High Levels Of Energy Expenditure Research Articles

The global diversity of eating patterns: Human nutritional health in comparative perspective

This paper draws on comparative data to explore the evolutionary origins of human nutritional needs and the diverse strategies used by human populations to meet those needs. Humans have evolved distinctive nutritional characteristics associated with the high metabolic costs of our large brains. The evolution of larger hominid brain size necessitated the development of foraging strategies that both provided high quality foods, and required larger ranges and higher levels of energy expenditure. Over time, human subsistence strategies have become ever more efficient in obtaining energy with minimal time and effort. Compared to data from traditional, subsistence-level societies, the US diet differs markedly in its fat and carbohydrate composition, but not in its absolute energy content. Energy expenditure levels of subsistence populations are significantly higher than those of the US and other industrialized societies. These data suggest that rising rates of obesity associated with lifestyle ‘modernization’ is not simply the product of greater energy intakes, but rather shifts energy balance and diet composition.

Impulse Conduction Increases Mitochondrial Transport in Adult Mammalian Peripheral Nerves In Vivo

Author SummaryAs mitochondria are the main power source for most cells, their correct localization is vital for cellular homeostasis. The morphological and functional complexity of neurons, and the unpredictability of energy demand resulting from sustained impulse activity, means that correct mitochondrial function and location is particularly important for these cells. However, it is unclear how mitochondrial transport responds to the wide range of physiological conduction frequencies experienced by an intact nervous system. Here we image mitochondria moving along mouse saphenous nerve axons in vivo and observe the effects of sustained trains of impulses, evoked either by electrical stimulation of myelinated axons at physiological frequencies (1 and 50 Hz), or chemical stimulation (cutaneous capsaicin) in unmyelinated axons. We find that the number and speed of mitochondria moving towards the peripheral sensory terminals dramatically increases in active axons. The increased numbers of mobile mitochondria seem to originate from “pinched off” segments of stationary mitochondria (mitochondrial fission), and from recruitment of small stationary mitochondria. The transported mitochondria appear to accumulate in sensory nerve terminals in the skin. This study suggests that mitochondrial fission is involved in rapidly supplying mobile mitochondria to aid their re-distribution to regions of increased metabolic demand along axons.

Free-living physical activity and energy expenditure of rural children and adolescents in the Nandi region of Kenya

Purpose: To examine the relationship between physical activity and energy demands in children and adolescents with highly active lifestyles.Methods: Physical activity patterns of 30 rural Kenyan children and adolescents (14 ± 1 years, mean ± SD) with median body mass index (BMI) z-score = −1.06 [−3.29–0.67] median [range] were assessed by accelerometry over 1 week. Daily energy expenditure (DEE), activity-induced energy expenditure (AEE) and physical activity level (PAL) were simultaneously determined using doubly-labelled water (DLW). Active commuting to school was assessed by global positioning system.Results: Mean DEE, AEE and PAL were 12.2 ± 3.4, 5.7 ± 3.0 MJ/day and 2.3 ± 0.6, respectively. A model combining body mass, average accelerometer counts per minute and time in light activities predicted 45% of the variance in DEE (p < 0.05) with a standard error of DEE estimate of 2.7 MJ/day. Furthermore, AEE accounted for ∼47% of DEE. Distance to school was not related to variation in DEE, AEE or PAL and there was no association between active commuting and adiposity.Conclusion: High physical activity levels were associated with much higher levels of energy expenditure than observed in Western societies. These results oppose the concept of physical activity being stable and constrained in humans.

Energy expenditure by multisensor armband in overweight and obese lactating women validated by doubly labeled water

To validate total energy expenditure (TEE) and activity energy expenditure (AEE) from the portable SenseWear armband (SWA) Pro 2 (TEESWA and AEESWA ; InnerView software versions SWA 5.1 and SWA 6.1) against TEE from doubly labeled water (DLW) and AEE from DLW and indirect calorimetry (TEEDLW and AEEDLW ) in overweight/obese lactating women at 10 weeks postpartum. TEE was measured simultaneously with DLW (14 days) and SWA (first 7 days). Lactating women (n = 62), non-smoking, with a BMI > 25 kg/m(2) and wearing time SWA ≥ 90% were included. Mean TEESWA5.1 was overestimated with 85 kcal/day compared to TEEDLW (P = 0.040), while mean TEESWA6.1 was underestimated with 241 kcal/day compared to TEEDLW (P < 0.001). Mean AEESWA5.1 was similar to mean AEEDLW (P = 0.818), while mean AEESWA6.1 was underestimated with 581 kcal/day compared to AEEDLW (P < 0.001). TEESWA6.1 and AEESWA6.1 were systematically underestimated at higher levels of energy expenditure and BMI while only AEESWA5.1 was systematically overestimated at higher levels of energy expenditure. TEESWA5.1 and AEESWA5.1 were fairly estimated on a group level while TEESWA6.1 and AEESWA6.1 were significantly and systematically underestimated. Both SWA software versions showed large individual variation in agreement with TEEDLW and AEEDLW , limiting the validity on individual level.

Thyroid hormones correlate with resting metabolic rate, not daily energy expenditure, in two charadriiform seabirds

SummaryThyroid hormones affect in vitro metabolic intensity, increase basal metabolic rate (BMR) in the lab, and are sometimes correlated with basal and/or resting metabolic rate (RMR) in a field environment. Given the difficulty of measuring metabolic rate in the field—and the likelihood that capture and long-term restraint necessary to measure metabolic rate in the field jeopardizes other measurements—we examined the possibility that circulating thyroid hormone levels were correlated with RMR in two free-ranging bird species with high levels of energy expenditure (the black-legged kittiwake, Rissa tridactyla, and thick-billed murre, Uria lomvia). Because BMR and daily energy expenditure (DEE) are purported to be linked, we also tested for a correlation between thyroid hormones and DEE. We examined the relationships between free and bound levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) with DEE and with 4-hour long measurements of post-absorptive and thermoneutral resting metabolism (resting metabolic rate; RMR). RMR but not DEE increased with T3 in both species; both metabolic rates were independent of T4. T3 and T4 were not correlated with one another. DEE correlated with body mass in kittiwakes but not in murres, presumably owing to the larger coefficient of variation in body mass during chick rearing for the more sexually dimorphic kittiwakes. We suggest T3 provides a good proxy for resting metabolism but not DEE in these seabird species.

Circadian Rhythm of Energy Expenditure and Oxygen Consumption

This study aimed to evaluate the effect of continuous and intermittent methods of enteral nutrition (EN) administration on circadian rhythm. Thirty-four individuals, aged between 52 and 80 years, were fed through a nasoenteric tube. Fifteen individuals received a continuous infusion for 24 hours/d, and 19 received an intermittent infusion in comparable quantities, every 4 hours from 8:00 to 20:00. In each patient, 4 indirect calorimetric measurements were carried out over 24 hours (A: 7:30, B: 10:30, C: 14:30, and D: 21:30) for 3 days. Energy expenditure and oxygen consumption were significantly higher in the intermittent group than in the continuous group (1782 ± 862 vs 1478 ± 817 kcal/24 hours, P = .05; 257 125 vs 212 117 ml/min, P = .048, respectively). The intermittent group had higher levels of energy expenditure and oxygen consumption at all the measured time points compared with the continuous group. energy expenditure and oxygen consumption in both groups were significantly different throughout the day for 3 days. There is circadian rhythm variation of energy expenditure and oxygen consumption with continuous and intermittent infusion for EN. This suggests that only one indirect daily calorimetric measurement is not able to show the patient's true needs. Energy expenditure is higher at night with both food administration methods. Moreover, energy expenditure and oxygen consumption are higher with the intermittent administration method at all times.

Energy Balance and Obesity

This article describes the interplay among energy intake, energy expenditure, and body energy stores and illustrates how an understanding of energy balance can help us develop strategies to reduce obesity. First, reducing obesity requires modifying both energy intake and energy expenditure, not simply focusing on either alone. Food restriction alone will not be effective in reducing obesity if human physiology is biased toward achieving energy balance at a high energy flux (ie, at a high level of energy intake and expenditure). In previous environments, a high energy flux was achieved with a high level of physical activity, but in today's sedentary environment, it is increasingly achieved through weight gain. Matching energy intake to a high level of energy expenditure will likely be more feasible for most people than restricting food intake to meet a low level of energy expenditure. Second, from an energy balance point of view, we are likely to be more successful in preventing excessive weight gain than in treating obesity. The reason is that the energy balance system shows stronger opposition to weight loss than to weight gain. Although large behavior changes are needed to produce and maintain reductions in body weight, small behavior changes may be sufficient to prevent excessive weight gain. The concept of energy balance combined with an understanding of how the body achieves balance may be a useful framework for developing strategies to reduce obesity rates. Obesity is often considered to be a result of either excessive food intake or insufficient physical activity. There is a great debate about which behavior deserves the most responsibility, but this approach has not yet produced effective or innovative solutions. We believe that obesity can best be viewed in terms of energy balance. The first law of thermodynamics states that body weight cannot change if, over a …

Do red squirrels (Tamiasciurus hudsonicus) use daily torpor during winter?

Given their relatively small body size, high thermoregulatory costs, and low metabolic rate, we tested the hypothesis that red squirrels (Tamiasciurus hudsonicus) would employ bouts of daily torpor to save energy during winter. We collected data on body temperature (Tb) using surgically implanted data loggers for squirrels in the Cypress Hills region of Saskatchewan, where extended periods of cold snowy weather make foraging difficult and should lead to high levels of energy expenditure. Based on over 8000 measurements from 4 animals over 3 winters, we found no evidence for torpor use. However, Tb was lowest in January and highest in September and May, and mean monthly Tb was correlated with mean monthly ambient temperature (Ta). Given that taxonomically related species can and do use torpor, it remains to be determined what makes heterothermy in this species costly to the extent that its use is precluded.

Fatigability as a function of physical activity energy expenditure: proof of concept

Increased fatigue is a predictor of morbidity and mortality in older adults. Fatigability defines a change in performance or self‐reported fatigue in response to physical activity (PA). Changes in performance, fatigue, and energy expenditure (EE) were measured simultaneously in 17 adults (11 females, 74–94‐year‐old) performing 8 standardized PA tasks with various EE requirements in a whole‐room indirect calorimeter. Change in performance was measured using a PA movement monitor and change in fatigue was self‐reported on a 7‐point scale for each task. Performance and perceived fatigability severity scores were calculated as a ratio of change in performance and fatigue, respectively, and PAEE. Change in both objective performance and self‐reported fatigue were associated with EE (Spearman rho= −0.72 and −0.68, p&lt;0.001) on a task requiring relatively high level of EE. The performance and perceived fatigability severity scores were significantly correlated (rho=0.77, p&lt; 0.001) and were related to PAEE‐induced fatigue on tasks requiring relatively high EE level. We conclude that fatigability severity is a valid measure of PAEE induced fatigue in older adults.

Seasonal variation in energy expenditure is not related to activity level or water temperature in a large diving bird

There is considerable interest in understanding how the energy budget of an endotherm is modulated from a physiological and ecological point of view. In this paper, we used daily (24 h) heart rate (f(H24)), as a proxy of daily energy expenditure (DEE) across seasons, to test the effect of locomotion activity and water temperature on the energy budget of a large diving bird. f(H24) was monitored continuously in common eiders (Somateria mollissima) during 7 months together with measures of time spent flying and time spent feeding. f(H24) varied substantially during the recording period, with numerous increases and decreases that occurred across seasons, although we did not find any relationship between f(H24) and the time spent active (feeding and flying). However, inactive heart rate (f(H,inactive)) decreased as locomotion activity increased, suggesting that common eiders were using some form of compensation when under a high work load. We were also unable to detect a negative relationship between water temperature and resting heart rate, a proxy of resting metabolic rate. This was unexpected, based on the assumption that high thermoregulation costs would be associated with cold waters. We showed instead that a high level of energy expenditure coincided with feather moult and warm waters, which suggests that the observed variable pattern of seasonal DEE was driven by these two factors. Nevertheless, our results indicate that compensation and possibly the timing of moult may be used as mechanisms to reduce seasonal variation in energy expenditure.

Hormone and metabolite changes associated with extended breeding fasts in male northern elephant seals (Mirounga angustirostris)

We measured metabolic hormones and several key metabolites in breeding adult male northern elephant seals to examine the regulation of fuel metabolism during extended natural fasts of over 3months associated with high levels of energy expenditure. Males were sampled twice, early and late in the fast, losing an average of 23% of body mass and 47% of adipose stores between measurements. Males exhibited metabolic homeostasis over the breeding fast with no changes in glucose, non-esterified fatty acids, or blood urea nitrogen. Ketoacids increased over the fast but were very low when compared to other fasting species. Changes within individuals in total triiodothyronine (tT3) were positively related to daily energy expenditure (DEE) and protein catabolism. Differences in levels of thyroid hormones relative to that observed in weaned pups and females suggest a greater deiodination of T4 to support the high DEE of breeding males. Relative levels of leptin and ghrelin were consistent with the suppression of appetite but a significant reduction in growth hormone across the fast was contrary to expectation in fasting mammals. The lack of the increase in cortisol during fasting found in conspecific weaned pups and lactating females may contribute to the ability of breeding males to spare protein despite high levels of energy expenditure. Together these findings reveal significant differences with conspecifics under varying nutrient demands, suggesting metabolic adaptation to extended high energy fasts.

Fatigability as a function of physical activity energy expenditure in older adults

Increased fatigue is a predictor of morbidity and mortality in older adults. Fatigability defines a change in performance or self-reported fatigue in response to physical activity (PA). However, the relationship of fatigability to PA-related energy expenditure (PAEE) is unknown. Changes in performance, fatigue, and energy expenditure were measured simultaneously in 17 adults (11 females, 74-94years old) performing eight standardized PA tasks with various energy expenditure requirements in a whole-room indirect calorimeter. Change in performance was objectively measured using a PA movement monitor and change in fatigue was self-reported on a seven-point scale for each task. Performance and perceived fatigability severity scores were calculated as a ratio of change in performance and fatigue, respectively, and PAEE. We found that change in both objective performance and self-reported fatigue were associated with energy expenditure (Spearman rho = -0.72 and -0.68, respectively, p < 0.001) on a task requiring relatively high level of energy expenditure. The performance and perceived fatigability severity scores were significantly correlated (rho = 0.77, p < 0.001) on this task. In summary, results of this proof of concept pilot study show that both perceived and performance fatigability severity scores are related to PAEE-induced fatigue on a task requiring relatively high level of energy expenditure. We conclude that fatigability severity is a valid measure of PAEE-induced fatigue in older adults.

Physical activity, sedentary behavior, and health: paradigm paralysis or paradigm shift?

Perhaps the greatest barriers to achieving major public health advances in the 21st century will result from pandemic paradigm paralysis or the widespread inability to envision alternative or new models of thinking. One potential example of this phenomenon could turn out to be the continued focus on moderate and vigorous physical activity as the dominant health-related aspect of human movement. The current model of physical activity and health is well supported by over 60 years of scientific inquiry, and the beneficial effects of moderate-to-vigorous physical activity have been more clearly defined in recent years (1–4). However, if we are complacent with the existing paradigm—that increasing levels of moderate and vigorous levels of physical activity will result in the greatest improvements in public health—then we may not obtain the full return on investment with respect to improving quality of life and life expectancy through patterns of human movement. Emerging evidence for the role of sedentary behavior on health, which may be independent of physical activity per se, finds us at a crossroad with respect to prescribing optimal daily human movement patterns for health. Human movement represents a complex behavior that is influenced by personal motivation, health and mobility issues, genetic factors, and the social and physical environments in which people live. These factors undoubtedly exert an influence on the propensity to engage in sedentary behaviors as well as in physical activity. However, the biological, social, and environmental pathways leading to sedentary behavior versus physical activity may be different. Further, the health effects associated with sedentary behavior and physical activity may be the result of different biological mechanisms (5). ### Humans are designed for movement. Energy balance has been a central selective force throughout human evolutionary history, and humans have evolved to have high levels of energy expenditure, even more so than modern nonhuman primates …

Qualidade de sono, atividade física durante o tempo de lazer e esforço físico no trabalho entre trabalhadores noturnos de uma indústria cerâmica

Este estudo teve o objetivo de verificar a relação entre qualidade do sono e atividade física durante o tempo de lazer entre trabalhadores noturnos com um elevado esforço físico no trabalho (média de 14.245; DP 3.456 kcal/semana). Também foi avaliada a relação entre a qualidade do sono e o nível do esforço físico no trabalho. Um total de 19 trabalhadores noturnos de uma indústria cerâmica respondeu o índice da qualidade do sono de Pittsburgh (PSQI) e o questionário internacional da atividade física (IPAQ). Foi calculado o dispêndio calórico total por semana para cada trabalhador através do equivalente metabólico (METs). Os trabalhadores foram distribuídos em dois grupos, de acordo com os escores do PSQI. Foi realizada a análise descritiva dos dados por meio de médias, valores mínimo e máximo, proporções e desvios-padrão. A relação entre qualidade do sono e atividade física foi avaliada pelo teste Mann-Whitney. O grupo de qualidade do sono ruim mostrou nível mais elevado de gasto energético no trabalho que o outro grupo, o que sugere uma relação entre gasto energético no trabalho e qualidade de sono. Distúrbios do sono e sonolência diurna também contribuíram para a qualidade de sono ruim. Esses resultados, embora preliminares, revelam uma tendência de que o elevado esforço físico no trabalho noturno contribui para baixa qualidade de sono.

The relationship between a short measure of health status and physical activity in a workplace population

Many interventions promoting physical activity (PA) are effective in preventing disease onset, and although studies have found a positive relationship between health-related quality of life (HRQL) and PA, most of these studies have focused on older adults and those with chronic conditions. Less is known regarding the association between PA level and HRQL among healthy adults. Our objective was to analyse the relationship between PA level and HRQL among a sample of 573 employees aged 20–68 taking part in a workplace intervention to promote PA. Measures included HRQL (using a single item) and PA (i.e. Godin Leisure-Time Questionnaire). The Modified Canadian Aerobic Fitness Test (MCAFT) was also completed by 10% of the employees. MET-minute scores (assessing energy expenditure over one week) were compared across HRQL categories using ANOVA. A multiple linear regression analysis was conducted to further examine the relationship between HRQL and PA, controlling for potential covariates. Participants in the higher health status categories were found to report higher levels of energy expenditure (one-way ANOVA, p < 0.001). In the multiple linear regression model, each unit increase in health status level translated in a mean increase of 356 MET-minutes in energy expenditure (p < 0.001). This single-item assessment of health status explained six percent of the variance in energy expenditure. The study concludes that higher energy expenditure through PA among an adult workplace population is positively associated with increased health status, and it also suggests that a single-item HRQL measure is suitable for community- and population-based studies, reducing response burden and research costs.

Lipid profile in men and women with different levels of sports participation and physical activity

The purpose of the present study was to analyse the lipid profile in men and women differentiated according to energy expenditure during sports participation (EE(SPORT)), energy expenditure during active leisure time (EE(ALT)) and overall energy expenditure (EE(TOTAL)). The subjects were grouped by sex, age, EE(SPORT), EE(ALT) and EE(TOTAL). Group differences were analysed using analyses of covariance with BMI and alcohol consumption as covariates. Physical activity was assessed using the Flemish Physical Activity Computerised Questionnaire. Fasting blood samples were taken to measure total cholesterol (TC), TAG, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C) and the ratio TC:HDL-C. The study sample consisted of 1170 Flemish men and women between 18 and 75 years of age. Differences in lipid profile were observed in the younger age group (<45 years), all in favour of the most active group. More specifically, when differentiating by EE(ALT) and EE(TOTAL), men had a healthier lipid profile for TAG, HDL-C and TC:HDL-C. Differentiation according to EE(SPORT) revealed the same significant results except for TAG. In women significant results for HDL-C, LDL-C and TC:HDL-C were found when differentiated by EE(SPORT). Men and women <45 years of age with higher levels of energy expenditure due to sport show a better lipid profile than their sedentary counterparts. When differentiating subjects according to energy expenditure during active leisure time or overall energy expenditure, only in men was a healthier lipid profile observed in favour of the most active subjects.

Energy expenditure among farmers in developing countries: What do we know?

The trend toward overweight and obesity in developing countries is often assumed to be due, in part, to reductions in energy expenditure associated with the transition from agrarian to urban lifestyles. In this article we first review the published studies on energy expenditure in farming populations living in developing countries, populations generally assumed to have high levels of energy expenditure. To facilitate comparison we express energy expenditure as physical activity level (PAL), i.e. the ratio of total daily energy expenditure to basal metabolic rate. Then, with the goal of better understanding variability in energy expenditure between different human groups, we focus on case studies of women farmers in Colombia and Brazil for whom we have good ethnographic data. The published studies reviewed indicate that most farmers have PAL values in the moderate physical activity range, but toward the high end of that range. PAL values of male farmers tend to be higher than female, and show greater seasonal variation. The case studies illustrate that women farmers, living in broadly similar environments, and dependent on the cultivation of the same crop can have quite different patterns of physical activity and hence PAL values. These differences are a function of differences in behavior related to social and cultural variables like the organization of work at the household level and perceptions of how food crops should be processed, as well as micro-level ecological factors.

Physical Activity Levels of College Freshman

PURPOSE: This study compared measures of physical activity (PA) taken from the 7- day Physical Activity Recall (PAR) and the International Physical Activity Questionnaire (IPAQ) with those obtained from the NL 2000 (NL) and Lifecorder (LC) accelerometers in entering, college freshmen. METHODS: 47 males and 64 females (overall age =18.5±.3 yrs, wt. = 68.7±14.4 kg, and BMI = 23.7 ±4.9) volunteered and signed an informed consent form. All subjects wore the NL for 7 days, and half wore the LC as well. After the 7 days the subjects completed the PAR and IPAQ. RESULTS: There was a strong agreement between accelerometers with PAEE expressed in kcal/wk (r = 0.958, p= 0.000). However, the NL recorded significantly higher values (p= 0.0001) for PAEE than the LC (Md= 2705 vs. 2120). Both PAR kcal/wk and IPAQ kcal/wk were significantly related to the NL kcal/wk, r = 0.275 (p= 0.004) and r= 0.430 (p= 0.000), respectively. In addition, there were no significant differences in overall PAEE between the NL and PAR (p= 0.148) or the NL and IPAQ (p= 0.198). However, both the PAR and IPAQ reported more PAEE as energy expenditure exceeded 3000 kcal/wk. PAR moderate and vigorous MET-min/wk were not significantly related to LC moderate (p= 0.411) and vigorous MET-min/wk (p= 0.204), respectively. In addition, there were significant differences in MET-min/wk between the PAR and LC for moderate (p= 0.019) and vigorous (p= 0.000) activity. PAR reported relatively the same PAEE at lower amounts of moderate intensity exercise, but reported more PAEE as energy expenditure increased. PAR systematically reported more vigorous PAEE across the full range of energy expenditure. CONCLUSION: The accelerometers correlated highly and were in close agreement with one another. In first year freshmen, both surveys provided overall estimates of PAEE that were significantly related to objective measures of PA. However, at high levels of energy expenditure, the questionnaires captured more of the vigorous PA that the accelerometers could not monitor.

Moderate Exercise-Induced Energy Expenditure Does Not Alter Leptin Levels in Sedentary Obese Men

The purpose of the study was to determine whether exercise-induced increases in energy expenditure (EE) alter circulating leptin levels in obese individuals. Participants were randomized to an exercise intervention group (n = 8) or nonexercising control (n = 7). All data were collected on an outpatient basis at the exercise physiology laboratory at the University of Central Florida. Fifteen healthy obese males (24.9 +/- 1.4 years old, body mass index 33.4 +/- 0.7 kg . m). Members of the intervention group underwent a single exercise session of moderate intensity (58.4 +/- 1.3% of VO2max) for 60 minutes. Postexercise, 24 hour postexercise, and 48 hour postexercise levels of leptin, insulin, and ghrelin. The exercise session elicited an EE of 567 +/- 25 Kcal. No significant main effect or time-by-group interactions for leptin or ghrelin were observed immediately after the exercise bout or in the days following the intervention. These preliminary data suggest that a bout of acute exercise of moderate intensity and duration does not affect leptin concentration. It is possible that a higher level of EE is required to elicit substantial changes.

The sinuous bedrock channel of the Tapi River, Central India: Its form and processes

The Tapi Gorge lies in the monsoon-dominated region of the Indian subcontinent. Because of the seasonality of rainfall and flows all the fluvial activity in the bedrock gorge is confined to the monsoon season, in general, and during a few high-magnitude monsoon floods in particular. Field investigations along a 30-km reach of the sinuous bedrock gorge indicate that the river displays all the morphologic properties of a meandering alluvial channel albeit with a much higher level of energy expenditure. Considering the perimeter lithology and channel morphology two types of reaches are evident in the field: a predominantly rocky and relatively straight reach close to the gorge-head, and a longer, sinuous reach of gravel deposition downstream. Hydraulic modeling of a rainfall-induced dam-failure flood indicates that large-magnitude events that exceed the threshold of bedrock resistance for a sustained length of time are capable of erosion. It appears that the overall channel and gorge morphology is adjusted to two types of thresholds. A threshold of boulder-transport, which is associated with large floods that are competent to entrain boulders but are incapable of bedrock erosion; and another higher threshold that is exceeded by truly high-energy processes that generate large total energy and exceed the threshold of bedrock resistance. The later threshold is exceeded only episodically, with fairly long periods of little or no bedrock erosion in between. Interestingly, meso-scale erosional features such as inner channels and well-developed potholes are nearly absent or inconspicuous within the gorge section. Whilst this could be partly attributed to the bedrock resistance, it appears that under the present hydro-geomorphic conditions the dominant fluvial activity is not directed towards the channel bed, but towards the banks. This is evident from the concentration of erosion on the outer banks and deposition of coarse gravel on the inner banks, and armoring of the channel bed. The main conclusion of the study is that the bedrock channel is increasing the flow resistance and energy losses by developing and enhancing the meandering pattern.