Abstract— Objectives: This study recognized the effectiveness of cold-water immersion recovery post short-term exhaustive exercise. The purpose of this study was to understand if 16- 20°C of cold-water immersion would be beneficial in a tropical environment to achieve an optimal recovery in sprint swim performance in comparison to 10- 15°C of water immersion. Method: Two 100m-sprint swim performance times were measured along with blood lactate (Bla), heart rate (HR) and rate of perceived exertion (RPE) in a 25m swimming pool with full body head out horizontal water immersions of 10-15°C, 16-20°C and 29-32°C (pool temperature) for 10 minutes followed by 5 minutes of minutes of seated passive rest outside; in between the two swim performances. Twelve well-trained adult swimmers (5 male and 5 female) within the top twenty in the Sri Lankan nationals swimming championships in 100m Butterfly and Freestyle in the years 2020 & 2021 volunteered for this study. Results: One-way ANOVA analysis (p<0.05) suggested performance time, Bla and HR had no significant differences between the 3 conditions after the second sprint, however RPE was significantly different with p=0.034 between 10-15°C and 16-20°C immersion conditions. Conclusion: The study suggested that the recovery post the two cold-water immersion conditions were similar in terms of performance and physiological factors however the 16-20°C temperature had a better “feel good” factor post sprint 2. Further study is recommended as there was participant bias with the swimmers not reaching optimal levels in sprint 1. Therefore, they might have been possibly fully recovered before sprint 2 invalidating the physiological effect of recovery. Keywords— Hydrotherapy, Blood Lactate, Fatigue, Recovery, Sprint-Performance, Sprint-Swimming I. INTRODUCTION wimming is a high intensity sport that is energetically supported by the phosphocreatine, glycolytic and the aerobic combustion of carbohydrate, fats and proteins [1]Competitive swimmers might have to swim multiple high intensity swimming events with a short period (60 min – 24 hours) of rest [2],[3].Whilst there is very little data in swimmers itself, the duration and intensity of a 100m swim is similar to a 400m run. During such events the athlete sprint utilizes phosphocreatine in the first phase of the run 5-10 seconds [4], then followed by a gradual increase of glycolysis until the event is primarily dependent of glycolysis [5]. Likewise, in a 100m swim the contribution of the glycolytic energy system is around 60-70%. The high dependence on the glycolytic system can result in the elevation of plasma lactate levels and other metabolic and physiological changes which can affect performance [2], while changing the muscle and blood Thanura Abeywardena, independent author, head of sports science, TASS (Pvt) Ltd (corresponding author, phone: +94773073199; e-mail: thanura@tass.lk). homeostasis [6]. Therefore, measuring the levels of blood lactate (BLa) after a sprint swim and after recovery is a common practice to understand the level of performance in competitive swimming [7] and recovery in maximal and submaximal exercise [8]. Fatigue has been defined in many ways in sports science; for biochemists’ fatigue is seen as the reduction of force out of the muscle, for psychologists it is the sensation of tiredness, and for physiologists it may be the failure of a particular physiological system [9]. Fatigue has also been viewed as either central fatigue, where the central nervous system (CNS) stops the muscle from exerting extraordinary effort to protect the muscle from injury, or peripheral, where the muscles homeostasis has been disturbed due to physical muscle damage and biochemical changes [10]. In swimming the level of BLa can be as high as 12.6mmol/L-1 [11],[12] and the main problem with lactate increase and the subsequent accumulation is the prevention of muscle contraction [13]. The increase of Bla leads to the increase in hydrogen ions which as a result increase the level of Adenosine diphosphate (ADP) and impairs the function of the muscle by creating a sodium-potassium-ATPase (Na-K- ATPase) imbalance [12]. Apart from this direct impact to performance, the increase in lactate and hydrogen ions inhibit the rate-limiting enzymes phosphofructokinase (PFK) and lactate dehydrogenase of glycolysis [12], thus affecting the subsequent high intensity exercise (sprint) bout. However, it is debatable whether lactate alone can be attributed to the onset of fatigue [14], but it is used widely as an indicator of fatigue. Recovery has been defined as the return of muscle to its pre- existing state after an exercise bout [15]. Reference [10] in their study divided recovery into immediate recovery, short-term recovery and training recovery. Immediate is the rapid recovery you get in a stroke cycle in swimming between the left and right arm or between the left leg and right leg during walking. Short- term recovery is the recovery time between two interval sprints and training recovery is the recovery between two successive workouts or competitions. Recovery through completely restoring homeostasis (i.e bring back BLa to the pre-exercise level) can be achieved with long-term passive rest (approximately 72 hours) [16]. However, during competition, the natural recovery process of 72 hours [15] is not possible. Therefore, in sports such as cycling, swimming and running Water Immersion Recovery for Swimming in Hot Environments Thanura Abeywardena S