Locomotor Subsystolic Occlusion Transition Effects on On‐transient VO2 Kinetics during Submaximal Hyperbolic Exercise
Authors: Van Iterson Erik H. , Olson Thomas P. 
Published: November 2023

IntroductionAlthough used as an experimental approach to stimulate group III/IV afferents by causing venous congestion, locomotor subsystolic regional circulatory occlusion (SubRCO) during exercise may lead to accelerated local metabolic acidosis, whilst complicating the interpretation of cardiovascular reflexes using this technique. Moreover, compared to low pedal rate, greater type II fiber recruitment is expected during high pedal rate cycling. Thus, inordinate changes in muscle blood flow and muscle oxygen requirements provoked by augmented energy demands should elicit delayed or absent steady‐state oxygen uptake (VO2), which would not be adequately described using a single‐component exponential on‐transient VO2 kinetics model. This study aimed to test the hypothesis that increased pedal rate combined with SubRCO during low intensity hyperbolic exercise would shift the exponential fit of on‐transient VO2 kinetics from a single to a two‐component model.MethodsHealthy adults (N = 15, 53% male; age 36 ± 17 years; BMI 24 ± 4 kg/m2) completed 2 study visits of 3 identical sessions of fixed‐load (20W) ergometry at fixed pedal rates of 35 or 100 rpm (randomized). Sessions began with 5 min of rest, followed by 3 min of exercise without SubRCO, and immediately transitioning to a 5 min period of exercise+SubRCO at 90 mm Hg bilateral‐thigh cuff inflation pressure. A metabolic system integrated with gas mass‐spectrometry was used to measure breath‐by‐breath VO2. Data were linearly interpolated to 1 sec intervals and ensemble averaged across 3 sessions/day for each participant prior to modeling. All models excluded the cardiodynamic phase. Exponential models were: single‐component, VO2REST + A [1 − e−(t−TD)/τ]; two‐component, VO2REST + A [1 − e−(t−TD)/τ] + A2 [1 − e− (t−TD2)/τ2]; where τ = time‐constant; A = asymptote; TD = time delay.ResultsBest‐fit residuals for single vs. two‐component models did not differ within either 35 rpm (0.031 ± 0.009 vs 0.028 ± 0.007, P = 0.15) or 100 rpm (0.052 ± 0.013 vs 0.050 ± 0.013, P = 0.48) sessions, respectively; suggesting SubRCO does not influence on‐transient VO2 kinetics. Thus, 35 rpm single‐component parameters were: τ = 48 ± 24 sec, A = 0.32 ± 0.04 L/min, and TD = 12 ± 10 sec, which differed significantly vs 100 rpm single‐component parameters: τ = 25 ± 20 sec, A = 0.87 ± 0.12 L/min, and TD = 1 ± 9 sec (all P<0.05), suggesting an independent effect of pedal rate on on‐transient VO2 kinetics.ConclusionsThese data do not support our hypothesis, whilst suggesting that the oxygen requirement during hyperbolic exercise for a transition from low‐intensity ergometry without SubRCO to a longer period with SubRCO is not exaggerated to appreciably evoke a phase III on‐transient VO2 kinetic response in healthy adults. Therefore, if on‐transient VO2 kinetics mirror muscle oxygen utilization patterns at steady‐state moderate exercise, these data suggest locomotor SubRCO during moderate exercise does not exacerbate local metabolic acidosis in healthy adults.Support or Funding InformationNHLBI R01 HL126638; AHA 16POST30260021