Rachel E. Wood

Effect of training on the response of plasma vascular endothelial growth factor to exercise in patients with peripheral arterial disease

Expansion of the capillary network, or angiogenesis, occurs following endurance training. This process, which is reliant on the presence of VEGF (vascular endothelial growth factor), is an adaptation to a chronic mismatch between oxygen demand and supply. Patients with IC (intermittent claudication) experience pain during exercise associated with an inadequate oxygen delivery to the muscles. Therefore the aims of the present study were to examine the plasma VEGF response to acute exercise, and to establish whether exercise training alters this response in patients with IC. In Part A, blood was collected from patients with IC (n=18) before and after (+20 and +60 min post-exercise) a maximal walking test to determine the plasma VEGF response to acute exercise. VEGF was present in the plasma of patients (45.11+/-29.96 pg/ml) and was unchanged in response to acute exercise. Part B was a training study to determine whether exercise training altered the VEGF response to acute exercise. Patients were randomly assigned to a treatment group (TMT; n=7) that completed 6 weeks of high-intensity treadmill training, or to a control group (CON; n=6). All patients completed a maximal walking test before and after the intervention, with blood samples drawn as for Part A. Training had no effect on plasma VEGF at rest or in response to acute exercise, despite a significant increase in maximal walking time in the TMT group (915+/-533 to 1206+/-500 s; P=0.009) following the intervention. The absence of a change in plasma VEGF may reflect altered VEGF binding at the endothelium, although this cannot be confirmed by the present data.

Does metabolic compensation explain the majority of less-than-expected weight loss in obese adults during a short-term severe diet and exercise intervention?

Objective:We investigated to what extent changes in metabolic rate and composition of weight loss explained the less-than-expected weight loss in obese men and women during a diet-plus-exercise intervention.Design:In all, 16 obese men and women (41±9 years; body mass index (BMI) 39±6 kg m−2) were investigated in energy balance before, after and twice during a 12-week very-low-energy diet(565–650 kcal per day) plus exercise (aerobic plus resistance training) intervention. The relative energy deficit (EDef) from baseline requirements was severe (74%–87%). Body composition was measured by deuterium dilution and dual energy X-ray absorptiometry, and resting metabolic rate (RMR) was measured by indirect calorimetry. Fat mass (FM) and fat-free mass (FFM) were converted into energy equivalents using constants 9.45 kcal per g FM and 1.13 kcal per g FFM. Predicted weight loss was calculated from the EDef using the ′7700 kcal kg−1 rule′.Results:Changes in weight (−18.6±5.0 kg), FM (−15.5±4.3 kg) and FFM (−3.1±1.9 kg) did not differ between genders. Measured weight loss was on average 67% of the predicted value, but ranged from 39% to 94%. Relative EDef was correlated with the decrease in RMR (R=0.70, P<0.01), and the decrease in RMR correlated with the difference between actual and expected weight loss (R=0.51, P<0.01). Changes in metabolic rate explained on average 67% of the less-than-expected weight loss, and variability in the proportion of weight lost as FM accounted for a further 5%. On average, after adjustment for changes in metabolic rate and body composition of weight lost, actual weight loss reached 90% of the predicted values.Conclusion:Although weight loss was 33% lower than predicted at baseline from standard energy equivalents, the majority of this differential was explained by physiological variables. Although lower-than-expected weight loss is often attributed to incomplete adherence to prescribed interventions, the influence of baseline calculation errors and metabolic downregulation should not be discounted.

Fat oxidation over a range of exercise intensities: fitness versus fatness

Maximal fat oxidation (MFO), as well as the exercise intensity at which it occurs (Fatmax), have been reported as lower in sedentary overweight individuals but have not been studied in trained overweight individuals. The aim of this study was to compare Fatmax and MFO in lean and overweight recreationally trained males matched for cardiorespiratory fitness (CRF) and to study the relationships between these variables, anthropometric characteristics, and CRF. Twelve recreationally trained overweight (high fatness (HiFat) group, 30.0% ± 5.3% body fat) and 12 lean males (low fatness (LoFat), 17.2% ± 5.7% body fat) matched for CRF (maximal oxygen consumption (V̇O2max) 39.0 ± 5.5 vs. 41.4 ± 7.6 mL·kg(-1)·min(-1), p = 0.31) and age (p = 0.93) performed a graded exercise test on a cycle ergometer. V̇O2max and fat and carbohydrate oxidation rates were determined using indirect calorimetry; Fatmax and MFO were determined with a mathematical model (SIN); and % body fat was assessed by air displacement plethysmography. MFO (0.38 ± 0.19 vs. 0.42 ± 0.16 g·min(-1), p = 0.58), Fatmax (46.7% ± 8.6% vs. 45.4% ± 7.2% V̇O2max, p = 0.71), and fat oxidation rates over a wide range of exercise intensities were not significantly different (p > 0.05) between HiFat and LoFat groups. In the overall cohort (n = 24), MFO and Fatmax were correlated with V̇O2max (r = 0.46, p = 0.02; r = 0.61, p = 0.002) but not with % body fat or body mass index (p > 0.05). Fat oxidation during exercise was similar in recreationally trained overweight and lean males matched for CRF. Consistently, substrate oxidation rates during exercise were not related to adiposity (% body fat) but were related to CRF. The benefits of high CRF independent of body weight and % body fat should be further highlighted in the management of obesity.

Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study

Background/Objectives:The MATADOR (Minimising Adaptive Thermogenesis And Deactivating Obesity Rebound) study examined whether intermittent energy restriction (ER) improved weight loss efficiency compared with continuous ER and, if so, whether intermittent ER attenuated compensatory responses associated with ER.Subjects/Methods:Fifty-one men with obesity were randomised to 16 weeks of either: (1) continuous (CON), or (2) intermittent (INT) ER completed as 8 × 2-week blocks of ER alternating with 7 × 2-week blocks of energy balance (30 weeks total). Forty-seven participants completed a 4-week baseline phase and commenced the intervention (CON: N=23, 39.4±6.8 years, 111.1±9.1 kg, 34.3±3.0 kg m−2; INT: N=24, 39.8±9.5 years, 110.2±13.8 kg, 34.1±4.0 kg m−2). During ER, energy intake was equivalent to 67% of weight maintenance requirements in both groups. Body weight, fat mass (FM), fat-free mass (FFM) and resting energy expenditure (REE) were measured throughout the study.Results:For the N=19 CON and N=17 INT who completed the intervention per protocol, weight loss was greater for INT (14.1±5.6 vs 9.1±2.9 kg; P<0.001). INT had greater FM loss (12.3±4.8 vs 8.0±4.2 kg; P<0.01), but FFM loss was similar (INT: 1.8±1.6 vs CON: 1.2±2.5 kg; P=0.4). Mean weight change during the 7 × 2-week INT energy balance blocks was minimal (0.0±0.3 kg). While reduction in absolute REE did not differ between groups (INT: -502±481 vs CON: −624±557 kJ d−1; P=0.5), after adjusting for changes in body composition, it was significantly lower in INT (INT: −360±502 vs CON: −749±498 kJ d−1; P<0.05).Conclusions:Greater weight and fat loss was achieved with intermittent ER. Interrupting ER with energy balance ‘rest periods’ may reduce compensatory metabolic responses and, in turn, improve weight loss efficiency.

Plasma ATP concentration and venous oxygen content in the forearm during dynamic handgrip exercise

BackgroundIt has been proposed that adenosine triphosphate (ATP) released from red blood cells (RBCs) may contribute to the tight coupling between blood flow and oxygen demand in contracting skeletal muscle. To determine whether ATP may contribute to the vasodilatory response to exercise in the forearm, we measured arterialised and venous plasma ATP concentration and venous oxygen content in 10 healthy young males at rest, and at 30 and 180 seconds during dynamic handgrip exercise at 45% of maximum voluntary contraction (MVC).ResultsVenous plasma ATP concentration was elevated above rest after 30 seconds of exercise (P < 0.05), and remained at this higher level 180 seconds into exercise (P < 0.05 versus rest). The increase in ATP was mirrored by a decrease in venous oxygen content. While there was no significant relationship between ATP concentration and venous oxygen content at 30 seconds of exercise, they were moderately and inversely correlated at 180 seconds of exercise (r = -0.651, P = 0.021). Arterial ATP concentration remained unchanged throughout exercise, resulting in an increase in the venous-arterial ATP difference.ConclusionsCollectively these results indicate that ATP in the plasma originated from the muscle microcirculation, and are consistent with the notion that deoxygenation of the blood perfusing the muscle acts as a stimulus for ATP release. That ATP concentration was elevated just 30 seconds after the onset of exercise also suggests that ATP may be a contributing factor to the blood flow response in the transition from rest to steady state exercise.

The effect of changing limb position on the validity of venous occlusion plethysmography.

Venous occlusion plethysmography (VOP) is a technique used for the non-invasive measurement of limb blood flow. A fundamental technical consideration of venous occlusion plethysmography is that the limb in question must be placed above heart level. However, in light of advances in technology and methodology, the necessity of this has been questioned. We investigated the validity of the VOP technique with the forearm approximately 10 cm above and below the level of the heart in both resting and dynamic conditions. Nine healthy male participants performed four bouts of handgrip exercise, two at each of 15% and 30% maximum voluntary contraction (MVC) (one above and one below the heart). As hypothesized, resting forearm blood flow (FBF) measured below the level of the heart was significantly lower than for above the heart (p = 0.046). However, the opposite occurred during exercise, where FBF measured after the fifth minute of handgrip contractions was significantly higher below the level of the heart (p = 0.013). Furthermore, the ability to accurately quantify FBF below the level of the heart was severely impeded by artifact, and as such VOP appears to remain constricted to use above the phlebostatic level.

Impaired Physical Function Associated with Childhood Obesity: How Should We Intervene?

BACKGROUND This study examined relationships between adiposity, physical functioning, and physical activity. METHODS Obese (N = 107) and healthy-weight (N = 132) children aged 10-13 years underwent assessments of percent body fat (%BF, dual energy X-ray absorptiometry); knee extensor strength (KE, isokinetic dynamometry); cardiorespiratory fitness (CRF, peak oxygen uptake by cycle ergometry); physical health-related quality of life (HRQOL); and worst pain intensity and walking capacity [six-minute walk (6MWT)]. Structural equation modelling was used to assess relationships between variables. RESULTS Moderate relationships were observed between %BF and (1) 6MWT, (2) KE strength corrected for mass, and (3) CRF relative to mass (r -0.36 to -0.69, p ≤ 0.007). Weak relationships were found between %BF and physical HRQOL (r -0.27, p = 0.008); CRF relative to mass and physical HRQOL (r -0.24, p = 0.003); physical activity and 6MWT (r 0.17, p = 0.004). Squared multiple correlations showed that 29.6% variance in physical HRQOL was explained by %BF, pain, and CRF relative to mass; while 28.0% variance in 6MWT was explained by %BF and physical activity. CONCLUSIONS It appears that children with a higher body fat percentage have poorer KE strength, CRF, and overall physical functioning. Reducing percent fat appears to be the best target to improve functioning. However, a combined approach to intervention, targeting reductions in body fat percentage, reductions in pain, and improvements in physical activity and CRF may assist physical functioning.

The Interaction Between Exercise, Appetite, and Food Intake: Implications for Weight Control

Exercise could indirectly affect body weight by exerting changes on various components of appetite control, including nutrient and taste preferences, meal size and frequency, and the drive to eat. This review summarizes the evidence on how exercise affects appetite and eating behavior and in particular answers the question, “Does exercise induce an increase in food intake to compensate for the increase in energy expenditure?” Evidence will be presented to demonstrate that there is no automatic increase in food intake in response to acute exercise and that the response to repeated exercise is variable. The review will also identify areas of further study required to explain the variability. One limitation with studies that assess the efficacy of exercise as a method of weight control is that only mean data are presented—the individual variability tends to be overlooked. Recent evidence highlights the importance of characterizing the individual variability by demonstrating exercise-induced changes in appetite. Individuals who experience lower than theoretically predicted reductions in body weight can be characterized by hedonic (eg, pleasure) and homeostatic (eg, hunger) features.