Older adults typically experience greater levels of thermal strain during physical efforts in the heat compared to young individuals. While this may be related to an age-dependent reduction in whole-body sweating, no study has clearly delineated at what age this occurs. In the present study, we report direct measurements of human heat dissipation during physical activity in the heat in males ranging in age from 20–70 years. Eighty-five males performed four 15-min bouts of cycling separated by 15-min rest periods, in a calorimeter regulated to 35°C and 20% relative humidity. Direct calorimetry was used to measure total heat loss (whole-body evaporative heat loss and dry heat exchange). We also used indirect calorimetry as a continuous measure of metabolic heat production. Body heat storage was calculated as the temporal summation of heat production and total heat loss over the experimental session. Whole-body sweat rate (WBSR) was calculated from measurements of evaporative heat loss. Males were divided into five age categories for the analysis of WBSR and body heat storage: 20–31 years (n = 18), 40–44 years (n = 15), 45–49 years (n = 15), 50–55 years (n = 21) and 56–70 years (n = 16). Relative to young males, WBSR was reduced in males aged 56–70 during each exercise (all P<0.05), in males aged 50–55 during the second (P = 0.031) and third exercises (P = 0.028) and in males aged 45–49 during the final exercise bout (P = 0.046). Although not significantly different, 40–44 years old males also had a lower rate of heat loss compared to younger males. Over the sum of two hours, the change in body heat content was greater in males 40–70 years compared to young males (all P<0.05). Our findings suggest that middle-aged and older adults have impairments in heat dissipation when doing physical activity in the heat, thus possibly increasing their risk of heat-related illness under such conditions.

Aim/hypothesis In people with type 2 diabetes, exercise improves glucose control (as reflected in HbA 1c ) and physical fitness, but it is not clear to what extent these exercise-induced improvements are correlated with one another. We hypothesised that reductions in HbA 1c would be related: (1) to increases in aerobic fitness and strength respectively in patients performing aerobic training or resistance training; and (2) to changes in strength and aerobic fitness in patients performing aerobic and resistance training. Methods We randomly allocated 251 type 2 diabetes patients to aerobic, resistance, or aerobic plus resistance training, or to a sedentary control group. Peak oxygen consumption (V : O 2peak ), workload, treadmill time and ventilatory threshold measurements from maximal treadmill exercise testing were measured at baseline and 6 months.Muscular strength was measured as the maximum weight that could be lifted eight times on the leg press, bench press and seated row exercises. Results With aerobic training, significant associations were found between changes in both V : O 2peak (p=0.040) and workload (p=0.022), and changes in HbA 1c. With combined training, improvements in V : O 2peak (p = 0.008), workload (p=0.034) and ventilatory threshold (p=0.003) were significantly associated with changes in HbA 1c. Increases in strength on the seated row (p=0.006) and in mid-thigh muscle cross-sectional area (p=0.030) were significantly associated with changes in HbA 1c after resistance exercise, whereas the association between increases in muscle cross-sectional area and HbA 1c in participants doing aerobic plus resistance exercise (p= 0.059) was of borderline significance. Conclusions/interpretation There appears to be a link between changes in fitness and HbA 1c . The improvements in cardiorespiratory fitness with aerobic training may be a better predictor of changes in HbA 1c than improvements in strength.

Hardcastle S, Kenny GP. Whole body heat loss is reduced in older males during short bouts of intermittent exercise. Am J Physiol Regul Integr Comp Physiol 305: R619 -R629, 2013. First published July 24, 2013 doi:10.1152/ajpregu.00157.2013.-Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short-duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (HE) and changes in body heat content (⌬Hb) between young (20 -30 yr), middle-aged (40 -45 yr), and older males (60 -70 yr) of similar body mass and surface area, during successive exercise (4 ϫ 15 min) and recovery periods (4 ϫ 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). HE was lower in older males vs. young males during each exercise (Ex1: 283 Ϯ 10 vs. 332 Ϯ 11 kJ, Ex2: 334 Ϯ 10 vs. 379 Ϯ 5 kJ, Ex3: 347 Ϯ 11 vs. 392 Ϯ 5 kJ, and Ex4: 347 Ϯ 10 vs. 387 Ϯ 5 kJ, all P Ͻ 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 Ϯ 13, Ex2: 355 Ϯ 13, Ex3: 371 Ϯ 13, and Ex4: 365 Ϯ 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ⌬Hb in older (267 Ϯ 33 kJ; P ϭ 0.016) and middle-aged adults (245 Ϯ 16 kJ; P ϭ 0.073) relative to younger counterparts (164 Ϯ 20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-aged males had a progressively greater rate of heat storage compared with young males over 2 h of intermittent exercise. evaporative heat loss; aging; calorimetry; thermal transients A NUMBER OF STUDIES HAVE EXAMINED age-related differences in thermoregulatory control during prolonged exercise (range 30 -90 min) in the heat [range: 30 -49°C/20 -60% relative humidity (RH)] (4, 11-13, 20, 23, 26, 29, 33, 34). Some studies reported no differences in thermoregulatory function (4,20,23,29,33), whereas others found significant age-related impairments in heat loss capacity (e.g., reduced local sweating rate/onset/sensitivity and/or greater increments in core and skin temperatures) (11-13, 26, 34). It is possible that these discrepancies reflect that in some studies, older adults were able to achieve heat balance, while in other studies, heat load exceeded their physiological maximal sweating capacity; hence, differences in local sweat rate and/or core temperature were evident. What these studies did not examine, however, is whether age-related impairments in heat loss capacity occur during exercise of short duration (i.e., 15 min) when the rate of heat storage has been shown to be the greatest (21).At the onset of exercise, the rate of metabolic heat production increases immediately and is not i...

Combined training did not provide additional benefits nor did it mitigate improvements in fitness in younger subjects compared with aerobic and resistance training alone. In older subjects, there was a trend to greater aerobic fitness gains with A + R versus A alone.

Aims/hypothesis Some previous studies suggested that metformin might attenuate the effects of exercise on glycaemia or fitness. We therefore examined whether metformin use influenced changes in glycaemic control, fitness, body weight or waist circumference resulting from aerobic and/or resistance training in people with type 2 diabetes participating in an exercise intervention trial. Methods After a 4 week run-in period, participants from the Diabetes Aerobic and Resistance Exercise (DARE) trial were randomly assigned to 22 weeks of aerobic training alone, resistance training alone, combined aerobic and resistance exercise training or a waiting-list control group. Of the 251 randomised, 143 participants reported using metformin throughout the entire study period and 82 reported not using metformin at all. Results Compared with control, aerobic training led to a significant reduction in HbA 1c in the metformin users (−0.57%, 95% CI −1.05, −0.10; −6.3 mmol/mol, 95% CI −11.5, −1.1) but not in the non-metformin users (−0.17, 95% CI −0.78, 0.43; −1.9 mmol/mol, 95% CI −8.5, 4.7). However, there were no significant differences in the changes in HbA 1c (or fasting glucose) between metformin users and non-users in any of the exercise groups compared with control (p>0.32 for all metformin by group by time interactions). Similarly, metformin did not affect changes in indicators of aerobic fitness, strength and body weight or waist circumference (p ≥0.15 for all metformin by group by time interactions). Conclusions/interpretation Contrary to our hypothesis and to previous short-term studies, metformin did not significantly attenuate the benefits of exercise on glycaemic control or fitness.