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 O2 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), 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 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.