The Science behind staying cool to get the most out of your workout

Contributor - Gillian White, MSc, PhD (Candidate) University of Toronto, Graduate Department of Exercise Sciences 

We’ve all seen it - the athlete finishes training at max effort and then hops into a bath of ice to recover. This practice used to be reserved mainly for treating injuries – “put some ice on it” was a go-to of athletic trainers and coaches for almost any possible injury. Nowadays, cold is being repurposed to maximize effort during a workout and to speed recovery following a workout. This post breaks down how staying cool during your workout can help you work harder longer.

How cold helps during your workout:

Depending on the nature of your workout, keeping cool has different potential effects. Workouts that benefit most from cooling would be anything that is moderate to high intensity – HIIT, Tabata or CrossFit, Spin/cycling, running or even (to a lesser extent) typical resistance training workouts. The underlying principle is cooling the core/blood to keep heat-related fatigue at bay. Although there are a lot of possible causes of fatigue during exercise, when you’re working hard (especially in the heat), it comes largely from a high core temperature (aka hot blood) signalling to your brain that it’s time to shut’er down (as well as dehydration from sweating to try and cool yourself naturally). Cooling your body (specifically your core) slows the increase in temperature of your body and lets you exercise longer until you hit the critical core temperature that your brain deems a no fly zone (technically 40ºC for heat stroke but significant fatigue by 38ºC or less depending on your level of experience in the heat). This can also be achieved by cooling the areas where blood will be entering the head/neck before it gets to the brain – a sort of heat interference. The idea with staying cool during your workout and dampening the fatigue associated with high core temperatures is that you’ll be able to put in better effort throughout your workout - maintaining your intensity from beginning to end by reducing the effects that a hot core has on a brain that wants to stop the exercise that’s generating the heat! 

How do you maximize the fatigue fighting benefits of cold during a workout?

In a word (or two): Pulse points. Essentially anywhere on your body that you could take/feel your pulse can be exploited for cooling the body. The same reason that we use them to feel our pulse (because they are a large blood vessel traveling close enough to the surface of the body for us to feel our blood movement) is why they are good targets for cooling.  

Your blood not only carries oxygen and nutrients (i.e. glucose) to your working muscles, but also carries wastes away. Carbon dioxide and lactate (lactic acid) are two metabolic wastes that we often think of but one of the most critical wastes that blood removes from an active muscle is heat! Making energy to support the activity of muscles creates a lot of heat as a by-product, which can inhibit the function of the muscle. So, while increased blood flow (via increased heart rate) increases oxygen delivery to support aerobic energy production by the muscle, it also carries heat away. So while that heat is being carried in the blood, the best place for us to cool the blood is when it’s passing near the surface of the body – at pulse points!  

The brain is the most sensitive tissue to changes in blood/core temperature. This is why exercising in the heat feels so much harder – your body gets hotter and your brain’s ability to activate your muscles to keep moving starts to slow down. This is known as central fatigue - which originates in the brain and nervous system as opposed to in the muscles.

Central fatigue doesn’t only occur in hot environments. Any highly metabolic exercise (ie. cardio) or interval training that uses large muscle groups can result in this type of fatigue. So finding a way to cool yourself – especially at pulse points around the head and neck where blood is passing the brain and central nervous tissues can be expected to have the greatest effects on central fatigue.

So the next time you’re gearing up for a great workout, think about how you can stay cool to keep your intensity high and maximize your effort to get the most out of it!