Sedentary Day Research Articles

On being chronically ill.

On being chronically ill.

Effect of an acute bout of aerobic exercise on chemerin levels in obese adults

Serum chemerin concentrations are elevated in obese individuals and may play a role in type 2 diabetes. Exercise improves insulin sensitivity, which may be related to changes in chemerin. This study explored how an acute bout of aerobic exercise affected chemerin levels in non-diabetic obese adults. Blood samples from 11 obese adults were obtained during two separate conditions: sedentary (SED) and exercise (EX; 60-65% VO2peak). Samples were drawn at baseline, immediately following exercise and hourly for an additional 2h. ANOVA was used to test for differences in chemerin between conditions. Unadjusted analysis showed no difference in overall change (baseline to 2h post) in chemerin between conditions. During the 2-h post-exercise period, chemerin decreased to 12% below baseline, compared to a 2.5% increase above baseline during that time period on the sedentary day (p=0.06, difference in post-to-2h change between conditions). Controlling for homeostatic model assessment of insulin resistance (HOMA-IR), a significant difference existed between EX and SED in the change in chemerin from baseline to 2-h post (p=0.02). Stratified analyses showed a consistent exercise-induced decrease in chemerin among non-insulin resistant subjects, while chemerin increased during exercise among insulin resistant subjects, and then decreased post-exercise. An acute bout of exercise in obese individuals may elicit a drop in chemerin levels during the post-exercise period, and this response may vary based on insulin resistance.

Accumulation of Light-intensity Activity or Standing During a Workday Reduces Ambulatory Blood Pressure in Prehypertension

INTRODUCTION: Accumulation of slow walking (1 mph) on a treadmill desk throughout a workday can lower ambulatory blood pressure (ABP) during and after work hours. The contribution of posture to this effect is unknown. PURPOSE: To compare ABP response to a worksite walking (WALK), standing (STAND), Cycling (CYCLE) and sedentary (SED) day in adults. METHODS: Nine overweight (BMI = 29±3 kg/m2) prehypertensive (130±15/76±11 mmHg) adults (30±15 yr) participated in this randomized repeated-measures study. Four conditions (WALK, STAND, CYCLE, SED) were randomly performed one week apart. WALK, STAND, and CYCLE conditions consisted of periodically increasing activity time to 2.5 hours over the course of an 8-hour work day. WALK (1.0 mph) and STAND (0.0 mph) were completed on a treadmill placed underneath a TREKDESK. During the CYCLE condition subjects pedaled on a Monark cycle ergometer at a cadence and energy expenditure equivalent to WALK. Subjects remained seated during the SED condition. Participants wore an ABP cuff (Oscar 2, SunTech Medical) from 8 am until 10 pm on all conditions. Linear Mixed Models were used to detect condition differences in systolic (SBP) and diastolic (DBP) blood pressure. Chi square was used to detect frequency difference of BP thresholds. RESULTS: There was a whole-day (during and after work hours) SBP and DBP treatment effect (P<0.001). SBP during STAND (132±4 mmHg), WALK (133±5 mmHg) and CYCLE (129±4 mmHg) were lower when compared to SED (137±4 mmHg) (P<0.001). CYCLE was lower than WALK (P=0.003). For DBP, nly CYCLE (70±4 mmHg) was lower than SED (73±4 mmHg; P=0.008). Compared to SED, WALK, STAND and CYCLE reduced SBP load (% of readings >140 mmHg) by 5%, 4%, and 14%, respectively (P<0.005). CONCLUSION: Compared to sitting, accumulating 2.5 h of light physical activity or standing during an 8-h workday may help reduce ABP during and after work hours.

Advances in exercise, physical activity, and diabetes mellitus.

Advances in exercise, physical activity, and diabetes mellitus.

Transient energy deficit induced by exercise increases 24-h fat oxidation in young trained men.

Whole body fat oxidation increases during exercise. However, 24-h fat oxidation on a day with exercise often remains similar to that of sedentary day, when energy intake is increased to achieve an energy-balanced condition. The present study aimed to examine a possibility that time of the day when exercise is performed makes differences in 24-h fat oxidation. As a potential mechanism of exercise affecting 24-h fat oxidation, its relation to exercise-induced transient energy deficit was examined. Nine young male endurance athletes underwent three trials of indirect calorimetry using a metabolic chamber, in which they performed a session of 100 min of exercise before breakfast (AM), after lunch (PM), or two sessions of 50 min of exercise before breakfast and after lunch (AM/PM) at 65% of maximal oxygen uptake. Experimental meals were designed to achieve individual energy balance. Twenty-four-hour energy expenditure was similar among the trials, but 24-h fat oxidation was 1,142 ± 97, 809 ± 88, and 608 ± 46 kcal/24 h in descending order of its magnitude for AM, AM/PM, and PM, respectively (P < 0.05). Twenty-four-hour carbohydrate oxidation was 2,558 ± 110, 2,374 ± 114, and 2,062 ± 96 kcal/24 h for PM, AM/PM, and AM, respectively. In spite of energy-balanced condition over 24 h, exercise induced a transient energy deficit, the magnitude of which was negatively correlated with 24-h fat oxidation (r = -0.72, P < 0.01). Similarly, transient carbohydrate deficit after exercise was negatively correlated with 24-h fat oxidation (r = -0.40, P < 0.05). The time of the day when exercise is performed affects 24-h fat oxidation, and the transient energy/carbohydrate deficit after exercise is implied as a factor affecting 24-h fat oxidation.

Exercise and food compensation: exploring diet-related beliefs and behaviors of regular exercisers.

The goal of this qualitative study is to identify common beliefs and behaviors related to exercise and diet. Data were collected in focus group discussions with regular exercisers who were physically active between 1 and 5 h per week. Exercise objectives, beliefs and behaviors regarding food intake before, during, and after exercise, consumption of sport supplements, and dietary patterns on sedentary days were explored. All focus groups were audio-taped and transcribed verbatim. Transcripts were analyzed using a grounded theory approach. Participants reported that they reward themselves for being active by consuming food. Other exercisers had specific beliefs about dietary needs and how to compensate for exercise-induced losses along with exercise-related food likes and dislikes. The participants' food intake also depended on their personal exercise objectives, such as the goal of performing well in competitions. External and physiological factors also played a role in determining participants' dietary patterns. Results of this study show that exercising and dietary patterns are closely intertwined. In addition, we articulate new hypotheses and outline a research agenda that can help improve how regular exercisers eat.

The Psychophysical Connection Between Exercise, Hunger, and Energy Intake

Exercise is vitally important in the prevention of weight gain or maintaining weight status, as well as weight loss. High-intensity exercise causes a short-term suppression of hunger of approximately 15 to 60 minutes. Although there is evidence for compensatory food consumption, it usually does not make up for the energy deficit created by exercise. The exception occurs when individuals consume or reward themselves with energy-dense foods or drink. Because people tend to eat the same volume of food each day, on days when they exercise, they will remain in an energy deficit. However, on sedentary days, a positive energy balance is likely if caloric restriction is not imposed, which could result in weight gain. Caloric restriction alone leads to loss of lean body mass, while the inclusion of exercise with an energy deficit helps conserve lean tissue. There are a myriad physiological factors such as the concentration of hormones (GLP-1, PYY3-36, leptin, and ghrelin) and metabolites (free fatty acids and glucose) that either stimulate or inhibit signals for hunger and/or energy intake, but the effect of exercise on these circulating factors is complex and not completely understood.

Reduced Hypoglycemia and Increased Time in Target Using Closed-Loop Insulin Delivery During Nights With or Without Antecedent Afternoon Exercise in Type 1 Diabetes

OBJECTIVEAfternoon exercise increases the risk of nocturnal hypoglycemia (NH) in subjects with type 1 diabetes. We hypothesized that automated feedback-controlled closed-loop (CL) insulin delivery would be superior to open-loop (OL) control in preventing NH and maintaining a higher proportion of blood glucose levels within the target blood glucose range on nights with and without antecedent afternoon exercise.RESEARCH DESIGN AND METHODSSubjects completed two 48-h inpatient study periods in random order: usual OL control and CL control using a proportional-integrative-derivative plus insulin feedback algorithm. Each admission included a sedentary day and an exercise day, with a standardized protocol of 60 min of brisk treadmill walking to 65–70% maximum heart rate at 3:00 p.m.RESULTSAmong 12 subjects (age 12–26 years, A1C 7.4 ± 0.6%), antecedent exercise increased the frequency of NH (reference blood glucose <60 mg/dL) during OL control from six to eight events. In contrast, there was only one NH event each on nights with and without antecedent exercise during CL control (P = 0.04 vs. OL nights). Overnight, the percentage of glucose values in target range was increased with CL control (P < 0.0001). Insulin delivery was lower between 10:00 p.m. and 2:00 a.m. on nights after exercise on CL versus OL, P = 0.008.CONCLUSIONSCL insulin delivery provides an effective means to reduce the risk of NH while increasing the percentage of time spent in target range, regardless of activity level in the mid-afternoon. These data suggest that CL control could be of benefit to patients with type 1 diabetes even if it is limited to the overnight period.

Effect of combined thermal and electrical muscle stimulation on cardiorespiratory fitness and adipose tissue in obese individuals

To better understand how prolonged electrical muscle stimulation can improve cardiorespiratory risk markers in obese subjects, we investigated the effect of prolonged combined thermal and electrical muscle stimulation (cTEMS) on peak oxygen consumption (VO2peak) and body composition with subsequent lipolytic and mitochondrial activity in adipocytes. Eleven obese (BMI ≥ 30 kg/m(2)) individuals received cTEMS in three 60-minute sessions per week for 8 weeks. Activity levels and dietary habits were kept unchanged. Before and after the stimulation period, functional capacity was assessed by VO2peak, and body composition was analysed. Lipolytic activity was determined in abdominal adipose tissue by 24 hours of microdialysis on a sedentary day, and adipose tissue biopsies were taken for the gene expression analysis. Eight weeks of cTEMS significantly increased VO2peak from 28.9 ± 5.7 to 31.7 ± 6.2 ml/kg/min (p < 0.05), corresponding to an average increase of 1.2% per week. Oxygen uptake and work capacity also increased at the anaerobic threshold. Mean microdialytic glycerol concentration over 24 hours, an index of sedentary lipolytic activity, increased from 238 ± 60 to 306 ± 55 µM (p < 0,0001), but no significant changes in body composition were observed. In addition, PGC-1α and carnitine-palmitoyltransferase-2 mRNAs were significantly upregulated in subcutaneous abdominal adipose tissue. In obese individuals with unchanged lifestyles, 8 weeks of cTEMS significantly improved functional capacity towards a higher fatigue resistance. This increase also gave rise to elevated lipolytic activity and increased mitochondrial activity in abdominal adipose tissue.

Appetite, energy intake and resting metabolic responses to 60 min treadmill running performed in a fasted versus a postprandial state

This study investigated the effect of fasted and postprandial exercise on appetite, energy intake and resting metabolic responses. Twelve healthy males (mean±SD: age 23±3years, body mass index 22.9±2.1kgm−2, maximum oxygen uptake 57.5±9.7mLkg−1min−1) performed three 10h experimental trials (control, fasted exercise and postprandial exercise) in a Latin Square design. Trials commenced at 8am after an overnight fast. Sixty min of treadmill running at ∼70% of maximum oxygen uptake was performed at 0–1h in the fasted exercise trial and 4–5h in the postprandial exercise trial. A standardised breakfast was provided at 1.5h and ad libitum buffet meals at 5.5 and 9.5h. Appetite ratings and resting expired air samples were collected throughout each trial. Postprandial exercise suppressed appetite to a greater extent than fasted exercise. Ad libitum energy intake was not different between trials, resulting in a negative energy balance in exercise trials relative to control after accounting for differences in energy expenditure (control: 9774±2694kJ; fasted exercise: 6481±2318kJ; postprandial exercise: 6017±3050kJ). These findings suggest that 60min treadmill running induces a negative daily energy balance relative to a sedentary day but is no more effective when performed before or after breakfast.

Continuous moderate‐intensity exercise with or without intermittent high‐intensity work: effects on acute and late glycaemia in athletes with Type 1 diabetes mellitus

Individuals with Type 1 diabetes mellitus are susceptible to hypoglycaemia during and after continuous moderate-intensity exercise, but hyperglycaemia during intermittent high-intensity exercise. The combination of both forms of exercise may have a moderating effect on glycaemia in recovery. The aims of this study were to compare the physiological responses and associated glycaemic changes to continuous moderate-intensity exercise vs. continuous moderate-intensity exercise + intermittent high-intensity exercise in athletes with Type 1 diabetes. Interstitial glucose levels were measured in a blinded fashion in 11 trained athletes with Type 1 diabetes during two sedentary days and during 2 days in which 45 min of afternoon continuous moderate-intensity exercise occurred either with or without intermittent high-intensity exercise. The total amount of work performed and the duration of exercise was identical between sessions. During exercise, heart rate, respiratory exchange ratio, oxygen utilization, ventilation and blood lactate levels were higher during continuous moderate-intensity + intermittent high-intensity exercise vs. continuous moderate-intensity exercise (all P < 0.05). Despite these marked cardiorespiratory differences between trials, there was no difference in the reduction of interstitial glucose or plasma glucose levels between the exercise trials. Nocturnal glucose levels were higher in continuous moderate-intensity + intermittent high-intensity exercise and in sedentary vs. continuous moderate-intensity exercise (P < 0.05). Compared with continuous moderate-intensity exercise alone, continuous moderate-intensity + intermittent high-intensity exercise was associated with less post-exercise hypoglycaemia (5.2 vs. 1.5% of the time spent with glucose < 4.0 mmol/l) and more post-exercise hyperglycaemia (33.8 vs. 20.4% of time > 11.0 mmol/l). Although the decreases in glucose level during continuous moderate-intensity exercise and continuous moderate-intensity + intermittent high-intensity exercise are similar, the latter form of exercise protects against nocturnal hypoglycaemia in athletes with Type 1 diabetes.

Journal of Diabetes NEWS

Journal of Diabetes NEWS

Effects of short-term exercise and energy surplus on hormones related to regulation of energy balance

Energy surplus raises circulating concentrations of leptin and insulin while lowering plasma ghrelin. Exercise has the opposite effects. The purpose of this study was to determine whether exercise counters the hormonal effects of energy surplus independent of changes in energy balance. To do that, we assessed plasma concentrations of leptin, insulin, and ghrelin at baseline, after overfeeding, and after overfeeding plus exercise. Baseline (B) leptin and insulin concentrations and ghrelin area under the curve were measured during an oral glucose challenge in 9 healthy, active subjects (6 male, 3 female) after 2 days in energy balance without exercise. Measurements were repeated after subjects were overfed by +3213 ± 849 kJ/d for 3 more sedentary days (OF). In the third condition, the same net energy surplus (+3125 ± 933 kJ/d) was generated for 24 hours by doubling the overfeeding (+6284 ± 1669 kJ/d) and countering it with a bout of exercise (expenditure = 3063 ± 803 kJ); and measurements were made the next day (OF + EX). Compared with B, leptin went up (5.8 ± 8.2 to 7.6 ± 10.6 ng/mL) after OF, but was not significantly higher after OF + EX (7.1 ± 10.2 ng/mL). Compared with B, insulin was +36% and +43% higher after OF and OF + EX, respectively. In contrast, ghrelin area under the curve did not change after OF but was significantly lower (−14%) than B or OF after OF + EX (indicating greater suppression). These data suggest that the effect of short-term exercise on fasting leptin and insulin depends on energy balance but the ghrelin response may be partially mediated by effects of exercise independent of energy balance.

Changes in 24-h substrate oxidation in older and younger men in response to exercise

The purpose of this study was to compare 24-h substrate oxidation in older (OM; 60-75 yr, n = 7) and younger (YM; 20-30 yr, n = 7) men studied on sedentary day (Con) and on a day with exercise (Ex; net energy expenditure = 300 kcal). Plasma glucose and free fatty acids were also measured at several time points during the 24-h measurement. Weight was not different in OM and YM (means +/- SD; 84.8 +/- 16.9 vs. 81.4 +/- 10.4 kg, respectively), although percent body fat was slightly higher in OM (25.9 +/- 3.5 vs. 21.9 +/- 9.7%; P = 0.17). Values of 24-h energy expenditure did not differ in OM and YM on the Con (means +/- SE; 2,449 +/- 162 vs. 2,484 +/- 104 kcal/day, respectively) or Ex (2,902 +/- 154 vs. 2,978 +/- 122 kcal/day) days. Under both conditions, 24-h respiratory quotient was significantly lower and fat oxidation significantly higher in OM. Glucose concentrations were not different at any time point, but plasma free fatty acid concentrations were higher in OM, particularly following meals. Thus, under these controlled conditions, 24-h fat oxidation was not reduced and was in fact greater in OM. We speculate that differences in the availability of circulating free fatty acids in the postprandial state contributed to the observed differences in 24-h fat oxidation in OM and YM.

Impact of Exercise on Overnight Glycemic Control in Children with Type 1 Diabetes Mellitus

To examine the effect of exercise on overnight hypoglycemia in children with type 1 diabetes mellitus (T1DM). At 5 clinical sites, 50 subjects with T1DM (age 11 to 17 years) were studied in a clinical research center on 2 separate days. One day included an afternoon exercise session on a treadmill. On both days, frequently sampled blood glucose levels were measured at the DirecNet central laboratory. Insulin doses were similar on both days. During exercise, plasma glucose levels fell in almost all subjects; 11 (22%) developed hypoglycemia. Mean glucose level from 10 pm to 6 am was lower on the exercise day than on the sedentary day (131 vs 154 mg/dL; P=.003). Hypoglycemia developed overnight more often on the exercise nights than on the sedentary nights (P=.009), occurring on the exercise night only in 13 (26%), on the sedentary night only in 3 (6%), on both nights in 11 (22%), and on neither night in 23 (46%). Hypoglycemia was unusual on the sedentary night if the pre-bedtime snack glucose level was>130 mg/dL. These findings indicate that overnight hypoglycemia after exercise is common in children with T1DM and support the importance of modifying diabetes management after afternoon exercise to reduce the risk of hypoglycemia.

Impact Of Energy Surplus And Exercise On The Insulin Response To Glucose

Short-term overfeeding (3–7 days) reduces insulin sensitivity whereas short-term exercise training enhances it. Despite real-world relevance, the impact of combined overfeeding and exercise has not been evaluated in humans. PURPOSE To test the hypothesis that a single exercise bout would improve the insulin response to a glucose challenge despite a considerable energy surplus. METHODS The baseline insulin sensitivity index (C-ISI) and area under the curves (AUC) for glucose and insulin were measured during an oral glucose tolerance test in nine healthy, recreationally active subjects (6 M, 3 F, 28.3 ± 7.5 yr, 74.9 ±13.5 kg, 54.9 ± 10.4 ml kg−1. min−1) after 48h without exercise while being fed a weight maintenance diet. The tests were repeated after 3 more sedentary days in which positive energy balance of+768 ± 68 kcal.d-1 was maintained by overfeeding (OF). Finally, C-ISI and AUC were assessed the day after overfeeding by +1502 ± 133 kcal.d which was offset by exercise expenditure of 732 ± 64 kcal to maintain approximately the same energy surplus (+747 ± 74 kcal ·d−1; OF+EX). RESULTS Blood glucose response did not differ under any condition. Compared to baseline, fasting insulin increased 41 % and 47% for OF and OF+EX, respectively. Compared to baseline, C-ISI was lower (indicating less insulin sensitivity) for OF and OF+EX (6.8 ± 0.9, 4.7 ± 0.6, 5.0 ± 2.3, respectively). OF increased the insulin AUC, whereas OF+EX decreased the insulin AUC but not to baseline levels. CONCLUSION When opposed by energy surplus a single exercise bout improves the insulin response to glucose, but the magnitude of this response may be blunted.

Effects of Short-Term Endurance Training on Aortic Distensibility in Young Males

Short-term endurance exercise training can increase aortic distensibility. The effect of exercise on arterial distensibility, however, may not last long term. We evaluated the effects of short-term exercise training and detraining on aortic distensibility in 10 sedentary young males (21.0 +/- 0.6 yr, mean +/- SE; range 19-24 yr). The subjects underwent 8 wk of endurance training on a cycle ergometer at 70% of maximal oxygen consumption (VO(2max)), for 60 min at a time and on alternate days (3-4 d.wk(-1). The detraining period consisted of a return to sedentary days for 8 wk. The aortic pulse wave velocity (APWV) was measured before and immediately after training and during the detraining period. The VO(2max) was significantly increased after training (pre: 2240.0 +/- 71.4 mL, after: 2728.8 +/- 82.5 mL, mean +/- SE, P < 0.0001) and remained at increased levels during the detraining period (after 4 wk: 2671.2 +/- 73.6 mL, P < 0.001; after 8 wk: 2628.0 +/- 85.0 mL, P < 0.001). The APWV was significantly decreased after training (pre: 5.80 +/- 0.15 m.s(-1), after: 5.50 +/- 0.21 m.s(-1), P < 0.01) but returned close to the baseline after detraining for 4 wk (5.66 +/- 0.13 m.s, P < 0.18). Our data suggest that short-term exercise training can improve aortic distensibility, but the effect cannot be maintained without continuing physical exercise.

A sedentary day: effects on subsequent sleep and body temperatures in trained athletes

Exercise effects on sleep in fit healthy people have been difficult to determine because their sleep is close to optimal, leaving little room for improvement. Another method for assessing exercise effects on sleep is to significantly reduce the degree of activity in highly active people. Fifteen trained athletes who exercised daily at a moderate to high intensity were employed. By requesting that subjects remain sedentary in the laboratory for an entire day, the effect of reduced exercise on subsequent sleep parameters was assessed. Sleep and temperature were recorded after a sedentary day and after a normal day of moderate to high activity (control condition) in a counterbalanced design. In the sedentary condition, slow-wave sleep (SWS) decreased by a mean of 15.5±7.0 min and slow-wave activity (SWA) differed significantly ( P<.05) between conditions in the first hour of sleep only. Rapid eye movement (REM) sleep increased by a mean of 17.9±5.7 min in the sedentary condition, while sleep onset latency (SOL) to Stages 1 and 2 increased by 10.2 and 10.7 min, respectively, and REM sleep latency decreased by 24.0±6.8 min (all P<.05). Between conditions, there was no overall effect on total sleep time (TST), sleep efficiency, wake after sleep onset or core or foot temperatures ( P>.05). With reduced exercise load, SWS pressure may have been reduced, resulting in lower levels of SWS and increased REM sleep. Thus, the data indicate that reducing exercise has significant effects on sleep that may have implications for athletes tapering for competition.

Occasional physical inactivity combined with a high-fat diet may be important in the development and maintenance of obesity in human subjects

A better understanding of the environmental factors that contribute to obesity is imperative if any therapeutic effect on the increasing prevalence of overweight and obesity in the United States is to be achieved. This study examined the effect of the interaction of diet composition and physical inactivity on energy and fat balances. Thirty-five normal-weight and obese subjects were randomly assigned to either a 15-d isoenergetic high-carbohydrate (HC) or high-fat (HF) diet according to a crossover design. During the first 14 d, body weight and physical activity were maintained. On day 15, subjects spent 23 h in a whole-room indirect calorimeter and were fed a diet similar to that consumed during the previous 7 d while remaining physically inactive. Energy intakes required to maintain body weight stability during the first 14 d were similar between diets. Normal-weight and obese subjects consuming both diets had a positive energy balance on the sedentary day (day 15), suggesting that subjects were less active in the calorimeter. There was no significant effect of diet composition on total energy balance and total protein-energy balance on day 15; however, carbohydrate balance was more positive with the HC (2497.8 +/- 301.2 kJ) than with the HF (1159 +/- 301.2 kJ) diet (P = 0.0032). Most importantly, fat balance was more positive with the HF (1790.8 +/- 510.4 kJ) than with the HC (-62.8 +/- 510.4 kJ) diet (P = 0.0011). Chronic consumption of a high-carbohydrate diet could provide some protection against body fat accumulation in persons with a pattern of physical activity that includes frequent sedentary days.

Effects of aerobic fitness on fat oxidation and body fatness.

This study investigated the contributions of physical fitness and body composition to 24-h fat oxidation in adults under sedentary conditions in a whole-room calorimeter. The following measurements were studied in 109 adults (49 male/45 female) at least 36 h after a bout of exercise: 1) aerobic fitness level assessed by VO2max, 2) body composition determined by underwater weighing, 3) resting metabolic rate (RMR) after an overnight fast, and 4) 24-h energy expenditure (EE) and substrate oxidation determined in a whole-room calorimeter. While in the calorimeter, subjects were provided with a diet (15% protein, 30% fat, and 55% carbohydrate) estimated to produce energy balance on a sedentary day and of similar nutritional composition to their daily dietary intake. We found strong negative correlations between VO2max and % body fat in both male and female subjects, but no relationship between VO2max and 24-h EE under the sedentary conditions of this study. In male subjects, VO2max (mL O2 x kg(-1) fat-free mass x min(-1)) was negatively related to fat oxidation (r = -0.397, P < 0.005), and fat oxidation was more closely related to fat mass (r = 0.434, P < 0.0002) than to fat-free mass (r = 0.165, NS). In contrast, none of these relationships were significant in females. The results show that in male subjects under sedentary conditions, 24-h fat oxidation is positively related to body fat mass and negatively related to VO2max (the marker used here for level of physical fitness). This supports our hypothesis that regularly active males maintain lower body fat stores as the low contribution to daily fat oxidation from a lower body fat mass is counterbalanced by the high contribution to fat oxidation from daily physical activity. The lack of a relationship between VO2max and 24-h EE under the sedentary conditions of this study suggests that the major effects of physical activity on total daily EE and fat oxidation may occur during and relatively quickly after an exercise bout. Further, these data also suggest that cessation of regular exercise will likely be associated with a high risk of positive fat balance and weight gain.