Cyclist
Hot to trot: the benefits of heat training
How the body adapts when it’s exposed to exercise in hot conditions is only just beginning to be properly understood, but the potential benefits are already becoming clear. Heat training is now being talked of in the same breath as altitude training, except adaptations occur more quickly and from training that is more convenient for athletes’ schedules.
As such, it is exploding in popularity, being used by both riders targeting one hot event and those looking for more general performance gains over the long term. To see what all the fuss is about, Cyclist visited Dorset-based sports nutrition brand Precision Fuel & Hydration to undertake a training session in its shiny new ‘heat chamber’, an insulated room where the temperature sits at a balmy 40°C.
Cycling sauna
‘That’s the best operating temperature for the protocol we use,’ says Lindsey Hunt, senior sports scientist at Precision Fuel & Hydration and the man overseeing my session today. ‘The body tends to rest around 37°C so this chamber gets you up to around 38.4-38.8°C. It’s hot enough to cause stress-based adaptations, but is a temperature that, once acclimatised to, the body is able to tolerate for extended periods.’
Stepping into the chamber, I am left in little doubt of Hunt’s assertions that this environment will induce stress. It’s like walking into an oven, the heat slapping me like it does when you’ve just stepped off an air-conditioned aeroplane onto the airport tarmac of a summer holiday destination. I clip into the static bike and before I’ve even begun the session proper the sweat is running off me. I’m surprised to learn that’s actually a good sign.
‘Being able to sweat quickly and from a large proportion of your skin helps your body cool itself more effectively,’ says Hunt. My hyper-efficient pores are all very well but they seem to be providing no help whatsoever with my mechanical output, as things are far less encouraging on the wattage front.
The session is simple in terms of structure: maintain a heart rate of around 150 beats per minute for one hour, with power adjusted accordingly throughout. I start at my normal functional threshold, but within minutes that has to drop by 30% to keep my heart rate in check.
Things only go one way. Halfway through the session my power output is less than half of what I would expect to maintain outdoors. By the end I’m struggling to push three figures, even though my legs feel fresh and my lungs aren’t heaving. It’s just my heart that feels like it wants to burst out of my ribcage. Usually in my case, all three are in similar states of disrepair at the same time, so experiencing just one in difficulty is a strange sensation. An elevated heart rate is one of the main reactions of the body when it first tries to cope with heat.
‘It’s because you don’t have enough blood volume,’ says Hunt. ‘As core temperature increases, there’s a massive uptick in skin blood flow to try to dissipate that heat. However, when exercising your working muscles also need that blood to deliver the oxygen they need to make energy, so your heart rate increases to try to deliver blood to both areas.’
It’s in this area that the first adaptations to heat stress occur. These can be achieved quickly and go a long way to mitigating decline in performance, so it’s the primary goal of riders targeting one hot event.
‘Basically your blood plasma goes through the roof,’ says Hunt. ‘This increases blood volume so you have enough of it to supply the skin to dissipate heat as well as the working muscles for energy. As a consequence your heart rate can be much lower and you can produce power outputs more reminiscent of those you’d expect in normal conditions.’
This is the genius of the heat training protocol Hunt has devised: it’s self-modulating. As the rider becomes better heat-adapted, they’re able to hold normal power outputs for longer into the session, which in turn provides the progressive overload needed to keep the body adapting.
‘Consecutive sessions done over ten days are what we’d normally recommend to ensure proper adaptation,’ says Hunt. ‘The good thing is, while it decays at a rate of about 2% per day, the adaptation is recovered by the body very quickly even after a month or more off. So athletes have the flexibility of doing some heat training, then going away to focus more on volume and intensity in the final weeks before competition before easily getting back in a heat-adapted state with just a few sessions immediately pre-event, just using the conditions the event is held in.’
Gaining the edge, legally
That strategy is effective for those with a singular focus, but it’s the more consistent approach to heat training that stands to benefit a wider demographic of riders in more conditions.
‘The initial block followed by maintenance doses – say one or two hours per week for four to five weeks – keeps your body in a heat-adapted state and triggers more robust hematological changes, which are physiological modifications in your blood,’ says Hunt. ‘Your body recognises the increased blood plasma has diluted its haematocrit – the concentration of red blood cells in your blood – so erythropoietin, or EPO, is stimulated to build more red blood cells.’
You read that right – it’s effectively natural blood doping, which is what happens during altitude training too.
‘More red blood cells directly improve your oxygen-carrying capacity, which equates to a better VO2 max and higher lactate threshold,’ says Hunt. ‘Put simply, you can push more power for longer.’
And all of this close to home for just an hour at a time, rather than weeks of isolation in some out-of-season ski resort. Pros and amateurs looking for a performance edge may be about to change their strategy for good.
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