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 A degrees C) up to their umbilicus, or at room temperature (27 A degrees 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 (), O-2 uptake (O-2), total muscle hemoglobin (t (Hb)) and oxygenation of the vastus lateralis were recorded (using near infrared spectroscopy); heart rate, , and O-2 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 [+4.4 % (-1.0; 10.3)], possibly slowed MRT [+18.3 % (-4.1; 46.0)], very likely slowed O-2 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 O-2 on-kinetics, leading to increased anaerobic contribution during HIIT2. This detrimental effect of CWI was likely related to peripheral adjustments, because the slowing of O-2 on-kinetics was twofold greater than that of central delivery of O-2 (i.e., ). CWI has detrimental effects on high-intensity aerobic exercise performance that persist for a parts per thousand yen45 min.