european college of sport science

Thursday, June 25th, 2009
Our data indicate that fat oxidation tended to increase after long term dietary intervention independent of the ratio between fat and
carbohydrate to total daily energy intake whilst CHO oxidation seems not to be affected. The improvement in relative aerobic capacity
was likely due to the reduced bodyweight considering that absolute aerobic capacity was unchanged. A 6 month hypocaloric diet without
additional participation in physical activity does not influence aerobic capacity or substrate oxidation to a significant extent during
exercise.
References
Blaak EE. (2004). Basic disturbances in skeletal muscle fatty acid metabolism in obesity and type 2 diabetes mellitus. Proc. Nutr. Soc. 63
323-330.
Frayn KN. (1983). Calculation of substrate oxidation rates in vivo from gaseous exchange. J. Appl. Physiol 55 628-634.
ACUTE EFFECT OF EXERCISE PERFORMED IN THE HEAT ON ENERGY INTAKE IN ACTIVE MALES
GUELFI, K.J., SHORTEN, A.L., WALLMAN, K.E.
THE UNIVERSITY OF WESTERN AUSTRALIA
Introduction: Maintenance of a healthy body weight is achieved when there is a balance between energy intake and energy expenditure.
However, the effect of exercise itself on subsequent energy intake is not well understood. In particular, the environmental temperature in
which exercise is performed may influence energy intake in the post-exercise meal. This study examined the effect of an acute bout of
exercise performed in the heat on energy intake, macronutrient selection and preferences for solid food or drinks in the subsequent
meal.
Methods: Eleven active males completed three experimental trials in a randomised counter-balanced design; exercise in the heat (36 C:
HEAT), exercise in a neutral temperature (25 C: NEUT) and a resting control trial (25 C: CON). The exercise trials consisted of treadmill
running for 40 min at 70% VO2 peak. Following exercise or rest (control), participants were presented with a buffet-style breakfast of
precisely known quantity and nutrient composition from which participants could consume ad libitum. From this, total energy intake and
consumption of each specific macronutrient was determined.
Results: There was no significant difference in total post-exercise energy intake between HEAT and NEUT. However, participants consumed
significantly more energy during NEUT compared to CON (p = 0.007). When accounting for the excess energy expended during
exercise, relative energy intake (REI) during HEAT was significantly lower than CON (p = 0.001), while there was no significant difference in
REI between the two exercise trials or between NEUT and CON. The lower REI following HEAT compared to CON, but not NEUT could not
be accounted for by significant differences in the circulating level of blood glucose or lactate between exercise trials (p > 0.05). In contrast,
body temperature was significantly elevated following exercise in the HEAT until the breakfast meal, a factor which may inhibit postexercise
energy intake. With respect to macronutrient preferences, there were no significant differences in carbohydrate, fat or protein
intake following the exercise trials, but there was a significantly greater intake of carbohydrate following NEUT compared to CON (p =
0.007). Also, a significantly greater proportion of kilojoules were consumed in the form of drinks during both exercise trials compared to
CON.
Discussion: In summary, when accounting for the excess energy expended during exercise, energy intake is lower following exercise in
the HEAT compared to rest in healthy males. Conversely, REI is similar following exercise in NEUT compared to rest. These findings suggest
that exercise performed in a warmer environmental temperature may be favourable for achieving acute negative energy balance.
HYDRATION STATUS OF THE OFF-ROAD BIKERS IN THE OFFROAD FINNMARK 2008 TESTRACE
MIKKILÄ, S., WEYDAHL, A.
FINNMARK UNIVERSITY COLLEGE
Offroad Finnmark 2008, a testrace for the 700 km one-stage off-road biking race took place in Alta, northern Norway. The race had 11
checkpoints with 3 mandatory 2hours stops. An adequate hydration status can be challenging to maintain during this prolonged exercise.
Dehydration reduces the exercise performance and may severely impair essential body functions(1). The purpose of the study was to
describe the hydration status throughout this physically demanding race.
Five well-trained (VO2max 73.3+/-7.5 ml/minxkg) male amateur bikers participated in this study. Urine samples for osmolality (Uosm)
and specific gravity (Usg) were collected a week before the race, during the race at 6 checkpoints and right after the race. The preexercise
samples with restricted fluid intake were analyzed to confirm bikers’ normal renal function. The other samples were analyzed to
determine dehydration during the race. Uosm samples were analyzed with a freezing point osmometer and Usg samples with a handheld
refractometer. The fluid intake during the race was registered at the same 6 checkpoints as urine samples were collected and right
after the race. The registration was based on the bikers’ recitations. Dehydration was determined by using the cut-off values of Uosm
=/>900 mosm/kg H2O and Usg=/> 1.020.
A total of 33 urine samples were collected. Three bikers completed the race giving each 8 samples. Two bikers quitted the race due to
injuries. However, one of them gave 4 and the other 5 samples.
A biker completing the race showed dehydration with all checkpoint samples by using the Uosm criteria. By using the Usg criteria, this
biker was dehydrated the entire race. Another biker completing the race showed mild dehydration at one checkpoint by using the Usg
criteria. The biker who broke the race after giving 3 checkpoint samples, was dehydrated at 2 checkpoints by using the Uosm criteria and
at 3 checkpoints by using the Usg criteria.
Fluid intake of the bikers during the race was 6113+/- 643 ml/24 hours. The biker, breaking the race and showing dehydration with 2 of
the Uosm and 3 of the Usg samples had the lowest fluid intake. The biker, who finished the race and showed dehydration throughout the
entire race with the Usg and at 6 checkpoints with the Uosm had the highest fluid intake. Most likely the bikers’ recall of the fluid intake is
not accurate as well as the fluid contents of the meals are not calculated.
The results show that maintaining an adequate hydration status was individually demanding.
However, the study shows that the dehydration was not a major problem during Offroad Finnmark 2008.
References
1. Barr S. Effects of dehydration on exercise performance. CANADIAN JOURNAL OF APPLIED PHYSIOLOGY-REVUE CANADIENNE DE PHYSI-
OLOGIE APPLIQUEE. 1999 APR 1999;24(2):164-72.
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