Even here in Canada, eventually hot summer weather will come. One strategy popular with athletes for reducing heat stress before or during competitions are ice vests. How effective are they?
For endurance sports, the evidence is clear and unequivocal that performance is impaired with higher ambient temperatures. It’s also reduced in cold temperatures or with a drop in core temperature. Data generally points to an “inverted-U” relationship, where performance is optimal at a moderate temperature, but becomes progressively reduced above or below this optimal range.
This optimal temperature might be lower than we think, with a classic study from my post-doc lab at U Aberdeen finding that cycling tolerance time at a constant hard effort was longest at 11°C, similarly reduced at 4 and 21°C, and further reduced at 31°C . So even what we consider as room temperature, such as when we ride on a trainer indoors, already generates significant heat stress.
There are numerous countermeasures, with the best option a thorough program of heat adaptation over the course of 1-2 weeks of gradual exercise-heat exposure. On the day of, there’s the possibility of pre-cooling with a pre-ride cool/cold bath; an ice vest or cold wet towels over the neck and torso; or drinking cold fluids or ice slurries.
Ice vests have been commonly used by elite athletes since the Australian Rowing Team pioneered their use while warming up at the 1996 Atlanta Olympics. The theory is to get the muscular and metabolic benefits of a warmup, but keep core temperature as low as possible.
VeloToze has recently introduced an ice vest for everyday athletes like us. As our lab is up and running again after 18 months of COVID-shutdown and we had an experiment we were piloting, I did a N=1 experiment using myself.
Test Setup
- I did a ride at a constant effort of 70% peak power output on a Velotron ergometer on two sessions separated by 48 h.
- Conditions were 22°C and about 40% relative humidity with no fan for airflow. While one of my own studies have shown the importance of adequate airflow, the lack of airflow simulates what might be common in many pre-race conditions.
- Test was a “ride to exhaustion” for as long as I can maintain. Note that one of my very first scientific papers reported fairly high variability of up to 10-15% difference day-to-day in sedentary individuals. This is reduced with a trained participant like myself, but some day-to-day variability is still likely present.
- No feedback (time, heart rate, encouragement, cadence) was provided during the trials, and I wasn’t told of any data until after both trials were done.
VeloToze Cooling Vest
In terms of the VeloToze cooling vest itself, it is extremely lightweight and fits closely, so it can be worn directly next to the skin to maximize cooling effectiveness. If you do decide to wear it during training or racing, you might need to go up a jersey size to accommodate the added bulk.
The vest has four pockets for the four included ice packs. There are three packs that slot in the middle back and the sides of the torso, and a larger pack on the upper back. The pockets are tight enough that the packs don’t really slosh side to side uncomfortably while riding in or out of the saddle when using the vest by itself. Of course, a jersey on top would further help with a tight fit.
In use, I found the cooling sensation to be fairly diffuse and evenly distributed, rather than at very specific points. The ice packs lasted easily throughout our test, though of course longer and hotter rides will see the packs melting more.
Test Results
The first graph was my heart rate response, with the ice vest trial in blue and the control (vest and room temperature ice packs) in red. You can see that the heart rate tracked pretty much identically over the trial, but the Vest condition lasted 4.5 min longer.
This second graph is my core temperature response, graphed as the change from my starting core temperature (to account for day-to-day different in resting core temperature). As with heart rate, core temperature tracked pretty much identically for both trials.
Subjective Sensations
While I haven’t graphed it here, we periodically recorded thermal sensation (how hot/cold are you?), thermal comfort (how comfortable/uncomfortable do you feel?), and ratings of perceived exertion. These data did see some difference between the two conditions, with the Vest condition generally reporting one “unit” improvement in all three measures.
This disconnect between physiological and perceptual data really highlights the importance of skin temperature and perception. Many cooling tools may not actually alter your core temperature, but the reduced skin temperature increases comfort, which in turn leads to a reduced perception of effort or willingness to push harder.
Summary
While there is some day-to-day variability in a time-to-exhaustion test, my N=1 test suggest that there is some potential benefit for using an ice vest during a hard effort. While there is minimal physiological difference, the main benefit appears to be an improved thermal perception, which in turn could have contributed to a reduced perceived effort and willingness to work longer or harder.
And if you are interested in trying out a cooling vest, I found the VeloToze vest to be an affordable and well-designed option. You can check it out here.
Disclosure. I was sent a VeloToze vest, but the company had no input of any kind into the test, nor were they provided any of the data or a draft of this article prior to publication.
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