The effect of age on pulmonary and muscle oxygenation kinetics following high-intensity interval training

Introduction Physiological measures of pulmonary and muscle oxygenation follow an exponential trends following exercise until reaching baseline values. A steeper exponential trend suggests faster post-exercise recovery. To date, no study has investigated the effect of age on off-transient pulmonary and muscle oxygenation kinetics following a high-intensity interval training bout (HIIT) typical of training undertaken by both competitive endurance and sprint cyclists. Therefore, this study examined the effect of age on the off-transient pulmonary and muscle oxygenation kinetics in well-trained masters and young cyclists following HIIT. Methods Pulmonary (VO2) and muscle oxygenation (Total Oxygenation Index [TOI] and change in deoxyhemoglobin concentration (∆[HHb])) were monitored continuously in well-trained masters (n = 9, age: 55.6 ± 5.0 yr) and young (n = 8, age: 25.9 ± 3.0 yr) cyclists during HIIT and recovery. The HIIT consisted of 6 x 30 second intervals at 175% maximal aerobic power with 4.5 minutes rest between intervals. Following HIIT, 20 minutes of passive supine rest was undertaken. The off-transient responses of VO2, TOI and ∆[HHb] from the cessation of the HIIT were then modelled using a mono-exponential function. Results The time constant (τ) of the VO2 response (τVO2) was significantly longer in the masters (mean ± SD; 217.49 ± 44.43 s) compared to young (169.69 ± 35.73 s) cyclists (P = 0.029). The amplitude of the VO2 response was also lower in masters (d = 0.69, moderate), although not significant (P = 0.18). A trend for a slowed τTOI was found in the masters cyclists, however this was not found to be significant (P = 0.40, d = 0.42, small). Significant correlations were observed between τTOI, and both τVO2 (r= 0.49, P = 0.049) and τ[HHb] (r = 0.75, P < 0.001), and a non-significant moderate relationship was found between age and τVO2 (r = 0.48, P = 0.05). Discussion The significantly slowed τVO2 suggests that masters athletes exhibit longer time for metabolic recovery following HIIT. Additionally, although no significant age-related differences for muscle re-oxygenation kinetics where observed a trend for a slower τTOI during the recovery phase was found. The slowed pulmonary and muscle oxygenation kinetics may have a negative effect on repeat sprint performance in masters athletes and greater recovery periods between exercise bouts may be necessary to maintain power output.