Cytoplasmic Protein Responses to Load-Carriage Intervention

PURPOSE: Examine the effect of a five-day hiking intervention with load carriage on cytoplasmic protein fractional synthetic rates in apparently healthy males and females. METHOD: 18 recreationally active participants (8M, 10F; 28 ± 6 yr; VO₂peak: 47.7 ± 8.2 mL･kg-1･min-1) consumed labeled (2H2O) water for 10 days prior and throughout a 5-day pack-loaded hiking protocol. Participants completed two 60-minute hiking laps, with distance and elevation gain of 3.3 ± 0.6 km, 431 ± 86 m per lap, respectively. Participants returned to the starting point between each lap and rested for 15 minutes. Intensity was controlled at 70% of age-predicted HRmax, averaging 135 ± 4 bpm, and weighted hiking packs were worn during each hike and normalized to 30% of DXA derived fat-free mass. Total daily hiking time was 3:40:15 ± 0:13:22 (h:mm:ss). This protocol was repeated each day for 5 days. Muscle biopsies were taken from the vastus lateralis on days 10 and 16 (pre and post load carriage intervention) and analyzed for fractional synthesis of cytoplasmic-related proteins using mass spectrometric analysis. RESULT: Fractional synthetic rates of beta-actin like protein 2 (ACTB2), heat shock protein 90-alpha (HSP90a), alpha actinin-3 (ACTN3), SRSF protein kinase 2 (SRPK2), and caskin-2 (CSKI2) all decreased (p < 0.05). Creatine kinase M-type (CKM), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), triosephosphate isomerase (TPI1) heat shock protein beta-1 (HSPB1), Parkinson-disease protein 7 (PARK7), Kelch-like protein 41 (KLHL41) and ethanolamine kinase 1 (ENTK1) all increased (p < 0.05). 27 other cytoplasmic proteins were unchanged (p > 0.05). CONCLUSION: These data suggest that fractional synthetic rates of cytoplasmic proteins are sensitive to the intervention and duration of a five-day hiking protocol with load carriage in men and women.