Integrative physiological and behavioural responses to sudden cold-water immersion are similar in skilled and less-skilled swimmers

• Severity of cold shock whilst treading water not influenced by swimming skill
• Treading water increased brain blood flow despite cold shock-induced hypocapnia.
• Cold-water swimming capacity was at least one third lower than in temperate water.

We examined the initial physiological responses and subsequent capacity to swim following cold-water immersion. An ecologically-valid model was used whereby immersion was sudden (< 2 s) and participants had to actively remain afloat. Participants (15 skilled swimmers, 17 less-skilled swimmers) undertook four experimental test sessions: a physiological test and a swimming test in both cold (10 °C) water and temperate (27 °C) water in a swimming flume (temperature order counter-balanced). For physiological testing, measures of brain perfusion [flow velocity (MCAv, Doppler) and oxygenation (NIRS)] and cardiorespiratory function [ventilation parameters and end-tidal PCO2 (PETCO2)] were recorded whilst treading water for 150 s. The swimming test involved treading water (150 s) before swimming at 60% (up to 120 s) and 90% (to intolerance) of pre-determined maximum velocity. Multifactorial analysis revealed that swimming duration was influenced most heavily by water temperature, followed by respiratory variables and MCAv in the first 30 s of immersion. The time course and severity of cold shock were similar in both groups (p = 0.99), in terms of initial physiological changes (MCAv down ~ 20 ± 11%, respiratory frequency increased to 58 ± 18 breaths·min− 1, PETCO2 dropped to 12 ± 9 mm Hg). Treading water following cold-water immersion increased MCAv by 30% above resting values despite maintained cold-shock-induced hyperventilation. In comparison to temperate water, swimming capacity was also reduced similarly between groups in the cold (i.e., distance decreased by 34 ± 26% skilled; 41 ± 33% less-skilled, p = 0.99). These integrative findings verify that sudden cold-water immersion followed by physical activity leads to similar physiological responses in humans when contrasting between skilled and less-skilled swimmers.