Prolonged exercise shifts ventilatory parameters at the moderate-to-heavy intensity transition

To quantify the effects of prolonged cycling on the rate of ventilation ([Formula: see text]), frequency of respiration (F_R), and tidal volume (V_T) associated with the moderate-to-heavy intensity transition.

Fourteen endurance-trained cyclists and triathletes (one female) completed an assessment of the moderate-to-heavy intensity transition, determined as the first ventilatory threshold (VT₁), before (PRE) and after (POST) two hours of moderate-intensity cycling. The power output, [Formula: see text], F_R, and V_T associated with VT₁ were determined PRE and POST.

As previously reported, power output at VT₁ significantly decreased by ~ 10% from PRE to POST. The [Formula: see text] associated with VT₁ was unchanged from PRE to POST (72 ± 12 vs. 69 ± 13 L^.min^-1, ∆ - 3 ± 5 L^.min^-1, ∆ - 4 ± 8%, P = 0.075), and relatively consistent (within-subject coefficient of variation, 5.4% [3.7, 8.0%]). The [Formula: see text] associated with VT₁ was produced with increased F_R (27.6 ± 5.8 vs. 31.9 ± 6.5 breaths^.min^-1, ∆ 4.3 ± 3.1 breaths^.min^-1, ∆ 16 ± 11%, P = 0.0002) and decreased V_T (2.62 ± 0.43 vs. 2.19 ± 0.36 L^.breath^-1, ∆ - 0.44 ± 0.22 L^.breath^-1, ∆ - 16 ± 7%, P = 0.0002) in POST.

These data suggest prolonged exercise shifts ventilatory parameters at the moderate-to-heavy intensity transition, but [Formula: see text] remains stable. Real-time monitoring of [Formula: see text] may be a useful means of assessing proximity to the moderate-to-heavy intensity transition during prolonged exercise and is worthy of further research.