2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
MAINTAINED COGNITIVE FUNCTION AND BLOOD-BRAIN
BARRIER (BBB) PERMEABILITY DURING EXERCISE IN THE
HEAT FOR BOTH HIGHLY TRAINED AND MODERATELY
TRAINED HUMANS
Shawnda A. Morrison 1 , Roger D. Hurst 2 , Stephen S. Cheung 3 , Philip N. Ainslie 4 ,
James D. Cotter 1
1 School of Physical Education, University of Otago, Dunedin, New Zealand
2 Human Health & Performance Team, Health & Food Group, Hortresearch Ltd, New
Zealand
3 Department of Physical Education & Kinesiology, Brock University, St. Catharines,
Canada
4 Department of Physiology, University of Otago, Dunedin, New Zealand
Contact person: jim.cotter@otago.ac.nz
INTRODUCTION
The effects of thermal environments on cognition remain equivocal. Generally, it is
assumed that the higher the heat strain, the greater the compromise in cognition,
physiological capacity and perceived exertion; however the interactions between such
variables are complex. Recent reports indicate that the blood-brain barrier (BBB) can
be compromised with exercise in hot conditions 1 , particularly in conjunction with
dehydration 2 . It is not known, however, if alterations in BBB integrity may affect
central nervous function. Although cognition in particular has been shown to improve
after acute exercise 3 , if one is in a hot environment, central nervous system function
may be reduced via an elevation in BBB permeability. In addition, the training status
of an individual can play a key role in their ability to tolerate heat strain 4 , while the
interactions of these variables (fitness, heat, cognition) have not established.
Therefore, the purpose of this study was to explore the impact of training status on the
ability to maintain BBB integrity and cognitive function during intense exercise in the
heat.
METHODS
Fifteen men (age: 22 ± 3 years) completed two exercising heat stress trials after
fitness testing (graded cycling test to maximum) and a familiarisation trial.
Participants were recruited into two training groups; a highly fit group (HF, N=7)
having a maximal aerobic power of 64 ± 4 mL·kg -1 ·min -1 and training at least six
times per week, and a moderately fit group (MF, N=8) having a maximal aerobic
power of 46 ± 4 mL·kg -1 ·min -1 and participating in physical activity less than three
times per week. Participants were not acclimatised to the heat, and their two
experimental trials were separated by at least one week.
Upon arrival at the lab, participants voided their bladders, after which urine specific
gravity (USG) and pre-exercise body mass were recorded. Participants were then
instrumented with four skin thermistors (right side: bicep, chest, thigh, calf), and one
core temperature thermistor (oesophageal) and remained seated for at least 20 min
before a baseline venous blood sample was obtained via cannula. The exercise
protocol took place in an environmental chamber (30°C, 50% rh) and airflow was
graded across fitness groups based on their running speed (Wind speed: HF~ 4.5 m·s -
1 , MF~ 3.5 m·s -1 ). Exercise consisted of 15-min cycling at a fixed load eliciting 50%
heart rate reserve (HRR, Cycle 1) before running for 30 minutes at a fixed speed
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