The Science Behind The Sweat: Heat Adaptation Explained
NOTE: This series originally appears on the blog of Thanyapura Sport Resort Phuket, partners of WTW where we are regular contributors to their content. You can check them out here, and please use our name if you book a visit for discounted rates 🙂
Do you even Science? We do, and today it’s time to get nerdy. Strap in, we’re in for a fun one!
What actually happens to the body when you train in heated environmental conditions?
There are a number of physiological processes: cardiovascular, thermoregulatory, and metabolic adaptations happen when you exercise outside under the sun which affect the perception of effort, fatigue, and eventually performance. Luckily, these adaptations instigated by training in the heat through Short or Medium Term Heat Adaptation (STHA and MTHA) protocols can reduce anaerobic energy release and elevate the anaerobic threshold while reducing perceived exertion (RPE) and improving fluid regulation, among other changes which enhance performance (Galloway et al 1997). Lets dive into these processes.
During exercise in heated conditions, the physiological burden of supporting high sweating rates, skin and muscle blood flow imposes real cardiovascular strain and can impair performance greatly (Garrett 2009, Burke 2012). Elite athletes competing in the International Association of Athletics Federations (IAAF) World Championships between 1999-2011 fared worse (~3% slower) in hot conditions of over 25°C than those in cool temperate conditions under 25°C (Guy et al 2014). Deliberate training in the heat in the form of STHA and MTHA delivers novel systemic (acclimation) and cellular (thermal tolerance) adaptations which prevent extreme reactions such as heat stroke and improve performance in hot environments (Chen 2012).
Both STHA and MTHA protocols positively influence the adaptations you make from training which enhance eventual performance on race-day. Changes in key physiological parameters include plasma volume expansion, lower core temperature (and sweating at lower core temperature) and lower heart rate at given exercise intensities–meaning your cardiovascular system does not have to work as hard to be able to power you onwards once you’ve adjusted to the environment (Sawka et al 2011). When your body is dealing with heated conditions which you have not yet adapted to and your core and skin are overheating, it struggles to activate the sympathetic nervous system properly, meaning inefficient use of energy (Iwase et al 2002). Given the potential fluid (sweat) losses likely to occur in a hot race location such as Kona, this is a game-changer. Let’s dig into how these physiological changes occur and the direct potential effects of STHA and MTHA on performance.
As bodily plasma volume (PV) is expanded, postulated changes in PV to plasma protein ratio will elicit enhanced delivery of functional proteins to the working muscles, reducing the cardiac demand by increased efficiency of plasma protein delivery, therefore enhancing aerobic capacity and along with it endurance performance (Garrett et al 2011). Furthermore, keeping in mind that sweating heavily and losing fluids significantly affects blood pressure and therefore cardiovascular demand; the increases in plasma volume from heat adaptation mediate this (O’Sullivan et al 2003; Sawka et al 1983; Cadarette et al 1984). Essentially, your heart doesn’t have to work as hard or pump as fast because your pulmonary (blood) system is better equipped to deal with the heat and this increases the amount of blood (and other useful fluids, think hydration!!) your heart is able to pump out. These collective adaptations allow for reduced demand for effort/exertion and enhanced ability to thermoregulate, important changes for endurance events which involve sweating!
As detailed above, chronic exposure to a stressor elicits adaptations which enhance the tolerance of that stressor.
What can these adaptations do for your performance in all conditions?
Increased maximal oxygen uptake and lactate threshold as well as enhanced running economy are all, as discussed, adaptations which can aid you even in normal environmental conditions when performance is not thermally limited (Shapiro et al 1981; Taylor et al 2006). This ergogenic (performance enhancing) effect of STHA and MTHA is not to be underestimated. While further research is needed in this area, examples including literature detailing direct measures of performance enhancement such as increased power output in cycling (Racinais et al 2014) have already been recorded, directly implying that STHA and MTHA can enhance specific events such as triathlon and road cycling.
Check back in next week for detailed instructions on the best STHA and MTHA protocols to use in a hot location (like Thailand!) to improve your performance! In the meantime, Click Here to Subscribe To Our Mailing List, and Check Out Our Facebook