. Total mitochondrial volume content was a strong predictor of VO2max per LBM. Further, IMF mitochondrial content is a better predictor of a subject’s VO2max per LBM than SS mitochondrial content. The fiber type specific correlations revealed that, total, IMF and SS in different fiber types are associated with VO2max per LBM, except SS mitochondrial content in type2 is not associated (Fig 1). CONCLUSION: There is a strong correlation between mitochondrial content and VO2max per LBM, however, VO2max and relative VO2max are not associated with mitochondrial content. Also, there is a clear correlation between total and IMF mitochondrial content and VO2max per LBM in both type 1 and type 2 fibers, whole this was only the case for SS in type 1 fibers.
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