title: Older adults with type 2 diabetes store more heat during exercise.
abstract: BACKGROUND
  It is unknown if diabetes-related reductions in local skin blood flow (SkBF) and sweating (LSR) measured during passive heat stress translate into greater heat storage during exercise in the heat in individuals with type 2 diabetes (T2D) compared with nondiabetic control (CON) subjects.
  
  
  OBJECTIVE
  This study aimed to examine the effects of T2D on whole-body heat exchange during exercise in the heat.
  
  
  METHODS
  Ten adults (6 males and 4 females) with T2D and 10 adults (6 males and 4 females) without diabetes matched for age, sex, body surface area, and body surface area and aerobic fitness cycled continuously for 60 min at a fixed rate of metabolic heat production (∼370 W) in a whole-body direct calorimeter (30°C and 20% relative humidity). Upper back LSR, forearm SkBF, rectal temperature, and heart rate were measured continuously. Whole-body heat loss and changes in body heat content (ΔHb) were determined using simultaneous direct whole-body and indirect calorimetry.
  
  
  RESULTS
  Whole-body heat loss was significantly attenuated from 15 min throughout the remaining exercise with the differences becoming more pronounced over time for T2D relative to CON (P = 0.004). This resulted in a significantly greater ΔHb in T2D (367 ± 35; CON, 238 ± 25 kJ, P = 0.002). No differences were measured during recovery (T2D, -79 ± 23; CON, -132 ± 23 kJ, P = 0.083). By the end of the 60-min recovery, the T2D group lost only 21% (79 kJ) of the total heat gained during exercise, whereas their nondiabetic counterparts lost in excess of 55% (131 kJ). No difference were observed in LSR, SkBF, rectal temperature or heart rate during exercise. Similarly, no differences were measured during recovery with the exception that heart rate was elevated in the T2D group relative to CON (p=0.004).
  
  
  CONCLUSIONS
  Older adults with T2D have a reduced capacity to dissipate heat during exercise, resulting in a greater heat storage and therefore level of thermal strain.
authors.affiliation: 1Human and Environmental Physiology Research Unit, University of Ottawa, Ottawa, CANADA; 2Faculty of Physical Education and Sports, University of Sherbrooke, Sherbrooke, QC, CANADA; and 3Departments of Medicine, Cardiac Sciences and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Calgary, AB, CANADA.
authors.forename: Glen P
authors.initials: GP
authors.lastname: Kenny
authors.forename: Jill M
authors.initials: JM
authors.lastname: Stapleton
authors.forename: Jane E
authors.initials: JE
authors.lastname: Yardley
authors.forename: Pierre
authors.initials: P
authors.lastname: Boulay
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Sigal
mesh_terms: D000375:Aging / Q000502:physiology*; D001642:Bicycling / Q000502:physiology; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000502:physiology*; D016022:Case-Control Studies; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D005082:Physical Exertion / Q000502:physiology*; D012039:Regional Blood Flow; D012867:Skin / Q000098:blood supply; D013546:Sweating