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Abstract
Introduction Exercise tolerance is an important factor regarding quality of life. The maximal oxygen uptake (VO2 max) is a good indicator of pulmonary, cardiovascular and muscular functional integration during exercise.
Oxygen uptake (VO2) kinetics is a reliable determinant of sports performance, in terms of oxygen (O2) transport adjustment, muscular metabolism during exercise, and exercise intensity. The time constant (τ) and the amplitude of the VO2 response (ΔVO2) are parameters of the VO2 kinetics, and allow the determination of the O2 deficit, calculated as τ × Δ VO2. For a given work rate in the moderate intensity domain, τ is lowest in subjects with the highest VO2 max.
Methods To determine the effect of different training backgrounds on VO2 kinetics parameters, six endurance-trained (T) and six sedentary (S) healthy males, aged 30–53 years, were recruited to perform 3-bouts of constant-work-rate (CWR) exercise in moderate intensity domain, in a treadmill ergometer.
The selected work rate for each subject was previously determined from a maximal incremental stress test in a treadmill ergometer with gas-exchange analysis, as 10% below their individual first ventilatory threshold (VT1), also known as anaerobic threshold. Level of fitness and body composition were also determined.
Results VO2 max was higher in T than in S (median T 60, 90 vs. S 42, 45 mL Kg-1 min-1, p=0.002). Body weight was lower in T than in S (median T 72.6 vs. S 77.15 Kg, p = 0.015), and muscle mass percentage was higher (median T 62% vs. S, 47%, p=0.009).
During the CWR exercise, VO2 rest was not different between groups (median T, 5.75 vs. S, 5.07 mL Kg-1 min-1, p = 0.132), and work rate selected for each subject was higher in T than in S (median T 174 vs. S 101 Watt, p = 0.002), as was ΔVO2 (median T 32.63 vs. S 24.75 mL Kg-1 min-1, p=0.002). The time constant was not significantly different between groups (median T, 31.75 vs. S, 37.00 seconds, p = 0.240) nor was the O2 cost (median T, 0.20 vs. S 0.22 mL Kg-1.min-1, p = 0.485), or the O2 deficit (median T 17.30 vs. S 14.46 mL Kg-1, p = 0.132).
O2 deficit and τ in trained and sedentary subjects
Representation of O2 deficit in one trained and one sedentary subject
Discussion Given that trained individuals performed CWR exercise at higher work rates and attained greater ΔVO2 than those in the sedentary group, and that τ was not significantly different between groups, we were also expecting differences in the O2 deficit.
However, at this normalized exercise intensity, the O2 deficit was not significantly different between groups. This is due to bigger τ values in the sedentary group, that despite not being significantly different, once multiplied by the ΔVO2, elicited similar O2 deficit.
Conclusion Our data suggests that individuals with different aerobic capacities, performing normalized CWR exercise, develop similar O2 deficit