ORCID Profile
0000-0001-7053-6319
Current Organisation
University of Tasmania
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Publisher: Springer Science and Business Media LLC
Date: 12-2009
Abstract: It 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). Venous 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. Collectively 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.
Publisher: SAGE Publications
Date: 06-02-2013
Abstract: 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 in idual variability tends to be overlooked. Recent evidence highlights the importance of characterizing the in idual variability by demonstrating exercise-induced changes in appetite. In iduals who experience lower than theoretically predicted reductions in body weight can be characterized by hedonic (eg, pleasure) and homeostatic (eg, hunger) features.
Publisher: Springer Science and Business Media LLC
Date: 17-08-2018
DOI: 10.1038/IJO.2017.206
Publisher: Springer Science and Business Media LLC
Date: 12-03-2005
DOI: 10.1007/S00421-005-1319-2
Abstract: This study investigated physiological and psychological correlates of the positive and negative components of a systems model in a well-trained male middle-distance runner. In the systems model, performance at any given point in time is seen as the difference between two antagonistic components, fitness and fatigue, which represent the positive and negative adaptation to training, respectively. Each component comprises a set of parameters unique to the in idual, which were estimated by fitting model-predicted performance to performance measured weekly throughout a 12-week training period. The model fitness component was correlated with extrapolated VO(2max) (ml.kg(-1).min(-1)), running economy (RE) (VO(2) at 17 km.h(-1)), and running speed (km.h(-1)) at ventilatory threshold (VTRS). The model fatigue component was correlated with the fatigue subset of the profile of mood states (POMS). The fit between model and actual performance was significant (r(2)=0.92, P< 0.01). In the case of fitness, both VTRS (r=0.94, P=0.0001) and RE (r=-0.61, P=0.04) were significantly correlated with the model fitness component. There was also a moderate correlation between the fatigue subset of the POMS and the fatigue component (r=0.75, p< 0.05). In summary, this is the first time VTRS and the POMS have been used in an attempt to validate the model components. The findings of the present study support previous validation attempts using biochemical and hormonal markers of fitness and fatigue.
Publisher: Wiley
Date: 06-05-2016
DOI: 10.1111/IJPO.12037
Abstract: Obese children are typically less physically active than their normal-weight peers and are often assumed to be 'unfit'. Investigate the relationships between adiposity, physical activity levels and cardiorespiratory fitness (CRF) in obese and normal-weight children. A secondary aim was to examine obese/normal-weight differences in CRF. Obese (N = 107) and normal-weight (N = 132) 10-13-year-olds participated. Fat-free mass (FFM), percent fat, physical activity and peak oxygen uptake (VO2peak ) were assessed. Analyses were adjusted for socioeconomic status (SES). Higher percent fat was inversely associated with VO2peak normalized for mass (r = -0.780, P < 0.001) even after controlling for physical activity (r = -0.673, P < 0.001). While higher percent fat was also inversely associated with VO2peak normalized for FFM, this was only significant in males (r = -0.247, P = 0.004) and did not persist after controlling for physical activity (r = -0.059 P = 0.526). Compared with normal-weight children, obese children had higher absolute VO2peak , lower VO2peak corrected for mass (P ≤ 0.009) and lower VO2peak corrected for FFM (P = 0.041) that did not persist after controlling for SES (P = 0.086). Obesity-related inefficiencies in CRF were evident. Higher adiposity was associated with poorer CRF relative to mass, irrespective of physical activity levels. However, low physical activity levels may be responsible for associations between adiposity and CRF relative to FFM seen in boys, indicating the importance of encouraging physical activity.
Publisher: BMJ
Date: 19-05-2012
Abstract: Does exercise promote weight loss? One of the key problems with studies assessing the efficacy of exercise as a method of weight management and obesity is that mean data are presented and the in idual variability in response is overlooked. Recent data have highlighted the need to demonstrate and characterise the in idual variability in response to exercise. Do people who exercise compensate for the increase in energy expenditure via compensatory increases in hunger and food intake? The authors address the physiological, psychological and behavioural factors potentially involved in the relationship between exercise and appetite, and identify the research questions that remain unanswered. A negative consequence of the phenomena of in idual variability and compensatory responses has been the focus on those who lose little weight in response to exercise this has been used unreasonably as evidence to suggest that exercise is a futile method of controlling weight and managing obesity. Most of the evidence suggests that exercise is useful for improving body composition and health. For ex le, when exercise-induced mean weight loss is <1.0 kg, significant improvements in aerobic capacity (+6.3 ml/kg/min), systolic (-6.00 mm Hg) and diastolic (-3.9 mm Hg) blood pressure, waist circumference (-3.7 cm) and positive mood still occur. However, people will vary in their responses to exercise understanding and characterising this variability will help tailor weight loss strategies to suit in iduals.
Publisher: Public Library of Science (PLoS)
Date: 17-11-2014
Publisher: Wiley
Date: 12-2018
DOI: 10.1111/OBR.12787
Abstract: Eating patterns involving intermittent energy restriction (IER) include 'intermittent fasting' where energy intake is severely restricted for several 'fasting' days per week, with 'refeeding' days (involving greater energy intake than during fasting days) at other times. Intermittent fasting does not improve weight loss compared to continuous energy restriction (CER), where energy intake is restricted every day. We hypothesize that weight loss from IER could be improved if refeeding phases involved restoration of energy balance (i.e. not ongoing energy restriction, as during intermittent fasting). There is some evidence in adults with overweight or obesity showing that maintenance of a lower weight may attenuate (completely or partially) some of the adaptive responses to energy restriction that oppose ongoing weight loss. Other studies show some adaptive responses persist unabated for years after weight loss. Only five randomized controlled trials in adults with overweight or obesity have compared CER with IER interventions that achieved energy balance (or absence of energy restriction) during refeeding phases. Two reported greater weight loss than CER, whereas three reported similar weight loss between interventions. While inconclusive, it is possible that achieving energy balance (i.e. avoiding energy restriction or energy excess) during refeeding phases may be important in realizing the potential of IER.
Publisher: Canadian Science Publishing
Date: 12-2014
Abstract: Maximal fat oxidation (MFO), as well as the exercise intensity at which it occurs (Fat max ), have been reported as lower in sedentary overweight in iduals but have not been studied in trained overweight in iduals. The aim of this study was to compare Fat max 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 (V̇O 2max ) 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. V̇O 2max and fat and carbohydrate oxidation rates were determined using indirect calorimetry Fat max 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), Fat max (46.7% ± 8.6% vs. 45.4% ± 7.2% V̇O 2max , 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 Fat max were correlated with V̇O 2max (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.
Publisher: IOP Publishing
Date: 06-07-2007
DOI: 10.1088/0967-3334/28/8/009
Abstract: 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.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 03-2010
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.MCE.2015.09.014
Abstract: Energy restriction induces physiological effects that hinder further weight loss. Thus, deliberate periods of energy balance during weight loss interventions may attenuate these adaptive responses to energy restriction and thereby increase the efficiency of weight loss (i.e. the amount of weight or fat lost per unit of energy deficit). To address this possibility, we systematically searched MEDLINE, PreMEDLINE, PubMed and Cinahl and reviewed adaptive responses to energy restriction in 40 publications involving humans of any age or body mass index that had undergone a diet involving intermittent energy restriction, 12 with direct comparison to continuous energy restriction. Included publications needed to measure one or more of body weight, body mass index, or body composition before and at the end of energy restriction. 31 of the 40 publications involved 'intermittent fasting' of 1-7-day periods of severe energy restriction. While intermittent fasting appears to produce similar effects to continuous energy restriction to reduce body weight, fat mass, fat-free mass and improve glucose homeostasis, and may reduce appetite, it does not appear to attenuate other adaptive responses to energy restriction or improve weight loss efficiency, albeit most of the reviewed publications were not powered to assess these outcomes. Intermittent fasting thus represents a valid--albeit apparently not superior--option to continuous energy restriction for weight loss.
Publisher: Portland Press Ltd.
Date: 14-11-2006
DOI: 10.1042/CS20060151
Abstract: 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 s les 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.
Publisher: Mary Ann Liebert Inc
Date: 04-2016
Abstract: This study examined relationships between adiposity, physical functioning, and physical activity. 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. 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. 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.
Publisher: Springer Science and Business Media LLC
Date: 24-07-2012
DOI: 10.1038/IJO.2012.109
Abstract: 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. 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'. 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. 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.
Publisher: Springer Science and Business Media LLC
Date: 23-09-2010
DOI: 10.1007/S00421-009-1208-1
Abstract: To investigate whether venous occlusion plethysmography (VOP) may be used to measure high rates of arterial inflow associated with exercise, venous occlusions were performed at rest, and following dynamic handgrip exercise at 15, 30, 45, and 60% of maximum voluntary contraction (MVC) in seven healthy males. The effect of including more than one cardiac cycle in the calculation of blood flow was assessed by comparing the cumulative blood flow over one, two, three, or four cardiac cycles. The inclusion of more than one cardiac cycle at 30 and 60% MVC, and more than two cardiac cycles at 15 and 45% MVC resulted in a lower blood flow compared to using only the first cardiac cycle (P < 0.05). Despite the small time interval over which arterial inflow was measured (~1 s), this did not affect the reproducibility of the technique. Reproducibility (coefficient of variation for arterial inflow over three trials) tended to be poorer at the higher workloads, although this was not significant (12.7 +/- 6.6, 16.2 +/- 7.3, and 22.9 +/- 9.9% for the 15, 30, and 45% MVC workloads P = 0.102). There was also a tendency for greater reproducibility with the inclusion of more cardiac cycles at the highest workload, but this did not reach significance (P = 0.070). In conclusion, when calculated over the first cardiac cycle only during venous occlusion, high rates of forearm blood flow can be measured using VOP, and this can be achieved without a significant decrease in the reproducibility of the measurement.
Publisher: Cambridge University Press (CUP)
Date: 20-05-2013
DOI: 10.1017/S0007114513001451
Abstract: Meal-induced thermogenesis (MIT) research findings have been highly inconsistent, in part, due to the variety of durations and protocols used to measure MIT. In the present study, we aimed to determine the following: (1) the proportion of a 6 h MIT response completed at 3, 4 and 5 h (2) the associations between the shorter durations and the 6 h measures (3) whether shorter durations improved the reproducibility of the measurement. MIT was measured in response to a 2410 kJ mixed composition meal in ten in iduals (five males and five females) on two occasions. Energy expenditure was measured continuously for 6 h post-meal using indirect calorimetry, and MIT was calculated as the increase in energy expenditure above the pre-meal RMR. On average, 76, 89 and 96 % of the 6 h MIT response was completed within 3, 4 and 5 h, respectively, and MIT at each of these time points was strongly correlated with the 6 h MIT response (range for correlations, r 0·990–0·998 P 0·01). The between-day CV for the 6 h measurement was 33 %, but it was significantly lower after 3 h of measurement (CV 26 % P = 0·02). Despite variability in the total MIT between days, the proportion of MIT that was completed at 3, 4 and 5 h was reproducible (mean CV: 5 %). While 6 h are typically required to measure the complete MIT response, the 3 h measures provide sufficient information about the magnitude of the MIT response and may be applicable for testing in iduals on repeated occasions.
No related grants have been discovered for Rachel Wood.