Effect of endurance and strength training on the slow component of O2 kinetics in elderly humans

We compared the effects of 8 weeks of high intensity, aerobic interval training (HIT) and isoinertial resistance training (IRT) on: i) V'O2 kinetics during heavy (HiEx) intensity exercise and; ii) work economy during moderate (ModEx) intensity exercise in 12 healthy men (69.3 ± 4.2 years). Breath-by-breath V'O2 and muscle deoxygenation ([HHb] by means of NIRS) were measured in HiEx and ModEx at identical workloads before and after trainings. In HiEx, V'O2 and HHb responses were modeled as tri-exponential and mono-exponential increasing functions, respectively. After HIT the amplitude and the time delay of the slow component of O2 uptake (V'O2sc) during HiEx were smaller (-32%; P = 0.045) and longer (+19.5%; P = 0.001), respectively. At Post IRT: i) during ModEx, gain was lower (-5%; P = 0.050); ii) during HiEx, τ2 (+14.4%; P = 0.050), d3 (+8.6%; P = 0.050) and τ3 (+17.2%; P = 0.050) were longer than at Pre IRT. After HIT, the decrease of the V'O2sc amplitude was likely induced by the beneficial effects of training on muscle metabolic stability. IRT training was able to increase exercise economy during ModEx and to reduce the recruitment of Type II fibers during HiEx, wherefrom a delayed onset of V'O2sc derived. The better exercise economy and the delayed appearance of V'O2sc induced by IRT suggests that strength training might be included in endurance training programs to improve exercise economy and resistance to fatigue in this population of old subjects.