Effect of Endurance and Strength Training on the Slow Component of O ₂ 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) O ₂ kinetics during heavy (HiEx) intensity exercise and; (ii) work economy during moderate (ModEx) intensity exercise in 12 healthy elderly men (69.3 ± 4.2 years). Breath-by-breath O ₂ and muscle deoxygenation ([HHb] by means of NIRS) were measured in HiEx and ModEx at identical workloads before and after trainings. In HiEx, O ₂ and HHb responses were modeled as tri-exponential and mono-exponential increasing functions, respectively. A two-way ANOVA for repeated measures analysis was made; Effect size (η²) was also evaluated. After HIT the amplitude and the time delay of the slow component of O uptake (O _2sc) 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), d (+8.6%; P = 0.050), and τ₃ (+17.2%; P = 0.050) were longer than at Pre IRT. After HIT, the decrease of the O _2sc amplitude was likely induced by the beneficial effects of training on a more responsive O ₂ delivery and consumption cascade leading to a better muscle metabolic stability. IRT training was able to increase exercise economy during ModEx and to reduce the amplitude and delay the onset of O _2sc during HiEx. These effects should be due to the reduction and the delayed recruitment of Type II muscle fibers. The better exercise economy and the delayed appearance of O _2sc 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.