Hot Environments Decrease Exercise Capacity While Elevating

Multiple Neurotransmitters Independent of Humidity

Jiexiu Zhao

, Lili Lai

, Stephen S. Cheung

, Shuqiang Cui

, Nan An

Wenping Feng

, Santiago Lorenzo

and Ye Tian

Sport Biological Center, China Institute of Sport Science, Beijing, China

Department of Kinesiology, Brock University, Ontario, Canada

Departments of Kinesiology, Beijing Institute of Sport Science, Beijing, China

L|E|C|O|M, Bradenton, FL, U.S.A.

1 INTRODUCTION

The purpose of this study was to test the hypothesis

that different neurotransmitters and hormones are

presented at exercise fatigue in hot temperatures

with differing relative humidities (RH).

2 METHODS

Eight trained male athletes performed a graded

maximum oxygen uptake (VO2max) test in five

different environmental conditions: 21°C/20% RH

(Normal); 33°C/20% RH (Hot 20%), 33°C/40% RH

(Hot 40%), 33°C/60% RH (Hot 60%), and

33°C/80% RH (Hot 80%). Blood samples were

taken pre- and post-exercise and analyzed for

noradrenaline (NA), adrenaline (ADR), dopamine

(DA), serontonin (5-HT), 5-hydroxyindoleacetic

acid (5-HIAA), and prolactin (PRL). Weight, oral

temperature and skin temperature were recorded pre-

and post-exercise. Heart rate was monitored

continuously throughout exercise.

3 RESULTS

Compared to Normal, Hot 20%, Hot 40% and Hot

80% had lower VO2max levels (P < 0.05). Pooling

data across all five conditions, NA (P < 0.0001),

PRL (P < 0.0001), 5-HT (P = 0.002), 5-HIAA (P =

0.029), and DA (P = 0.016) levels were affected by

exercise, with the levels each being significantly

associated with performance time. However, ADR

did not show any significant effect between pre- and

post-exercise (P = 0.187).

4 DISCUSSION

The main findings of this study were two aspects.

First, hot-wet condition (Hot 80%) and hot-dry

conditions (Hot 20%, Hot 40%) have similar

negative effects on VO2max performance. This is in

a protocol with a relative short duration – “in real”

life – e.g. a prolonged competition the negative

effect of high humidity on thermoregulation would

be expected to aggravate hyperthermia and hence

have a larger effect on VO2max and performance.

Second, irrespective of thermal status, NA, DA,

PRL, 5-HT, and 5-HIAA are associated with the

performance time of the VO2max protocol.

Although the finding of neurotransmitters being

impacted by exercise fatigue in heat is not a new

concept, this is one of the first laboratory studies to

systematically investigate the effects of hot

temperature and different humidities on multiple

neurotransmitters simultaneously. The effects of a

hot environment on aerobic performance have been

well documented, but the specific influence of

relative humidity on performance and on the

physiological response to exercise remains largely

unexplored. Although exercise capacity at moderate

intensity in a warm environment is progressively

impaired as the relative humidity increases, the

present investigation demonstrated that VO2max

was generally lower in hot conditions than in

Normal and there were no differences across

humidity levels. There was a significant effect of

time for NA, PRL, 5-HT, 5-HIAA, and DA

concentrations after exercise in the five different

conditions. The levels of NA, DA, PRL, 5-HT, and

5-HIAA were strongly associated with exercise time,

suggesting that the duration and/or intensity of

exercise had an important influence on

neurotransmitter levels irrespective of environmental

conditions. High correlation of NA, DA and 5-HT

with performance time of VO2max provides support

for the hypothesis that central fatigue should be

determined by the collaboration of the different

neurotransmitter systems, with the most important

role possibly being for the catecholamines DA, NA,

and 5-HT in high temperature.

Zhao J., Lai L., S. Cheung S., Cui S., An N., Feng W., Lorenzo S. and Tian Y..

Hot Environments Decrease Exercise Capacity While Elevating Multiple Neurotransmitters Independent of Humidity.

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: Relationships between performance time versus post-exercise concentrations of Dopamine (A), ADRrenaline (B),

Noradrenaline (C), Serotonin (D), 5-hydroxyindoleacetic acid (E) and Prolactin (F).

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