Thermoneutral immersion exercise accelerates heart rate recovery: A potential novel training modality

This study compared heart rate recovery (HRR) after incremental maximal exercise performed at the same external power output ( P ext ) on dry land ergocycle (DE) vs. immersible ergocycle (IE). Fifteen young healthy participants (30 ± 7 years, 13 men and 2 women) performed incremental maximal exercise tests on DE and on IE. The initial P ext on DE was 25 W and was increased by 25 W/min at a pedalling cadence between 60 and 80 rpm, while during IE immersion at chest level in thermoneutral water (30°C), the initial P ext deployment was at a cadence of 40 rpm which was increased by 10 rpm until 70 rpm and thereafter by 5 rpm until exhaustion. Gas exchange and heart rate (HR) were measured continuously during exercise and recovery for 5 min. Maximal HR (DE: 176 ± 15 vs. IE 169 ± 12 bpm) reached by the subjects in the two conditions did not differ ( P > .05). Parasympathetic reactivation parameters (ΔHR from 10 to 300 s) were compared during the DE and IE HR recovery recordings. During the IE recovery, parasympathetic reactivation in the early phase was more predominant (HRR at Δ10–Δ60 s, P < .05), but similar in the late phase (HRR at Δ120–Δ300 s, P > .05) when compared to the DE condition. In conclusion, incremental maximal IE exercise at chest level immersion in thermoneutral water accelerates the early phase parasympathetic reactivation compared to DE in healthy young participants.