Whole body protein turnover at altitude

Skeletal muscle loss has often been reported as a common feature of long term exposure to high altitude. Although the muscle loss has been reported for decades the underlying regulating mechanisms are relatively unknown. We studied protein turnover in nine male subjects at sea level and after seven days exposure to 4559 m. Three days prior to experiments subjects were confined to live in our laboratory or inside the Margeritha hut at 4559 m. For this period diet and activity levels were matched. Protein turnover was studied during 4 hours of supine rest by a primed constant infusion of [1− 13 C]leucine and sodium bicarbonate. Blood and pulmonary CO 2 samples were obtained, before and every hour after the start of the isotope infusion. Muscle biopsies were obtained pre‐infusion, and then after one and four hours. Whole body protein synthesis for the last 2 hours of the study was similar at sea level and altitude with 0.22±0.02 and 0.24±0.01 g.(kg.h) −1 , respectively. Also the net whole body protein balance was similar at sea level and altitude with a net protein degradation of 0.025±0.002 and 0.030±0.002 g.(kg.h) −1 , respectively. In conclusion, whole body protein synthesis and the net protein balance are unchanged after 7–9 days of acclimatization to 4559 m if activity level and diet are maintained. In addition, the previous reported altitude depended muscle loss might be related to decreased energy intake and/or activity level.