Training Ironman triathletes in the real-world: Case study of a heat stress training camp

Feb 26, 2020

In Endure IQ LDT102: Training Program Fundamentals for Long Distance Triathlon, we explore the best training methods used by long-distance triathletes that facilitate optimal performance, and in LDT103: Heat and Long Distance Triathlon, we focus on something all long-distance triathletes seeking to cross the finish line at the World Championships will encounter, heat. In this blog, we are going to touch the surface of both of these crucial topics by describing a case study that we published this year on a three-week heat stress training camp in Kona, Hawaii undertaken by two elite Ironman triathletes (10). This case study gives strong practical insight into how a very successful three-week block of training can be performed by two elite Ironman triathletes, and the additional considerations that are encountered when temperatures rise.

 Heat stress training camps: What are they? Why do endurance athletes do them?

The first things to ask, then, are what exactly is a ‘heat stress training camp’, and why do endurance athletes do them? We refer to a ‘heat stress training camp’ as a block of training – in this case a three week block of training – that is undertaken by endurance athletes in a specifically hot environment – in this case Kona, Hawaii.

Heat and endurance sport is increasingly synonymous. Obviously, the World Ironman Championships takes place every year in Kona, Hawaii at temperatures exceeding 30°C (86°F), with parts of the course reaching closer to 40°C (104°F). On the Ironman circuit, heat is also encountered in Bahrain, Cairns, Lanzarote, Malaysia, and Port Macquarie, to name a few, and in other endurance sports such as road cycling, sweaty stage races are also competed across Europe, with the World Championships even taking place in Qatar in 2016. Being properly prepared for the specific challenges posed by high temperatures on race-day is therefore of paramount importance for many long-distance triathletes and endurance athletes in general. 

The need to be properly prepared for the specific challenges posed by high temperatures on race-day is well-known to endurance athletes. This process is known as heat acclimatisation or acclimation, where acclimatisation refers to preparation taking place in natural environments like the roads of Kona, and acclimation refers to preparation taking place in artificial environments like laboratory heat chambers, make-shift heat rooms, or saunas. The purpose of acclimatisation and acclimation is to familiarise the athlete with high temperatures and drive physiological and behavioural adaptations that enable the athlete to better cope with the thermoregulatory demands of competing in the heat. I won’t dwell on them here, but these adaptations  include reduced resting body temperatures and exercise heart rates, increased sweat rates and fluid intake rates, and an altered perception of the heat, all of which enable an athlete to better regulate their internal temperature and physiological functioning on race day when the temperature is high and pressing (1, 13). The need for heat acclimatisation is therefore one of the main reasons why endurance athletes take off to perform a ‘heat stress training camp’.

There is another reason why endurance athletes perform heat stress training camps, and this relates to driving other metabolic adaptations to training that we cover in LDT102, such as evoking mitochondrial changes in the muscle, pushing up the lactate threshold. The logic behind this is very similar to the logic used by endurance athletes who perform specific training blocks up mountains at high altitude – to use the heat as an additional training stress (4). The elevated environmental temperature challenges our body’s ‘homeostasis’ – that is, the happy conditions in which it likes to operate – with higher core body and working muscle temperatures compared to when a training session is performed on a chilly morning here in Auckland, New Zealand. Those temperature-related challenges to homeostasis may act as a warning to the body, telling it to adapt and make changes that will help with endurance performance (4). That is the theory, anyway, and something we are currently investigating and recruiting subjects for in our laboratory at AUT.

However, endurance athletes considering undertaking these heat stress training camps should in advance understand the extra challenges faced when training in hot conditions. As we’ve already said, heat makes us hot – in our muscles and core, and also increases things like circulating stress hormones (3), sweating and the associated potential for marked dehydration (5), heart rate for a given running speed or power output on the bike (2), as well as decreasing the speed or power reached at lactate threshold (6, 9). Therefore, training in the heat, when not managed correctly, has the potential to chronically up-regulate relative training intensity from a physiological standpoint, which has been associated with impaired cardiac autonomic balance (11) – a fancy way of saying that the body’s nervous system becomes overly stressed – which can result in fatigue and non-functional overreaching (12). Ultimately, this impairs the athlete’s ability to train, and sets them on a path for missed training and poor performance.

 What did the athletes in this case study do? 

The athletes went off to train for three weeks in Kona, Hawaii, the purpose of which was to generate some heat acclimatisation and thermoregulatory adaptations to withstand the heat at last year’s World Championships, to familiarize themselves with the course as some race-specific preparation, but also to use the heat as an additional training stimulus to stoke the engines and generate sought-after metabolic adaptations for power and speed on race-day. To avoid the associated risk of maladaptation, a number of steps were taken to ensure that a chronic up-regulation of relative training intensity was avoided.

Firstly, before departing for Kona, the athletes underwent some physiological testing in our laboratory. These athletes make frequent use of blood lactate measurements and expired gas analysis in controlled laboratory conditions to identify individualized lactate thresholds and training zones for use in training prescription. These values were integrated into the specific plans put in place for these athletes while they were away, to ensure that low-intensity, recovery sessions were of a physiologically low-intensity, and that high-intensity demanding workouts were sufficiently physiologically demanding to stress the adaptive pathways that lead to improved performance. These precise values could therefore be used to ensure the athletes continued to follow their habitually polarized training model of high-volume, largely low-intensity training program, the merits of which is covered extensively in Endure IQ LDT102.

The athletes also continued their typical practice of taking heart rate variability (HRV) measures upon waking during the heat stress training camp, and filled in some Likert scale wellbeing scales. These measures – physiological and perceptual, respectively – are incredibly useful tools in training monitoring for endurance athletes, and give us an idea of when to back-off, and when to put the hammer down. HRV gives us some insight into that cardiac autonomic balance I referred to earlier, and can be used to give us day-to-day feedback on whether we are ready for a big, hard session, or whether our long term success might be best served with something low and slow, or even rest (12). Indeed, studies are now emerging that demonstrate how using HRV to adjust our carefully-planned training programs at a day-to-day level can produce superior results compared to blindly following a plan set out in advance (7, 8).

 What happened? 

As expected, Kona was hot, with the average temperature during training sessions being ~30°C (86°F). As intended, training volumes were high throughout the camp (25-33 hours per week), and continued to emphasize low-intensity work, with ~78-88 % of total training time spent below the aerobic threshold or first lactate threshold. Perceptual wellbeing and HRV was successfully unperturbed throughout the camp, indicative of a well-managed block of training.

When the triathletes returned home, we re-tested them in our laboratory. Now, it is important to note that, a case study like this cannot tell us about the merits, or lack of merits, of heat stress training camps for generating positive functional adaptations to training, we’d prefer to leave that to controlled trials. These tests were performed as part of the athletes’ own serial testing for training monitoring, and to give us some insight into the progress made over the course of the camp. 

We were pleased to see evidence of positive changes to the aerobic threshold from pre-to-post-camp (~17 W in one athlete, ~28 W in the other), and beneficial changes to the power vs. blood lactate curves. Indeed, the often-used 4 mmol.L-1 training marker appeared to increase by ~15 W in one athlete, and by ~16 W in the other. These were the main rewards for what was a carefully-managed heat stress training camp.

A more practical benefit of the heat stress training camp was the simple break in the monotony of normal training routines. Going somewhere new, into a focused training environment away from the copious distractions of home life can be invaluable to athletes in serious training. The heat posed a new challenge, and the landscape provided a new backdrop for training. Endurance training can – and is indeed supposed to become – quite monotonous, so for those fortunate enough to have the opportunity to take-off to Kona, Hawaii for three weeks, heat stress training camps can be a useful tool in the arsenal of the endurance coach to keep things fresh and interesting.

 What can we take away from this?

Describing the experience of these Ironman triathletes on a three-week heat stress training camp in Kona, Hawaii gives us some insight into (a) the use and relevance of heat stress as a consideration in real-world endurance sport and (b) potential strategies for the management of successful training blocks of high volume in demanding environments. These concepts and more will be explored in much more detail in Endure IQ LDT103 which will be released in May 2020.

 -Written by Dr Dan Plews & Ed Maunder 

Image - Cameron Graves


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