High-altitude exposure results in a decrease in myoglobin protein expression in skeletal muscle. The individual variations in myoglobin levels in muscle biopsies obtained from vastus lateralis under normoxic conditions at SL and during exposure to HA (4559 m) for 7 to 9 days are shown. Myoglobin content in extracts of muscle biopsies was analyzed by 2D gel electrophoresis followed by SYPRO Ruby staining. The quantification of the separated isoforms was performed by the Image Quant software. The values are given in arbitrary units (AU). Due to technical reasons, the analysis of 1 sample (no. 5) could not be performed. (A) A typical 2D gel electrophoresis spot image, showing the 3 myoglobins isoforms, is presented for participant no. 7 at SL and during HA. The individual quantitative changes for all study participants relative to myoglobin isoform 1 (main isoform) (B), myoglobin isoform 2 (C), and myoglobin isoform 3 (D) (isoforms 2 and 3 being expressed at lower levels also under normoxic conditions) are presented. The data are representative of 3 independent experiments. The calculation of statistical differences from normoxia was performed using the Wilcoxon test. **P < .01; *P < .05; +P = .05.