Maureen J. MacDonald

Similar metabolic adaptations during exercise after low volume sprint interval and traditional endurance training in humans

Low‐volume ‘sprint’ interval training (SIT) stimulates rapid improvements in muscle oxidative capacity that are comparable to levels reached following traditional endurance training (ET) but no study has examined metabolic adaptations during exercise after these different training strategies. We hypothesized that SIT and ET would induce similar adaptations in markers of skeletal muscle carbohydrate (CHO) and lipid metabolism and metabolic control during exercise despite large differences in training volume and time commitment. Active but untrained subjects (23 ± 1 years) performed a constant‐load cycling challenge (1 h at 65% of peak oxygen uptake before and after 6 weeks of either SIT or ET (n= 5 men and 5 women per group). SIT consisted of four to six repeats of a 30 s ‘all out’ Wingate Test (mean power output ∼500 W) with 4.5 min recovery between repeats, 3 days per week. ET consisted of 40–60 min of continuous cycling at a workload that elicited ∼65% (mean power output ∼150 W) per day, 5 days per week. Weekly time commitment (∼1.5 versus∼4.5 h) and total training volume (∼225 versus∼2250 kJ week−1) were substantially lower in SIT versus ET. Despite these differences, both protocols induced similar increases (P < 0.05) in mitochondrial markers for skeletal muscle CHO (pyruvate dehydrogenase E1α protein content) and lipid oxidation (3‐hydroxyacyl CoA dehydrogenase maximal activity) and protein content of peroxisome proliferator‐activated receptor‐γ coactivator‐1α. Glycogen and phosphocreatine utilization during exercise were reduced after training, and calculated rates of whole‐body CHO and lipid oxidation were decreased and increased, respectively, with no differences between groups (all main effects, P < 0.05). Given the markedly lower training volume in the SIT group, these data suggest that high‐intensity interval training is a time‐efficient strategy to increase skeletal muscle oxidative capacity and induce specific metabolic adaptations during exercise that are comparable to traditional ET.

Physiological adaptations to low‐volume, high‐intensity interval training in health and disease

Abstract  Exercise training is a clinically proven, cost‐effective, primary intervention that delays and in many cases prevents the health burdens associated with many chronic diseases. However, the precise type and dose of exercise needed to accrue health benefits is a contentious issue with no clear consensus recommendations for the prevention of inactivity‐related disorders and chronic diseases. A growing body of evidence demonstrates that high‐intensity interval training (HIT) can serve as an effective alternate to traditional endurance‐based training, inducing similar or even superior physiological adaptations in healthy individuals and diseased populations, at least when compared on a matched‐work basis. While less well studied, low‐volume HIT can also stimulate physiological remodelling comparable to moderate‐intensity continuous training despite a substantially lower time commitment and reduced total exercise volume. Such findings are important given that ‘lack of time’ remains the most commonly cited barrier to regular exercise participation. Here we review some of the mechanisms responsible for improved skeletal muscle metabolic control and changes in cardiovascular function in response to low‐volume HIT. We also consider the limited evidence regarding the potential application of HIT to people with, or at risk for, cardiometabolic disorders including type 2 diabetes. Finally, we provide insight on the utility of low‐volume HIT for improving performance in athletes and highlight suggestions for future research.

Effect of whole body resistance training on arterial compliance in young men.

The effect of resistance training on arterial stiffening is controversial. We tested the hypothesis that resistance training would not alter central arterial compliance. Young healthy men (age, 23 ± 3.9 (mean ±s.e.m.) years; n= 28,) were whole‐body resistance trained five times a week for 12 weeks, using a rotating 3‐day split‐body routine. Resting brachial blood pressure (BP), carotid pulse pressure, carotid cross‐sectional compliance (CSC), carotid initima–media thickness (IMT) and left ventricular dimensions were evaluated before beginning exercise (PRE), after 6 weeks of exercise (MID) and at the end of 12 weeks of exercise (POST). CSC was measured using the pressure‐sonography method. Results indicate reductions in brachial (61.1 ± 1.4 versus 57.6 ± 1.2 mmHg; P < 0.01) and carotid pulse pressure (52.2 ± 1.9 versus 46.8 ± 2.0 mmHg; P < 0.01) PRE to POST. In contrast, carotid CSC, β‐stiffness index, IMT and cardiac dimensions were unchanged. In young men, central arterial compliance is unaltered with 12 weeks of resistance training and the mechanisms responsible for cardiac hypertrophy and reduced arterial compliance are either not inherent to all resistance‐training programmes or may require a prolonged stimulus.

Carbohydrate Does Not Augment Exercise-Induced Protein Accretion versus Protein Alone

PURPOSE We tested the thesis that CHO and protein coingestion would augment muscle protein synthesis (MPS) and inhibit muscle protein breakdown (MPB) at rest and after resistance exercise. METHODS Nine men (age=23.0±1.9 yr, body mass index=24.2±2.1 kg·m) performed two unilateral knee extension trials (four sets×8-12 repetitions to failure) followed by consumption of 25 g of whey protein (PRO) or 25 g of whey protein plus 50 g of maltodextrin (PRO+CARB). Muscle biopsies and stable isotope methodology were used to measure MPS and MPB. RESULTS The areas under the glucose and insulin curves were 17.5-fold (P<0.05) and 5-fold (P<0.05) greater, respectively, for PRO+CARB than for PRO. Exercise increased MPS and MPB (both P<0.05), but there were no differences between PRO and PRO+CARB in the rested or exercised legs. Phosphorylation of Akt was greater in the PRO+CARB than in the PRO trial (P<0.05); phosphorylations of Akt (P=0.05) and acetyl coA carboxylase-β (P<0.05) were greater after exercise than at rest. The concurrent ingestion of 50 g of CHO with 25 g of protein did not stimulate mixed MPS or inhibit MPB more than 25 g of protein alone either at rest or after resistance exercise. CONCLUSIONS Our data suggest that insulin is not additive or synergistic to rates of MPS or MPB when CHO is coingested with a dose of protein that maximally stimulates rates of MPS.

Low-volume, high-intensity interval training in patients with CAD

PURPOSE Isocaloric interval exercise training programs have been shown to elicit improvements in numerous physiological indices in patients with CAD. Low-volume high-intensity interval exercise training (HIT) is effective in healthy populations; however, its effectiveness in cardiac rehabilitation has not been established. This study compared the effects of 12-wk of HIT and higher-volume moderate-intensity endurance exercise (END) on brachial artery flow-mediated dilation (FMD) and cardiorespiratory fitness (VO2 peak) in patients with CAD. METHODS Twenty-two patients with documented CAD were randomized into HIT (n = 11) or END (n = 11) based on pretraining FMD. Both groups attended two supervised sessions per week for 12 wk. END performed 30-50 min of continuous cycling at 58% peak power output (PPO), whereas HIT performed ten 1-min intervals at 89% PPO separated by 1-min intervals at 10% PPO per session. RESULTS Relative FMD was increased posttraining (END, 4.4% ± 2.6% vs 5.9% ± 3.6%; HIT, 4.6% ± 3.6% vs 6.1% ± 3.4%, P ≤ 0.001 pre- vs posttraining) with no differences between groups. A training effect was also observed for relative VO2 peak (END, 18.7 ± 5.7 vs 22.3 ± 6.1 mL · kg(-1) · min(-1); HIT, 19.8 ± 3.7 vs 24.5 ± 4.5 mL · kg(-1) · min(-1), P < 0.001 for pre- vs posttraining), with no group differences. CONCLUSIONS Low-volume HIT provides an alternative to the current, more time-intensive prescription for cardiac rehabilitation. HIT elicited similar improvements in fitness and FMD as END, despite differences in exercise duration and intensity.

Bolus Arginine Supplementation Affects neither Muscle Blood Flow nor Muscle Protein Synthesis in Young Men at Rest or After Resistance Exercise

The aim of this study was to investigate the ergogenic potential of arginine on NO synthesis, muscle blood flow, and skeletal muscle protein synthesis (MPS). Eight healthy young men (22.1 ± 2.6 y, 1.79 ± 0.06 m, 76.6 ± 6.2 kg; mean ± SD) participated in 2 trials where they performed a bout of unilateral leg resistance exercise and ingested a drink containing either 10 g essential amino acids with 10 g l-arginine (ARG) or an isonitrogenous control (CON). Femoral artery blood flow of both the nonexercised and exercised leg was measured continuously using pulsed-wave Doppler ultrasound, while rates of mixed and myofibrillar MPS were determined using a primed continuous infusion of L-[ring-(13)C(6)] or L-[ring-(2)H(5)]phenylalanine. The plasma arginine concentration increased 300% during the ARG trial but not during the CON trial (P < 0.001). Plasma nitrate, nitrite, and endothelin-1, all markers of NO synthesis, did not change during either the ARG or CON trial. Plasma growth hormone increased to a greater degree after exercise in the ARG trial than CON trial (P < 0.05). Femoral artery blood flow increased 270% above basal in the exercised leg (P < 0.001) but not in the nonexercised leg, with no differences between the ARG and CON trials. Mixed and myofibrillar MPS were both greater in the exercised leg compared with the nonexercised leg (P < 0.001), but did not differ between the ARG and CON treatments. We conclude that an oral bolus (10 g) of arginine does not increase NO synthesis or muscle blood flow. Furthermore, arginine does not enhance mixed or myofibrillar MPS either at rest or after resistance exercise beyond that achieved by feeding alone.

The hypotensive effects of isometric handgrip training using an inexpensive spring handgrip training device.

PURPOSE Research has demonstrated the efficacy of isometric handgrip (IHG) training to attenuate resting blood pressure. These studies have relied on the use of programmable digital handgrips for training. This study aimed to determine the effectiveness of simple, inexpensive spring-loaded handgrip devices in producing hypotensive effects. METHODS The study was a randomized controlled trial of 49 normotensive participants (66.4 ± 0.9 years; 57% women). Participants in the exercise group (n = 25) trained and had blood pressure measured twice weekly for 8 weeks. Control participants (n = 24) completed weekly blood pressure measurements. Pre- and posttraining measurements were each assessed over 3 visits. Statistical analysis of the pre-post data involved analyses of variance and hierarchical linear modeling was used to examine changes over time. RESULTS Following 8 weeks, IHG participants demonstrated significant reductions in resting blood pressure. Systolic and diastolic blood pressures were reduced from 122 ± 3 mm Hg to 112 ± 3 mm Hg (P < .001) and from 70 ± 1 mm Hg to 67 ± 1 mm Hg (P < .05), respectively. Hierarchical linear modeling analysis also revealed a significant cross-level (ie, group ÷ time) interaction, with an estimated reduction in systolic blood pressure of 5.4 mm Hg (P < .001) over the training period in the IHG group. CONCLUSIONS In agreement with previous studies, IHG training reduced resting arterial pressure following 8 weeks of training. Hypotensive effects linked to IHG training may be achieved using simple, inexpensive spring handgrip training devices and may provide a convenient and affordable therapeutic alternative or adjunctive therapy for lowering blood pressure.

Effect of glycogen availability on human skeletal muscle protein turnover during exercise and recovery

We examined the effect of carbohydrate (CHO) availability on whole body and skeletal muscle protein utilization at rest, during exercise, and during recovery in humans. Six men cycled at approximately 75% peak O(2) uptake (Vo(2peak)) to exhaustion to reduce body CHO stores and then consumed either a high-CHO (H-CHO; 71 + or - 3% CHO) or low-CHO (L-CHO; 11 + or - 1% CHO) diet for 2 days before the trial in random order. After each dietary intervention, subjects received a primed constant infusion of [1-(13)C]leucine and l-[ring-(2)H(5)]phenylalanine for measurements of the whole body net protein balance and skeletal muscle protein turnover. Muscle, breath, and arterial and venous blood samples were obtained at rest, during 2 h of two-legged kicking exercise at approximately 45% of kicking Vo(2peak), and during 1 h of recovery. Biopsy samples confirmed that the muscle glycogen concentration was lower in the L-CHO group versus the H-CHO group at rest, after exercise, and after recovery. The net leg protein balance was decreased in the L-CHO group compared with at rest and compared with the H-CHO condition, which was primarily due to an increase in protein degradation (area under the curve of the phenylalanine rate of appearance: 1,331 + or - 162 micromol in the L-CHO group vs. 786 + or - 51 micromol in the H-CHO group, P < 0.05) but also due to a decrease in protein synthesis late in exercise. There were no changes during exercise in the rate of appearance compared with rest in the H-CHO group. Whole body leucine oxidation increased above rest in the L-CHO group only and was higher than in the H-CHO group. The whole body net protein balance was reduced in the L-CHO group, largely due to a decrease in whole body protein synthesis. These data extend previous findings by others and demonstrate, using contemporary stable isotope methodology, that CHO availability influences the rates of skeletal muscle and whole body protein synthesis, degradation, and net balance during prolonged exercise in humans.

The effects of body-weight supported treadmill training on cardiovascular regulation in individuals with motor-complete SCI

Study design:Four-month longitudinal within-subject exercise training study.Objective:Although body-weight supported treadmill training (BWSTT) has not shown promise as a means of improving ambulation in individuals with motor-complete spinal cord injury (SCI), it may still improve cardiovascular health and function in this population. The purpose of this study was to (i) investigate the effects of BWSTT on peripheral muscular and elastic artery dimension and function and measures of heart rate variability (HRV) and blood pressure variability (BPV) in individuals with motor-complete SCI, and (ii) to make a preliminary examination of what factors may predict favourable cardiovascular outcomes following BWSTT in this population.Setting:Centre for Health Promotion and Rehabilitation, McMaster University, Hamilton, Ontario, Canada.Methods:Six individuals (four male, two female; age 37.7±15.4 years) with chronic SCI (C4-T12; ASIA A-B; 7.6±9.4 years post-injury) were included in the present investigation. Doppler ultrasound was used to determine femoral (exercising; muscular), carotid (elastic) and brachial (nonexercising control; muscular) artery dimension and function before and after 4 months of BWSTT. Continuous heart rate and blood pressure were also recorded before and after 4-months of BWSTT to determine frequency domain measures of HRV and BPV; clinically valuable indices of neurocardiac and neurovascular control, respectively.Results:Two-way ANOVA (vessel × time) revealed no exercise-induced change in femoral or carotid artery cross-sectional area, blood flow or resistance and no change in carotid artery compliance following the 4 months of BWSTT compared to the nonexercising control brachial artery. However, there was a significant exercise-induced increase in femoral artery compliance. There were no exercise-induced changes in HRV or BPV when all participants were considered together. However, the results suggest that the subgroup of individuals who had a substantial heart rate response to BWSTT (n=3), experienced exercise-training induced changes in HRV reflective of a relative shift toward cardiac vagal predominance and reductions in BPV.Conclusions:BWSTT may cause an increase in femoral artery compliance in individuals with motor-complete SCI and therefore, should be encouraged as a means of improving cardiovascular health in this population. BWSTT may also cause modest improvements in measures of HRV and BPV in a select subgroup of individuals who respond to ambulation with moderate to large increases in HR. In the present study, factors associated with a substantial HR response to BWSTT were a propensity to orthostatic intolerance and muscular spasticity.

Effects of isometric handgrip training among people medicated for hypertension: a multilevel analysis.

ObjectiveTo examine the longitudinal effects of isometric handgrip (IHG) exercise training on blood pressure using hierarchical linear modeling. MethodsData from 43 participants who were medicated for hypertension at the time of training were amalgamated from three previous investigations. In each study, IHG training was completed 3 days/week for 8 weeks at 30% of maximal voluntary contraction and resting blood pressure was assessed at twice-weekly intervals throughout. ResultsHierarchical linear modeling analysis revealed a linear pattern of blood pressure decline over time with estimated reductions of 5.7 and 3 mmHg reductions in systolic and diastolic pressure, respectively. Participants with higher initial systolic pressure showed greater rates of blood pressure decline (r=−0.67), inferring that individuals with higher blood pressure stand to achieve greater benefits from this method of training. ConclusionsThese results provide further evidence that IHG training lowers resting blood pressure among persons medicated for hypertension.