Myofibrillar Proteomics of Sustained Load-Carriage Hiking

Load-carriage hiking is a popular recreational activity and an integral part of daily tasks for military personnel and wildland firefighters. Investigation is therefore warranted into myofibrillar responses to such activities. PURPOSE: To evaluate myofibrillar adaptations to acute load-carriage hiking. METHODS: Thirty-two recreationally active adults (12M, 20F; 28±6 yr; VO₂peak: 47.7±8.2 mL･kg-1･min-1) participated in a 5-day load-carriage study. Participants consumed 50ml deuterated water(2H2O) thrice daily for the 10 days prior to and twice daily during the five consecutive days of hiking for the measurement of fractional protein synthesis rates (FSR) of myofibrillar proteins. Participants completed two 1-hour ascents (distance 3.3±0.6 km; elevation 431±86 m) on an out-and-back dirt trail with 15 minutes of rest in between. Intensity during the ascents was set at 70% age-predicted HRmax (135±4 bpm) with descents completed at a comfortable pace (42.5±0.08 min/descent) without HR prescription. Participants carried packs weighing 30% of their DXA-derived fat-free mass (15.2±3.8 kg). Muscle biopsies were taken pre- (day 10) and post-hiking (day 16) from the vastus lateralis and analyzed for myofibrillar protein dynamics. RESULTS: Myofibrillar protein kinetics data were calculated for 37 proteins. There were increases in FSRs of skeletal muscle troponin C, troponin I and tropomyosin β-chain, as well as decreases in myosin-9 & 10, myosin light chain 1 & 3, and myosin binding protein C (p < 0.05). 29 myofibrillar proteins were not altered (p > 0.05). CONCLUSION: The present data highlight that acute load-carriage hiking elicited observable myofibrillar adaptations within a relatively short timeframe in men and women. Support by the United States Department of Defense, United States Army (22-02-MPAI-007)