Biomedical subjects

R T Withers

Publications and source records attributed to R T Withers.

At least 55 records · Page 3Linked to original sources

PubMed1992

Differences in energy metabolism between normal weight 'large-eating' and 'small-eating' women.

Nine 'large-eating' (approximately 12 MJ/d) and nine 'small-eating' (approximately 5.3 MJ/d) women were selected from the population on the basis of diet and activity diaries. At rest and in the post-absorptive state the rate of oxygen consumption (VO2)/kg fat-free mass (FFM) and rate of carbon dioxide production (VCO2)/kg FFM were 9-17% higher (P < 0.05) in the 'large-eaters' than in the 'small-eaters'. As energy expenditure was increased by walking at 2.4, 3.9 and 5.4 km/h the differences between the two experimental groups for both VO2/kg FFM and VCO2/kg FFM were decreased to negligible values, but energy expended on a body-weight basis (MJ/kg per min) remained significantly higher (5-10%) in 'large-eaters'. Oral temperature was also consistently higher (up to 0.5 degrees) in this group both at rest and during sitting, standing and walking activities. Although the average thermic effect of a standardized liquid meal tended to be higher (27%; not significant) in the 'small-eaters', the other results demonstrate that the 'large-eating' females had a markedly higher rate of energy expenditure at rest and during light physical activities.

Adult↗

PubMed1992

No differences in rates of energy expenditure between post-obese women and their matched, lean controls.

Rates of energy expenditure at rest, during different daily activities and following a standardized liquid meal were compared in eight post-obese women, with a mean weight loss of 21.5 kg (range 14.1 to 33.3 kg) and eight controls who had never been overweight. Age, height, body mass index, fat-free mass and average daily energy intake were similar for both experimental groups. Resting metabolic rate averaged 23.04 cal/min/kg FFM (s.e.m. 1.14) in the post-obese and 22.70 cal/min/kg FFM (s.e.m. 0.64) in the controls on their first visit to the laboratory. Metabolic rates in the two groups rose in parallel as energy expenditure was increased by sitting, standing and walking at three different speeds (2.4, 3.9 and 5.4 km/h). At the highest walking speed energy expenditure averaged 95.30 cal/min/kg FFM (s.e.m. 4.18) in the post-obese and 93.42 cal/min/kg FFM (s.e.m. 2.97) in the control women. Comparisons of postprandial thermogenesis revealed no significant differences between the two groups. The results of the present study do not support the thesis that rates of energy expenditure, whether at rest, during different activities, or after eating, are reduced in post-obese women.

Adult↗

PubMed1992

A comparison of four methods of estimating the body composition of male endurance athletes.

Comparisons were effected of the following four methods of estimating the percent body fat (%BF) of 12 highly trained male endurance athletes (mean +/- SD = 2.20 +/- 4.9 years, 176.8 +/- 5.9 cm 64.2 +/- 6.4 kg): underwater weighing (UWW), total body water (TBW), total body potassium (TBK) and dual-energy X-ray absorptiometry (DEXA). The DEXA mean of 6.8% BF was significantly less (P < 0.05) than those estimated via UWW: 9.7% BF; TBW: 10.6% BF (fat-free mass of FFM = 72.0% H2O); and TBK: 9.7% BF (FFM = 66.6 mmol K.kg-1). Nevertheless, the DEXA % BF correlated 0.746 and 0.737 (both P < 0.01) with those from UWW and TBW, respectively; these were the only correlation coefficients to attain statistical significance (P < or = 0.05). Despite the similar means for UWW, TBW and TBK, 12 of the 36 individual differences between these three methods ranged from 3.2 to 10.4% BF. A critical assumption of UWW, which is regarded by many as the criterion method for the estimation of % BF, is that the FFM has a density of 1.100 g.cm-3. Use of in vivo-measured TBW and bone mineral (via DEXA) for the computation of FFM densities for our subjects, while assuming that the two other components of the FFM (protein and non-bone mineral) remained constant, resulted in scores ranging from 1.09541 to 1.10246 g.cm-3 (mean +/- SD = 1.09881 +/- 0.00254 g.cm-3). FFM and % BF differences between use of a constant FFM density of 1.100 g.cm-3 and the individual values ranged from -1.02 to 0.57 kg (mean +/- SD = -0.28 +/- 0.60 kg) and from -0.9 to 1.7% BF (mean +/- SD = 0.5 +/- 0.9% BF), respectively. It may be concluded that with young male athletes: (1) use of constants based on normal male cadavers yielded similar group means for % BF determined by UWW, TBW and TBK but the DEXA % BF correlated significantly with those from UWW and TBW; and (2) in vivo measurements of individual differences in TBW and bone mineral support the use of conventional UWW for the estimation of % BF.

Absorptiometry, Photon↗

PubMed1992

The accuracy of dry gas meters at continuous and sinusoidal flows.

Dry gas meters are used in physiology laboratories to measure minute ventilation. The accuracy of these meters must be known since an error, of for instance 5%, affects the subsequent calculations for oxygen consumption by the same amount. Two precalibrated DTM-325 dry gas meters (American Meter Co., Philadelphia, PA, USA) were therefore tested for accuracy against a 350 l Collins chain-compensated gasometer. Provided that at least 25 l was passed per measurement then: a. continuous flows (air saturated with water vapour) between 60 and 150 l.min-1 were measured with an error of < 1%; and b. sinusoidal flows (ambient air) between 8 and 100 l.min-1 were misread by < 1% and the error was still within 2% at 140 l.min-1. It may, therefore, be concluded that the two precalibrated dry gas meters studied are valid volume measuring devices.

Calibration↗

PubMed1992

Physical training effects on the fitness and habitual activity patterns of elderly women.

This study investigated the effect of a twice-weekly, six-month progressive walking program on 80 healthy women aged 60 to 70 years. Aerobic fitness, blood pressure, skinfold thickness, spirometric variables, and activity profile were studied. No significant differences existed between the training group (TG) and the control group (CG) at the commencement of the study. However, after 26 weeks of training, the TG registered significantly lower heart rates than the CG, both at rest (p = .019) and during the five to six minutes of an ergometer work test (p = .003). A Mann-Whitney U test on the difference scores (26 weeks-0 week) indicated higher scores for the TG compared with the CG for Maximum Current Activity (p = .001) and Normative Impairment Index (p = .002), which are both components of the Human Activity Profile. These data suggest that adherence to a low-frequency training program can elicit positive physiologic changes in elderly women. Furthermore, increased habitual activity patterns are likely to be indicative of improvements in functional ability, lifestyle, and independence.

Aged↗

PubMed1991

Muscle metabolism during 30, 60 and 90 s of maximal cycling on an air-braked ergometer.

This study examined the anaerobic and aerobic contributions to muscle metabolism during high intensity short duration exercise. Six males [mean (SD): age 25.0 (6.0) years, height 179.0 (8.2) cm, mass 70.01 (7.42) kg, VO2max 4.63 (0.53) l.min-1, body fat 12.7 (2.3)%] performed three counterbalanced treatments of 30, 60 and 90 s of maximal cycling on an air-braked ergometer. All treatments were also performed on days when biopsies were not taken from the vastus lateralis muscle and cannulae not inserted into a forearm vein to ascertain whether these procedures adversely affected performance. The mean results can be summarised as follows: (Table: see text). The muscle lactate and O2 deficit data suggested that 60 and 90 s were more appropriate durations than 30 s for assessing the anaerobic capacity on an air-braked cycle ergometer. The mean power outputs also indicated that the invasive procedures did not adversely affect performance [corrected].

Adenosine Triphosphate↗

PubMed1991

Some aspects of metabolism following a 35 km road run.

The metabolism of eight men (mean: age, 26.0 years; maximal oxygen consumption, 65.0 ml.kg-1.min-1; body fat, 10.3%) was measured on counterbalanced control (baseline values for 8 h) and experimental (post 35 km run values for 8 h) days. The excess postexercise volume of oxygen consumed of 32.37 l and increase in energy used of 594 kJ during the 8 h after completion of the run were equivalent to average increases of 23.7 and 21.1%, respectively, when compared with time-matched controls. Furthermore, the oxygen uptake and energy expenditure were still elevated by 12.7 (P less than 0.0005) and 9.7% (P = 0.001), respectively, at the end of this period but the fact that they had returned to baseline 24 h after the 35 km road run contrasts with some reports in the literature that metabolism is still elevated at this time following less demanding exercise intensities. Rectal temperature was elevated by 2.3 degrees C at the end of the run but the difference had decreased to 0.2 degrees C by 7 h postexercise. The respiratory exchange ratio and changes in blood metabolites (nonesterified fatty acids, glycerol and ketone bodies) indicated a greater postexercise utilisation of fat notwithstanding a 6300 kJ meal ingested on both control and experimental days. The highest measured serum creatine kinase enzyme activity of 1151 U.l-1 (P less than 0.05) occurred 24 h postexercise, as compared with the control value of 145 U.l-1, and indicates the possibility of skeletal muscle damage.

3-Hydroxybutyric Acid↗

PubMed1991

The Drinkwater-Ross anthropometric fractionation of body mass: comparison with measured body mass and densitometrically estimated fat and fat-free masses.

The Drinkwater-Ross anthropometric fractionation of body mass (mass = sigma skeletal, residual, fat and muscle masses), lean body mass (LBM = sigma skeletal, residual and muscle masses) and fat mass (FM) were compared with the measured body mass, together with the densitometrically estimated fat-free mass (FFM) and fat mass (FM), of 205 male (mean +/- S.D.: 74.66 +/- 10.55 kg; 10.1 +/- 3.7% BF by densitometry) and 177 female (mean +/- S.D.: 59.14 +/- 8.85 kg; 18.5 +/- 5.1% BF by densitometry) South Australian State representatives in a variety of sports. Most absolute differences (d) between the measured body masses and those resultant from the sum of the four fractionated masses (male: d = 2.15 kg or 2.9%; female: d = 1.27 kg or 2.2%) were within what one would expect from random day-to-day variation. However, this was not so for the comparisons between the fractionated LBM (male: d = 2.54 kg or 3.8%; female: d = 2.45 kg or 5.2%) and FM scores (male: d = 1.67 kg or 30.0%; female: d = 2.40 kg or 20.0%) and their densitometric counterparts. These differences are probably related to a combination of the densitometric and fractionation assumptions.

Adipose Tissue↗

PubMed1990

The effect of exercise intensity and duration on the oxygen deficit and excess post-exercise oxygen consumption.

Nine males with mean maximal oxygen consumption (VO2max) = 63.0 ml.kg-1.min-1, SD 5.7 and mean body fat = 10.6%, SD 3.1 each completed nine counterbalanced treatments comprising 20, 50 and 80 min of treadmill exercise at 30, 50 and 70% VO2max. The O2 deficit, 8 h excess post-exercise oxygen consumption (EPOC) and EPOC:O2 deficit ratio were calculated for all subjects relative to mean values obtained from 2 control days each lasting 9.3 h. The O2 deficit, which was essentially independent of exercise duration, increased significantly (P less than 0.05) with intensity such that the overall mean values for the three 30%, 50% and 70% VO2max workloads were 0.83, 1.89 and 3.09 l, respectively. While there were no significant differences (P greater than 0.05) between the three EPOCs after walking at 30% VO2max for 20 (1.01 l), 50 (1.43 l) and 80 min (1.04 l), respectively, the EPOC thereafter increased (P less than 0.05) with both intensity and duration such that the increments were much greater for the three 70% VO2max workloads (EPOC: 20 min = 5.68 l; 50 min = 10.04 l; 80 min = 14.59 l) than for the three 50% VO2max workloads (EPOC: 20 min = 3.14 l; 50 min = 5.19 l; 80 min = 6.10 l). An analysis of variance indicated that exercise intensity was the major determinant of the EPOC since it explained five times more of the EPOC variance than either exercise duration or the intensity times duration interaction. The mean EPOC:O2 deficit ratio ranged from 0.8 to 4.5 and generally increased with both exercise intensity and duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

A comparison of the effects of measured, predicted, estimated and constant residual volumes on the body density of male athletes.

The aim of this study was to use the measured residual volume (RV) of male athletes (n = 207) as a criterion and assess the error in their RV, body density (BD) and relative body fat (%BF) associated with using RVs predicted from regression equations, RVs estimated from vital capacity (VC) and an assumed constant RV of 1300 ml. The ventilated residual volume (RV) was determined both before and after the underwater weighing by helium dilution with the subject immersed to neck level. The mean of the absolute differences Idl and SEE between the 2 RV trials were 66 and 89 ml, respectively. These increased to values ranging 195-747 and 259-308 ml, respectively, when the means of the 2 RV trials for each subject were compared with the RVs predicted via regression equations, estimated from the VC and assumed to be a constant of 1300 ml. A similar trend emerged with variation of only the RV in the BD formula for each subject. The 2 RV trials resulted in a Idl and SEE of .00109 (.5% BF) and .00145 g.cm-3 (.6% BF), respectively, but these increased to values ranging .00306 (1.3% BF)-.01207 (5.1% BF) and .00394 (1.7% BF)-.00441 g.cm-3 (1.9% BF), respectively, for predicted, estimated and assumed constant RVs. In all cases the lowest Idl and SEE were associated with the RVs predicted by a multiple regression equation (R = .616; SEE = 259 ml) which was generated on our sample.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗

PubMed1990

Effect of exercise intensity and duration on postexercise metabolism.

Data are reported on the net recovery O2 consumption (VO2) for nine male subjects (mean age 21.9 yr, VO2max 63.0 ml.kg-1.min-1, body fat 10.6%) used in a 3 (independent variables: intensities of 30, 50, and 70% VO2max) x 3 (independent variables: durations of 20, 50, and 80 min) repeated measures design (P less than or equal to 0.05). The 8-h mean excess postexercise O2 consumptions (EPOCs) for the 20-, 50-, and 80-min bouts, respectively, were 1.01, 1.43, and 1.04 liters at 30% VO2max (6.8 km/h); 3.14, 5.19, and 6.10 liters at 50% VO2max (9.5 km/h); and 5.68, 10.04, and 14.59 liters at 70% VO2max (13.4 km/h). The mean net total O2 costs (NTOC = net exercise VO2 + EPOC) for the 20-, 50-, and 80-min bouts, respectively, were 20.48, 53.20, and 84.23 liters at 30% VO2max; 38.95, 100.46, and 160.59 liters at 50% VO2max; and 58.30, 147.48, and 237.17 liters at 70% VO2max. The nine EPOCs ranged only from 1.0 to 8.9% of the NTOC (mean 4.8%) of the exercise. These data, therefore, indicate that in well-trained subjects the 8-h EPOC per se comprises a very small percentage of the NTOC of exercise.

Adult↗

PubMed1989

Effect of immersion on lung capacities and volumes: implications for the densitometric estimation of relative body fat.

Immersion of 18 male subjects in water caused a 20.4% (787 ml) increase (P less than 0.05) in the mean inspiratory capacity (IC) whereas there were no changes (P greater than 0.05) in tidal volume (VT) and the frequency of respiration. All the means for the other pulmonary variables decreased (P less than 0.05) by varying amounts: total lung capacity (TLC) = 8.4% (599 ml), vital capacity (VC) = 5.5% (308 ml), functional residual capacity (FRC) = 42.6% (1386 ml), expiratory reserve volume (ERV) = 61.9% (1095 ml) and residual volume (RV) = 19.7% (292 ml). Variation of only the RV in the body density (BD) formula from which the percentage body fat (%BF) is estimated resulted in a significantly (P less than 0.05) lower mean of 15.2% BF for the RV in air (means = 1482 ml) compared with that of 17.1% BF for the RV in water (means = 1190 ml). All but one of the subjects exhibited a smaller RV in water than in air; the six largest differences were equivalent to 2.4-5.1% BF. These results indicate that the net effect of the hydrostatic pressure (decreases RV), pulmonary vascular engorgement (decreases RV) and diminished compliance (increases RV) is to reduce the ventilated RV. It is therefore advisable to measure the RV when the subject is immersed in order to minimize error in the determination of BD and hence the estimation of % BF.

Adipose Tissue↗

PubMed1989

Spirometric standards for healthy male lifetime nonsmokers.

The FVC, FEV1.0, FEF25-75%, and FEV1.0/FVC (%) were measured in 162 males aged 18.9-78.6 yr using a Stead-Wells spirometer. Multiple regression equations were generated to predict these lung parameters from the best weighted combination (p less than or equal to 0.05) of age, standing height, sitting height, biacromial breadth, and chest expansion (FVC: R = 0.843, SEE = 513 ml BTPS; FEV1.0: R = 0.850, SEE = 436 ml BTPS; FEF25-75%: R = 0.665, SEE = 997 ml/s BTPS; FEV1.0/FVC: R = 0.537, SEE = 4.95%). The lower limit of normality was defined as the predicted value minus the 95% confidence interval (one-tailed test). Cross-validation of other FVC, FEV1.0, and FEF25-75% equations in the literature indicate that all the FVC and FEV1.0 ones are unsuitable for the sample and instrumentation used in this investigation.

Adult↗

PubMed1989

Lung volume and spirometric standards for healthy female lifetime nonsmokers.

The FRC, RV, VC, TLC, RV/TLC (%), FVC, FEV1.0, FEF25-75%, and FEV1.0/FVC (%) were measured in 161 South Australian females aged 18.4-81.2 yr using a Stead-Wells spirometer and helium analyzer. Multiple regression equations were generated to predict these lung volume and spirometric parameters from the best weighted combination of age, mass, standing height, and various other anthropometric variables (FRC: R = 0.715, SEE = 387 ml; RV: R = 0.684, SEE = 256 ml; VC: R = 0.815, SEE = 383 ml; TLC: R = 0.754, SEE = 468 ml; RV/TLC: R = 0.780, SEE = 4.2%; FVC: R = 0.839, SEE = 375 ml; FEV1.0: R = 0.869, SEE = 326 ml; FEV1.0/FVC: R = 0.644, SEE = 5.7%; FEF25-75%: R = 0.753, SEE = 802 ml/s). The range of normality for the lung volumes was defined as the predicted value plus or minus the 95% confidence interval (two-tailed test), and the lower limit of normality for the spirometric variables was designated as the predicted value minus the 95% confidence interval (one-tailed test). Cross-validation of other equations in the literature indicates that they are of limited use for the sample and instrumentation used in this study.

Adult↗

PubMed1988

An on-line microcomputer program for the monitoring of physiological variables during rest and exercise.

This paper describes a microcomputer system for the on-line display of physiological variables such as: lung ventilation, tidal volume, respiratory frequency, oxygen consumption, heart rate, oxygen pulse, respiratory exchange ratio, grams of fat and carbohydrate metabolised, mean skin temperature, rectal temperature and mean body temperature. The program has been written in Pascal. The modular nature of this language facilitates modification of the program to make it compatible with a variety of hardware and peripherals.

Calibration↗

PubMed1988

A comparison of the effects of measured, predicted, estimated and constant residual volumes on the body density of female athletes.

The body density (BD), and hence the relative body fat (% BF) was measured for 182 female athletes. The residual volume (RV) was determined both before and after the underwater weighing by a multiple breath helium dilution technique with the subject immersed to neck level. The absolute mean difference (lXdl) and SEE between the two RV trials were 63 and 75 ml, respectively. These increased to values ranging 144-685 and 187-252 ml, respectively, when the mean of the two RV trials for each subject was compared with the RVs predicted via regression equations, estimated from the vital capacity (VC) and assumed to be a constant of 1000 ml. A similar trend resulted from variation of only the RV in the BD formula for each subject. The two RV trials resulted in an lXdl and SEE of .00121 (.5% BF) and .00141 g.cm-3 (.6% BF), respectively, but these increased to values ranging .00283 (1.3% BF) -.01291 (5.7% BF) and .00362 (1.6% BF) -.00527 g.cm-3 (2.5% BF), respectively, for predicted, estimated and assumed constant RVs. In all cases, the lowest lXdl and SEE were associated with the RVs predicted by a multiple regression equation (R = .725; SEE = 187 ml) which was generated on our sample while the largest lXdl values were registered by the other regression equations. These data emphasize that the use of predicted, estimated and constant RVs result in substantial errors in BD and % BF compared with those when the RV is measured.

Adipose Tissue↗

PubMed1988

Glucose transport: locus of muscle insulin resistance in obese Zucker rats.

The purposes of this study were to determine whether the muscle insulin resistance of the obese rat is due to a defect in the glucose transport process and whether the insulin resistance is fiber-type specific. The hindlimbs of fasted, 14-wk-old obese (fa/fa) and lean (fa/?) Zucker rats were perfused with perfusate containing 8 mM glucose and no insulin or 8 mM glucose and either a physiological (0.15 mU/ml), a submaximal (1.50 mU/ml), or a maximal (15.0 mU/ml) insulin concentration. Glucose uptake was determined after which the initial rate of glucose transport was determined using 3-O-methyl-D-glucose (3-OMG). Glucose uptake of the obese rats was depressed by 40, 33, 42, and 47% in the absence of insulin and in the presence of the physiological, submaximal, and maximal insulin concentrations, respectively, when compared with lean littermates. Glucose transport in the absence and in the presence of the three insulin concentrations was significantly lower in the soleus (slow-twitch, oxidative fibers), red quadriceps (fast-twitch, oxidative, glycolytic fibers), and gastrocnemius (mixed fibers) of the obese rats when compared with lean rats. Glucose transport in the white quadriceps (fast-twitch, glycolytic fibers) was significantly lower in the obese rats in the absence of insulin and in the presence of the submaximal and maximal insulin concentrations. The glycogen concentration and the activity of hexokinase were the same and the glycogen synthase activity was higher in the muscles for the obese rats when compared to lean rats.(ABSTRACT TRUNCATED AT 250 WORDS)

3-O-Methylglucose↗

PubMed1988

Lung volume standards for healthy male lifetime nonsmokers.

Functional residual capacity (FRC), residual volume (RV), vital capacity (VC), and total lung capacity (TLC) were measured in 162 men aged 18.9 to 78.6 years using a multiple breath helium dilution technique. Multiple regression equations were generated to predict these lung parameters from the best weighted combination (p less than or equal to 0.05) of age, mass, standing height, body surface area, sitting height, biacromial breadth, end-tidal chest girth, expanded chest girth, and chest expansion (FRC: R = .748, SEE = 504 ml; RV: R = .725, SEE = 301 ml; VC: R = .808, SEE = 537 ml; TLC: R = .808, SEE = 551 ml; RV/TLC: R = .778, SEE = 4.15 percent). The range of normality was defined as the predicted value +/- the 95 percent confidence interval (two-tailed test). Cross-validation of other FRC, RV, VC, and TLC equations in the literature indicated that they were unsuitable for use with our data.

Adolescent↗