Table 2. Peak Responses in Patients With and Without Type 2 Diabetes During Exercise Before and After Heat Acclimationa.
| Variables, Mean (SD) | All Participants | Subgroups Completing Heat Acclimationb | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Type 2 Diabetes | Type 2 Diabetes vs No Diabetes, Difference (95% CI) | P Valuec | Type 2 Diabetes | Type 2 Diabetes vs No Diabetes, Difference (95% CI) | P Valuec | |||||
| Yes (n = 17) | No (n = 17) | Yes (n = 8) | P Valued | No (n = 10) | P Valued | |||||
| Whole-body heat loss, W/m2e | ||||||||||
| Before heat acclimation | 187 (28) | 215 (23) | −28 (−46 to −10) | .003 | 197 (20) | 225 (13) | −28 (−44 to −12) | .002 | ||
| After heat acclimation | 225 (23) | 236 (12) | −11 (−29 to 6) | .20 | ||||||
| Difference (95% CI) | 28 (15 to 41) |
.001 | 11 (1 to 22) |
.04 | 17 (2 to 32) | .03 | ||||
| Dry heat loss, W/m2e | ||||||||||
| Before acclimation | −49 (18) | −53 (19) | 4 (−9 to 17) | .52 | −45 (12) | −51 (23) | 6 (−13 to 25) | .49 | ||
| After heat acclimation | −54 (15) | −57 (13) | 3 (−11 to 17) | .63 | ||||||
| Difference (95% CI) | −9 (−20 to 1) |
.08 | −6 (−18 to 6) |
.27 | −3 (−18 to 12) | .66 | ||||
| Evaporative heat loss, W/m2e | ||||||||||
| Before heat acclimation | 236 (35) | 268 (31) | −32 (−56 to −9) | .008 | 242 (29) | 276 (26) | −34 (−62 to −7) | .02 | ||
| After heat acclimation | 279 (27) | 293 (19) | −14 (−38 to 9) | .21 | ||||||
| Difference (95% CI) | 37 (26 to 48) |
<.001 | 17 (6 to 28) |
.007 | 20 (5 to 35) | .01 | ||||
| Body heat storage, W/m2e | ||||||||||
| Before heat acclimation | 68 (32) | 40 (23) | 28 (9 to 47) | .005 | 56 (21) | 33 (17) | 23 (4 to 42) | .02 | ||
| After heat acclimation | 24 (23) | 16 (12) | 8 (−9 to 26) | .33 | ||||||
| Difference (95% CI) | −32 (−49 to −15) |
.003 | −17 (−28 to −6) |
.008 | −15 (−33 to 3) | .09 | ||||
| Change in body temperature, °Ce | ||||||||||
| Before heat acclimation | 2.2 (0.8) | 1.6 (0.5) | 0.6 (−1.1 to −0.1) | .01 | 1.8 (0.4) | 1.4 (0.3) | 0.4 (−0.0 to 0.7) | .07 | ||
| After heat acclimation | 1.3 (0.4) | 1.0 (0.4) | 0.2 (−0.2 to 0.6) | .32 | ||||||
| Difference (95% CI) | −0.5 (−0.8 to −0.2) |
.003 | −0.4 (−0.6 to −0.1) |
.008 | 0.1 (−0.2 to 0.5) | .40 | ||||
| Heart rate reserve, %e | ||||||||||
| Before heat acclimation | 84 (13) | 71 (18) | 13 (2 to 25) | .02 | 81 (15) | 71 (18) | 10 (−6 to 27) | .21 | ||
| After heat acclimation | 66 (12) | 62 (17) | 4 (−11 to 19) | .58 | ||||||
| Difference (95% CI) | −15 (−29 to −2) |
.03 | −9 (−16 to −2) |
.02 | −6 (−20 to 7) | .32 | ||||
Data represent peak responses (mean over the final 5 minutes of exercise at the highest metabolic heat production [250 W/m2]) or cumulative changes over the entire exercise protocol (change in mean body temperature) performed in dry heat (40°C, 15% relative humidity) within a direct air calorimeter (a device to precisely measure whole-body heat loss).
Subgroups refer to participants who volunteered to complete the exercise protocol again after a 7-day heat acclimation.
Between-group comparison of those with and without type 2 diabetes (unpaired 2-tailed t test).
Within-group comparison before vs after heat acclimation (paired 2-tailed t test).
Higher whole-body heat loss and evaporative heat loss with lower dry heat loss (ie, heat gain from the environment) are advantageous for thermoregulation, while lower body heat storage, mean body temperature change, and heart rate reserve indicate lower thermoregulatory and cardiovascular strain.