Comparison of methods to estimate physical activity and energy expenditure in African American children.

Low levels of physical activity and high levels of obesity among children in the US is a public health concern. Accurate methods to estimate physical activity are needed to determine the efficacy of intervention programs and to explore relationships between daily physical activity and health status in children. The purpose of this study was to compare the simultaneous use of the Tritrac-R3D accelerometer (Tritrac), Yamax SW-200 Digiwalker step-counter (Digiwalker) and the Self Administered Physical Activity Checklist (SAPAC) to assess physical activity (PA) and energy expenditure (EE) in African-American children aged 7 to 10 years, using the doubly-labeled water (DLW) as the criterion method. Physical activity and energy expenditure were measured over seven consecutive days under free-living conditions. Resting metabolic rate and peak VO(2) were measured before the experimental period. There was no difference in physical activity energy expenditure (PAEE) measured by Tritrac or DLW (p > 0.05). Tritrac activity counts were highly correlated with DLW-PAEE (r = 0.81). High correlations between Digiwalker and DLW were observed when body weight was considered. A low correlation (r = 0.49) was observed between the physical activity energy expenditure by SAPAC and DLW. In conclusion, with some limitations the Tritrac and Digiwalker can provide useful and accurate information about PA and EE in 7- to 10-year-old children.

Ability of different physical activity monitors to detect movement during treadmill walking.

This study assessed the ability of four different activity monitors to discriminate changes in treadmill walking velocity. The relationships between walking velocity and bodily movement and between bodily movement and energy expenditure determined by indirect calorimetry (IC-EE or METs) were determined. Twenty-eight subjects walked at 3.2, 4.0, 4.8, 5.6, and 6.4 km/h (0 % grade) for 30 min on separate occasions. The Tritrac-R3D (TT), Computer Science & Applications, Inc. (CSA), and Mini-Logger (ML) activity monitors that measure bodily acceleration in one or three planes, and a Yamax Digiwalker-500 (YX) that records footsteps, were secured at the waistline of each subject. CSA monitors were also worn at the wrist and ankle. Walking velocity and bodily movement were significantly related (r = 0.89 to 0.93) for TT, CSA, ML, and YX. Importantly, changing each walking velocity produced significant changes in bodily movement that was detected by each monitor. Bodily movement and IC-EE were significantly related for TT, CSA, ML, and YX (r = 0.47 to 0.94). Compared to IC-EE, and at all walking speeds, EE was significantly overestimated by the TT, and EE was significantly underestimated by the YX. These results indicate that the activity monitors can differentiate bodily movement associated with walking at slow speeds better than they can estimate energy expenditure associated with walking at slow speeds.

Evaluation of methods to assess physical activity in free-living conditions.

PURPOSE: The purpose of this study was to compare different methods of measuring physical activity (PA) in women by the doubly labeled water method (DLW). METHODS: Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Body composition, basal metabolic rate (BMR), and peak oxygen consumption were also measured. Physical activity-related energy expenditure (PAEE) was then calculated by subtracting measured BMR and the estimated thermic effect of food from TDEE. Simultaneously, over the 7 d, PA was assessed via a 7-d Physical Activity Recall questionnaire (PAR), and subjects wore secured at the waist, a Tritrac-R3D (Madison, WI), a Computer Science Application Inc. activity monitor (CSA; Shalimar, FL), and a Yamax Digi Walker-500 (Tokyo, Japan). Pearson-product moment correlations were calculated to determine the relationships among the different methods for estimating PAEE. Paired t-tests with appropriate adjustments were used to compare the different methods with DLW-PAEE. RESULTS: There was no significant difference between PAEE determined from PAR and DLW. The differences between the two methods ranged from -633 to 280 kcal.d(-1). Compared with DLW, PAEE determined from CSA, Tritrac, and Yamax was significantly underestimated by 59% (-495 kcal.d(-1)), 35% (-320 kcal.d(-1)) and 59% (-497 kcal.d(-1)), respectively. VO2peak explained 43% of the variation in DLW-PAEE. CONCLUSION: Although the group average for PAR-PAEE agreed with DLW-PAEE, there were differences in the methods among the subjects. PAEE determined by Tritrac, CSA, and Yamax significantly underestimate free-living PAEE in women.

Characteristics of exercise behavior among college students: application of social cognitive theory to predicting stage of change.

BACKGROUND: Young adulthood is characterized by a steep decline in the level of physical activity, but few theory-based studies have examined characteristics associated with regular exercise in this population. This study applied Social Cognitive Theory (SCT) and the Stages of Change Model (SCM) to determine personal, behavioral, and environmental characteristics associated with exercise behavior and intentions among undergraduate university students. METHODS: A random sample of 937 undergraduate students (mean age 22.0 +/- 5.6 years; 84.7% ages 17-24 years) enrolled at a large Midwestern university completed a mailed questionnaire. Valid and reliable instruments were used to measure personal, behavioral, and environmental variables based on the SCT that were hypothesized to influence stage of exercise behavior change. Multivariate discriminant analysis was used to determine associations among these variables with stage of exercise behavior change. RESULTS: Exercise self-efficacy, physical activity history, and nonexercise estimation of aerobic capacity were significant predictors of the stage of exercise behavior change for both males and females. Among females, exercise self-efficacy (P < 0.001) and family social support (P < 0. 001) for physical activity were the best predictors of stage of exercise behavior change. Friend social support (P < 0.001), physical activity history (P < 0.001), and exercise self-efficacy (P < 0.001) were significant predictors of stage of exercise behavior change among males. CONCLUSIONS: The SCT framework predicted stage of exercise behavior change as defined by the SCM. Exercise self-efficacy was associated with exercise stage, but the source of significant social support (family versus friends) was different for males and females.

Comparisons of four methods of estimating physical activity in adult women.

PURPOSE: To compare four different methods of measuring physical activity (PA) in adult women under free-living conditions. METHODS: Twelve women participated in a 7-d period during which PA was assessed via self-report, accelerometry and step-counting. Subjects wore at the waist a Tritrac-R3D accelerometer, a Computer Science Application Inc. activity monitor (CSA), both of which measure bodily accelerations in various planes, and a Yamax Digi-Walker-500 that records steps. After the 7-d period subjects responded to a 7-d Physical Activity Recall interview (PAR). RESULTS: Physical activity-related energy expenditure (PAEE) determined from PAR was significantly higher than PAEE estimated from either the Tritrac, CSA, or the Yamax data. Time spent in light, moderate, and hard physical activity was not significantly different between PAR, CSA, and Tritrac. Log-transformed activity counts from CSA were highly correlated with log-transformed Tritrac results (r > 0.90). Number of steps recorded by the Yamax was significantly correlated with untransformed Tritrac and CSA results. CONCLUSIONS: Based upon comparisons with PAR, Tritrac, CSA, and Yamax underestimate the amount of PAEE by 25, 46, and 48%, respectively. The correspondence between the Tritrac and CSA results suggests that both devices produce similar estimates of bodily movement in free-living women. The relationships among results for Tritrac, CSA, and Yamax indicate that the number of steps recorded by the Yamax is representative of the amount of physical activity performed during the day as estimated by Tritrac and CSA. These results should be useful when selecting a method to measure PA in individuals under free-living conditions.

Reliability of power output during intermittent high-intensity cycling.

PURPOSE: We determined the number of trials on consecutive days required to establish high reliability of an intermittent high-intensity cycling test in subjects unfamiliar with multiple-sprint exercise. We also examined the extent to which this reliability could be maintained for 6 d. METHODS: Five untrained men performed a multiple-sprint test (10 x 7 s, with each sprint separated by 30 s) on each of four consecutive days (days 1-4), then rested for 6 d, and finally performed two additional tests on consecutive days (days 11 and 12). For statistical comparisons (analyses of variance), mean power outputs during sprints 8, 9, and 10 (MP8-10) on each test day were calculated for each of the 4th, 5th, and 6th seconds of the sprints, i.e., MP8-10(4th), MP8-10(5th), and MP8-10(6th). Peak power during each sprint was also examined. RESULTS: For days 3 and 4, values for MP8-10(4th), MP8-10(5th), and MP8-10(6th) were greater than on day 1 (P < 0.05). MP8-10(6th) on day 2 was also greater than on day 1 (P < 0.05). There were no differences in MP8-10 among days 2, 3, 4, 11, and 12. Also, peak power on day 1 was lower (P < 0.05) than peak power for all other days, which were not different from one another. The coefficients of variation (CV) for MP8-10 on day 3 versus day 4 were 3.3%, 2.5%, and 2.9% for MP8-10(4th), MP8-10(5th), and MP8-10(6th), respectively. The CV for MP8-10(4th), MP8-10(5th), and MP8-10(6th) on days 4, 11, and 12 ranged from 2.1 to 3.9%, with an overall mean of 3.1%. The greatest CV for MP8-10 was 5.2% for MP8-10(6th) on days 2 versus 3 and 2 versus 4. The mean CV for peak power for all pairwise combinations of days 4, 11, and 12 was 2.8%. CONCLUSIONS: In conclusion, satisfactory reliability of intermittent cycling tests is achieved after two familiarization sessions identical to the tests, and that reliability can be maintained for 6 d.

The efficacy of carbohydrate supplementation and chronic high- carbohydrate diets for improving endurance performance.

Carbohydrate (CHO) is the body's most limited fuel and the most heavily metabolized during moderate-intensity exercise. For this reason it is recommended that endurance athletes consume a high-CHO diet (8-10 g CHO . kg body weight-1 . day-1) to enhance training and performance. A review of the literature supports the benefits of CHO supplementation on endurance performance. The benefits of chronic high-CHO diets on endurance performance are not as clear. Recent evidence suggests that a high-CHO diet may be necessary for optimal adaptations to training. However, the paucity of date in this area precludes any concrete conclusions. The practicality of high-CHO diets is not well understood. The available evidence would indicate that a high-CHO diet is the best dietary recommendation for endurance athletes.

Evaluation of a commercial accelerometer (Tritrac-R3 D) to measure energy expenditure during ambulation.

This study evaluated the ability of a commercially available accelerometer (Tritrac-R3 D) to measure energy expenditure in 16 subjects at rest (pre- and post-exercise) and during three different intensities of steady-state exercise (40-70% of peak oxygen consumption [VO2peak]) while ambulating on a treadmill (no grade). Oxygen consumption and the respiratory exchange ratio from indirect calorimetry and the vector magnitude of triaxial accelerations were used to estimate energy expenditure using the manufacturers' equations. There was a significant relationship between indirect calorimetry-derived energy expenditure and the energy expenditure derived from the accelerometer (r=0.96). Using analysis of variance, there was no difference in the energy expenditure derived by the two methods at rest before exercise and during the three different intensities of ambulatory exercise. There was a significant difference between energy expenditure derived via indirect calorimetry and with the accelerometer during rest after exercise, probably due to the failure of the accelerometer to accurately estimate the energy expenditure associated with the progressive decline in post-exercise oxygen consumption. Thus, this commercially available accelerometer appears to provide statistically acceptable estimates of energy expenditure at rest and during zero-grade treadmill ambulation up to about 70% VO2peak. This may indicate its acceptable utility for large-scale population studies of physical activity involving this mode of movement. The failure of the accelerometer to accurately estimate energy expenditure during recovery from exercise may contribute to an underestimation of energy expenditure in some physically active individuals.

Temperature of ingested water and thermoregulation during moderate-intensity exercise.

The effect of the temperature of ingested water on the rise in core temperature (Tco) during exercise is not clear. Seven trained subjects were recruited to complete 2 hr of recumbent cycling at 51% VO2peak in a temperate environment (Ta = 26 degrees C, relative humidity = 40%) on four occasions, while ingesting either no fluid (trial NF26), cold water (0.5 degree C; trial CD26), cool water (19 degrees C; trial CL26), or warm water (38 degrees C; trial WA26) during the second hour of exercise. A fifth trial was conducted during which convective and radiative heat loss were reduced by raising Ta to 31 degrees C. During this trial, subjects ingested cold water (0.5 degree C; trial CD31). When compared to WA26, over the second hour of exercise, CD26 attenuated the time-averaged changes in (Tco) and forearm blood flow and decreased whole-body sweat rate and forearm sweat rate (p < .05). Similarly, relative to WA26, the CL26 trial attenuated the time-averaged changes in Tco and reduced whole-body sweat rate (p < .05) during the second hour of exercise, but CL26 had no significant effect on forearm sweat rate or blood flow. Finally, regardless of beverage temperature, water ingestion (vs. NF26) reduced the time-averaged changes in Tco and in heat storage during the second hour of exercise (p < .05).

Exercise training down-regulates ob gene expression in the genetically obese SHHF/Mcc-fa(cp) rat.

The recently cloned obesity gene (ob) encodes a protein, leptin, which is secreted from adipose tissue and interacts with hypothalamic receptors to decrease appetite, increase energy expenditure, and reduce body lipid stores. The levels of ob mRNA are increased in several models of obesity, consistent with the hypothesis that obese animals may be resistant to the actions of leptin. The present study examined the impact of increased energy expenditure through exercise training on ob mRNA gene expression and body composition in the SHHF/Mc-fa(cp) male rat, a rodent model of obesity, insulin resistance, and type II diabetes. Six week old lean and obese animals were trained 8-12 weeks by treadmill running at 70% peak oxygen uptake, 5 days/wk, for 1.5 hr/day. After endurance training, exercised rats had significantly lower total body fat compared to sedentary rats of the same age, despite maintaining the same body weight. In the obese SHHF/Mcc-fa(cp) rat, the level of ob mRNA expression was markedly increased by four fold in subcutaneous adipose tissue compared to lean controls (p<0.05). In response to exercise training, there was a significant 85 % decrease in ob mRNA in exercised-training lean rats (p < 0.05) compared with non-exercised controls, while in obese-exercised rats, ob gene expression was significantly reduced only by 50% relative to non-exercised obese rats (p < 0.05). These results demonstrate that exercise training reduces fat mass and ob mRNA in lean and obese rats, and supports the hypothesis of a feedback loop between the adipocyte and hypothalamus that attempts to maintain body weight at a constant level by reducing ob gene expression in response to increased energy expenditure.

Exercise training and the glucose transport system in obese SHHF/Mcc-fa(cp) rats.

The effects of a similar exercise training stimulus on maximal insulin-stimulated (MIS) plasma membrane glucose transporter number and glucose transport were determined in lean and obese SHHF/Mcc-facp rats. Six-week-old lean and obese male rats were randomly divided into four groups: lean sedentary (LSed), obese sedentary (OSed), lean exercise (LEx), and obese exercise (OEx). An 8- to 12-wk treadmill running program equalized daily muscular work for LEx and OEx. Plasma membranes were isolated from control and MIS muscles of mixed fiber types. MIS significantly increased glucose transport (3.4- and 2.8-fold) in LSed and OSed, respectively. MIS significantly increased glucose transporter number (2.5-fold) in LSed, but there was no increase in glucose transporter number in OSed. Peak oxygen uptake and citrate synthase activity were increased a similar amount for LEx and OEx groups, demonstrating a similar training stimulus. MIS significantly and similarly increased glucose transport in LEx and OEx (4.4- and 5.1-fold, respectively). The effects of MIS on plasma membrane glucose transporter number in the exercise-trained rats were similar to the responses observed in the sedentary lean and obese groups. MIS significantly increased glucose transporter number (2.6-fold) in LEx, whereas there was no increase in glucose transporter number in OEx. The reduction in MIS glucose transport in OSed appears to be related to a defect in the processes associated with the translocation of glucose transporters to the plasma membrane. Exercise training of the obese rats apparently did not alter this defect. Similar increases in peak oxygen uptake, citrate synthase, and MIS glucose transport in LEx and OEx groups suggest that insulin resistance does not limit the ability of the glucose transport system to adapt to exercise training in the obese male SHHF/Mcc-facp rats.

American College of Sports Medicine position stand. Exercise and fluid replacement.

It is the position of the American College of Sports Medicine that adequate fluid replacement helps maintain hydration and, therefore, promotes the health, safety, and optimal physical performance of individuals participating in regular physical activity. This position statement is based on a comprehensive review and interpretation of scientific literature concerning the influence of fluid replacement on exercise performance and the risk of thermal injury associated with dehydration and hyperthermia. Based on available evidence, the American College of Sports Medicine makes the following general recommendations on the amount and composition of fluid that should be ingested in preparation for, during, and after exercise or athletic competition: 1) It is recommended that individuals consume a nutritionally balanced diet and drink adequate fluids during the 24-hr period before an event, especially during the period that includes the meal prior to exercise, to promote proper hydration before exercise or competition. 2) It is recommended that individuals drink about 500 ml (about 17 ounces) of fluid about 2 h before exercise to promote adequate hydration and allow time for excretion of excess ingested water. 3) During exercise, athletes should start drinking early and at regular intervals in an attempt to consume fluids at a rate sufficient to replace all the water lost through sweating (i.e., body weight loss), or consume the maximal amount that can be tolerated. 4) It is recommended that ingested fluids be cooler than ambient temperature [between 15 degrees and 22 degrees C (59 degrees and 72 degrees F])] and flavored to enhance palatability and promote fluid replacement. Fluids should be readily available and served in containers that allow adequate volumes to be ingested with ease and with minimal interruption of exercise. 5) Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration greater than 1 h since it does not significantly impair water delivery to the body and may enhance performance. During exercise lasting less than 1 h, there is little evidence of physiological or physical performance differences between consuming a carbohydrate-electrolyte drink and plain water. 6) During intense exercise lasting longer than 1 h, it is recommended that carbohydrates be ingested at a rate of 30-60 g.h(-1) to maintain oxidation of carbohydrates and delay fatigue. This rate of carbohydrate intake can be achieved without compromising fluid delivery by drinking 600-1200 ml.h(-1) of solutions containing 4%-8% carbohydrates (g.100 ml(-1)). The carbohydrates can be sugars (glucose or sucrose) or starch (e.g., maltodextrin). 7) Inclusion of sodium (0.5-0.7 g.1(-1) of water) in the rehydration solution ingested during exercise lasting longer than 1 h is recommended since it may be advantageous in enhancing palatability, promoting fluid retention, and possibly preventing hyponatremia in certain individuals who drink excessive quantities of fluid. There is little physiological basis for the presence of sodium in n oral rehydration solution for enhancing intestinal water absorption as long as sodium is sufficiently available from the previous meal.

Diabetic nephropathy in an aerobically trained rat model of diabetes.

The purpose of this study was to determine the effects of aerobic training on indices of glycemic control, blood pressure, serum lipids, and diabetic nephropathy (DN) in an animal model of insulin deficient diabetes mellitus. Thirty-four male Sprague-Dawley rats made diabetic with streptozocin were randomly assigned to a trained group or a sedentary group. Fifteen sedentary-nondiabetic rats served as a control group. The animals were trained on a treadmill at 18 m.min-1, 8 degrees incline for 120 min.d-1, 5 d.wk-1. Blood and 24 h urine collections were obtained at various intervals throughout the study. At 21 wk of age systolic blood pressure was measured and kidney tissue was obtained for light and electron microscopy. Analysis of variance was used to detect differences among the groups (P < or = 0.05). The diabetes produced in this investigation resulted in hyperglycemia, increased urine albumin and total protein excretion, elevated systolic blood pressure, increased fractional volume of the mesangium, and widening of the glomerular basement membrane in the sedentary-diabetic animals. Aerobic training significantly reduced the increase in fractional volume of the mesangium and fructosamine. Most importantly, aerobic training did not augment the renal damage seen in DN.

Metabolism of sugars and physical performance.

Physical activity in the form of exercise requires the metabolism of bodily fuel reserves to provide energy for muscle contraction. Under normal circumstances, very little protein is metabolized to provide the energy for muscle contraction. At rest and at low exercise intensities, the metabolism of fat provides a considerable proportion of the energy for resting metabolic processes and muscle contraction. However, at exercise intensities at which athletes train and compete, the metabolism of bodily carbohydrate reserves (eg, blood glucose and liver and muscle glycogen) provides the predominant fuel for muscle contraction. Furthermore, when these substrates reach critically low amounts or are decreased by some amount, fatigue occurs. There is a significant body of literature examining the effects of ingestion of various types of sugars at various times during exercise and during recovery from exercise on carbohydrate fuel reserves and on physical performance.

Fat loading: the next magic bullet?

The depletion or reduction of bodily carbohydrate reserves is associated with fatigue during endurance exercise. Various carbohydrate supplementation and exercise regimens have been used experimentally to increase carbohydrate reserves before exercise or to maintain the availability of carbohydrate for oxidation during exercise. On the other hand, the improved endurance capability observed after aerobic training has been attributed to an increased oxidation of fat relative to carbohydrate; this carbohydrate sparing presumably delays the point at which reduced carbohydrate reserves cause fatigue. This effect has led to the suggestion that a greater availability of fat during exercise can improve performance via the carbohydrate-sparing effect of "fat loading." Although this is a plausible hypothesis, it is not supported by a sufficient number of valid, credible, and replicated studies. Thus, it appears prudent to advise endurance athletes to consume a diet that is largely carbohydrate to optimize training and competitive performance and, more importantly, to promote optimal health.

Effects of acute running exercise on whole body insulin action in obese male SHHF/Mcc-facp rats.

This study utilized the obese male spontaneously hypertensive heart failure rat (SHHF/Mcc-facp), which has metabolic features very similar to human non-insulin-dependent diabetes mellitus. The purpose of this study was to assess the insulin sensitivity and responsiveness of whole body glucose disposal and insulin suppressability of hepatic glucose production with use of the euglycemic-hyperinsulinemic clamp procedure in 12- to 15-wk-old SHHF/Mcc-facp rats at rest (OS) and 2.5 h after a single session of acute exercise (OE). Lean male SHHF/Mcc-facp rats were sedentary (LS) control animals. At least three clamps producing different insulin-stimulated responses were performed on each animal in a randomized order. At this age the obese animals are normotensive and have not developed congestive heart failure. Compared with LS, OS were significantly hyperglycemic and hyperinsulinemic and insulin sensitivity and responsiveness of whole body glucose uptake and insulin suppressability of hepatic glucose production were significantly decreased. Compared with LS and OS, acute exercise significantly decreased resting plasma glucose but did not alter plasma insulin. Compared with OS, acute exercise significantly increased the insulin responsiveness of whole body glucose disposal but did not affect the sensitivity of whole body glucose disposal or insulin suppressability of hepatic glucose production. Compared with LS, however, acute exercise did not "normalize" the insulin responsiveness of whole body glucose disposal. Thus a single acute exercise session improves but does not normalize whole body insulin resistance in the SHHF/Mcc-facp rat.

Aerobic training and diabetic nephropathy in the obese Zucker rat.

The effects of aerobic exercise training on diabetes control and the development of renal microvascular disease were studied in the obese Zucker rat, an animal model of noninsulin dependent diabetes mellitus (NIDDM). Training consisted of 12 weeks of treadmill running, beginning at six weeks of age. Eight trained obese Zucker rats were compared to 15 obese sedentary controls and to 22 sedentary lean nondiseased littermates. Fasting blood glucose, percent of glycated hemoglobin, serum insulin, serum total cholesterol, body weight and kidney weight, creatinine clearance, urine total protein excretion, urine albumin excretion, and morphometric analyses of cortical glomeruli by light and electron microscopy were performed to evaluate metabolic control, renal function, and structure. Training was associated with less albuminuria, less mesangial volume expansion, and less glomerular basement membrane thickening compared to obese sedentary NIDDM animals. These results suggest that exercise training reduces the glomerular ultrastructural lesions and attenuates the albumin excretion rate in this rat model of obesity-related diabetes.

Effects of long-term cocaine administration and exercise on cardiac metabolism and isomyosin expression.

Although chronic cocaine use is cardiotoxic, its use remains problematic in athletics. Hence adaptive changes induced in the heart by superimposing chronic cocaine use on an exercise training are of interest but remain poorly understood. Therefore this study investigated the effects of cocaine treatment combined with exercise training on the metabolic and contractile properties of the heart. Male Sprague-Dawley rats were assigned to one of four groups: normal sedentary (NS, n = 6), cocaine sedentary (CS, n = 6), normal trained (NT, n = 6), and cocaine trained (CT, n = 6). Trained animals were sprint trained 4 times/week. CS and CT animals received cocaine (25 mg/kg, ip) 6 times/week, 15 min before each exercise bout and 2 additional times per week. After 12 weeks, all animals were sacrificed, and the hearts were removed and analyzed for citrate synthase activity, 3-hydroxyacyl-CoA dehydrogenase activity, Ca(2+)-activated myofibrillar ATPase activity, and myosin isoform distribution. None of the groups demonstrated altered cardiac metabolic properties, but cocaine alone and in conjunction with exercise reduced myofibrillar ATPase activity (p < 0.05) and increased expression of the low ATPase myosin isoform, V3. These data suggest that the potential of the citric acid cycle and beta-oxidation is not sensitive to chronic cocaine treatment, but the distribution of cardiac myosin among its three isoforms is affected. Furthermore, high-intensity treadmill training does not interact with cocaine to further alter these properties.

Metabolic responses when different forms of carbohydrate energy are consumed during cycling.

This study examined the effects of consuming the same amount of carbohydrate in solid form, liquid form, or both on metabolic responses during 2 hrs of cycling at 70% peak VO2 and on cycling time-trial performance. Subjects consumed 0.4 g carbohydrate/kg body mass before and every 30 min during exercise. The liquid was a 7% carbohydrate-electrolyte beverage and the solid was a sports bar (1171 kJ) in which 76%, 18%, and 6% of total energy was derived from carbohydrate, fat, and protein, respectively. Blood obtained at baseline, before exercise, and every 30 min was analyzed for glucose, insulin, lactate, hemoglobin, hematocrit, and plasma volume. There were no differences among the treatments for the blood parameters. Total carbohydrate oxidation and time-trial performance were also similar among treatments. Under thermoneutral conditions with equal liquid ingestion, the metabolic and performance responses are similar when consuming carbohydrate as a liquid, solid, or in combination during prolonged, moderate intensity cycling.

Duration of improved muscle glucose uptake after acute exercise in obese Zucker rats.

Skeletal muscle is insulin resistant in the obese Zucker rat. Endurance training reduces muscle insulin resistance, but the effects of a single acute exercise session on muscle insulin resistance in the obese Zucker rat are unknown. Therefore, insulin responsiveness of muscle glucose uptake was measured in 15-week-old obese rats either 1, 48, or 72 hours after two hours of intermittent exercise (30:30 min; work:rest). Hindlimbs of sedentary lean (LS) and obese (OS) rats and exercised obese (OE) rats were perfused after a 10-hour fast under both basal (0 mU x ml(-1)) and maximal (20 mU x ml(-1)) insulin concentrations to measure net glucose uptake. Insulin responsiveness of net glucose uptake was significantly reduced in OS compared to LS (8.5 +/- 1.6 vs 15.3 +/- 2.0 micromol x g(-1) x h(-1), respectively). Compared to OS, insulin responsiveness of net glucose uptake was significantly increased by 56% and 80% at 1 hour and 48 hours after acute exercise. However, 72 hours after acute exercise, the increased insulin responsiveness of net glucose uptake was no longer evident. These results indicate that improved responsiveness of muscle glucose uptake persists for at least 48 hours after two hours of acute intermittent exercise in 15-week-old obese Zucker rats.