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Menstrual Cycle Phase does not Influence Whole Body Heat Loss Responses During Exercise in the Heat
Author(s) -
Dervis Sheila,
Poirier Martin P.,
Paull Gabrielle,
Zhang Sarah Y.,
Kenny Glen P.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1290.14
Subject(s) - menstrual cycle , follicular phase , endocrinology , luteal phase , medicine , estrogen , calorimetry , chemistry , thermoregulation , hormone , thermodynamics , physics
Traditionally, female reproductive hormones (i.e., estrogen and progesterone) have been shown to independently influence local thermal responses during exercise in the heat. Consequently, studies examining thermal responses during exercise usually only test females during the early follicular phase of the menstrual cycle (i.e., first five days) when estrogen and progesterone are at their lowest levels. However, it remains unclear whether local thermal responses translate into comparable changes in whole‐body heat loss throughout the menstrual cycle. Therefore, we examined changes in whole‐body evaporative heat loss as determined using direct calorimetry in the early follicular (i.e., when both estrogen and progesterone levels are low), late follicular (i.e., when estrogen levels are high) and mid‐luteal (i.e., when both progesterone and estrogen levels are high) phases in young females (n=5, 21±2 years). Participants performed three 30‐min bouts of semi‐recumbent cycling at a fixed rate of metabolic heat production equal to 250 (Ex1), 325 (Ex2) and 415 W (Ex3) in the heat (40°C and 15% relative humidity), each bout followed by 15‐min of recovery. Whole‐body heat loss (evaporative and dry) and metabolic heat production were measured by direct and indirect calorimetry, respectively. Whole‐body heat content was calculated as the temporal summation of heat production and heat loss. Our preliminary results demonstrate that the combined rate of metabolic heat production and dry heat gain (i.e., net heat load) was similar between hormonal phases throughout the incremental intermittent exercise protocol (P>0.05). The rate of whole‐body evaporative heat loss measured during the early follicular (Ex1: 259±10 W, Ex2: 328±17 W, Ex3: 353±20 W), late follicular (Ex1: 248±27 W, Ex2: 306±36 W, Ex3: 337±31 W) and mid‐luteal phases (Ex1: 246±21 W, Ex2: 304±52 W, Ex3: 346±46 W) of the menstrual cycle were similar between phases for each exercise bout (P≥0.05). Accordingly, whole‐body heat content was also similar (early follicular: Ex1: 124±80 kJ, Ex2: 147±80 kJ, Ex3: 247±78 kJ; late follicular: Ex1: 125±27 kJ, Ex2: 139±17 kJ, Ex3: 180±59 kJ; mid‐luteal: Ex1: 121±28 kJ, Ex2: 147±39 kJ, Ex3: 213±49 kJ) (P>0.05). Our preliminary findings suggest that ovarian hormone fluctuations (i.e., estrogen and progesterone) during the menstrual cycle in young females do not influence whole‐body heat dissipation and therefore the amount of heat stored during exercise in the heat. Support or Funding Information Funding support: This study was supported by grants from the Natural Sciences and Engineering Research Council of Canada (Discover grant, RGPIN‐06313‐2014; Discovery Grants Program ‐ Accelerator Supplement, RGPAS‐462252‐2014; funds held by Dr. Glen P. Kenny).