#Tracklife – Why the heat beats us + how to fight back

Imagine this, it’s post-COVID-19, it’s summer, and it’s HOT – maybe that is not so hard to imagine. You just got on the track to start your event, maybe it’s a keirin final, or perhaps a points race. Soon, much sooner than you expected, you feel your heart rate increase, followed by a decrease in leg speed, and maybe, if you are unfortunate you end up at the tail end of the bunch, or worse yet, you see the gloomy hand of a commissaire telling you to get off the track. Well, you were probably impacted by the heat, and here is why. 

Exercising in the heat imposes two major challenges on our bodies. 

1. The first is the challenges of the physiological system – and when you think about it our body does a phenomenal job. Briefly, exercising challenges our resting state in that blood is diverted away from non-essential functions (like digestion), our heart rate increases, blood pressure rises, and the working muscle must provide work that may be above what they are accustomed to.  
2. The second is thermal regulation (aka heat). Now that’s the big one. Humans have tightly regulated body temperature, veer either way from the magic 37°C and you’re in trouble. Heat in of itself challenges our resting state as our body must undertake steps to keep it’s cool. For example, a common response is increasing blood flow to the skin to increase the release of heat into the environment.

When you exercise your heart beats faster. Between each heartbeat, your ventricle (one of the heart’s chambers) fills up with blood, that amount of blood is called stroke volume. When your heart beats again the blood gets squeezed out of your aorta and sent to your whole body (note this is very simplified). 

Many studies have shown that when exercising in the heat your heart rate is higher, your power output lower, and your sensation of how hard you are working is also higher. 

Bringing this back to the velodrome, I would say the endurance riders are at a disadvantage while the sprinters may actually benefit! 

Endurance riders are disadvantaged because their races are longer and near the athlete’s maximal aerobic effort. As such, exercise in the heat increases the strain to your circulatory system in addition to the strain caused by the exercise itself. For example, a higher heart rate may allow less time for filling of the pump in between beats thus limiting the amount of blood that is being pumped.  In addition, your brain will only let you exercise so hard after reaching a certain critical temperature (usually around ~40°C).  

Sprint events on the other hand are short and lightning bolt fast. Heat in this scenario may be of benefit as most chemical reactions in our body happen faster in a warm environment, and warm air is less dense meaning you can ride faster with less air resistance. This being said, if multiple back-to-back sprints are done, or if a sprinter is “overheating” before their event, then decrements in performance could be expected.  

OK, what can you do about it? 

Acclimate. By gradually exposing yourself to heat over several weeks, you can become better at tolerating it. There are many ways to go about this from exercising in a hot climate, exercising with extra clothes on, or using passive tools like warm baths or saunas. A hint of caution here, do some research beforehand or seek expert help to prevent heat-related illnesses like heat stroke or heat exhaustion.  

Stay cool. There are lots of ways to keep cool. For example, at an outdoor venue seek/create shade. Use tools like cooling vests or ice socks, fans, and cold beverages.  

The take-home message is that heat can slow you down in any type of track event. This decrement can be prevented by proactively acclimatizing to the heat first and then keeping cool before and after races.  

References: 

Périard JD, Cramer MN, Chapman PG, Caillaud C, Thompson MW. Cardiovascular strain impairs prolonged self-paced exercise in the heat. Exp Physiol. 2011 Feb;96(2):134-44. doi: 10.1113/expphysiol.2010.054213. Epub 2010 Sep 17. PMID: 20851861. 

Nybo L. Hyperthermia and fatigue. J Appl Physiol (1985). 2008 Mar;104(3):871-8. doi: 10.1152/japplphysiol.00910.2007. Epub 2007 Oct 25. PMID: 17962572. 

González-Alonso J, Calbet JA. Reductions in systemic and skeletal muscle blood flow and oxygen delivery limit maximal aerobic capacity in humans. Circulation. 2003 Feb 18;107(6):824-30. doi: 10.1161/01.cir.0000049746.29175.3f. PMID: 12591751. 

Racinais S, Alonso JM, Coutts AJ, Flouris AD, Girard O, González-Alonso J, Hausswirth C, Jay O, Lee JK, Mitchell N, Nassis GP, Nybo L, Pluim BM, Roelands B, Sawka MN, Wingo JE, Périard JD. Consensus recommendations on training and competing in the heat. Scand J Med Sci Sports. 2015 Jun;25 Suppl 1:6-19. doi: 10.1111/sms.12467. PMID: 25943653. 

Normand Richard, MSc, CSEP-CEP, ACSM-CET.
Richard Physiological Services
Physiologist & Occupational Fitness Consultant

Normand has been involved in physiology for more than 10 years. He has research, clinical, occupational, and performance experience, and a professional consulting firm (richardphysiology.com) Outside of work he enjoys track racing for its community, simplicity, and challenge.