Author(s): REBULL-BARRERA, J., NIVET, M., LE-FUR, Y., VILMEN, C., MILLET, G.P., RUPP, T., BEN DAHAN, D., Institution: AIX-MARSEILLE UNIVERSITÉ, Country: FRANCE, Abstract-ID: 2691

INTRODUCTION:
Ageing is associated with progressive decline in muscle function yet the underlying metabolic alterations remain incompletely understood. 31P-NMR spectroscopy provides a non-invasive method to assess in vivo skeletal muscle oxidative metabolism through phosphocreatine (PCr) recovery kinetics (1). In the present study, we comparatively assessed muscle oxidative metabolism in physically active young and elderly adults during a maximum voluntary intermittent and isometric contractions (1.5/0.5 s work rest) exercise (MVIIC) under two oxygen conditions i.e. normoxia and simulated hypoxia.
METHODS:
Healthy and active (Leisure Score Index >25) participants matched on body-weight and physical activity (young n=13; elderly n=9) completed two randomized exercise sessions: normoxia (FiO2=20.9%) and hypoxia (FiO2=13.0%). Quadriceps 31P NMR spectra were acquired at 3T (TR=1.5 s) during a standardized rest (2 min), exercise (12 s, MVIIC), passive recovery (6 min) protocol. High-energy phosphate metabolites (PCr, Pi, ATP) and pH changes were continuously assessed during each session. Recognized indices of oxidative metabolism as PCr recovery time constant (tau), initial recovery rate (Vi) and theoretical maximal rate of oxidative ATP production (Vmax) were computed.
RESULTS:
No significant effect of oxygen Condition nor AgeXCondition interactions were observed for any metabolic variable throughout sessions. No Age effect was identified during the exercise phase exercise phase (p=0.654 for PCr, p=0.173 for pH, p=0.771 for Pi). Although the initial rate of PCr recovery in the recovery phase was significantly larger in elderly (tau=22.6+/-4.8 s; Vi=0.43+/-0.16 mmol/s,) as compared to young subjects (tau=29.7+/-8.7 s; Vi=0.32+/-0.09 mmol/s, p=0.035 and p=0.050, respectively), Vmax was similar in both groups (0.80+/-0.25 mmol/s vs 0.85+/-0.24 mmol/s, p=0.625), regardless of oxygen Condition.
CONCLUSION:
This 31P-NMR study indicated paradoxical findings in healthy, physically active elderly individuals. On the contrary to what has been reported so far in highly aerobic exercise (2), PCr consumption and acidosis were not increased in older subjects after a short high-intensity intermittent exercise. In our case, exercise is likely to be highly ischemic given the frequency and high intramuscular pressure with MVIIC. Hypoxic conditions would not then be expected to create an additional oxygen delivery limitation. In this context, the whole set of oxidative indices indicated a preserved aerobic function in older subjects compared to matched active young adults (2). The preserved Vmax suggests that the mitochondrial function of our elderly group is unchanged likely because of preserved physical activity (3). These results challenge the traditional interpretations of aging-related metabolic decline.

REFERENCES:
1. Conley KE et al. J Appl Physiol. 2000;89(5):1937-44.
2. Layec G et al. Age (Dordr). 2013;35(4):1183-92.
3. Layec G et al. J Physiol. 2018;596:5337-9.