A reduced core to skin temperature gradient, not a critical core temperature, affects aerobic capacity in the heat

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Abstract

The purpose of this study was to determine the impact of the core to skin temperature gradient during incremental running to volitional fatigue across varying environmental conditions. A secondary aim was to determine if a "critical" core temperature would dictate volitional fatigue during running in the heat. 60 participants (n=49 male, n=11 female; 24±5yrs, 177±11cm, 75±13kg) completed the study. Participants were uniformly stratified into a specific exercise temperature group (18°C, 26°C, 34°C, or 42°C) based on a 3-mile run performance. Participants were equipped with core and chest skin temperature sensors and a heart rate monitor, entered an environmental chamber (18°C, 26°C, 34°C, or 42°C), and rested in the seated position for 10min before performing a walk/run to volitional exhaustion. Initial treadmill speed was 3.2kmh-1 with a 0% grade. Every 3min, starting with speed, speed and grade increased in an alternating pattern (speed increased by 0.805kmh-1, grade increased by 0.5%). Time to volitional fatigue was longer for the 18°C and 26°C group compared to the 42°C group, (58.1±9.3 and 62.6±6.5min vs. 51.3±8.3min, respectively, p<0.05). At the half-way point and finish, the core to skin gradient for the 18°C and 26°C groups was larger compared to 42°C group (halfway: 2.6±0.7 and 2.0±0.6 vs. 1.3±0.5 for the 18°C, 26°C and 42°C groups, respectively; finish: 3.3±0.7 and 3.5±1.1 vs. 2.1±0.9 for the 26°C, 34°C, and 42°C groups, respectively, p<0.05). Sweat rate was lower in the 18°C group compared to the 26°C, 34°C, and 42°C groups, 3.6±1.3 vs. 7.2±3.0, 7.1±2.0, and 7.6±1.7gm-2min-1, respectively, p<0.05. There were no group differences in core temperature and heart rate response during the exercise trials. The current data demonstrate a 13% and 22% longer run time to exhaustion for the 18°C and 26°C group, respectively, compared to the 42°C group despite no differences in beginning and ending core temperatures or baseline 3-mile run time. This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.

Original languageEnglish
Pages (from-to)7-12
Number of pages6
JournalJournal of Thermal Biology
Volume43
Issue number1
DOIs
StatePublished - Jul 2014

Keywords

  • Environmental physiology
  • Heat stress
  • Hyperthermia
  • Thermotolerance
  • Volitional fatigue

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