Are small (though statistically significant) mean differences physiologically meaningful?
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Absorptiometry, Photon↗
Biomedical subjects
P A Molé
Publications and source records attributed to P A Molé.
Randomized trial of the short-term effects of dieting compared with dieting plus aerobic exercise on lactation performance.
BACKGROUND: Limiting postpartum weight retention is important for preventing adult obesity, but the effect of weight loss on lactation has not been studied adequately. OBJECTIVE: We evaluated whether weight loss by dieting, with or without aerobic exercise, adversely affects lactation performance. DESIGN: At 12+/-4 wk postpartum, exclusively breast-feeding women were randomly assigned for 11 d to a diet group (35% energy deficit; n = 22), a diet plus exercise group (35% net energy deficit; n = 22), or a control group (n = 23). Milk volume, composition, and energy output; maternal weight, body composition, and plasma prolactin concentration; and infant weight were measured before and after the intervention. RESULTS: Weight loss averaged 1.9, 1.6, and 0.2 kg in the diet, diet + exercise, and control groups, respectively (P < 0.0001) and was composed of 67% fat in the diet group and nearly 100% fat in the diet + exercise group. Change in milk volume, composition, and energy output and infant weight did not differ significantly among groups. However, there was a significant interaction between group and baseline percentage body fat: in the diet group only, milk energy output increased in fatter women and decreased in leaner women. The plasma prolactin concentration was higher in the diet and diet + exercise groups than in the control group. CONCLUSIONS: Short-term weight loss (approximately 1 kg/wk) through a combination of dieting and aerobic exercise appears safe for breast-feeding mothers and is preferable to weight loss achieved primarily by dieting because the latter reduces maternal lean body mass. Longer-term studies are needed to confirm these findings.
Adult↗
Myoglobin desaturation with exercise intensity in human gastrocnemius muscle.
The present study evaluated whether intracellular partial pressure of O(2) (PO(2)) modulates the muscle O(2) uptake (VO(2)) as exercise intensity increased. Indirect calorimetry followed VO(2), whereas nuclear magnetic resonance (NMR) monitored the high-energy phosphate levels, intracellular pH, and intracellular PO(2) in the gastrocnemius muscle of four untrained subjects at rest, during plantar flexion exercise with a constant load at a repetition rate of 0.75, 0.92, and 1.17 Hz, and during postexercise recovery. VO(2) increased linearly with exercise intensity and peaked at 1.17 Hz (15. 1 +/- 0.37 watts), when the subjects could maintain the exercise for only 3 min. VO(2) reached a peak value of 13.0 +/- 1.59 ml O(2). min(-1). 100 ml leg volume(-1). The (31)P spectra indicated that phosphocreatine decreased to 32% of its resting value, whereas intracellular pH decreased linearly with power output, reaching 6.86. Muscle ATP concentration, however, remained constant throughout the exercise protocol. The (1)H NMR deoxymyoglobin signal, reflecting the cellular PO(2), decreased in proportion to increments in power output and VO(2). At the highest exercise intensity and peak VO(2), myoglobin was approximately 50% desaturated. These findings, taken together, suggest that the O(2) gradient from hemoglobin to the mitochondria can modulate the O(2) flux to meet the increased VO(2) in exercising muscle, but declining cellular PO(2) during enhanced mitochondrial respiration suggests that O(2) availability is not limiting VO(2) during exercise.
Adolescent↗
VO(2) kinetics of mild exercise are altered by RER.
We propose that variations in fat and carbohydrate (CHO) oxidation by working muscle alter O(2) uptake (VO(2)) kinetics. This hypothesis provides two predictions: 1) the kinetics should comprise two exponential components, one fast and the other slow, and 2) their contribution should change with variations in fat and CHO oxidation, as predicted by steady-state respiratory exchange ratio (RER). The purpose of this study was to test these predictions by evaluating the VO(2) kinetic model: VO(2)(t) = alpha(R) + alpha(F)(1 - exp[(t - TD)/-tau(F)]) + alpha(C)(1 - exp[(t - TD)/-tau(C)]) for short-term, mild leg cycling in 38 women and 44 men, where VO(2)(t) describes the time course, alpha(R) is resting VO(2), t is time after onset of exercise, TD is time delay, alpha(F) and tau(F) are asymptote and time constant, respectively, for the fast (fat) oxidative term, and alpha(C) and tau(C) are the corresponding parameters for the slow (CHO) oxidative term. We found that 1) this biexponential model accurately described the VO(2) kinetics over a wide range of RERs, 2) the contribution of the fast (alpha(F), fat) component was inversely related to RER, whereas the slow (alpha(C), CHO) component was positively related to RER, and 3) this assignment of the fast and slow terms accurately predicted steady-state respiratory quotient and CO(2) output. Therefore, the kinetic model can quantify the dynamics of fat and CHO oxidation over the first 5-10 min of mild exercise in young adult men and women.
Adult↗
Dietary and performance assessment of elite soccer players during a period of intense training.
This study examined the nutritional and performance status of elite soccer players during intense training. Eight male players (age 17+/-2 years) of the Puerto Rican Olympic Team recorded daily activities and food intake over 12 days. Daily energy expenditure was 3,833+/-571 (SD) kcal, and energy intake was 3,952+/-1,071 kcal, of which 53.2+/-6.2% (8.3 g x kg BW(-1)) was from carbohydrates (CHO), 32.4+/-4.0% from fat, and 14.4+/-2.3% from protein. With the exception of calcium, all micronutrients examined were in accordance with dietary guidelines. Body fat was 7.6+/-1.1% of body weight. Time to completion of three runs of the soccer-specific test was 37.65+/-0.62 s, and peak torques of the knee flexors and extensors at 60 degrees x s(-1) were 139+/-6 and 225+/-9 N x m, respectively. Players' absolute amounts of CHO seemed to be above the minimum recommended intake to maximize glycogen storage, but calcium intakes were below recommended. Their body fat was unremarkable, and they had a comparatively good capacity to endure repeated bouts of intense soccer-specific exercise and to exert force with their knee extensors and flexors.
Activities of Daily Living↗
Body composition by air-displacement plethysmography by using predicted and measured thoracic gas volumes.
The BOD POD, a new air-displacement plethysmograph for measuring human body composition, utilizes the inverse relationship between pressure and volume (Boyle's law) to measure body volume directly. The quantity of air in the lungs during tidal breathing, the average thoracic gas volume (Vtg), is also measured by the BOD POD by using a standard plethysmographic technique. Alternatively, the BOD POD provides the use of a predicted Vtg (Vtgpred). The validity of using Vtgpred in place of measured Vtg (Vtgmeas) to determine the percentage of body fat (%BF) was evaluated in 50 subjects (36 women, 14 men; ages 18-56 yr). There was no significant difference between Vtgmeas and Vtgpred (mean difference +/- SE, 53.5 +/- 63.3 ml) nor in %BF by using Vtgmeas vs. Vtgpred (0.2 +/- 0.2 %BF). On an individual basis, %BF measured by using Vtgmeas vs. Vtgpred differed within +/-2.0% BF for 82% of the subjects; maximum differences were -2.9 to +3.0% BF. For comparison, data from 24 subjects who had undergone hydrostatic weighing were evaluated for the validity of using predicted vs. measured residual lung volume (VRpred vs. VRmeas, respectively). Differences between VRmeas and VRpred and in %BF calculated by using VRmeas vs. VRpred were significant (187 +/- 46 ml and 1.4 +/- 0.3% BF, respectively; P < 0.001). On an individual basis, %BF determined by using VRmeas vs. VRpred differed within +/-2.0% BF for 46% of the subjects; maximum differences were -2.9 to +3.8% BF. With respect to %BF measured by air displacement, our findings support the use of Vtgpred for group mean comparisons and for purposes such as screening in young to middle-aged individuals. This contrasts with the use of VRpred in hydrostatic weighing, which leads to significant errors in the estimation of %BF. Furthermore, although the use of Vtgpred has some application, determining Vtgmeas is relatively simple in most cases. Therefore, we recommend that the use of Vtgmeas remain as standard experimental and clinical practice.
Adipose Tissue↗
Effects of caffeine on blood pressure, heart rate, and forearm blood flow during dynamic leg exercise.
This study examined the acute effects of caffeine on the cardiovascular system during dynamic leg exercise. Ten trained, caffeine-naive cyclists (7 women and 3 men) were studied at rest and during bicycle ergometry before and after the ingestion of 6 mg/kg caffeine or 6 mg/kg fructose (placebo) with 250 ml of water. After consumption of caffeine or placebo, subjects either rested for 100 min (rest protocol) or rested for 45 min followed by 55 min of cycle ergometry at 65% of maximal oxygen consumption (exercise protocol). Measurement of mean arterial pressure (MAP), forearm blood flow (FBF), heart rate, skin temperature, and rectal temperature and calculation of forearm vascular conductance (FVC) were made at baseline and at 20-min intervals. Plasma ANG II was measured at baseline and at 60 min postingestion in the two exercise protocols. Before exercise, caffeine increased both systolic blood pressure (17%) and MAP (11%) without affecting FBF or FVC. During dynamic exercise, caffeine attenuated the increase in FBF (53%) and FVC (50%) and accentuated exercise-induced increases in ANG II (44%). Systolic blood pressure and MAP were also higher during exercise plus caffeine; however, these increases were secondary to the effects of caffeine on resting blood pressure. No significant differences were observed in heart rate, skin temperature, or rectal temperature. These findings indicate that caffeine can alter the cardiovascular response to dynamic exercise in a manner that may modify regional blood flow and conductance.
Adult↗
Between-day and within-day variability in the relation between heart rate and oxygen consumption: effect on the estimation of energy expenditure by heart-rate monitoring.
Estimation of energy expenditure (EE) by heart-rate (HR) monitoring (HRM) assumes that the relation between HR and oxygen consumption (VO2) is stable between days and within a day. To evaluate this assumption, 12 healthy subjects underwent an HR-VO2 calibration session on two mornings and two afternoons, with one morning and one afternoon session on the same day. Measurements were made while subjects were supine, sitting, standing while shifting body weight side-to-side, and walking at four intensities. Subjects wore an HR monitor during waking hours on another day (15.1 +/- 1.5 h). Regression analysis was used to determine the relation between HR and VO2 in the sedentary and active HR ranges, and four EE values (HRM-EE) based on the four calibration sessions were calculated for each subject. The four group mean HRM-EE values were nearly identical (CV: 1.1%). The regression equations generated from the four calibration sessions did not differ significantly for the group as a whole, but for some subjects there were significant differences among sessions in the slope of the active regression equation (P = 0.005). Intraindividual CVs for HRM-EE were generally < 10%, but ranged from 0.1% to 24.7%. In general, within an individual, HR was more variable than was VO2, and intraindividual variability in EE was associated with intraindividual variability in the flex HR and sedentary HR range. HRM is appropriate for assessment of EE for a group; however, caution is recommended when HRM is used for individual determinations of EE.
Adult↗
Phosphocreatine kinetics in humans during exercise and recovery.
System linearity was assessed for exercise induced changes in energetics of forearm exercise. 31P-NMR spectroscopy techniques, with 12.5-s serial measurements of [PCr], [Pi], [ATP], and [H+] were employed during exercise and recovery transitions in four untrained men for moderate (1.7 W) and heavy (3.6 W) exercise. Signal averaging was applied and data were analyzed by regression analysis using a first-order exponential model. The time constants for both [PCr] and [Pi] responses to moderate exercise and recovery were not different both within and between nuclei ranging from 32 to 35 s (P > 0.05). The time constants derived from moderate exercise and recovery, when employed to construct predictive equations for heavy exercise and recovery, did not adequately describe [PCr] dynamics. Underestimation of the net hydrolysis of PCr during heavy exercise was associated with increases in [H+] as predicted by the creatine kinase equilibrium reaction (CKeq). Calculation of [ADP] by CKeq revealed steady state [ADP] was achieved during moderate exercise and during recovery for both intensities much earlier than during heavy exercise. We conclude that the metabolic system does not behave as a linear system. Therefore, the time constant and the net change in [PCr].W-1 must themselves be determined by work dependent combinations of other system variables.
Adenosine Triphosphate↗
Evaluation of a new air displacement plethysmograph for measuring human body composition.
A new air displacement plethysmograph, the BOD POD (BP), was evaluated in comparison to hydrostatic weighing (HW). Sixty-eight adult subjects (26 F, 42 M) varying widely in age (range 20-56 yr), ethnicity, and fatness participated in this study. Same-day test-retest reliability was assessed in a subsample of 16 subjects (9 F, 7 M) and validity was assessed in all subjects (N = 68). The test-retest coefficients of variation (CV) for %FAT measured by BP (%FATBP) and HW (%FATHW) were not significantly different (1.7% +/- 1.1% and 2.3% +/- 1.9% for BP and HW, respectively (mean +/- SD)), indicating excellent reliability for both methods. Validity of percent fat measured by the BP (%FATBP) was also excellent. The mean difference in %FAT (BP - HW) was -0.3 +/- 0.2 (SEM), with a 95% confidence interval of -0.6 to 0 %FAT. The regression equation (%FATHW = 1.86 + 0.94 %FATBP; r2 = 0.93, SEE = 1.81) was not significantly different from the line of identity (%FATHW = %FATBP), and did not differ by gender. These findings indicate that the BOD POD is a highly reliable and valid method for determining %FAT in adult humans in comparison to HW. This new method has several advantages over HW in that it is quick, relatively simple to operate and may be able to accommodate special populations such as the obese, elderly, and disabled.
Adipose Tissue↗
Effect of suspending exercise training on resting metabolic rate in women.
We tested the hypothesis that enhanced resting metabolic rate (RMR) in highly trained endurance athletes is an acute effect of prior exercise induced by catecholamines and not serum thyroxine. RMR and energy-regulating hormones were studied in nine highly trained women runners during habitual training (period I), and suspension of training (period II). Data were collected during the follicular phase of two consecutive menstrual cycles, confirmed by serum progesterone and estradiol. Subjects maintained training between the two periods. Total energy intake and diet composition, body weight, and oral temperature did not change from period I to period II (P greater than 0.05). With suspension of training, urinary epinephrine and nonrepinephrine excretion dropped (P less than 0.022) while serum TSH rose (P = 0.011) and free T4 did not change (P = 0.182). RMR (mean +/- SEM) was 274 +/- 6.2 and 252 +/- 7.8 kJ.h-1 for periods I and II, respectively, with repeated measures ANOVA indicating a drop in RMR occurred with cessation of exercise (P = 0.048). The augmentation of RMR by exercise lasted more than 15 h but less than 39 h post-exercise. The results suggest that the drop in catecholamines may partly explain the lower RMR following suspension of training.
Basal Metabolism↗
Linear and nonlinear characteristics of oxygen uptake kinetics during heavy exercise.
We assessed the linearity of oxygen uptake (VO2) kinetics for several work intensities in four trained cyclists. VO2 was measured breath by breath during transitions from 33 W (baseline) to work rates requiring 38, 54, 85, and 100% of maximal aerobic capacity (VO2max). Each subject repeated each work rate four times over 8 test days. In every case, three phases (phases 1, 2, and 3) of the VO2 response could be identified. VO2 during phase 2 was fit by one of two models: model 1, a double exponential where both terms begin together close to the start of phase 2, and model 2, a double exponential where each of the exponential terms begins independently with separate time delays. VO2 rose linearly for the two lower work rates (slope 11 ml.min-1 W-1) but increased to a greater asymptote for the two heavier work rates. In all four subjects, for the two lighter work rates the double-exponential regression reduced to a single value for the time constant (average across subjects 16.1 +/- 7.7 s), indicating a truly monoexponential response. In addition, one of the responses to the heaviest work rate was monoexponential. For the remaining seven biexponential responses to the two heaviest work rates, model 2 produced a significantly better fit to the responses (P less than 0.05), with a mean time delay for the slow component of 105 +/- 46 s.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Impact of energy intake and exercise on resting metabolic rate.
Resting metabolic rate is modulated by the amount of calories consumed in the diet relative to energy expenditure. Excessive consumption of energy appears to increase resting metabolic rate while fasting and very low calorie dieting causes resting metabolic rate to decrease. Since the metabolic rate at rest is the primary component of daily energy expenditure, its reduction with caloric restriction makes it difficult for obese individuals to lose weight and to maintain weight that is lost. Whether exercise has a carry-over effect on resting metabolic rate remains controversial, even though this question has been studied extensively during the last 90 years. Reasons for contradictory results include variations in control of prior diet and exercise patterns, inadequate exercise frequency, intensity and duration, and the possibility of response to exercise varying between individuals. Several lines of evidence suggest exercise may modulate resting metabolic rate. Bed rest in sedentary individuals leads to a reduction in resting metabolic rate. Similarly, in highly trained runners, cessation of daily exercise training lowers resting metabolic rate by about 7 to 10%. Resting metabolic rate is depressed in previously sedentary obese individuals on a very low calorie diet, but it quickly returns to the predieting level when exercise of sufficient frequency, intensity and duration is undertaken while dieting. These findings suggest caloric intake and daily exercise can modulate resting metabolic rate. Exercise of adequate intensity and duration may also enhance resting metabolic rate.
Basal Metabolism↗
Exercise reverses depressed metabolic rate produced by severe caloric restriction.
The effects of caloric restriction and exercise on resting metabolic rate (RMR) were studied in five obese humans. Subjects consumed a 500 kcal.d-1 diet for 4 wk, with the subjects remaining sedentary during the first 2 wk and then exercising 30 min daily at 60% VO2max during the last 2 wk of caloric restriction. After 2 wk of dieting, RMR decreased to approximately 87% of the pre-dieting control value. Over the last 2 wk of dieting with the addition of daily exercise, the fall in RMR was reversed as it returned to the pre-dieting level. In summary, daily exercise reversed the drop in RMR associated with severe caloric restriction.
Adult↗
Body composition analysis by bioelectrical impedance: effect of skin temperature.
Bioelectrical impedance analysis (BIA) was used to estimate body water and composition under both cool (14.4 degrees C, dry bulb) and warm (35.0 degrees C) ambient conditions in eight healthy adult men. The prediction equation provided with the commercially available instrument (RJL Systems) was used with the BIA measurements to estimate body composition. Skin temperature increased from 24.1 +/- 1.81 degrees C in the cool condition to 33.4 +/- 1.36 degrees C in the warm condition. (Mean increase was 9.3 +/- 1.75 degrees C, t = 15.05, P less than 0.01). The corresponding BIA resistances were 461 +/- 48 omega and 426 +/- 47 omega, respectively. (Mean reduction was 35.0 +/- 9.8 omega, t = 10.13, P less than 0.01). This resulted in a significant increase in predicted total body water (cool 47.4 +/- 5.5 l vs. warm 49.9 +/- 5.6 l, t = 3.88, P less than 0.01). Consequently, predicted fat mass was significantly lower in the warm than in the cool condition (8.8 +/- 3.2 kg vs. 11.0 +/- 3.7 kg; mean difference 2.23 +/- 0.69 kg, t = 9.22, P less than 0.01). These findings indicate that varying skin temperature by altering ambient temperature significantly changes resistance measurements and the estimation of total body water and percent fat by BIA. The observed changes in resistance are consistent with an apparent expansion of conductor volume in the warm environment and a reduction in the cooler condition. In this regard, the temperature-induced change in resistance could be due to alterations in cutaneous blood flow and/or compartmental distribution of body water. Thus, BIA measurements should be taken only under well-standardized ambient conditions.
Adipose Tissue↗
Discrepancy in stoichiometry of steady-state muscle [Pi] and [PCr] induced by exercise.
Phosphorus nuclear magnetic resonance was used to quantify the relations between metabolic phosphates, intracellular pH, and work rate in forearm muscle of six adult men over a range of work rates from 1.0 to 3.5 W. Three work rates were studied in each of four sessions (either 1.0, 2.0, and 3.0 or 1.5, 2.5, and 3.5 W), with measurements made before and during each bout, thereby permitting the partition of the variance attributable to rest, work-dependent, and time-dependent metabolic functions by regression analysis. There were no time-dependent changes in either [ATP] or intracellular [H+] as assessed during the rest intervals between bouts of exercise. In contrast, the total nuclear magnetic resonance (NMR)-visible phosphorus pool (TVPP) decreased with time, with both phosphocreatine (PCr) and inorganic phosphate (Pi) contributing significantly to TVPP reduction. Muscle [ATP] was unchanged by work at all intensities. Intracellular [H+] increased moderately and proportionately to work rate. [PCr] decreased and [Pi] increased in proportion to work rate, with the work-dependent coefficient for PCr consumption approximately 1.5 times that of Pi production. Neither Pi line width nor motion artifact accounted for the decrease in TVPP, so the reduced Pi accumulation in exercise may represent its sequestering in some NMR-invisible muscle pool and/or loss to the blood. Whatever the process involved, it is proportional to work rate and persists for at least 10-15 min after exercise.
Adenosine Triphosphate↗
Simulation of pulmonary O2 uptake during exercise transients in humans.
Computer simulation of blood flow and O2 consumption (QO2) of leg muscles and of blood flow through other vascular compartments was made to estimate the potential effects of circulatory adjustments to moderate leg exercise on pulmonary O2 uptake (VO2) kinetics in humans. The model revealed a biphasic rise in pulmonary VO2 after the onset of constant-load exercise. The length of the first phase represented a circulatory transit time from the contracting muscles to the lung. The duration and magnitude of rise in VO2 during phase 1 were determined solely by the rate of rise in venous return and by the venous volume separating the muscle from the lung gas exchange sites. The second phase of VO2 represented increased muscle metabolism (QO2) of exercise. With the use of a single-exponential model for muscle QO2 and physiological estimates of other model parameters, phase 2 VO2 could be well described as a first-order exponential whose time constant was within 2 s of that for muscle QO2. The use of unphysiological estimates for certain parameters led to responses for VO2 during phase 2 that were qualitatively different from QO2. It is concluded that 1) the normal response of VO2 in humans to step increases in muscle work contains two components or phases, the first determined by cardiovascular phenomena and the second primarily reflecting muscle metabolism and 2) the kinetics of VO2 during phase 2 can be used to estimate the kinetics of muscle QO2. The simulation results are consistent with previously published profiles of VO2 kinetics for square-wave transients.
Computer Simulation↗
Measurement of solute proton spin-lattice relaxation times in water using the 1,3,3,1 sequence.
1H NMR spin-lattice relaxation times (T1) of the N-CH3 proton resonances of phosphocreatine (PCr) and creatine (Cr) in water solutions were obtained using the 1,3,3,1 pulse sequence. These T1 values were equivalent to those obtained in D2O and water using either the conventional inversion-recovery experiment or the 1,3,3,1 pulse sequence. Thus, the 1,3,3,1 sequence of proton NMR can provide an independent means along with phosphorous NMR for assess PCr and for the study of the creatine kinase reaction (PCr + ADP in equilibrium ATP + Cr) in aqueous solutions and perhaps in biological preparations.
Adenosine Diphosphate↗