Central and peripheral adjustments during high-intensity exercise following cold water immersion

We investigated the acute effects of cold water immersion (CWI) or passive recovery (PAS) on physiological responses during high-intensity interval training (HIIT).

In a crossover design, 14 cyclists completed 2 HIIT sessions (HIIT1 and HIIT2) separated by 30 min. Between HIIT sessions, they stood in cold water (10 °C) up to their umbilicus, or at room temperature (27 °C) for 5 min. The natural logarithm of square-root of mean squared differences of successive R-R intervals (ln rMSSD) was assessed pre- and post-HIIT1 and HIIT2. Stroke volume (SV), cardiac output (Q), O2 uptake (VO2), total muscle hemoglobin (t Hb) and oxygenation of the vastus lateralis were recorded (using near infrared spectroscopy); heart rate, Q, and VO2 on-kinetics (i.e., mean response time, MRT), muscle de-oxygenation rate, and anaerobic contribution to exercise were calculated for HIIT1 and HIIT2.

ln rMSSD was likely higher [between-trial difference (90% confidence interval) [+13.2% (3.3; 24.0)] after CWI compared with PAS. CWI also likely increased SV [+5.9% (-0.1; 12.1)], possibly increased Q [+4.4% (-1.0; 10.3)], possibly slowed Q MRT [+18.3% (-4.1; 46.0)], very likely slowed VO2 MRT [+16.5% (5.8; 28.4)], and likely increased the anaerobic contribution to exercise [+9.7% (-1.7; 22.5)].

CWI between HIIT slowed VO2 on-kinetics, leading to increased anaerobic contribution during HIIT2. This detrimental effect of CWI was likely related to peripheral adjustments, because the slowing of VO2 on-kinetics was twofold greater than that of central delivery of O2 (i.e., Q). CWI has detrimental effects on high-intensity aerobic exercise performance that persist for ≥ 45 min.