Lower Percent Leg Muscle Mass is Associated with Reduced Ventilatory Efficiency in Sedentary Adults

Abstract

A high ventilatory equivalent to carbon dioxide production (VE/VCO2) slope, or reduced ventilatory efficiency, is associated with disease severity and is a strong predictor of mortality in patients with heart failure (HF). We have demonstrated that a high VE/VCO2 slope during exercise is associated with lower %leg muscle mass in HF. This association was abolished with inhibition of skeletal muscle afferent feedback by lumbar fentanyl injections, demonstrating an important link between muscle mass, afferent feedback and VE/VCO2 slope. We hypothesized that %leg muscle mass would be associated with VE/VCO2 slope in sedentary adults.ObjectiveDetermine the relationship between %leg muscle mass and VE/VCO2 slope in sedentary (SED) and trained (TR) adults.MethodsFor 38 adults (23 SED [6M/17F], 31±8 yrs and 15 TR [9M/6F], 29±6 yrs (mean±SD)) measures of gas exchange and ventilation were collected during a treadmill maximal oxygen uptake (VO2max) test and measures of total fat, regional fat and muscle mass were done by dual X‐ray absorptiometry (DXA). Participants were classified as trained by self‐report of aerobic exercise training for at least 30 min/day, 5 days/week.ResultsIn the SED group, men had greater %leg muscle mass and VO2max, and less %leg fat mass than women (all p<0.05). In the TR group, VO2max and %leg fat were similar (p>0.05), but men had greater %leg muscle mass than women (p<0.05). Percent leg muscle mass was greater in TR than SED (80±8 vs. 58±9%, respectively, p<0.01), while %leg fat mass was lower in TR than SED (20±9 vs. 42±9%, respectively, p<0.01). VO2max was greater in TR than SED (55±10 vs. 29±6 ml/kg/min, p<0.01). When the TR and SED groups were combined, VO2max was associated with %leg muscle mass (r= 0.85, p<0.01). The VE/VCO2 slope was similar between TR and SED groups (25±3 vs. 24±3, p=0.10), without any sex‐specific differences (p>0.05). Specific to the SED group, VE/VCO2 slope was inversely associated with %leg muscle mass (r= −0.51, p=0.01) indicating the lower the %leg muscle mass, the steeper the VE/VCO2 slope. This relationship persisted with sex‐specific analysis (men: r= −0.80, p=0.05 and women: r= −0.57, p=0.02). The relationship between VE/VCO2 slope and %leg muscle mass not was not observed in the TR group overall or with sex‐specific analysis (p>0.05).ConclusionsThese findings suggest that in sedentary adults, lower %leg muscle mass may contribute to a reduced ventilatory efficiency during exercise.Support or Funding InformationNIH 1R01DK098203‐01