Pierre Boulay

Effects of Performing Resistance Exercise Before Versus After Aerobic Exercise on Glycemia in Type 1 Diabetes

OBJECTIVE To determine the effects of exercise order on acute glycemic responses in individuals with type 1 diabetes performing both aerobic and resistance exercise in the same session. RESEARCH DESIGN AND METHODS Twelve physically active individuals with type 1 diabetes (HbA1c 7.1 ± 1.0%) performed aerobic exercise (45 min of running at 60% V̇o2peak) before 45 min of resistance training (three sets of eight, seven different exercises) (AR) or performed the resistance exercise before aerobic exercise (RA). Plasma glucose was measured during exercise and for 60 min after exercise. Interstitial glucose was measured by continuous glucose monitoring 24 h before, during, and 24 h after exercise. RESULTS Significant declines in blood glucose levels were seen in AR but not in RA throughout the first exercise modality, resulting in higher glucose levels in RA (AR = 5.5 ± 0.7, RA = 9.2 ± 1.2 mmol/L, P = 0.006 after 45 min of exercise). Glucose subsequently decreased in RA and increased in AR over the course of the second 45-min exercise bout, resulting in levels that were not significantly different by the end of exercise (AR = 7.5 ± 0.8, RA = 6.9 ± 1.0 mmol/L, P = 0.436). Although there were no differences in frequency of postexercise hypoglycemia, the duration (105 vs. 48 min) and severity (area under the curve 112 vs. 59 units ⋅ min) of hypoglycemia were nonsignificantly greater after AR compared with RA. CONCLUSIONS Performing resistance exercise before aerobic exercise improves glycemic stability throughout exercise and reduces the duration and severity of postexercise hypoglycemia for individuals with type 1 diabetes.

Resistance Versus Aerobic Exercise: Acute effects on glycemia in type 1 diabetes

OBJECTIVE In type 1 diabetes, small studies have found that resistance exercise (weight lifting) reduces HbA1c. In the current study, we examined the acute impacts of resistance exercise on glycemia during exercise and in the subsequent 24 h compared with aerobic exercise and no exercise. RESEARCH DESIGN AND METHODS Twelve physically active individuals with type 1 diabetes (HbA1c 7.1 ± 1.0%) performed 45 min of resistance exercise (three sets of seven exercises at eight repetitions maximum), 45 min of aerobic exercise (running at 60% of Vo2max), or no exercise on separate days. Plasma glucose was measured during and for 60 min after exercise. Interstitial glucose was measured by continuous glucose monitoring 24 h before, during, and 24 h after exercise. RESULTS Treatment-by-time interactions (P < 0.001) were found for changes in plasma glucose during and after exercise. Plasma glucose decreased from 8.4 ± 2.7 to 6.8 ± 2.3 mmol/L (P = 0.008) during resistance exercise and from 9.2 ± 3.4 to 5.8 ± 2.0 mmol/L (P = 0.001) during aerobic exercise. No significant changes were seen during the no-exercise control session. During recovery, glucose levels did not change significantly after resistance exercise but increased by 2.2 ± 0.6 mmol/L (P = 0.023) after aerobic exercise. Mean interstitial glucose from 4.5 to 6.0 h postexercise was significantly lower after resistance exercise versus aerobic exercise. CONCLUSIONS Resistance exercise causes less initial decline in blood glucose during the activity but is associated with more prolonged reductions in postexercise glycemia than aerobic exercise. This might account for HbA1c reductions found in studies of resistance exercise but not aerobic exercise in type 1 diabetes.

The physical activity counselling (PAC) randomized controlled trial: rationale, methods, and interventions.

Primary care is a promising venue to build patient motivation and confidence to increase physical activity (PA). Physician PA counselling has demonstrated some success; however, maintenance of behaviour change appears to require more intensive interventions. In reality, most physicians do not have the necessary training nor the time for this type of counselling. The purpose of this paper is to outline the rationale, methods, and interventions for the ongoing physical activity counselling (PAC) randomized controlled trial (RCT), which aims to assess the impact of integrating a PA counsellor into a primary care practice. This RCT has 2 arms: (i) brief PA counselling (2-4 min) from a health care provider and (ii) brief PA counselling+intensive PA counselling from a PA counsellor (3 months). The impact of this intervention is being evaluated using the comprehensive RE-AIM framework. One hundred twenty insufficiently active adult patients, aged 18 to 69 y and recruited during regular primary care visits have been randomized. Dependent measures include psychological mediators, PA participation, quality of life, and physical and metabolic outcomes. The PAC project represents an innovative, theoretically-based approach to promoting PA in primary care, focusing on psychological mediators of change. We anticipate that key lessons from this study will be useful for shaping future public health interventions, theories, and research.

Age-Related Decrements in Heat Dissipation during Physical Activity Occur as Early as the Age of 40

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.

Whole-body heat loss is reduced in older males during short bouts of intermittent exercise

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 (ΔHb) 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 × 15 min) and recovery periods (4 × 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 ± 10 vs. 332 ± 11 kJ, Ex2: 334 ± 10 vs. 379 ± 5 kJ, Ex3: 347 ± 11 vs. 392 ± 5 kJ, and Ex4: 347 ± 10 vs. 387 ± 5 kJ, all P < 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 ± 13, Ex2: 355 ± 13, Ex3: 371 ± 13, and Ex4: 365 ± 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ΔHb in older (267 ± 33 kJ; P = 0.016) and middle-aged adults (245 ± 16 kJ; P = 0.073) relative to younger counterparts (164 ± 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.

Impact of integrating a physical activity counsellor into the primary health care team: physical activity and health outcomes of the Physical Activity Counselling randomized controlled trial.

The purpose of this paper was to report the physical activity and health outcomes results from the Physical Activity Counselling (PAC) trial. Patients (n = 120, mean age 47.3 ± 11.1 years, 69.2% female) who reported less than 150 min of physical activity per week were recruited from a large community-based Canadian primary care practice. After receiving brief physical activity counselling from their provider, they were randomized to receive 6 additional patient-centered counselling sessions over 3 months from a physical activity counsellor (intensive-counselling group; n = 61), or no further intervention (brief-counselling group; n = 59). Physical activity (self-reported and accelerometer) was measured every 6 weeks up to 25 weeks (12 weeks postintervention). Quality of life was also assessed, and physical and metabolic outcomes were evaluated in a randomly selected subset of patients (33%). In the intent-to-treat analyses of covariance, the intensive-counselling group self-reported significantly higher levels of physical activity at 6 weeks (p = 0.009) and 13 weeks (p = 0.01). There were no differences in self-reported physical activity between the groups after the intervention in the follow-up period, nor was there any increase in accelerometer-measured physical activity. Finally, the intensive-counselling patients showed greater decreases in percent body fat and total fat mass from 13 weeks to 25 weeks. Results for physical activity depended on the method used, with positive short-term results with self-report and no effects with the accelerometers. Between-group differences were found for body composition in that the intensive-counselling patients decreased more. A multisite randomized controlled trial with a longer intensive intervention and follow-up is warranted.

Older adults with type 2 diabetes store more heat during exercise.

INTRODUCTION 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. PURPOSE 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). CONCLUSION 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.

Age-related differences in heat loss capacity occur under both dry and humid heat stress conditions

This study examined the progression of impairments in heat dissipation as a function of age and environmental conditions. Sixty men (n = 12 per group; 20-30, 40-44, 45-49, 50-54, and 55-70 yr) performed four intermittent exercise/recovery cycles for a duration of 2 h in dry (35°C, 20% relative humidity) and humid (35°C, 60% relative humidity) conditions. Evaporative heat loss and metabolic heat production were measured by direct and indirect calorimetry, respectively. Body heat storage was measured as the temporal summation of heat production and heat loss during the sessions. Evaporative heat loss was reduced during exercise in the humid vs. dry condition in age groups 20-30 (-17%), 40-44 (-18%), 45-49 (-21%), 50-54 (-25%), and 55-70 yr (-20%). HE fell short of being significantly different between groups in the dry condition, but was greater in age group 20-30 yr (279 ± 10 W) compared with age groups 45-49 (248 ± 8 W), 50-54 (242 ± 6 W), and 55-70 yr (240 ± 7 W) in the humid condition. As a result of a reduced rate of heat dissipation predominantly during exercise, age groups 40-70 yr stored between 60-85 and 13-38% more heat than age group 20-30 yr in the dry and humid conditions, respectively. These age-related differences in heat dissipation and heat storage were not paralleled by significant differences in local sweating and skin blood flow, or by differences in core temperature between groups. From a whole body perspective, combined heat and humidity impeded heat dissipation to a similar extent across age groups, but, more importantly, intermittent exercise in dry and humid heat stress conditions created a greater thermoregulatory challenge for middle-aged and older adults.

Aging impairs heat loss, but when does it matter?

Aging is associated with an attenuated physiological ability to dissipate heat. However, it remains unclear if age-related impairments in heat dissipation only occur above a certain level of heat stress and whether this response is altered by aerobic fitness. Therefore, we examined changes in whole body evaporative heat loss (HE) as determined using whole body direct calorimetry in young (n = 10; 21 ± 1 yr), untrained middle-aged (n = 10; 48 ± 5 yr), and older (n = 10; 65 ± 3 yr) males matched for body surface area. We also studied a group of trained middle-aged males (n = 10; 49 ± 5 yr) matched for body surface area with all groups and for aerobic fitness with the young group. Participants performed intermittent aerobic exercise (30-min exercise bouts separated by 15-min rest) in the heat (40°C and 15% relative humidity) at progressively greater fixed rates of heat production equal to 300 (Ex1), 400 (Ex2), and 500 (Ex3) W. Results showed that HE was significantly lower in middle-aged untrained (Ex2: 426 ± 34; and Ex3: 497 ± 17 W) and older (Ex2: 424 ± 38; and Ex3: 485 ± 44 W) compared with young (Ex2: 472 ± 42; and Ex3: 558 ± 51 W) and middle-aged trained (474 ± 21; Ex3: 552 ± 23 W) males at the end of Ex2 and Ex3 (P < 0.05). No differences among groups were observed during recovery. We conclude that impairments in HE in older and middle-aged untrained males occur at exercise-induced heat loads of ≥400 W when performed in a hot environment. These impairments in untrained middle-aged males can be minimized through regular aerobic exercise training.

Do older females store more heat than younger females during exercise in the heat

INTRODUCTION Aging is associated with a reduction in the bodys capacity to dissipate heat. To date, few studies have examined age-related changes in thermoregulatory function during short exercise periods in the heat in older females. PURPOSE This study aimed to investigate the effects of age on whole-body heat loss during intermittent exercise in the heat in young and older females. METHODS Direct and indirect calorimetry was used to measure whole-body evaporative heat loss (EHL), change in body heat content, and metabolic heat production. Eleven young (Y) (mean ± SD age = 24 ± 4 yr) and 13 older (O) (51 ± 8 yr) females matched for body surface area (Y, 1.72 ± 0.15; O, 1.75 ± 0.12 m²) and fitness (V(˙)O(2max)) (Y, 36.7 ± 6.8 mL O₂·kg⁻¹·min⁻¹; O, 33.8 ± 8.0 mL O₂·kg⁻¹·min⁻¹) performed four bouts of 15-min cycling (Ex1, Ex2, Ex3, and Ex4) at a constant rate of heat production (300 W) at 35°C and 20% relative humidity. Each exercise bout was separated by 15 min of rest. RESULTS EHL was reduced in O compared with Y during Ex1 (O, 199 ± 6 W; Y, 240 ± 9 W; P = 0.001), Ex2 (O, 238 ± 4 W; Y, 261 ± 9 W, P = 0.023), and Ex3 (O, 249 ± 4 W; Y, 274 ± 11 W; P = 0.040). EHL was not different between groups during Ex4 or during the recovery periods. Older females had a greater change in body heat content compared with young females (O, 270 ± 20 kJ; Y, 166 ± 20 kJ; P = 0.001). CONCLUSION These findings suggest that older females have a lower capacity for whole-body EHL compared with younger females during short intermittent exercise in the heat performed at a fixed rate of metabolic heat production.