Core Temperature and Maximal Oxygen Uptake During Exercise in the Heat

This work measured maximal oxygen uptake (VO2max) and
core temperature (TC) at exhaustion, and oxygen
uptake and heart rate during submaximal exercise in
22 runners under 7 conditions. The conditions were:
1) 25 degrees C (dC), no preheating; 2-4 and 6) 25,
35, 40, and 45 dC, with preheating by a 20-min walk;
5) 45 dC, no preheating; and 7) 45 dC, with passive
preheating raising TC to the same degree as at the
end of the 20-min walk in Condition 6. Compared to
the Condition 1, VO2max was reduced 3-9% under
Conditions 2-5 when TC at VO2max was below the
apparent critical TC, but was reduced 17-19% under
Conditions 6-7 when a critical TC appeared to have
been attained. Heart rate and relative metabolic
intensity (%VO2max) during submaximal exercise
increased in an identical fashion in the heat, and
the elevations in heart rate were significantly
related to the reductions in VO2max (r = 0.79). It
was concluded that large reductions in VO2max in
uncompensable heat stress are associated with
attainment of a critical TC. Elevation in heart rate
during submaximal exercise in the heat is
proportional to reduced VO2max, and not indicative of
dissociation between heart rate and %VO2max.

Autorentext

The Icelander Sigurbjörn Árni Arngrímsson received his Ph.D. in Excercise Physiology from the University of Georgia under the guidance of Dr Kirk J. Cureton. He has published papers on Environmental Physiology and Body Composition. He has also competed on the National Team in Athletics and is multiple National Champion in 800 and 1500 m runs.

Klappentext

This work measured maximal oxygen uptake (VO2max) andcore temperature (TC) at exhaustion, and oxygenuptake and heart rate during submaximal exercise in22 runners under 7 conditions. The conditions were:1) 25 degrees C (dC), no preheating; 2-4 and 6) 25,35, 40, and 45 dC, with preheating by a 20-min walk;5) 45 dC, no preheating; and 7) 45 dC, with passivepreheating raising TC to the same degree as at theend of the 20-min walk in Condition 6. Compared tothe Condition 1, VO2max was reduced 3-9% underConditions 2-5 when TC at VO2max was below theapparent critical TC, but was reduced 17-19% underConditions 6-7 when a critical TC appeared to havebeen attained. Heart rate and relative metabolicintensity (%VO2max) during submaximal exerciseincreased in an identical fashion in the heat, andthe elevations in heart rate were significantlyrelated to the reductions in VO2max (r = 0.79). Itwas concluded that large reductions in VO2max inuncompensable heat stress are associated withattainment of a critical TC. Elevation in heart rateduring submaximal exercise in the heat isproportional to reduced VO2max, and not indicative ofdissociation between heart rate and %VO2max.