Heat and Exercise – Are They a Dangerous Combination for Masters Athletes?

Introduction

The Hawaii Ironman has just been run, swum and ridden! Having done it myself in 2005, I know how tough it can be. The wind blows from all directions and speeds and heat is just suffocating. You feel like you are running through water at times – and given the humidity in the air, you propbably are! There is conflicting research about whether as we age our ability to regulate our body temperature (sweat rate, body temperature maintenance, and skin blood flow) is reduced compared to younger people. However, most previous studies have not used well-trained older athletes as the subjects in their study or have not matched young and older athletes for training status and aerobic capacity – two factors that can influence our ability to tolerate heat.

The Research

A team of ozzie sport scientists matched seven older highly trained cyclists aged 51–63 years with two groups of young cyclists aged 19–35 years. One group of seven youngsters (!) were matched for training status (5 sessions per week, 1-2 hours per session) and the other group of seven younger cyclists were matched for aerobic capacity or VO2max. Each of the cyclists exercised at 70% of the aerobic capacity in hot (35°C, 40% relative humidity) and thermoneutral (20°C, 40% relative humidity) conditions for 60 min. The cyclists were able to drink one water bottle whenever they liked during the hour of cycling. The research team measured rectal temperature (yep! thermometer up the behind!), skin temperature, heart rates, skin blood flow, sweat loss, and evaporative heat loss in each of the athletes during each of their cycling sessions in the cooler and hot temperatures.

The Results

Final rectal temperature in both the thermoneutral (cool) and heat (Young highly-trained = 39.13 ± 0.33°C, Young matched for aerobic capacity = 39.11 ± 0.38°C, Older highly-trained= 39.11 ± 0.51°C) tests were similar between all three groups. %HRmax (heat test: Young highly-trained= 92.5 ± 6.0%, Young matched for aerobic capacity = 91.6 ± 4.4%, Older highly-trained = 88.6 ± 5.1%), skin temperature, and skin blood flow during cycling in both environments were also similar between groups. However, lower sweat loss and evaporative heat loss in the heat test in the Older highly-trained and Young matched for aerobic capacity groups when compared with the Young highly-trained group reflected lower metabolic heat production.

The So What?

The findings of the study study suggest that thermoregulatory response is maintained with age in highly-trained older athletes. The findings also suggest that during training and racing in hot environments, older adults up to the seventh decade of life and who are well trained, can safely complete the same relative workloads (% of capacity) without an increased risk of heat injuries. Heart rate, skin blood flow responses and evaporative heat loss were both found to be a function of an age-related drop in maximal aerobic capacity with age. This measn the higher your aerobic capacity, the better you will handle the heat. Chapter 11 (Exercising in the Heat and Cold) of my book The Masters Athlete (Exercising in the Heat and Cold) spells out in detail the ways older athletes can manage training and racing in both temperature extremes. Although the present study found no evidence that cardiovascular adjustments during prolonged, severe exercise-heat stress are compromised with age, careful screening for any preexisting cardiac abnormalities is extremely important. Chapter 3 of The Masters Athlete (Medical Screening and the Masters Athlete) presents the current guidelines for screening older athletes.

Best, S. and others (2012). The effect of ageing and fitness on thermoregulatory response to high-intensity exercise. Scandinavian Journal of Medicine and Science in Sports. 22(4): e29-e37.