Field validation of the MTI Actigraph and BodyMedia armband monitor using the IDEEA monitor

Objective: Accelerometers offer considerable promise for improving estimates of physical activity (PA) and energy expenditure (EE) in free‐living subjects. Differences in calibration equations and cut‐off points have made it difficult to determine the most accurate way to process these data. The objective of this study was to compare the accuracy of various calibration equations and algorithms that are currently used with the MTI Actigraph (MTI) and the Sensewear Pro II (SP2) armband monitor. Research Methods and Procedures: College‐age participants (n = 30) wore an MTI and an SP2 while participating in normal activities of daily living. Activity patterns were simultaneously monitored with the Intelligent Device for Estimating Energy Expenditure and Activity (IDEEA) monitor to provide an accurate estimate (criterion measure) of EE and PA for this field‐based method comparison study. Results: The EE estimates from various MTI equations varied considerably, with mean differences ranging from ?1.10 to 0.46 METS. The EE estimates from the two SP2 equations were within 0.10 METS of the value from the IDEEA. Estimates of time spent in PA from the MTI and SP2 ranged from 34.3 to 107.1 minutes per day, while the IDEEA yielded estimates of 52 minutes per day. Discussion: The lowest errors in estimation of time spent in PA and the highest correlations were found for the new SP2 equation and for the recently proposed MTI cut‐off point of 760 counts/min (Matthews, 2005). The study indicates that the Matthews MTI cut‐off point and the new SP2 equation provide the most accurate indicators of PA.     

Cardiorespiratory and metabolic responses associated with children's physical activity during self-paced games

The aim of this study was to explore the possibility of identifying clusters of children's games based on estimated energy expenditures and (or) intensity when performed in a guided active play format. The study also investigated whether the identified active play game clusters were repeatable when the games were performed on different days. Children (9.7?± 1.1?years; n?= 12) were assessed for oxygen consumption, heart rate, energy expenditure (EE), and metabolic equivalent (MET) on a treadmill (at 4, 6, and 8?km·h(-1) (0% grade)). HR and ActiGraph GT1M accelerometer (ACC) generated linear regression equations were used to estimate EE. The ACC (3?s epochs) were used for estimating METs in assigning percent time at medium-vigorous physical activity (%MVPA) of 10 self-paced games. The results showed a consistent range of EEs (ACC-equation) from 13.57?kcal·(5?min)(-1) to 25.00?kcal·(5?min)(-1) (p?< 0.05); EEs (HR-equation) from 29.72 to 42.49?kcal·(5?min)(-1) (p?< 0.05); and %MVPA from 10% to 34% (p?< 0.05) (from ACC equations) across all games. These were reproducible from day to day (p?> 0.05). This study confirms the existence of active play children's game clusters that might be useful in formatting guided active play in a dose-response manner for children.     

Influences of calorie restriction and age on energy expenditure in the rhesus monkey

Caloric restriction (CR) is known to retard the aging process, and a marker of aging is decreased energy expenditure (EE). To assess longitudinal effects of CR on EE in rhesus monkeys (Macaca mulatta), data from 41 males (M) and 26 females (F) subjected to 9 or 15 yr of CR were studied. EE and body composition of monkeys 11-28 yr of age were measured using indirect calorimetry and dual X-ray absorptiometry. Total EE (24-h EE) was divided into daytime (day EE), nighttime (night EE), and daytime minus nighttime (D - N EE). M calorie-restricted monkeys showed a lower 24-h EE (means +/- SD = 568 +/- 96 kcal/day, P < 0.0001) than controls (C; 630 +/- 129 kcal/day). Calorie-restricted M had a lower night EE (difference = 36 kcal P < 0.0001) compared with C M, but after adjusting for FFM and FM, night EE was not different between calorie-restricted and C males (P = 0.72). The 24-h EE decreased with age (13 kcal decrease/yr, P < 0.0001), but there was no difference between CR and C. Adjusted for FFM and FM, D - N EE decreased with age (9 kcal/yr, P < 0.0001), with no interaction with age (P = 0.72). The F were compared with age-matched M selected from the male cohort. F had a lower 24-h EE (496 +/- 84 kcal/day) than M (636 +/- 139 kcal/day) (P < 0.0001). Adjusting for FFM and FM, night EE was lower in F compared with M (difference = 18 kcal, P = 0.077). Night EE did not differ between calorie-restricted and C younger monkeys after adjusting for FFM and FM. In conclusion, CR did not alter the age-related decrease in EE with CR.     

Doubly labeled water measurement of human energy expenditure during strenuous exercise

The energy expenditures (EE) of 23 adult male Marines were measured during a strenuous 11-day cold-weather field exercise at 2,200- to 2,550-m elevation by both doubly labeled water (2H2 18O, DLW) and intake balance methods. The DLW EE calculations were corrected for changes in baseline isotopic abundances in a control group that did not receive 2H2 18O. Intake balance EE was estimated from the change in body energy stores and food intake. Body energy-store changes were calculated from anthropometric [-1,574 +/- 144 (SE) kcal/day] and isotope dilution (-1,872 +/- 293 kcal/day) measurements made before and after the field exercise. The subjects kept daily logbook records of ration consumption (3,132 +/- 165 kcal/day). Mean DLW EE (4,919 +/- 190 kcal/day) did not differ significantly from intake balance EE estimated from food intake and either anthropometric (4,705 +/- 181 kcal/day) or isotope dilution (5,004 +/- 240 kcal/day) estimates of the change in body energy stores. The DLW method can be used with at least the same degree of confidence as the intake balance method to measure the EE of active free-living humans.     

Thermogenic responsiveness to nonspecific beta-adrenergic stimulation is not related to genetic variation in codon 16 of the beta2-adrenergic receptor

Stimulation of beta-adrenergic receptors (beta-AR) by the sympathetic nervous system (SNS) modulates energy expenditure (EE), but substantial interindividual variability is observed. We determined whether the thermogenic response to beta-AR stimulation is related to genetic variation in codon 16 of the beta(2)-AR, a biologically important beta-AR polymorphism, and whether differences in SNS activity (i.e., the stimulus for agonist-promoted downregulation) are involved. The increase in EE (DeltaEE, indirect calorimetry, ventilated hood) above resting EE in response to nonspecific beta-AR stimulation [iv isoproterenol: 6, 12, and 24 ng/kg fat-free mass (FFM)/min] was measured in 46 healthy adult humans [Arg16Arg: 9 male, 7 female, 48 +/- 5 yr; Arg16Gly: 11 male, 4 female, 53 +/- 5 yr; Gly16Gly: 3 male, 12 female, 48 +/- 5 yr (means +/- SE)]. Neither FFM-adjusted baseline resting EE (P = 0.83) nor the dose of isoproterenol required to increase EE 10% above resting (P = 0.87) differed among the three groups (Arg16Arg: 5,409 +/- 209 kJ/day, 11.2 +/- 2.1 ng x kg FFM(-1) x min(-1); Arg16Gly: 5,367 +/- 272 kJ/day, 11.1 +/- 2.1 ng x kg FFM(-1) x min(-1); Gly16Gly: 5,305 +/- 159 kJ/day, 10.5 +/- 1.4 ng x kg FFM(-1) x min(-1)). Consistent with this, muscle sympathetic nerve activity and plasma norepinephrine concentrations were not different among the groups. Group differences in sex composition did not influence the results. Our findings indicate that the thermogenic response to nonspecific beta-AR stimulation, an important mechanistic component of overall beta-AR modulation of EE, is not related to this beta(2)-AR polymorphism in healthy humans. This may be explained in part by a lack of association between this gene variant and tonic SNS activity.     

Validity of Physical Activity Intensity Predictions by ActiGraph,Actical, and RT3 Accelerometers

Objective: Accelerometers are promising tools for characterizing physical activity (PA) patterns in free‐living persons. To date, validation of energy expenditure (EE) predictions from accelerometers has been restricted to short laboratory or simulated free‐living protocols. This study seeks to determine the capabilities of eight previously published regression equations for three commercially available accelerometers to predict summary measures of daily EE. Methods and Procedures: Study participants were outfitted with ActiGraph, Actical, and RT3 accelerometers, while measurements were simultaneously made during overnight stays in a room calorimeter, which provided minute‐by‐minute EE measurements, in a diverse subject population (n = 85). Regression equations for each device were used to predict the minute‐by‐minute metabolic equivalents (METs) along with the daily PA level (PAL). Results: Two RT3 regressions and one ActiGraph regression were not significantly different from calorimeter measured PAL. When data from the entire visit were divided into four intensity categories—sedentary, light, moderate, and vigorous—significant (P < 0.001) over‐ and underpredictions were detected in numerous regression equations and intensity categories. Discussion: Most EE prediction equations showed differences of <2% in the moderate and vigorous intensity categories. These differences, though small in magnitude, may limit the ability of these regressions to accurately characterize whether specific PA goals have been met in the field setting. New regression equations should be developed if more accurate prediction of the daily PAL or higher precision in determining the time spent in specific PA intensity categories is desired.     

Energy expenditure of elite female runners measured by respiratory chamber and doubly labeled water.

To determine whether female athletes have unusually low energy requirements as suggested by many food intake studies, energy expenditure (EE) and intake were assessed in nine elite distance runners [26 +/- 3 (SD) yr, 53 +/- 4 kg, 12 +/- 3% body fat, and 66 +/- 4 ml.kg-1.min-1 maximal O2 uptake]. Subjects were admitted to a metabolic ward for 40 h during which 24-h sedentary EE was measured in a respiratory chamber. Free-living EE was then assessed by the doubly labeled water method for the next 6 days while the women recorded all food intake, daily body weight, and training mileage (10 +/- 3 miles/day). Energy intakes estimated from free-living EE (2,826 +/- 312 kcal/day) and body weight changes (-84 +/- 71 g/day) averaged 221 +/- 550 kcal/day in excess of those calculated from food records (2,193 +/- 466 kcal/day). The energy cost of training (1,087 +/- 244 kcal/day) was calculated as the difference between free-living EE and 24-h EE in the respiratory chamber (1,681 +/- 84 kcal/day) corrected for the thermic effect of food of the extra energy intake. These data do not support the hypothesis that training as a distance runner results in metabolic adaptations that lower energy requirements in women.     

Evaluation of low-intensity physical activity by triaxial accelerometry

Objective: To develop regression‐based equations that estimate physical activity ratios [energy expenditure (EE) per minute/sleeping metabolic rate] for low‐to‐moderate intensity activities using total acceleration obtained by triaxial accelerometry. Research Methods and Procedures: Twenty‐one Japanese adults were fitted with a triaxial accelerometer while also in a whole‐body human calorimeter for 22.5 hours. The protocol time was composed of sleep (8 hours), four structured activity periods totaling 4 hours (sitting, standing, housework, and walking on a treadmill at speeds of 71 and 95 m/min, 2 × 30 minutes for each activity), and residual time (10.5 hours). Acceleration data (milligausse) from the different periods and their relationship to physical activity ratio obtained from the human calorimeter allowed for the development of EE equations for each activity. The EE equations were validated on the residual times, and the percentage difference for the prediction errors was calculated as (predicted value ? measured value)/measured value × 100. Results: Using data from triaxial accelerations and the ratio of horizontal to vertical accelerations, there was relatively high accuracy in identifying the four different periods of activity. The predicted EE (882 ± 150 kcal/10.5 hours) was strongly correlated with the actual EE measured by human calorimetry (846 ± 146 kcal/10.5 hours, r = 0.94 p < 0.01), although the predicted EE was slightly higher than the measured EE. Discussion: Triaxial accelerometry, when total, vertical, and horizontal accelerations are utilized, can effectively evaluate different types of activities and estimate EE for low‐intensity physical activities associated with modern lifestyles.     

Thermic effect of food and beta-adrenergic thermogenic responsiveness in habitually exercising and sedentary healthy adult humans.

The thermic effect of food (TEF) is an important physiological determinant of total daily energy expenditure (EE) and energy balance. TEF is believed to be mediated in part by sympathetic nervous system activation and consequent beta-adrenergic receptor (beta-AR) stimulation of metabolism. TEF is greater in habitually exercising than in sedentary adults, despite similar postprandial sympathetic nervous system activation. We determined whether augmented TEF in habitually exercising adults is associated with enhanced peripheral thermogenic responsiveness to beta-AR stimulation. In separate experiments in 22 sedentary and 29 habitually exercising adults, we measured the increase in EE (indirect calorimetry, ventilated hood) during beta-AR stimulation (intravenous isoproterenol: 6, 12, and 24 ng x kg fat-free mass(-1) x min(-1)) and EE before and after a liquid meal (40% of resting EE; 53% carbohydrate, 32% fat, 15% protein). The increase in EE during incremental isoproterenol administration was greater (P = 0.01) in habitual exercisers (0.34 +/- 0.03, 0.54 +/- 0.04, 0.81 +/- 0.05 kJ/min; means +/- SE) than in sedentary adults (0.26 +/- 0.03, 0.40 +/- 0.03, 0.64 +/- 0.04 kJ/min). The area under the TEF response curve was also greater (P = 0.04) in habitual exercisers (160 +/- 9 kJ) than in sedentary adults (130 +/- 11 kJ) and was positively related to beta-AR thermogenic responsiveness (r = 0.32, P = 0.02). We conclude that TEF is related to beta-AR thermogenic responsiveness and that the greater TEF in habitual exercisers is attributable in part to their augmented beta-AR thermogenic responsiveness. Our results also suggest that peripheral thermogenic responsiveness to beta-AR stimulation is a physiological determinant of TEF and hence energy balance in healthy adult humans.     

Thermodynamic and kinetic characterization of Co-C bond homolysis catalyzed by coenzyme B(12)-dependent methylmalonyl-CoA mutase

Methylmalonyl-CoA mutase is a member of the family of coenzyme B(12)-dependent isomerases and catalyzes the 1,2-rearrangement of methylmalonyl-CoA to succinyl-CoA. A common first step in the reactions catalyzed by coenzyme B(12)-dependent enzymes is cleavage of the cobalt-carbon bond of the cofactor, leading to radical-based rearrangement reactions. Comparison of the homolysis rate for the free and enzyme-bound cofactors reveals an enormous rate enhancement which is on the order of a trillion-fold. To address how this large rate acceleration is achieved, we have examined the kinetic and thermodynamic parameters associated with the homolysis reaction catalyzed by methylmalonyl-CoA mutase. Both the rate and the amount of cob(II)alamin formation have been analyzed as a function of temperature with the protiated substrate. These studies yield the following activation parameters for the homolytic reaction at 37 degrees C: DeltaH(f)() = 18.8 +/- 0.8 kcal/mol, DeltaS(f)() = 18.2 +/- 0.8 cal/(mol.K), and DeltaG(f)() = 13.1 +/- 0.6 kcal/mol. Our results reveal that the enzyme lowers the transition state barrier by 17 kcal/mol, corresponding to a rate acceleration of 0.9 x 10(12)-fold. Both entropic and enthalpic factors contribute to the observed rate acceleration, with the latter predominating. The substrate binding step is exothermic, with a DeltaG of -5.2 kcal/mol at 37 degrees C, and is favored by both entropic and enthalpic factors. We have employed the available kinetic and spectroscopic data to construct a qualitative free energy profile for the methylmalonyl-CoA mutase-catalyzed reaction.     

Metabolic equivalent: one size does not fit all.

The metabolic equivalent (MET) is a widely used physiological concept that represents a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate (RMR). The value equating 1 MET (3.5 ml O2 x kg(-1) x min(-1) or 1 kcal x kg(-1) x h(-1)) was first derived from the resting O2 consumption (VO2) of one person, a 70-kg, 40-yr-old man. Given the extensive use of MET levels to quantify physical activity level or work output, we investigated the adequacy of this scientific convention. Subjects consisted of 642 women and 127 men, 18-74 yr of age, 35-186 kg in weight, who were weight stable and healthy, albeit obese in some cases. RMR was measured by indirect calorimetry using a ventilated hood system, and the energy cost of walking on a treadmill at 5.6 km/h was measured in a subsample of 49 men and 49 women (26-45 kg/m2; 29-47 yr). Average VO2 and energy cost corresponding with rest (2.6 +/- 0.4 ml O2 x kg(-1) x min(-1) and 0.84 +/- 0.16 kcal x kg(-1) x h(-1), respectively) were significantly lower than the commonly accepted 1-MET values of 3.5 ml O2 x kg(-1) x min(-1) and 1 kcal x kg(-1) x h(-1), respectively. Body composition (fat mass and fat-free mass) accounted for 62% of the variance in resting VO2 compared with age, which accounted for only 14%. For a large heterogeneous sample, the 1-MET value of 3.5 ml O2 x kg(-1) x min(-1) overestimates the actual resting VO2 value on average by 35%, and the 1-MET of 1 kcal/h overestimates resting energy expenditure by 20%. Using measured or predicted RMR (ml O2 x kg(-1) x min(-1) or kcal x kg(-1) x h(-1)) as a correction factor can appropriately adjust for individual differences when estimating the energy cost of moderate intensity walking (5.6 km/h).     

A moderate-intensity exercise program fulfilling the American College of Sports Medicine net energy expenditure recommendation improves health outcomes in premenopausal women

The purpose of this study was to assess and quantify the health outcomes associated with a moderate-intensity (50% VO2R) exercise program designed to achieve the American College of Sports Medicine net caloric expenditure guideline of 1,000 kcal x wk(-1). Fifteen apparently healthy but sedentary premenopausal women with the baseline characteristics (mean +/- SD age, height, weight, body composition, and VO2max: 37.4 +/- 6.3 yr, 166.2 +/- 6.2 cm, 72.1 +/- 11.2 kg, 32.5 +/- 5.8%, and 34.8 +/- 5.8 mL x kg(-1) x min(-1), respectively) participated in and completed the study. Exercise training was performed 3-4 days per week for 10 weeks in a progressive manner at moderate intensity (50% VO2R). There were significant (P < 0.05) improvements in VO2max (+2.5 mL x kg(-1) x min(-1)), systolic (-13.7 mm Hg) and diastolic (-6.4 mm Hg) blood pressure, high-density lipoprotein cholesterol (+3.2 mg x dL(-1)), fasting blood glucose (-4.9 mg x dL(-1)), and percent body fat (-1.6%). Although the American College of Sports Medicine specifies that the energy expenditure goal should be a net caloric expenditure of 1,000 kcal x wk(-1) and classifies relative moderate intensity as 40-59% of heart rate reserve or VO2R, we are unaware of any previous investigations that have examined the specific health outcomes associated with an exercise program fulfilling these requirements. Results indicate that significant health benefits will be conferred to previously sedentary, premenopausal women who engage in a moderate-intensity, 10-week exercise program designed to fulfill the net energy expenditure guideline of 1,000 kcal x wk(-1).     

Effect of exercise intensity on 24-h energy expenditure and nutrient oxidation.

The aim of this study was to determine the effects of exercise at different intensities on 24-h energy expenditure (EE) and substrate oxidation. Sixteen adults (8 men and 8 women) were studied on three occasions [sedentary day (Con), a low-intensity exercise day (LI; 400 kcal at 40% of maximal oxygen consumption) and a high-intensity exercise day (HI; 400 kcal at 70% of maximal oxygen consumption)] by using whole room indirect calorimetry. Both 24-h EE and carbohydrate oxidation were significantly elevated on the exercise days (Con < LI = HI), but 24-h fat oxidation was not different across conditions. Muscle enzymatic profile was not consistently related to 24-h fat or carbohydrate oxidation. With further analysis, it was found that, compared with men, women sustained slightly higher rates of 24-h fat oxidation (mg x kg FFM(-1) x min(-1)) and had a muscle enzymatic profile favoring fat oxidation. It is concluded that exercise intensity has no effect on 24-h EE or nutrient oxidation. Additionally, it appears that women may sustain slightly greater 24-h fat oxidation rates during waking and active periods of the day.     

Twenty-four-hour metabolic responses to resistance exercise in women

Seven nonobese adult females (40 +/- 8 years) were studied in a room calorimeter on a day that resistance exercise (REX) was performed (4 sets of 10 exercises) and on a nonexercise control day (CON). Twenty-four-hour energy expenditure (EE) on the REX day (mean +/- SD, 2,328 +/- 327 kcal.d(-1)) was greater than CON (2,001 +/- 369 kcal.d(-1), p < 0.001). The net increase in EE during and immediately after (30 minutes) exercise represented 76 +/- 12% of the total increase in 24-hour EE. Twenty four-hour RQ on the REX day (0.86 +/- 0.06) did not differ from CON (0.87 +/- 0.02). Twenty four-hour carbohydrate oxidation was elevated on the REX day, but 24-hour fat and protein oxidation were not different. Thus, in women, the increase in EE due to resistance exercise is largely seen during and immediately after the exercise. The increased energy demand is met by increased carbohydrate oxidation, with no increase in 24-hour fat oxidation.     

Regulation of endogenous glucose production after a mixed meal in type 2 diabetes

The extent and time course of suppression of endogenous glucose production (EGP) in type 2 diabetes after a mixed meal have been determined using a new tracer methodology. Groups of age-, sex-, and weight-matched normal controls (n = 8) and diet-controlled type 2 diabetic subjects (n = 8) were studied after ingesting a standard mixed meal (550 kcal; 67% carbohydrate, 19% fat, 14% protein). There was an early insulin increment in both groups such that, by 20 min, plasma insulin levels were 266 +/- 54 and 190 +/- 53 pmol/l, respectively. EGP was similar basally [2.55 +/- 0.12 mg x kg(-1) x min(-1) in control subjects vs. 2.92 +/- 0.16 mg x kg(-1) x min(-1) in the patients (P = 0.09)]. After glucose ingestion, EGP declined rapidly in both groups to approximately 50% of basal within 30 min of the meal. Despite the initial rapid decrease, the EGP was significantly greater in the diabetic group at 60 min (1.75 +/- 0.12 vs. 1.05 +/- 0.14 mg x kg(-1) x min(-1); P < 0.01) and did not reach nadir until 210 min (0.96 +/- 0.17 mg x kg(-1) x min(-1)). Between 60 and 240 min, EGP was 47% higher in the diabetic group (0.89 +/- 0.09 vs. 1.31 +/- 0.13 mg x kg(-1) x min(-1), P < 0.02). These data quantitate the initial rapid suppression of EGP after a mixed meal in type 2 diabetes and the contribution of continuing excess glucose production to subsequent hyperglycemia.     

Endocardial endothelium in the avascular frog heart: role for diffusion of NO in control of cardiac O2 consumption

We investigated the role of nitric oxide (NO) in the control of myocardial O(2) consumption in the hearts of female Xenopus frogs, which lack a coronary vascular endothelium and in which the endocardial endothelium is the only source of NO to regulate cardiac myocyte function. Hence, frogs are an ideal model in which to explore the role of diffusion of NO from the endocardial endothelium (EE) without vascular endothelial or cardiac cell NO production. In Xenopus hearts we examined the regulation of cardiac O(2) consumption in vitro at 25 degrees C and 37 degrees C. The NO-mediated control of O(2) consumption by bradykinin or carbachol was significantly (P < 0.05) lower at 25 degrees C (79 +/- 13 or 73 +/- 11 nmol/min) than at 37 degrees C (159 +/- 26 or 201 +/- 13 nmol/min). The response to the NO donor S-nitroso-N-acetyl penicillamine was also markedly lower at 25 degrees C (90 +/- 8 nmol/min) compared with 37 degrees C (218 +/- 15 nmol/min). When Triton X-100 was perfused into hearts, the inhibition of myocardial O(2) consumption by bradykinin (18 +/- 2 nmol/min) or carbachol (29 +/- 4 nmol/min) was abolished. Hematoxylin and eosin slides of Triton X-100-perfused heart tissue confirmed the absence of the EE. Although endothelial NO synthase protein levels were decreased to a variable degree in the Triton X-100-perfused heart, NO(2) production (indicating eNOS activity) decreased by >80%. It appears that the EE of the frog heart is the sole source of NO to regulate myocyte O(2) consumption. When these cells are removed, the ability of NO to regulate O(2) consumption is severely limited. Thus our results suggest that the EE produces enough NO, which diffuses from the EE to cardiac myocytes, to regulate myocardial O(2) consumption. Because of the close proximity of the EE to underlying myocytes, NO can diffuse over a distance and act as a messenger between the EE and the rest of the heart to control mitochondrial function and O(2) consumption.     

Effects of carbohydrate supplementation on performance and carbohydrate oxidation after intensified cycling training.

To study the effects of carbohydrate (CHO) supplementation on performance changes and symptoms of overreaching, six male endurance cyclists completed 1 wk of normal (N), 8 days of intensified (ITP), and 2 wk of recovery training (R) on two occasions in a randomized crossover design. Subjects completed one trial with a 6% CHO solution provided before and during training and a 20% solution in the 1 h postexercise (H-CHO trial). On the other occasion, subjects consumed a 2% CHO solution at the same time points (L-CHO). A significant decline in time to fatigue at approximately 63% maximal power output (H-CHO: 17 +/- 3%; L-CHO: 26 +/- 7%) and a significant increase in mood disturbance occurred in both trials after ITP. The decline in performance was significantly greater in the L-CHO trial. After ITP, a significant decrease in estimated muscle glycogen oxidation (H-CHO: N 49.3 +/- 2.9 kcal/30 min, ITP 32.6 +/- 3.4 kcal/30 min; L-CHO: N 49.1 +/- 30 kcal/30 min, ITP 39.0 +/- 5.6 kcal/30 min) and increase in fat oxidation (H-CHO: N 16.3 +/- 2.4 kcal/30 min, ITP 27.8 +/- 2.3 kcal/30 min; L-CHO: N 16.9 +/- 2.6 kcal/30 min, ITP: 25.4 +/- 3.5 kcal/30 min) occurred alongside significant increases in glycerol and free fatty acids and decreases in free triglycerides in both trials. An interaction effect was observed for submaximal plasma concentrations of cortisol and epinephrine, with significantly greater reductions in these stress hormones in L-CHO compared with H-CHO after ITP. These findings suggest that CHO supplementation can reduce the symptoms of overreaching but cannot prevent its development. Decreased endocrine responsiveness to exercise may be implicated in the decreased performance and increased mood disturbance characteristic of overreaching.     

Volume and enthalpy profiles of CO rebinding to horse heart myoglobin

Carbon monoxide binding to myoglobin was characterized using the photothermal beam deflection method. The volume and enthalpy changes coupled to CO dissociation were found to be 9.3+/-0.8 mL x mol(-1) and 7.4+/-2.8 kcal x mol(-1), respectively. The corresponding values observed for CO rebinding have the same magnitude but opposite sign: Delta V=-8.6+/-0.9 mL x mol(-1) and Delta H=-5.8+/-2.9 kcal x mol(-1). Ligand rebinding occurs as a single conformational step with a rate constant of 5 x 10(5) M(-1) s(-1) and with activation enthalpy of 7.1+/-0.8 kcal x mol(-1) and activation entropy of -22.4+/-2.8 cal x mol(-1) K(-1). Activation parameters for the ligand binding correspond to the activation parameters previously obtained using the transient absorption methods. Hence, at room temperature the CO binding to Mb can be described as a two-state model and the observed volume contraction occurs during CO-Fe bond formation. Comparing these results with CO dissociation reactions, for which two discrete intermediates were characterized, indicates differences in mechanism by which the protein modulates ligand association and dissociation.