Effects of high-intensity progressive resistance training on self-reported health status in older persons with type 2 diabetes

Purpose: To evaluate the influence of high-intensity progressive resistance training (PRT) on self-reported physical and mental health in older persons with type 2 diabetes.

Methods: We performed a 12-month RCT with 36 overweight men and women with type 2 diabetes (aged 60-80 years) who were randomly assigned to a moderate weight-loss diet plus PRT (PRT&WL) or a moderate weight-loss diet plus a control (stretching) program (WL). Gymnasium-based training for 6 months was followed by an additional 6 months of home-based training. The SF-36 (v1) questionnaire was used to obtain physical (PCS) and mental (MCS) health component summary scores at baseline, 6 and 12 months.

Results: Subject retention was 81% and 72% after 6 and 12 months respectively. Exercise adherence during gymnasium- and home-based training was 88% and 73% for the PRT&WL group, and 85% and 78.1% for the WL group respectively. In a regression model adjusted for age and sex, PCS improved in the PRT&WL group compared to the WL group after 6 months of gymnasium-based training (2.3 versus -2.0, p = 0.05), which persisted after 12 months training (0.7 versus -4.1, p = 0.03). There were no between-group differences at 6 or 12 months for the MCS.

Conclusion: High-intensity PRT was effective in improving self-reported physical health, but not mental health. PRT provides an effective exercise alternative in lifestyle management for older adults with type 2 diabetes.

Effect of posture on high-intensity constant-load cycling performance in men and women

The time sustained during a graded cycle exercise is ~10% longer in an upright compared with a supine posture. However, during constant-load cycling this effect is unknown. Therefore, we tested the postural effect on the performance of high-intensity constant-load cycling. Twenty-two active subjects (11 men, 11 women) performed two graded tests (one upright, one supine), and of those 22, 10 subjects (5 men, 5 women) performed three high-intensity constant-load tests (one upright, two supine). To test the postural effect on performance at the same absolute intensity, during the upright and one of the supine constant-load tests subjects cycled at 80% of the peak power output achieved during the upright graded test. To test the postural effect on performance at the same relative intensities, during the second supine test subjects cycled at 80% of the peak power output achieved during the supine graded test. Exercise time on the graded and absolute intensity constant-load tests for all subjects was greater (P<0.05) in the upright compared with supine posture (17.9±3.5 vs. 16.1±3.1 min for graded; 13.2±8.7 vs. 5.2±1.9 min for constant-load). This postural effect at the same absolute intensity was larger in men (19.4±8.5 upright vs. 6.6±1.6 supine, P<0.001) than women (7.1±2 upright vs. 3.9±1.4 supine, P>0.05) and it was correlated (P<0.05) with both the difference in VO₂ between positions during the first minute of exercise (r=0.67) and the height of the subjects (r=0.72). In conclusion, there is a very large postural effect on performance during constant-load cycling exercise and this effect is significantly larger in men than women.

Metabolic adaptations to short-term high-intensity interval training : a little pain for a lot of gain?

High-intensity interval training (HIT) is a potent time-efficient strategy to induce numerous metabolic adaptations usually associated with traditional endurance training. As little as six sessions of HIT over 2 wk or a total of only approximately 15 min of very intense exercise (~600 kJ), can increase skeletal muscle oxidative capacity and endurance performance and alter metabolic control during aerobic-based exercise.

Pacing strategy and high-intensity cycling performance

This thesis found that a brief maximal acceleration, followed by a steady effort thereafter is the most effective pacing strategy for intense, short-term cycling performance. This strategy leads to an increase in aerobic energy supply early in exercise, which contributes to a faster speed throughout the race.

Exercise performance and V0₂ kinetics during upright and recumbent high-intensity cycling exercise

This study investigated cycling performance and oxygen uptake (VO₂) kinetics between upright and two commonly used recumbent (R) postures, 65ºR and 30ºR. On three occasions, ten young active males performed three bouts of high-intensity constant-load (85% peak workload achieved during a graded test) cycling in one of the three randomly assigned postures (upright, 65ºR or 30ºR). The first bout was performed to fatigue and second and third bouts were limited to 7 min. A subset of seven subjects performed a final constant-load test to failure in the supine posture. Exercise time to failure was not altered when the body inclination was lowered from the upright (13.1 ± 4.5 min) to 65ºR (10.5 ± 2.7 min) and 30ºR (11.5 ± 4.6 min) postures; but it was significantly shorter in the supine posture (5.8 ± 2.1 min) when compared with the three inclined postures. Resulting kinetic parameters from a tri-exponential analysis of breath-by-breath VO₂ data during the first 7 min of exercise were also not different between the three inclined postures. However, inert gas rebreathing analysis of cardiac output revealed a greater cardiac output and stroke volume in both recumbent postures compared with the upright posture at 30 s into the exercise. These data suggest that increased cardiac function may counteract the reduction of hydrostatic pressure from upright ~25 mmHg; to 65ºR ~22 mmHg; and 30ºR ~18 mmHg such that perfusion of active muscle presumably remains largely unchanged, and also therefore, VO₂ kinetics and performance during high-intensity cycling.

Accumulated oxygen deficit measurements during and after high-intensity exercise in trained male and female adolescents

The purpose of this study was to compare accumulated oxygen deficits and markers of anaerobic metabolism [plasma ammonia (NH3) and lactate (La⁻) concentrations] in anaerobically trained male [n = 8, age 14.8 (0.5) years; maximal oxygen consumption V˙O2 max 61.74 (2.23) ml ·  kg⁻¹ · min⁻¹] and female [n = 8, age 14.5 (0.2) years; V˙O2 max 49.62 (3.52) ml · kg⁻¹ · min⁻¹] adolescents. The exercise protocol consisted of runs to exhaustion at speeds predicted to represent 120% and 130% of V˙O2 max. Arterialised blood samples were obtained from a pre-warmed hand via a catheter inserted into a forearm vein. Samples were taken at rest and after 1, 3, 5, 7, 10, 15 and 20 min of recovery. The high-intensity exercise resulted in mean accumulated oxygen deficits that were less (P < 0.05) in females (52.3 ml · kg⁻¹) than in males (68.6 ml · kg⁻¹). Lower (P < 0.05) plasma concentrations of NH3 and La⁻¹, and a higher pH were evident in females compared with males during various stages of the 20-min recovery period. The increase in anaerobic performance in the male adolescent athletes when compared with their female counterparts was associated with an increased plasma concentration of selected plasma and blood metabolites. The observed results may reflect well-established differences between the sexes in the morphology and metabolic power of muscle.

Effect of streptozotocin-induced diabetes on glycogen resynthesis in fasted rats post-high-intensity exercise

It has recently been shown that food intake is not essential for the resynthesis of the stores of muscle glycogen in fasted animals recovering from high-intensity exercise. Because the effect of diabetes on this process has never been examined before, we undertook to explore this issue. To this end, groups of rats were treated with streptozotocin (60 mg/kg body mass ip) to induce mild diabetes. After 11 days, each animal was fasted for 24 h before swimming with a lead weight equivalent to 9% body mass attached to the tail. After exercise, the rate and the extent of glycogen repletion in muscles were not affected by diabetes, irrespective of muscle fiber composition. Consistent with these findings, the effect of exercise on the phosphorylation state of glycogen synthase in muscles was only minimally affected by diabetes. In contrast to its effects on nondiabetic animals, exercise in fasted diabetic rats was accompanied by a marked fall in hepatic glycogen levels, which, surprisingly, increased to preexercise levels during recovery despite the absence of food intake.

Fiber-specific responses of muscle glycogen repletion in fasted rats physically active during recovery from high-intensity physical exertion

Mild physical activity performed immediately after a bout of intense exercise in fasting humans results in net glycogen breakdown in their slow oxidative (SO) muscle fibers and glycogen repletion in their fast twitch (FT) fibers. Because several animal species carry a low proportion of SO fibers, it is unclear whether they can also replenish glycogen in their FT fibers under these conditions. Given that most skeletal muscles in rats are poor in SO fibers (<5%), this issue was examined using groups of 24-h fasted Wistar rats (n = 10) that swam for 3 min at high intensity with a 10% weight followed by either a 60-min rest (passive recovery, PR) or a 30-min swim with a 0.5% weight (active recovery, AR) preceding a 30-min rest. The 3-min sprint caused 61–79% glycogen fall across the muscles examined, but not in the soleus (SOL). Glycogen repletion during AR without food was similar to PR in the white gastrocnemius (WG), where glycogen increased by 71%, and less than PR in both the red and mixed gastrocnemius (RG, MG). Glycogen fell by 26% during AR in the SOL. Following AR, glycogen increased by 36%, 87%, and 37% in the SOL, RG, and MG, respectively, and this was accompanied by the sustained activation of glycogen synthase and inhibition of glycogen phosphorylase in the RG and MG. These results suggest that mammals with a low proportion of SO fibers can also replenish the glycogen stores of their FT fibers under extreme conditions combining physical activity and fasting.

Regulation of glycogen synthase and phosphorylase during recovery from high-intensity exercise in the rat

The aim of this study was to determine the role of the phosphorylation state of glycogen synthase and glycogen phosphorylase in the regulation of muscle glycogen repletion in fasted animals recovering from high-intensity exercise. Groups of rats were swum to exhaustion and allowed to recover for up to 120 min without access to food. Swimming to exhaustion caused substantial glycogen breakdown and lactate accumulation in the red, white and mixed gastrocnemius muscles, whereas the glycogen content in the soleus muscle remained stable. During the first 40 min of recovery, significant repletion of glycogen occurred in all muscles examined except the soleus muscle. At the onset of recovery, the activity ratios and fractional velocities of glycogen synthase in the red, white and mixed gastrocnemius muscles were higher than basal, but returned to pre-exercise levels within 20 min after exercise. In contrast, after exercise the activity ratios of glycogen phosphorylase in the same muscles were lower than basal, and increased to pre-exercise levels within 20 min. This pattern of changes in glycogen synthase and phosphorylase activities, never reported before, suggests that the integrated regulation of the phosphorylation state of both glycogen synthase and phosphorylase might be involved in the control of glycogen deposition after high-intensity exercise.

Repeated bouts of high-intensity exercise and muscle glycogen sparing in the rat

Even in the absence of food intake, several animal species recovering from physical activity of high intensity can replenish completely their muscle glycogen stores. In some species of mammals, such as in rats and humans, glycogen repletion is only partial, thus suggesting that a few consecutive bouts of high-intensity exercise might eventually lead to the sustained depletion of their muscle glycogen. In order to test this prediction, groups of rats with a lead weight of 10% body mass attached to their tails were subjected to either one, two or three bouts of high-intensity swimming, each bout being separated from the next by a 1 h recovery period. Although glycogen repletion after the first bout of exercise was only partial, all the glycogen mobilised in subsequent bouts was completely replenished during the corresponding recovery periods and irrespective of muscle fibre compositions. The impact of repeated bouts of high-intensity exercise on plasma levels of fatty acids, acetoacetate and β-hydroxybutyrate suggests that the metabolic state of the rat prior to the second and third bouts of exercise was different from that before the first bout. In conclusion, rats resemble other vertebrate species in that without food intake there are conditions under which they can replenish completely their muscle glycogen stores from endogenous carbon sources when recovering from high-intensity exercise. It remains to be established, however, whether this capacity is typical of mammals in general.