The Influence of Cold-Water Immersion on Limb Blood Flow and Thermoregulatory Responses to Exercise

The accumulated stresses of training and competition may temporarily cause impairments in an athlete’s physiological and muscular function, leading to suboptimal performance levels. Cold-water immersion (CWI) has become a widely used post-exercise recovery method to accelerate the recovery process by purportedly reducing the symptoms associated with exercise-induced muscle damage (EIMD). However, the underlying physiological mechanisms, which mediate the effects of CWI, are not well understood. Therefore, the aim of this thesis was to investigate the influence of cold-water immersion (CWI) on limb blood flow and thermoregulatory responses following different modes of exercise. In study 1 (Chapter 4), the reliability of Doppler ultrasound in the assessment of superficial femoral artery blood flow (FABF) was examined under resting conditions. A Doppler ultrasound scan of the superficial femoral artery was measured on eight recreationally active male participants; twice on the same day separated by 5-min (within-day), and on a separate day (between-days). The coefficient of variation (CV) for mean blood flow (MBF) was ~16 % and ~20 % for within and between-days, respectively. A relatively small standard error of measurement (SEM) was found both within day, 13.30 mL·min-1 (95% CI, -14.79 to 38.40 mL·min-1) and between-day, 17.75 mL·min-1 (95% CI, -40.12 to 30.88 mL·min-1) for MBF differences. These findings suggest duplex Doppler ultrasound is a reliable method to collect measurements of FABF under resting conditions. The purpose of study 2 and 3 was to determine the influence of different degrees of water immersion cooling on FABF and cutaneous blood flow (CBF) and thermoregulatory responses after endurance (Chapter 5) and resistance (Chapter 6) exercise, respectively. Participants completed a prescribed endurance of resistance exercise protocol prior to immersion into 8 ºC (cold) or 22 ºC (cool) water to the iliac crest or rested non-immersion (CON) in a randomized order. Limb blood flow and thermoregulatory responses were measured before and up to 30-min after immersion. In both studies, thigh skin temperature (Tskthigh) (P < 0.001) and muscle temperature (Tmuscle) (P < 0.01) were lowest in the 8 ºC trial compared with 22 ºC and control trials. However, femoral artery conductance (FVC) was similar after immersion in both cooling conditions and was reduced (~50-55 %) compared with the CON condition 30-min after immersion (P < 0.01). Similarly, there was a greater thigh (P < 0.01) and calf (P < 0.05) cutaneous vasoconstriction during and after immersion in both cooling conditions relative to CON with no differences noted between 8 and 22 ºC immersion. Together, these findings suggest that colder water temperatures may be more effective in the treatment of EIMD and injury after both endurance and resistance exercise, respectively, due to greater reductions in Tmuscle and not limb blood flow per se. The aim of study 4 (Chapter 7) was to compare the influence of CWI and whole body cryotherapy (WBC) on FABF and CBF and thermoregulatory responses after endurance exercise. On separate days, participants completed a continuous cycle ergometer protocol before being immersed semi-reclined into 8 ºC water to the iliac crest for 10 min (CWI), or exposed to 2.5 min (30 s -60 ºC, 2 min -110 ºC) WBC in a specialized cryotherapy chamber, in a randomized order. Limb blood flow and thermoregulatory responses were measured before and up to 40-min after immersion Reductions in Tskthigh (P < 0.001) and Tmuscle (P < 0.001) were larger in CWI during recovery. Similarly, decreases in FVC were greater (~45-50 %) in the CWI condition throughout the recovery period (P < 0.05). There was also a greater skin vasoconstriction observed in CWI at the thigh (P < 0.001) and calf (P < 0.001) throughout the post-cooling recovery period. These results demonstrate that CWI may be a better recovery strategy compared with WBC due greater reductions in both Tmuscle and limb blood flow. This thesis provides a novel insight into the influence of different degrees of water immersion cooling, as well as WBC, on limb blood flow and thermoregulatory responses after different modes of exercise. These findings provide practical application for athletes and an important insight into the possible mechanisms responsible for CWI in alleviating inflammation in sport and athletic contexts