The Effect of Prolonged Bed Rest on Muscle Oxidative Capacity and Muscle O₂ Diffusive Sensitivity in Young and Elderly Participants

Authors

Alessio Marciano, University of Pavia, ItalyFollow
Andrea Pilotto, University of Pavia, ItalyFollow
Alessandra Adami, University of Rhode IslandFollow
Harry B. Rossiter FACSM, The Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical CenterFollow
Simone Porcelli, University of Pavia, ItalyFollow

Abstract

Whole body maximum oxygen uptake (V̇O_2MAX) is dependent on the capacity for convective and diffusive oxygen transport and skeletal muscle O₂ extraction. V̇O_2MAX declines after bed rest (BR), accompanied by reductions in convective O₂ transport and muscle oxidative capacity. The effect of BR on diffusive O₂ transport limitation is unknown.

PURPOSE: To determine vastus lateralis (VL) oxidative capacity and limitation in O₂ diffusion at skeletal muscle level in young (Y) and elderly (E) participants after 21 and 10 days of BR, respectively.

METHODS: 9 Y (23±4 yrs) and 10 E (69±3 yrs) healthy males were tested before (BDC) and after (Y: BR₂₁; E: BR₁₀) horizontal BR. The recovery rate constant (k) of VL muscle oxygen consumption (mV̇O₂) was measured by NIRS, combined with repeated intermittent arterial occlusions, under two conditions: high O₂ availability (k_HIGH) and low O₂ availability (k_LOW). Their difference (Δk= k_HIGH - k_LOW) was used as an index of the relative resistance to O₂ diffusion.

RESULTS: In Y, k_HIGH decreased following BR₂₁ (2.34±0.46 vs. 2.03±0.40 min⁻¹ at BDC and BR₂₁ respectively; p=0.002), whereas k_LOW was not affected (1.63±0.19 vs. 1.66±0.45 min⁻¹; p=0.826). ∆k decreased after BR (0.75±0.40 vs. 0.37±0.45 min^-1; p=0.030), such that ∆k was greater than zero at BDC (p=0.001), but not at BR₂₁ (p=0.053). In E, k_HIGH did not significantly change after BR₁₀(2.28±0.29 vs. 2.13±0.27 min⁻¹ at BDC and BR₁₀ respectively; p=0.052), whereas k_LOW increased (1.80±0.35 vs. 2.05±0.32 min⁻¹; p=0.011). ∆k decreased after BR₁₀ (0.42±0.44 vs. 0.16±0.31 min⁻¹; p = 0.026), despite ∆k not differing from zero at BDC (p=0.068) or after BR₁₀ (p=0.160). The mean daily rate of percentage decline in k_HIGH with BR did not differ between Y and E (-0.62±0.41 vs. -0.64±0.78 % day^-1; p=0.923).

CONCLUSION: BR induced a similar rate of decline in muscle oxidative capacity (k_HIGH) in Y and E. The relative resistance to muscle O₂ diffusive flow (∆k) was also reduced in both Y and E following BR, suggesting that the decline in muscle oxidative capacity was greater than the alterations in structural and functional resistances to muscle O₂ diffusion induced by BR. The degree to which muscle O₂ diffusion limits muscle O₂ uptake is reduced by prolonged inactivity in both Y and E individuals.

Recommended Citation

Marciano, Alessio; Pilotto, Andrea; Adami, Alessandra; Rossiter, Harry B. FACSM; and Porcelli, Simone (2025) "The Effect of Prolonged Bed Rest on Muscle Oxidative Capacity and Muscle O₂ Diffusive Sensitivity in Young and Elderly Participants," International Journal of Exercise Science: Conference Proceedings: Vol. 14: Iss. 5, Article 31.
Available at: https://digitalcommons.wku.edu/ijesab/vol14/iss5/31