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Biomedical subjects

R T Withers

Publications and source records attributed to R T Withers.

At least 73 records · Page 4Linked to original sources
PubMed1987

Relative body fat and anthropometric prediction of body density of female athletes.

Ninety-one percent (n = 182) of the female members of South Australian representative squads in 14 sports volunteered to act as subjects. Twenty-seven percent of them had represented Australia. The underwater weighing method together with the measurement of residual volume (RV) by helium dilution were used to determine body density (BD); the percent body fat (% BF) was then computed according to Siri. A stepwise multiple regression analysis yielded a correlation coefficient (R) of 0.863 between the criterion (BD) and the best weighted sum of predictors (anthropometric variables): BD (g X cm-3) = 1.14075-0.04959 (log10 sigma triceps, subscapular, supraspinale and calf skinfolds in mm) + 0.00044 (age in decimal years)-0.000612 (waist girth in cm) + 0.000284 (height in cm)-0.000505 (gluteal girth in cm) + 0.000331 (breast girth in cm). Only those predictors which resulted in a statistically significant increase in R (p less than or equal to 0.05) were included. The standard error of estimate of 0.00597 g X cm-3 was equivalent to 2.7% BF at the mean. This equation was shown to be largely population specific. There was a range of 7.6-35.8% of BF and the overall mean 18.5% was significantly lower (p less than 0.001) than that of 23.4% obtained on a moderately active reference sample of similar age (n = 135). If group sizes of only one or two are regarded as too small for meaningful comparison, then the lowest mean of 13.5% was achieved by the long-distance runners (n = 14). The highest averages were registered by the heavyweight rowers (24.2%; n = 7) and soccer players (22.0%; n = 11). The overall average for games players (n = 107) was 19.4%.

Adipose Tissue↗
PubMed1987

The relative body fat and anthropometric prediction of body density of South Australian females aged 17-35 years.

One hundred and thirty-five females were tested in order to: produce some normative percentage body fat (% BF) data on an Australian sample which represented a cross-section of physical activity patterns, cross-validate existing multiple regression equations which predict body density (BD) from anthropometric measurements, and if necessary develop population specific equations. Measurements were taken of 10 girths, 3 widths and 7 skinfolds. Body density was measured by underwater weighing with the residual volume (RV) being determined by helium dilution. The Siri equation was then used to convert BD to % BF. The % BF scores had an overall mean of 23.4 (range 10.8-49.2). The very active group (n = 45) had a significantly lower (p less than 0.05) relative body fat (X = 20.6% BF) than either the active (n = 45; 23.5% BF) or sedentary groups (n = 45; 26.2% BF). Previously published equations were found to have limited applicability to Australian subjects. A stepwise multiple regression was therefore used to develop the following equation (R = 0.893): BD(g X cm-3) = 1.16957-0.06447 (log10 sigma triceps, subscapular, supraspinale, front thigh, abdominal and calf skinfolds in mm)-0.00081 (gluteal girth in cm) + 0.0017 (forearm girth in cm) + 0.00606 (biepicondylar humerus breadth in cm). Only those predictors which resulted in a statistically significant increase in r (p less than or equal to 0.05) were included. The standard error of estimate of 0.00568 g X cm-3 was equivalent to 2.6% BF at the mean.

Adipose Tissue↗
PubMed1987

Relative body fat and anthropometric prediction of body density of male athletes.

Two hundred and seven male members of South Australian representative squads in 18 sports (mean +/- s = 24.2 +/- 4.7 years) were tested in order to provide descriptive data on relative body fat (% BF), develop a population specific equation and cross-validate existing equations. Measurements were taken of 10 circumferences, 2 diameters and 8 skinfolds; body density (BD) was measured by underwater weighing with the residual volume (RV) being determined by He dilution. The overall mean BD was 1.0761 g X cm-3 (s = 0.0085 g X cm-3; range = 1.0465-1.0968 g X cm-3) which corresponded to 10.0% BF according to Siri (s = 3.7%; range = 1.3-23.0%). The games players (n = 129) registered an overall mean of 10.3% BF (s = 3.7%; range = 2.2-23.0%). There were significant differences (p less than 0.05) for % BF between the lacrosse players (mean = 12.3%) an both the Australian Rules footballers (mean = 8.0%) and track and field athletes (mean = 8.7%). A stepwise multiple regression on 185 subjects yielded the following equation, which had an R of 0.787: BD = 1.078865-0.000419 (sigma abdominal, medial calf, front thigh and juxta-nipple skinfolds in mm) +0.000948 (neck circumference in cm) -0.000266 (age in decimal years) -0.000564 (ankle circumference in cm). Only those predictors which resulted in a significantly increased correlation (p less than or equal to 0.05) were included. The standard error of estimate of 0.00537 g X cm-3 was equivalent to 2.3% BF at the mean. This equation was satisfactorily cross-validated against the BD of a separate sample (n = 22) from the same population. However, cross-validation of 11 previously published equations indicated that they have limited applicability to State representative sportsmen.

Adipose Tissue↗
PubMed1987

Inexpensive probes for the determination of body temperature.

Two-terminal integrated circuit temperature transducers (Analog Devices' AD 590) were used to fabricate skin and rectal probes for the monitoring of mean body temperature. They are inexpensive, robust, easily constructed and of low mass. The skin sensor system described is capable of being solidly attached regardless of the body contour such that it remains integral throughout profuse sweating and vigorous movement. Both types of probe are stable, accurate to within +/- 0.05 degree C over the physiological range of measurement and exhibit 100% response times of approximately 60 s to a square wave stimulus of 10 degrees C.

Body Temperature↗
PubMed1986

The computation of body composition data using a programmable calculator.

A body composition programme has been developed for the Texas Instruments TI 59 programmable calculator and printer. The methodology involves the determination of body density by underwater weighing with the ventilated residual volume being measured by helium dilution. Some of the labelled output variables included on the printout are: body density, percent body fat, fat mass and fat free mass.

Body Composition↗
PubMed1981

Isokinetic contractile properties of the quadriceps with relation to fiber type.

Fifteen subjects were assigned to three groups on the basis of the proportion of fast-twitch fibers (% FT) in their vastus lateralis muscles. Torque production per unit of fat free thigh volume was then determined during knee extension on an isokinetic dynamometer at 60, 120, 180, 240, and 300 degrees . s-1. Maximal isometric force was also obtained at 65 degrees from horizontal. Subjects with predominantly fast twitch muscle fibers demonstrated significantly greater peak power, rate of power production and work than subjects with predominantly slow twitch fibers at all but the lowest velocity of 60 degrees . s-1. Mean peak power for all subjects occurred at approximately 30% of maximal knee extension velocity (210 degrees x s-1) and 34% of maximal voluntary isometric contraction. When work, peak power and rate of power production were correlated with % FT fibers, then the highest correlations of 0.69, 0.57, and 0.73 respectively, all occurred at 180 degrees . s-1. These observations suggest that: 1) the torque-velocity, power-velocity relationship of the quadriceps is similar to the force-velocity, power-velocity relation found for excised muscle, 2) when using the knee extension exercise for the prediction of muscle fiber composition of the quadriceps the most appropriate speed for testing appears to be 80 degrees . s-1.

Adult↗
PubMed1981

Specificity of the anaerobic threshold in endurance trained cyclists and runners.

This study examined the specificity of maximum aerobic power and the anaerobic threshold (AT) in 10 endurance-trained cyclists and 10 endurance-trained runners who performed continuous progressive work tests on the bicycle ergometer and treadmill. Dependent 't' tests for VO2max l/min-1 indicated that the cyclists scored higher on the bicycle ergometer (X = 4.5 l/min-1) than the treadmill (X = 4.34 l/min-1) but the difference was not statistically significant. By contrast, the runners fared significantly better (p less than 0.05) on the treadmill (X = 68.1 ml/kg . min-1) compared with the bicycle ergometer (X = 61.7 ml/kg . min-1). When the AT was expressed as a percentage of VO2max, there were no significant differences between the cyclists (66.3%) and runners (61.2%) on the bicycle ergometer or the runners (77.3%) and cyclists (74.3%) on the treadmill. However, this tendency for the better score to be registered by the group tested on the activity for which it trained was most pronounced when the AT was expressed in l/min-1 and ml/kg . min-1. Independent 't' tests accordingly indicated that the cyclists (3.0 l/min-1) had significantly (p less than 0.05) greater AT's than the runners (2.56 l/min-1) on the bicycle ergometer whereas the runners (52.7 ml/kg . min-1) had significantly (p less than 0.05) higher AT's than the cyclists (46.8 ml/kg . min-1) on the treadmill. These data suggest that the adaptive responses to exercise are in part a function of the specific movement patterns executed in training. Thus, if VO2max and the AT are to be measured in the laboratory, the tests must allow optimal innervation of the specifically trained muscle fibres.

Adult↗
PubMed1980

Muscle respiratory capacity and fiber type as determinants of the lactate threshold.

This study examined the relationship between the respiratory capacity of an individual's skeletal muscle and the work rate at which blood lactate accumulation begins (lactate threshold). Comparisons were also made among fiber type, VO2max, and the lactate threshold. Muscle biopsies were taken from the vastus lateralis muscle for determination of respiratory capacity and fiber type (myosin ATPase). The lactate threshold was assessed in terms of both the absolute work rate (VO2) and relative work rate (%VO2max). The capacity of muscle homogenates to oxidize pyruvate was significantly (P less than 0.01) related to the absolute (r = 0.94) and relative (r = 0.83) lactate thresholds. Significant positive correlations (P less than 0.01) were also found between the percent of slow-twitch fibers and absolute (r = 0.74) and relative (r = 0.70) lactate thresholds. The results suggest that the muscle's respiratory capacity is of primary importance in determining the work rate at which blood lactate accumulation begins. They also suggest that the proportion of slow-twitch fibers may play an important role in determining the relative lactate threshold.

Adult↗
PubMed1978

Physiological responses of international female lacrosse players to pre-season conditioning.

This study examined the changes in body composition, maximum aerobic power (Vo2max) and maximum anaerobic power in seven Australian international women lacrosse players during a 3-month pre-season conditioning program. Monthly tests were conducted and the data were analyzed by an ANOVA repeated measures design and subjected to a polynomial orthogonal test of trend in the event of a significant F-ratio at the .05 level. The trend analysis for relative body fat (X = 24.9 [initial], 22.8, [first month], 23.1 [second month] and 23.1% [third month]) indicated significant linear and quadratic components since the major adjustment had occurred by the end of the first month. The players also experienced an overall average weight loss of 1.55 kg. The mean Vo2max values were: 44.0, 48.6, 52.3 and 52.9 ml/kg x min. Thus aerobic power had plateaued by the end of the second month and the trend analysis accordingly indicated significant linear and quadratic components. Anaerobic alactacid power was measured by Margaria's stair run. Both the times and power (kgm/kg x sec) exhibited significant linear trends. Post-exercise blood samples taken at the start and end of the 3-month training program indicated a significant increase (P less than .05) in lactate (X = 9.0 and 11.8 mmol/l) following a short duration maximum treadmill run.

Adult↗
PubMed1977

A comparison of three W170 protocols.

This study compared the W170 scores of 9 male subjects in kgm/kg X min resultant from the following protocols: 2 X 6 min workloads (3 min rest between each bout), 3 X 4 min workloads (1 1/2 min rest between each bout), and 4 X 3 min workloads (1 min rest between each bout). Each subject experienced 2 preliminary rides in order to overcome the problems of learning and habituation and the order of the 3 experimental treatments was randomly assigned to each subject. An analysis of variance repeated measures design revealed that there was no statistically significant difference between the 3 protocols at the 0.05 level. The scores for the three W170 protocols correlated -0.084, 0.040, and -0.142 with VO2 max in ml/kg X min. The correlation coefficient between actual VO2 max in ml/kg X min and that predicted from the Astrand-Ryhming nomogram was 0.723.

Adult↗
PubMedDate not supplied

Improved rig for dynamically calibrating skinfold calipers: comparison between Harpenden and Slim Guide instruments.

This article describes an improved rig for the dynamic calibration of skinfold calipers. The new unit is 5% lighter and almost 60% smaller than its predecessor (Carlyon et al., 1996, 1998) with a 9.5 mm solid aluminium base and a quick release caliper mount providing stability to both the rig and caliper. Automation of the gap controller with an electric motor standardizes the jaw opening and closing velocity, thereby enabling hands-free operation. Frictional losses in the moving components of the rig have been reduced by replacing the main bush of the swing arm with a bearing, reducing the mass of the swing arm, adding a support wheel to the end of the swing arm, and replacing fishing swivels with a universal joint to allow for changes in the opening screw angle as the caliper's arm moves through its arc. This rig can also be adapted to different types of calipers by changing the position of the load cell, microswitches, and the caliper mount. A universal mounting bracket that can be secured to almost any table supports the rig in a vertical plane when calibrating the load cell. To demonstrate the versatility of the calibration rig, preliminary data are presented for the upscale and downscale jaw pressures of seven Harpenden and seven Slim Guide calipers.

Anthropometry↗