Katharine D. Currie

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.

Flow-Mediated Dilation Is Acutely Improved after High-Intensity Interval Exercise

PURPOSE Cardiovascular disease is characterized by decreased endothelial function. Chronic exercise training improves endothelial function in individuals with cardiovascular diseases; however, the acute endothelial responses to a single bout of exercise are not consistent in the literature. This study investigated whether a single bout of moderate-intensity endurance exercise (END) and low-volume high-intensity interval exercise (HIT) on a cycle ergometer resulted in similar acute changes in endothelial function. METHODS Ten individuals (66 ± 11 yr) with coronary artery disease (CAD) participated in two exercise sessions (END and HIT). Endothelial-dependent function was assessed using brachial artery flow-mediated dilation (FMD) preexercise and 60 min postexercise. Brachial artery diameters and velocities were determined using Doppler ultrasound before and after a 5 min ischemic period at all time points. Endothelial-independent function was assessed using a 0.4-mg sublingual dose of nitroglycerin. RESULTS The total work performed was higher in END (166 ± 52 kJ) compared with HIT (93 ± 28 kJ) exercise (P < 0.001). Endothelial-dependent function improved (P = 0.01) after END (absolute FMD preexercise, 0.24 ± 0.18 mm; postexercise, 0.31 ± 0.24 mm) and HIT (absolute FMD preexercise, 0.25 ± 0.13 mm; postexercise, 0.29 ± 0.13 mm), with no differences between exercise conditions. A time effect for FMD normalized to the shear rate area under the curve was also observed (P = 0.02) after END (preexercise, 0.005 ± 0.004; postexercise, 0.010 ± 0.011) and HIT (preexercise, 0.005 ± 0.004; postexercise, 0.009 ± 0.011). Endothelial-independent function responses were unchanged after END and HIT (P > 0.05). CONCLUSIONS HIT and END resulted in similar acute increases in brachial artery endothelial-dependent function in a population with dysfunction at rest, despite the difference in exercise intensities.

Heart rate recovery and heart rate variability are unchanged in patients with coronary artery disease following 12 weeks of high-intensity interval and moderate-intensity endurance exercise training.

Decreased heart rate variability and attenuated heart rate recovery following exercise are associated with an increased risk of mortality in cardiac patients. This study investigated the effects of 12 weeks of moderate-intensity endurance exercise (END) and a novel low-volume high-intensity interval exercise protocol (HIT) on measures of heart rate recovery and heart rate variability in patients with coronary artery disease (CAD). Fourteen males with CAD participated in 12 weeks of END or HIT training, each consisting of 2 supervised exercise sessions per week. END consisted of 30-50 min of continuous cycling at 60% peak power output (PPO). HIT involved ten 1-min intervals at 88% PPO separated by 1-min intervals at 10% PPO. Heart rate recovery at 1 min and 2 min was measured before and after training (pre- and post-training, respectively) using a submaximal exercise bout. Resting time and spectral and nonlinear domain measures of heart rate variability were calculated. Following 12 weeks of END and HIT, there was no change in heart rate recovery at 1 min (END, 40 ± 12 beats·min(-1) vs. 37 ± 19 beats·min(-1); HIT, 31 ± 8 beats·min(-1) vs. 35 ± 8 beats·min(-1); p ≥ 0.05 for pre- vs. post-training) or 2 min (END, 44 ± 18 beats·min(-1) vs. 43 ± 19 beats·min(-1); HIT, 42 ± 10 beats·min(-1) vs. 50 ± 6 beats·min(-1); p ≥ 0.05 for pre- vs. post-training). All heart rate variability indices were unchanged following END and HIT training. In conclusion, neither END nor HIT exercise programs elicited training-induced improvements in cardiac autonomic function in patients with CAD. The absence of improvements with training may be attributed to the optimal medical management and normative pretraining state of our sample.

Passive hind-limb cycling improves cardiac function and reduces cardiovascular disease risk in experimental spinal cord injury

Using a wide array of experimental approaches, we demonstrate for the first time that spinal cord injury is associated with a rapid and sustained impairment in cardiac structure and function that is present as early as 1 week post‐injury. We provide novel data demonstrating that spinal cord injury elicits an altered Starling curve and myocardial fibrosis. The latter of these may be secondary to an up‐regulation of transforming growth factor beta‐1 and mothers against decapentaplegic homolog 3 mRNA, both of which form part of a well‐known fibrotic signalling pathway. Passive hind‐limb cycling averts the spinal cord injury‐induced impairments in cardiac structure and function, prevents myocardial fibrosis and improves blood lipid profiles. Passive lower‐limb cycling represents an elegant, cost‐effective and widely accessible therapeutic strategy that may reduce the clinical cardiovascular burden imposed by spinal cord injury and other neurological disorders.

Noninvasive measures of vascular health are reliable in preschool-aged children

Measures of vascular health are known to be important predictors of cardiovascular disease in adulthood. The reliability of commonly used measures of vascular health has been demonstrated in school-aged children, adolescents, and adults; however, their reliability in preschool-aged children remains to be determined. Twenty 2- to 6-year-old children participated in 2 identical testing sessions on different days. Following 10 min of supine rest, carotid artery blood pressures and common carotid artery images were assessed simultaneously for 10 heart cycles, using applanation tonometry and B-mode ultrasound, respectively, while electrocardiogram (ECG) and infrared measures of arterial pressure waves at the dorsalis pedis were recorded continuously. Brachial artery blood pressures were determined using an automated oscillometric device. Carotid artery diameters and intima-media thickness (IMT) were analyzed using a semiautomated detection software program. Carotid compliance, distensibility, and stiffness index were calculated from carotid diameters and carotid blood pressures. Whole-body pulse-wave velocity (PWV) was determined from the time delay between the R spike of the ECG and the foot of the dorsalis pedis arterial pressure wave. Reliability of all measures was assessed using the coefficient of variation (CV) and the intraclass correlation coefficient (ICC). The most reliable measures were carotid artery IMT and PWV with CVs of 2.6% and 3.5% and ICCs of 0.86 and 0.76, respectively. The lower reliability of carotid compliance and distensibility (ICC≤0.63) is likely attributable to the variability of blood pressure measurements. This study confirms that vascular measurements demonstrate substantial reliability in preschool-aged children as young as 2 years.

Effects of resistance training combined with moderate-intensity endurance or low-volume high-intensity interval exercise on cardiovascular risk factors in patients with coronary artery disease

OBJECTIVES To determine the effects of resistance training combined with either moderate-intensity endurance or low-volume high-intensity interval training on cardiovascular risk profiles in patients with coronary artery disease. DESIGN Factorial repeated-measures study design. METHODS Nineteen patients were randomized into moderate-intensity endurance (n = 10) or high-intensity interval (n = 9) groups, and attended 2 supervised exercise sessions a week for 6-months. The first 3-months involved exclusive moderate-intensity endurance or high-intensity interval exercise, after which progressive resistance training was added to both groups for the remaining 3-months. Fitness (VO(2)peak), blood pressure and heart rate, lipid profiles and health related quality of life assessments were performed at pretraining, 3 and 6-months training. RESULTS VO(2)peak increased from pretraining to 3-months in both groups (moderate-intensity endurance: 19.8 ± 7.3 vs. 23.2 ± 7.4 ml kg(-1)min(-1); high-intensity interval: 21.1 ± 3.3 vs. 26.4 ± 5.2 ml kg(-1)min(-1), p<0.001) with no further increase at 6-months. Self-evaluated health and high-density lipoprotein were increased following 6-months of moderate-intensity endurance exercise, while all remaining indices were unchanged. Low-volume high-intensity interval exercise did not elicit improvements in lipids or health related quality of life. Blood pressures and heart rates were unchanged with training in both groups. CONCLUSIONS Findings from our pilot study suggest improvements in fitness occur within the first few months of training in patients with coronary artery disease, after which the addition of resistance training to moderate-intensity endurance and high-intensity interval exercise elicited no further improvements. Given the importance of resistance training in cardiac rehabilitation, additional research is required to determine its effectiveness when combined with high-intensity interval exercise.

Peak heart rates and sympathetic function in tetraplegic nonathletes and athletes.

PURPOSE To examine differences in peak heart rate (HR) and measures of sympathetic function between nonathletes and athletes with chronic, motor-complete, cervical spinal cord injury (SCI). METHODS Eight nonathletic men with SCI (C4-C7; age 47 ± 9 yr, with injury duration of 16 ± 9 yr) and 13 athletic men with SCI (C5-C8; age 37 ± 8 yr, with injury duration of 16 ± 6 yr) participated in the study. Measures of sympathetic function included palmar sympathetic skin responses (SSR) to median nerve stimulation, and systolic (SBP) and diastolic (DBP) blood pressure responses to a passive sit-up test. Peak HR responses were assessed during a maximal exercise test. RESULTS Compared to the athletic group, the nonathletic group exhibited lower peak HR (102 ± 34 vs 161 ± 20 bpm, P < 0.001) and average SSR scores (0.13 ± 0.35 vs 2.41 ± 1.97, P = 0.008), along with greater reductions in SBP and DBP in response to passive sit-up (SBP: -22 ± 10 vs -9 ± 12 mm Hg, P = 0.019; DBP: -18 ± 8 mm Hg vs -4 ± 9 mm Hg, P = 0.003). On the basis of the criteria for orthostatic hypotension (OH) (drop in SBP ≥ 20 mm Hg or DBP ≥ 10 mm Hg), 88% and 23% of nonathletes and athletes had OH. CONCLUSIONS Attenuated peak HR in nonathletic individuals with tetraplegia may be secondary to impairments in sympathetic function including absent SSR and OH. Furthermore, the degree of preserved sympathetic function documented in tetraplegic athletes may suggest a predisposition to engage in high-performance sports. Collectively, our findings provide novel insight into the importance of the sympathetic nervous system for exercise performance.

Brachial Artery Endothelial Responses during Early Recovery from an Exercise Bout in Patients with Coronary Artery Disease

This study examined the acute endothelial responses to an exercise bout in coronary artery disease (CAD) patients. Nineteen males with CAD (63 ± 8 years) were assessed at rest and 15 minutes following a submaximal exercise bout (recovery). Brachial artery endothelial-dependent function was assessed using flow-mediated dilation (FMD). Brachial artery diameters and velocities were measured using Duplex ultrasound at baseline, and for 3 minutes following a 5-minute ischemic period. Endothelial-independent function was assessed using a 0.4 mg dose of nitroglycerin (NTG). FMD responses were unchanged from rest to recovery; however, there were 2 types of responses: negative and positive FMD responders. Post-hoc analysis revealed that positive responders had lower resting FMD compared to negative responders (3.2 ± 1.7 versus 6.0 ± 2.5%, P < 0.05). NTG-mediated dilation was reduced in recovery (22.0 ± 5.6 versus 14.4 ± 5.7%, P < 0.001 for rest versus recovery). In conclusion, acute endothelial-dependent responses to submaximal exercise are affected by the degree of resting endothelial dysfunction. The observation of attenuated NTG-mediated dilation during recovery is novel and warrants the investigation of possible mechanisms and clinical significance. Furthermore, it highlights the necessity of both endothelial-dependent and endothelial-independent assessments when evaluating endothelial function changes with an intervention.

Interval exercise is a path to good health, but how much, how often and for whom?

Interval exercise training has now been examined in a wide variety of individuals, ranging from elite athletes to patients with severe cardiovascular disease. The advantages of interval exercise training programmes in comparison with constant intensity exercise programmes are that they appear to deliver superior improvements in several cardiovascular risk factors, fitness and performance. Depending on the design, some interval exercise programmes result in a range of benefits, even though the time commitment may be dramatically less than more traditional continuous intensity programmes. In the present issue of Clinical Science, a study by Tjønna and co-workers demonstrates that aerobic interval training may also be a powerful tool in combating the increased cardiovascular risk observed in overweight adolescents.