Impairments Of Oxidative Metabolism In Relation To Different Stages Of Sarcopenia In The Elderly

In the elderly sarcopenia is a condition characterized by an excessive loss of muscle mass and strength, leading to an increased risk of falls, a reduced mobility and a loss of independence. The definition above, however, neglects possible alterations of oxidative metabolism, one of the main determinants of exercise tolerance during activities of daily life. PURPOSE: To evaluate, in older individuals, impairments of oxidative metabolism associated with different stages of sarcopenia. METHODS: 53 moderately active individuals (27 men, age 69-91 yrs) were stratified into non-sarcopenic (NS, n = 26), pre-sarcopenic (PS, n = 16) and sarcopenic (S, n = 11) according to guidelines of the European Working Group on Sarcopenia in Older People 2. Appendicular lean mass was determined by DEXA. Participants performed an incremental test (INCR) and a moderate-intensity (MOD) exercise on a cycle ergometer. Pulmonary gas exchange was determined. Microvascular/endothelial function was evaluated by Eco-Doppler by monitoring in the femoral artery the blood flow response during 1-min of passive leg movements (PLM). Skeletal muscle oxidative function was evaluated: a) in vivo by determining the recovery kinetics of skeletal muscle O2 uptake (V̇O2m), by near-infrared spectroscopy and the repeated occlusions method; b) ex vivo by determining mitochondrial respiration by high-resolution respirometry on permeabilized vastus lateralis fibers obtained by biopsy. RESULTS: S were older than PS and NS (p < 0.01) and an age-related linear decrease in appendicular lean mass was observed. During INCR, pulmonary V̇O2peak and ventilatory thresholds (L·min-1) were lower (-30%) in S vs. NS (p < 0.05); no differences were observed when data were normalized for body mass. During PLM the area under the blood flow vs. time curve was lower (-60%) in S vs. NS (p < 0.01). V̇O2m off-kinetics were slower (p = 0.01) in S (time constant +37%) and PS (+26%) vs. NS. Maximal ADP-stimulated mitochondrial respiration was lower (-31%) in PS vs. NS (p < 0.01). CONCLUSIONS: In the elderly the age-related decrease in muscle mass characterizing sarcopenia is accompanied by impairments of oxidative metabolism, which include both systemic (cardiorespiratory function) and peripheral (microvascular/endothelial and skeletal muscle oxidative function) components. Italian Ministry of University and Research, PRIN Project 2017CBF8NJ; PSD, Healthy Ageing 2020-2025, University of Udine