Research

Exercise and Sport Science Research at Charles Darwin University is conducted through the National Heat Training and Acclimatisation Centre (NHTAC) that operates as a partnership between the university and the Northern Territory Institute of Sport.

The Australian Institute of Sport established the NHTAC at the Northern Territory Institute of Sport because of the NT institute’s unique location in the tropics. The partnership with the university commenced in August 1999. The union has proved beneficial, yielding income from the Australian Defence Force, two federally funded full-time staff members (APAI’s), raised the Northern Territory profile through media coverage, national presentations and international peer-reviewed publications, and enabled the construction of a climate control chamber. NHTAC recommendations and procedures have aided the training of many Territory athletes, and those visiting the Northern Territory through maximising their physical performance and decreasing the risk of heat-induced illness. Pre-cooling, heat-mitigating strategies, heat stress monitoring and hydration education are examples of measures encouraged in the Northern Territory through the influence of the NHTAC.

The university/institute partnership works toward the NT Labor Government platform objective no:10 in promoting the Northern Territory as a centre for the training and acclimatisation of national and international sporting people and teams and is consistent with the university-wide agreement to work closely with the Northern Territory Government. However, the findings of NHTAC research are not limited to athletes and benefit all Territorians engaged in physical activity. Furthermore, the training, expertise brought into the Northern Territory, external collaboration, federally sourced funding, and work with local industry (sport, tourism, defence, and public utilities) with which the NHTAC is engaged have great potential for realising economic, social and health benefits for our community.

Investigations thus far include:

Incidence of Pre-game Dehydration in Athletes Competing at an International Event in Dry Tropical Conditions

Finn, J.P. ^1,2, Wood, R.J. ²

¹ School of Environmental and Life Sciences, Charles Darwin University, Darwin, Australia

² National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport, Darwin, Australia

The study tested the hypothesis that the pre-game hydration status of athletes competing at an international event in dry tropical conditions may be inadequate. Differences in hydration status among athletes due to the athlete’s origin and activities during the previous 24 hours were also investigated, as well as the suitability of urine colour as a marker of hydration status. Ninety-three male athletes were tested prior to their first game, with 68 retested 3-4 days later. A comparison between subject’s urine specific gravity (U_sg) was made with urine color (U_col), subjects’ origin and previous 24 hours’ activities as indicated in a questionnaire. No prior warning was given for either test. Subjects were selected on the basis of the environmental conditions they anticipated for competition and had therefore prepared for: indoor air-conditioned (volleyball n=43), outdoor (touch football n=32) and indoor non-air conditioned (basketball n=18). The U_sg of all samples (mean ± standard deviation) was 1.020 ± 0.008, with 6% classified with serious dehydration, 50% with significant dehydration, 31% with minimal dehydration and 14% were well hydrated. There was no difference between the first and second sample (p=0.166). There was a significant relationship between U_sg and fluid intake rating (p=0.015), but no relationships between U_sg and other questionnaire items. There was a high correlation (r=0.87) between U_col and U_sg, though U_col tended to underestimate hydration levels. Findings are of some concern as dehydration was prevalent among athletes. Recommendations are for hydration education to specifically target groups identified as high risk, irrespective of whether athletes had spent the previous 6 months in a tropical environment, and to promote U_col to be used by athletes for monitoring hydration status.

Responses to V8 Supercar driving in hot conditions

M.B. Brearley* ^1,2 J.P. Finn ^1,2, K Royal ¹

¹ National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport

² Charles Darwin University

Two male V8 Supercar drivers (age: 28.4, 31.3 yrs; peak VO2: 60.0, 47.3 mL.kg-1.min-1; height: 1.77, 1.79 m; body mass: 71.0, 78.7 kg) were studied during the Darwin round of the 2002 V8 Supercar championship to examine thermal, cardiovascular and perceptual responses to competitive driving in hot conditions. Urine specific gravity (USG) and colour was determined prior to each race. Body mass, thermal strain and thermal discomfort were measured pre- and post-race. An ingestible telemetric pill (CorTemp, HTI Technologies, USA) permitted continuous measurement of core body temperature while driving. Race 1 was contested over 58km while races 2 and 3 were 100km. A peak core temperature of 39.7oC was observed following race 2 (cabin temperature 52.1oC, WBGT Index 30.7oC). Although both drivers used cooling interventions, they generally perceived their post-race body temperature as very hot causing them to feel uncomfortable. While body mass loss was limited to 1% during the races, 3% was lost throughout the 30 hours spanning practice to race 3 completion. One driver was well hydrated prior to races (Usg 1.004, 1.007, 1.007), while the hydration status of the other varied (1.023, 1.007, 1.028). The data demonstrates that V8 Supercar drivers can attain core body temperatures approaching hyperthermic values which induce high levels of perceived thermal strain from short driving bouts in hot conditions.

Elite Hockey in a Tropical Environment

M.B. Brearley* ^1,2, J.P. Finn ¹, ², R. Wood ¹

¹ National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport

² Charles Darwin University

Field hockey rules prohibit provision of fluids on the pitch by team staff. In tropical conditions, such policy may compromise athletic performance as inadequate fluid intake promotes dehydration. Four heat acclimatised male Northern Territory (NT) representatives (age: 18.4±1.2 yrs; predicted VO2max: 50.4±2.4 mL.kg-1.min-1; height: 1.78±0.05 m; body mass: 77.3±17.3 kg (mean±SD)) were investigated for tympanic temperature, sweat rate, hydration status and heart rate responses during 3 Australian Hockey League games held in Darwin, NT. Analysis included pre warm-up (17 mins), warm-up (29 mins), game (97 mins) and warm-down (11 mins). Ice jackets (Bodycool, Neptune, Australia) were utilised prior, during halftime and substitution periods. Urine specific gravity was 1.012 (0.010) before each game. Sweat loss was 1.23 ± 0.14 L/h while a fluid intake of 0.90 ± 0.27 L/h resulted in a loss of 1.2% body mass. Fluid consumption was inversely related to time on the pitch (r=-0.56). Tympanic temperature rose 0.5oC from baseline to 37.7oC post-game. Despite the use of cooling interventions, acclimatised elite hockey players elicited high sweat rates and suffered dehydration. Team staff may need to provide access to fluids during stoppages and use substitutions to permit adequate fluid intake to match sweat losses in tropical conditions.

Effect of Environmental Temperature on Steady-State and Maximal Cycling

Finn, J.P. ^1,2, Marsden, J.F. ¹, Wood, R.J. ¹ and Travar, A.L. ¹

¹ School of Health, Education and Community Services, Charles Darwin University, Darwin, Australia

² National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport, Marrara, Australia

This study found no significant difference in oxygen consumption, heart rate, blood lactate or core temperature of six heat acclimatised athletes during steady-state and maximal cycling when comparing temperate (21.8 ± 0.5 °C; 52 ± 5 % humidity) with warm conditions (29.6 ± 9 % humidity).

Steady-state O2 was measured during six consecutive five-minute bouts of cycling, beginning at 75 W (females) and 100 W (males) and increasing by 25 W each period. Peak O2 while cycling was measured on separate occasions using a continuous incremental protocol to exhaustion (female 75 + 25 W.min-1, males 60 + 30 W.min-1). During the peak O2 test the anaerobic threshold was determined from the pulmonary ventilation curves (VE and VE/CO2. Test results observed in temperate conditions were then compared with the results for the same test in warm conditions.

The heat acclimatised athletes that took part in this study were able to perform adequately during the stress of relatively short duration exercise in 30 °C heat. As a group, there was no significant difference between temperate and warm conditions for heart rate at the anaerobic threshold. However, as individuals, three of the six subjects in this study had differences of 5, 6 and 9 b.min-1 in heart rate at anaerobic threshold between temperate and warm conditions. This suggests that heart rates used as a marker of the anaerobic threshold for training in the heat be derived from tests in the heat.

Effect of Environmental Temperature on the Anaerobic Capacity of Heat Acclimatised Athletes

Finn, J.P. ^1,2, Marsden, J.F. ¹, Wood, R.J. ¹ and Travar, A.L. ¹

¹ School of Health, Education and Community Services, Charles Darwin University, Darwin, NT 0909, Australia

² National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport, Marrara, NT 0812, Australia

This study found no significant difference in the anaerobic capacity of six heat acclimatised athletes when comparing temperate (21.8 ± 0.5 °C; 52 ± 5 % humidity) with warm conditions (29.6 ± 0.5 °C; 51 ± 9 % humidity).

Anaerobic capacity was estimated using the maximal accumulated oxygen deficit (MAOD) during constant intensity cycling at 120% O2 peak until exhaustion. This yielded similar mean MAOD values of 3.3 ± 0.9 and 3.5 ± 1.1 L (p=0.58) for temperate and warm conditions, respectively. Peak post-exercise lactate values were also not significantly different and were 14.7 ± 3.8 and 14.4 ± 4.5 mmol.L-1(p=0.72) for temperate and warm conditions, respectively. Time to exhaustion (TTE) was similarly unchanged in the heat, being 175 ± 19 and 170 ± 18 seconds (p=0.56) for temperate and warm conditions, respectively. Even though there was no significant difference in MAOD, peak post-exercise lactate or TTE between the two conditions, there was still a trend for greater reliance on anaerobic metabolism during exercise in the heat.

These results suggest that the MAOD is not affected by environmental temperature in the ambient temperature range of 20-30 °C and approximately 50 % humidity in heat acclimatised athletes. Despite the higher mean skin temperature, assumed higher cutaneous blood flow and potentially reduced muscle perfusion, the athletes' performance as measured by TTE was unaffected.

Acute responses of heat acclimatised cyclists to intermittent sprints in temperate and warm conditions

Finn, J.P. ^1,2, Marsden, J.F. ¹, Wood, R.J. ¹

¹National Heat Training and Acclimatisation Centre, Northern Territory Institute of Sport, Marrara, NT 0812, Australia

²School of Health, Education and Community Services, Charles Darwin University, Darwin, NT 0909, Australia

This study describes the performance and the acute physiological responses of heat acclimatised cyclists during 3 sets of 5 x 20 s sprints followed by a final sprint to exhaustion in temperate (mean ± standard deviation 20.2 ± 0.4 °C; 46 ± 2 % humidity, 108.5 ± 1.4 kPa water vapour pressure) and in warm conditions (30.5 ± 0.4 °C; 47 ± 10 % humidity, 206.8 ± 6.4 kPa water vapour pressure).

Oxygen consumption was greater in the warm condition and there was no evidence of an increased reliance on anaerobic metabolism as has been reported for submaximal exercise in the heat.

Subjects lost 2.1 ± 0.2 % of body mass in 53.8 ± 0.2 min during the warm condition. While the duration of the time to exhaustion final sprint was 50 ± 13 s during the warm condition it was 60 ± 7 s for the temperate condition (p=0.020).