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European Journal of Applied Physiology

, Volume 114, Issue 11, pp 2399–2410 | Cite as

Do greater rates of body heat storage precede the accelerated reduction of self-paced exercise intensity in the heat?

  • Nicholas M. Ravanelli
  • Matthew N. Cramer
  • Yannick Molgat-Seon
  • Anthony N. Carlsen
  • Ollie Jay
Original Article

Abstract

Aim

To reevaluate the previous hypothesis that greater reductions in self-paced exercise intensity in the heat are mediated by early differences in the rate of body heat storage (S).

Methods

Eight trained volunteers cycled in 19 °C/1.8 kPa (COOL), 25 °C/1.2 kPa (NORM), and 34 °C/1.6 kPa (HOT), while maintaining an RPE of 16. Potential differences in S following the onset of exercise were assessed by comparing rates of esophageal temperature change (ΔT est); and estimated S values using a traditional two-compartment thermometric model (S therm) of changes in rectal (T re) and skin (T sk) temperature, and partitional calorimetry (S cal).

Results

After 15 min of exercise, workload decreased more in HOT vs. COOL (P = 0.03), resulting in a shorter time (HOT: 40.7 ± 14.9 min; COOL: 53.5 ± 18.7 min; P = 0.04) to 70 % of initial workload. However, there were no preceding differences in ΔT est between conditions (P = 0.18). S therm values were different between HOT and COOL during the first 5 min of exercise (P < 0.05), primarily due to negative S therm values (−32 ± 15 kJ min−1) in COOL, which according to partitional calorimetric measurements, required improbably high (~56 kJ min−1) rates of evaporation when no sweating on the back and thigh was observed until after 7.6 ± 1.5 min and 4.8 ± 1.7 min of exercise, respectively. S cal values in the first 5 min of exercise confirmed S was actually positive in COOL (+21 ± 8 kJ min−1) and not negative. Different S therm values following the onset of exercise at different environmental temperatures are simply due to transient differences in the rate of change in T sk.

Conclusion

Reductions in self-paced exercise intensity in the heat are not mediated by early differences in S following the onset of exercise.

Keywords

Core temperature Exercise performance Partitional calorimetry Rating of perceived exertion Thermoregulation 

Abbreviations

Ar/AD

Effective radiant surface area (ND)

BF

Biceps femoris

AD

Body surface area (m2)

C

Convective heat exchange (W m−2)

Cres

Convective heat exchange via respiration (W m−2)

Esk

Evaporative heat loss from the skin (W m−2)

Eres

Evaporative heat loss via respiration (W m−2)

EC

Caloric equivalent of carbohydrates (kJ LO−2)

EF

Caloric equivalent of lipids (kJ LO−2)

EMG

Electromyography (% of initial EMG)

ε

Area-weighted emissivity of the skin (ND)

fcl

Area-weighted clothing factor (ND)

GM

Gluteus maximus

h

Combined heat transfer coefficient (W m−2 °C−1)

hc

Convective heat transfer coefficient (W m−2 °C−1)

hr

Radiative heat transfer coefficient (W m−2 °C−1)

Hprod

Rate of metabolic heat production (W m−2)

iEMG

Integrated electromyography (% of initial iEMG)

LG

Lateral gastrocnemius

LSRback

Local sweat rate on the lower back (mg cm−2 min−1)

LSRthigh

Local sweat rate on the thigh (mg cm−2 min−1)

M

Metabolic energy expenditure (W m−2)

PAR-Q

Physical Activity Readiness Questionnaire

Pa

Ambient water vapor pressure (kPa)

R

Radiant Heat exchange (W m−2)

Rcl

Thermal resistance of clothing (m2 °C W−1)

RER

Respiratory exchange ratio (ND)

RPE

Rating of perceived exertion

S

Rate of body heat storage (kJ min−1)

Scal

Rate of body heat storage measured with partitional calorimetry (kJ min−1)

Stherm

Rate of body heat storage estimated with a traditional 2-compartment thermometry model (kJ min−1)

σ

Stefan-Boltzmann constant (5.67 × 10−8W m−2 °C−4)

Ta

Ambient air temperature (°C)

ΔTb

Change in mean body temperature (°C)

Tcl

Temperature of the clothing (°C)

Tes

Esophageal temperature (°C)

ΔTest

Rate of oesophageal temperature change (°C min−1)

To

Operative temperature (°C)

Tr

Mean radiant temperature (°C)

Tre

Rectal temperature (°C)

Tsk

Mean skin temperature (°C)

VO2peak

Peak rate of oxygen consumption (L min−1)

VO2

Rate of oxygen consumption (L min−1)

v

Air velocity (m s−1)

VL

Vastus lateralis

W

Rate of external work (W m−2)

Wpeak

Peak rate of external work (W)

Notes

Acknowledgments

The authors thank the volunteers for their participation and effort. This research was supported by a Discovery Grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada (#386143-2010, held by O. Jay). Funding for the metabolic cart and dew point sensor were provided by a Canadian Foundation for Innovation (CFI) Infrastructure grant (co-applicant: O. Jay). N.M. Ravanelli was supported by a University of Ottawa Faculty of Health Sciences Research Bursary. M.N. Cramer is supported by a Postgraduate Scholarship (doctoral) from NSERC and an Excellence Scholarship from the University of Ottawa. Y. Molgat-Seon was supported by a University of Ottawa Master’s Scholarship. A.N. Carlsen is supported by NSERC and the University of Ottawa, Faculty of Health Sciences.

Conflict of interest

The authors report no competing interests, financial or otherwise.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Nicholas M. Ravanelli
    • 1
  • Matthew N. Cramer
    • 1
  • Yannick Molgat-Seon
    • 1
    • 2
  • Anthony N. Carlsen
    • 3
  • Ollie Jay
    • 1
    • 4
  1. 1.Thermal Ergonomics Laboratory, School of Human KineticsUniversity of OttawaOttawaCanada
  2. 2.Health and Integrative Physiology LaboratorySchool of Kinesiology, University of British ColumbiaVancouverCanada
  3. 3.Sensorimotor Neuroscience Laboratory, School of Human KineticsUniversity of OttawaOttawaCanada
  4. 4.Exercise and Sports Science, Faculty of Health SciencesUniversity of SydneyLidcombeAustralia

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