Key result
Inspiratory threshold loading during moderate exercise increases the VO2 ventilatory time constant by ~41%.
Why the study?
Does inspiratory threshold loading alter ventilatory kinetics during constant-load exercise in healthy trained men?
RCT (n=14)
randomized
Does inspiratory threshold loading alter ventilatory kinetics during constant-load exercise in healthy trained men?
Absolute Event Rate: 60.9% vs 43.1%
p-value: p=<0.001
Inspiratory threshold loading significantly slows ventilatory kinetics during moderate exercise, indicating that neuromechanical factors influence the ventilatory response.
Inspiratory loading delays VO2 kinetics in healthy men; extends neuromechanical control of exercise ventilatory response but leaves clinical relevance open.
Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (VO2), carbon dioxide output (VCO2), and ventilation (VE) during moderate intensity exercise. We did this by comparing the ventilatory time constants (tau) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 +/- 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (VO2max = 55.2 +/- 5.8 ml x min(-1) x kg(-1)). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their VO2max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (VO2, VCO2, and VE) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the tau during phase 2 of VO2 (43.1 +/- 8.6 vs. 60.9 +/- 14.1 s; P < 0.001), VCO2 (60.3 +/- 17.6 vs. 84.5 +/- 18.1 s; P < 0.001) and VE (59.4 +/- 16.1 vs. 85.9 +/- 17.1 s; P < 0.001). The average rise in tau was 41.3% for VO2, 40.1% for VCO2, and 44.6% for VE. The tau changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.
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Keslacy et al. (2005) conducted an RCT in Healthy, trained men (n=14). Inspiratory threshold load vs. No inspiratory load was evaluated on Ventilatory time constant (tau) during phase 2 of VO2 (p=<0.001). The addition of an inspiratory threshold load during moderate exercise significantly increased the ventilatory time constant for oxygen consumption compared to no load (60.9 vs 43.1 s; P<0.001).
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