Is hot the new cold for athlete recovery?

As heat immersion is being used more and more and often alongside cold water immersion for recovery purposes, we spoke to Senior Athletic Development Coach and Rehab Coordinator at Port Adelaide FC, Calvin Philp about this topic. He has recently published a great article in PLUS ONE which is well worth a read.

The use of heat for recovery seems to be coming back around, especially in team sport environments. What physiological benefits could heat have on upcoming activity vs. recovery from previous activity?

Heat has definitely gained popularity again from a recovery point of view, whether from a physiological or psychological perspective. Interestingly, heat can also drive training adaptations for upcoming events and activities. This is where our research has largely focused.

There is now a growing body of evidence that heat acclimation, the process of repeatedly exposing the body to a hot environment, can not only improve performance and heat tolerance for upcoming events in hot environments, but may also provide a potent stimulus to improve exercise performance in cool or temperate conditions. There is still considerable debate around this. The Journal of Physiology in 2016 hosted a great crosstalk between Minson and Cotter vs. Nybo and Lundby about the efficacy of heat acclimation for performance in cool and temperate conditions ^[5,6].

Our recent hot water immersion (HWI) study with semi-professional Australian rules footballers showed large improvements in V_IFT (intermittent running performance) and perceptions of in-game running performance after completing 2-3 sessions of HWI per week over a 6-week period. This supports the use of heat as a performance aid in temperate conditions ^[8].  

Although there is limited evidence on this topic, what would your recommendations be in terms of time after training, temperature, submersion level, etc?

I always believe the best intervention is what works best for your environment. With my background as an applied practitioner, this thinking has largely influenced any research question I tried to answer.

For example, if you are looking purely at the literature, Heathcote and colleagues ^[1] have published some great work in this space), then HWI should be completed as close as possible to a preceding aerobic exercise session. Immediately after would be best, with submersion up to shoulder height at a temperature of around 40ºC for approximately 30 minutes ^[8,10,11]. This appears to be best practice to achieve the highest levels of heat load and, consequently, acclimation / adaptation.

Unfortunately, such a stringent protocol isn’t possible in many sporting environments, especially team sports, as there are many competing time-demands such as meetings, strength sessions, treatment, etc. In our study, HWI sessions were as much as 45 minutes after on-field training. The players still showed large improvements in V_IFT compared to just completing the training and proceeding with their other commitments.

Furthermore, if you want to acclimate as quick as possible, the evidence indicates daily 30-minute HWI sessions. Our athletes only trained on-field 3x / week, with the HWI intervention performed in-season. So they only completed 2-3 HWI sessions per week and still saw beneficial results.

Hopefully applied research like ours allows fellow practitioners to take comfort in the fact that, even though they may not quite be able to complete best practice by way of academic literature, they may still be able to see benefit from HWI that fits into their program.

What psychological benefits can be gleaned from HWI post-training?

This is often such an underappreciated area of interventions such as heat acclimation, altitude training, etc, that regularly get dismissed in scientific literature as placebo. However, we are starting to see a greater appreciation of the belief effect that interventions such as HWI can have, with Dr. David Martin bringing these concepts to the forefront in elite sports science circles.

The idea that an athlete can believe they have a competitive advantage over their competition due to the training interventions employed is extremely powerful. That belief effect is exactly what we saw from our study. Both those who completed the HWI intervention and those in the control group thought HWI would improve intermittent running performance. Furthermore, those who completed HWI strongly believed their in-game running ability improved throughout the 6-week intervention, whilst the control group thought it was unlikely.

Helping the athlete believe in their ability to initially compete with and then hopefully dominate the opposition is such an important part of our job as practitioners. Of course, we should be able to back this up with sound scientific principles, so I’m glad we are starting to pay more attention in this area.

Just like CWI immersion, there are athletes who will be uncomfortable with HWI. Do you have any recommendations for practitioners who have those athletes? Would you offer an alternative?

I think the first thing to point out with HWI is that it will be uncomfortable. You are deliberately applying stress to the body. We had athletes find it challenging during our study, so I highly recommend that you have someone monitoring their physical and perceptual responses throughout.

I recommend a few things to help reduce some of this discomfort. First, apply a progressive overload of exposure to the heat stimulus. We did this in our study by progressing from an initial exposure of 2 x 15 minutes in Week 1 to 3 x 30 minutes in the final weeks of the study. This allows the body to adapt to the new stimulus more gradually, therefore reducing the thermal discomfort.

For those who still struggle with HWI despite trying to gradually increase their HWI exposure, sauna or exercise in heat chambers can also elicit heat acclimation. Depending on the individual and the protocol, these can be more comfortable. This has definitely been the case in my experience, so all modalities can potentially play a useful role in an athlete’s heat acclimation protocol. 

What are the most common mistakes young practitioners make and what advice would you give them to improve their practice?

There are plenty of mistakes I can talk about from my own journey as a practitioner, however, there are two I would like to focus on for the purpose of this article. Firstly, not taking the time to understand the organisation or environment you have come into. Each organisation, team and coach has a certain way of operating, with their own bias and belief usually shaped by their own previous experiences.

As young practitioners, we often come in wanting to prove our worth and make an immediate impact! This enthusiasm and energy cannot be faulted, however, I would suggest taking the time to understand what has previously been done before you, what they liked/ didn’t like from that, and where they think their greatest improvements can come from. I like to think that if you spend the time getting to know the subtleties of the environment it will allow you to take the players, coaches and staff along on the journey with you. Closely linked to this is being too rigid with your programming or application of an intervention. I have definitely been guilty of this in the past! This goes to what I mentioned earlier regarding the best intervention is what best fits your environment. Get to know what constraints may exist on the program or intervention you would like to include. Then by having a strong knowledge of the adaptation you are trying to achieve, not just a step-by-step recipe you have to follow, you should be able to manipulate variables (eg. exercises, drill design, timing and frequency of sessions) to achieve your desired result. Sometimes, this isn’t possible and that’s ok, you may have to learn to pivot or shelve that idea, at least for the short-term.

Despite our greatest intentions we need to understand that we are just one cog in the wheel that helps our team perform.