Original research
Exercise-heat acclimation in young and older trained cyclists

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Abstract

Objectives

The purpose of this study was to investigate the effect of age on the capacity to acclimatise to exercise-heat stress. This study hypothesised that age would not affect body temperature and heat loss effector responses to short-term exercise-heat acclimation in trained subjects.

Design

Seven young subjects (19–32 years) were matched with 7 older subjects (50–63 years). Subjects were highly trained but not specifically heat acclimated when they exercised for 60 min at 70%VO2max in hot-dry (35 °C, 40%RH) and thermoneutral (20 °C, 40%RH) conditions, pre and post 6 days of exercise-heat acclimation (70%VO2max, 35 °C, 40%RH).

Methods

Rectal temperature (Tr), skin temperature (Tsk), heart rate (HR), cutaneous vascular conductance (CVC) and whole body sweat loss (Msw) were measured during each testing session and Tr and HR were measured during each acclimation session.

Results

Tr, Tsk, %HRmax, CVC and Msw were similar across age groups both pre and post heat acclimation. Following heat acclimation relative decreases and increases in Tr and Msw, respectively, were similar in both subject groups. There was a significant reduction in heart rate (%HRmax) and increase in final CVC following the acclimation programme in the young group (all p < 0.05) but not the older group.

Conclusions

When comparing young and older well trained adults we found age affected the cardiovascular adaptation but not body temperature or whole body sweat loss to exercise-heat acclimation. These data suggest age does not affect the capacity to acclimatise to exercise-heat stress in highly trained adults undergoing short-term heat acclimation.

Introduction

Heat acclimation increases exercise time to fatigue,1 decreases core temperature,2, 3 lowers skin blood flow and sweating thresholds2, 4 as well as reduces heart rate2, 4, 5 during exercise in hot conditions. The attainment of an acclimated state is commonly defined by a plateau in core temperature, heart rate and sweat rate responses in consecutive bouts of thermal stress.1, 5, 6

Incidences of heat exhaustion and heat stroke in response to heat waves7 and exercise-heat stress8 increase rapidly with age from middle to old age. Heat acclimation reduces the thermoregulatory stress and therefore risk of heat exhaustion and heat stroke brought on by exercise-heat stress during athletic competition and/or physically demanding occupations. Therefore it is critically important to consider how age may affect the capacity to acclimatise to varying environmental conditions, particularly when subjected to exercise-heat stress.

Previous research has shown similar core temperature9, 10, 11 and sweating responses10, 11 between young and older adults following heat acclimation. However, when compared to young adults there are also reports of increased core temperatures12 as well as attenuated sweating12, 13 and skin blood flow13 responses in older adults. These inconclusive results could be due to differences in protocols as some studies have failed to match testing conditions,9 heat acclimation protocols12 or similarly acclimated subjects10, 11 between age groups.

No study has compared body temperatures and heat loss effector mechanisms of similarly, un-acclimatised young and older adults, pre, during and post short-term exercise-heat acclimation. This investigation is critical in the development of heat acclimation regimes for older athletes or employees.

Thus, the purpose of the present study was to investigate the effect of age on the capacity to acclimatise to exercise in the heat. Specifically, this study would compare thermoregulatory responses of young and late middle-aged highly trained subjects when exercising at the same relative exercise intensity pre, during and post short-term exercise-heat acclimation. The response prior to and following heat acclimation would be referenced against the same exercise in a thermoneutral environment. We hypothesised there would be no difference between age groups in the rate of core temperature and heart rate adaptation during the heat acclimation. Furthermore there would be no relative differences between age groups in the ability to dissipate metabolic heat through sweating and skin blood flow prior to and post heat acclimation.

Section snippets

Methods

The study was approved by the University of Sydney Human Ethics Committee. Each participant gave written, informed consent prior to participation in the study in accordance with the standards set by the Declaration of Helsinki.

Fourteen highly trained cyclists aged 19–32 (n = 7), and 50–63 (n = 7) volunteered for the study. Each cyclist competed regularly for >2 years, and trained 4–5 sessions/week (1–2 h/session) for >6 months prior to participation in the study. Young and older subjects were

Results

Tr and HR responses to the testing and acclimation sessions are shown in Fig. 1. All other body temperature, cardiovascular and sweating data for the thermoneutral and heat tests are shown in Table 1. Participant summary data (Table S1) and relative changes in key variables pre–post heat acclimation (Table S2) were reported in the online-only Data supplement.

VO2max (L min−1, p = 0.008) 70% power output (p = 0.007) and HRmax (p = 0.010) were significantly higher in the younger group than the older

Discussion

The aim of the present study was to investigate the effect of age on the adaptation to a short-term exercise-heat acclimation training programme in young and late-middle aged highly trained men. The main findings of the study were that: the relative magnitude of exercise-heat acclimation following 6 consecutive days of exercise-heat exposure were similar in the two age groups; but the rate and magnitude of change in heart rate and skin blood flow during the acclimation period did vary between

Conclusion

The findings of the present study suggest that heat acclimation regimes designed for young adults can be applied to older adults up to the 7th decade of life. The rate of adaptation of core body temperature and other thermoregulatory responses during the heat acclimation period were not significantly different in the older participant group. A small age effect on the heart rate and skin blood flow adaptations to exercise-heat acclimation were observed and require further investigation along

Practical implications

  • Trained older adults can achieve the same reduction in core body temperature during consecutive bouts of exercise-heat stress as younger adults.

  • The risk of heat exhaustion and heat stroke can be reduced in young and older adults using an exercise-heat acclimation regime.

  • There is no clear evidence that exercise-heat acclimation regimes designed for younger adults need to be modified for older adults providing similar relative intensities are used.

Acknowledgements

The present study was funded through the Faculty of Health Sciences, The University of Sydney. We would like to thank Ray Patton and Pat Ruell for their assistance with the study. We would also like to sincerely thank the participants for the time and effort they contributed to the study.

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