Mitochondrial Protein Dynamics in Response to Repeated Load Carriage in Men and Women

PURPOSE: To evaluate the early stages of adaptation in response to repeated load carriage on mitochondrial protein dynamics. METHODS: Over 15 days 32 subjects (12 male, 20 female; age 28±6 years; VO2 peak 47.7±8.2 mLkg-1min-1) consumed a loading dose of deuterated water (2H2O), and completed a 5-day load carriage hiking protocol. 2H2O enriched the amino acid pool for observation. Muscle biopsies from the vastus lateralis were taken on days 10 and 16, assessing protein fractional synthesis rate (FSR) pre- and post-hiking. During the hiking period, participants completed two laps on an out-and-back mountainous trail, averaging 3.3±0.6 km distance and 431±86 m gain, per lap. Total distance covered per day averaged 13.6±2.2 km distance and 870.9±163.8 m gain. Each lap was timed for an hour uphill, at 70% of age-predicted heart rate max (121.4±8.4 bpm), followed by returning to the start downhill untimed and self-paced. Between laps, participants rested for 15 minutes. The load carriage for each participant was set at 30% of their DXA-derived fat-free mass (15.2±3.8 kg). Paired t-tests were used to determine differences in individual proteins pre (day 10) to post (day 16) hike. RESULTS: There were decreases in FSR of Ubiquinone 1 beta subcomplex subunit 4 (NDUFB4) and Hydroxyacyl-coenzyme A dehydrogenase (HADH) (p<0.05). There were increases in FSR of ATP Synthase subunit beta (ATP5F1B), Fumarate Hydratase (p<0.05) and Cytochrome c oxidase subunit 6B1 (COX6B1) (p<0.05). Sixteen other mitochondrial proteins were observed with no significant alterations (p>0.05). CONCLUSION: Changes in FSR indicate that the 5-day hiking period was sufficient to induce changes in protein dynamics related to mitochondria. Information on the effects of changes in mitochondrial protein dynamics is limited, however these findings may indicate onset of mitochondrial anabolism.