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Biomedical subjects

A D Martin

Publications and source records attributed to A D Martin.

At least 37 records · Page 2Linked to original sources
PubMed1993

Oxygen cost of treadmill running in 24-month-old Fischer-344 rats.

The oxygen cost of treadmill running is well documented in young adult rats. However, to our knowledge there are no detailed reports concerning the oxygen cost of treadmill running in senescent rats. Young adult (4 months; N = 8) and senescent (24 months; N = 8) female Fischer-344 rats were tested for O2 cost of treadmill running. One-half of the animals tested in each age group had completed 10 wk of endurance training. Oxygen cost of treadmill running, using a flow-through system, was measured on a per minute basis from 7-10 min of each work bout and averaged. Separate work bouts were performed at 0%, 5%, and 10% grade at 15, 20, 25, and 30 m.min-1. Oxygen cost of treadmill running for trained rats for all speeds and grades were not significantly different (P = 0.77) from untrained animals; thus, data were pooled for oxygen cost of running. Results revealed significantly lower (P < 0.05) VO2 (expressed as ml.kg-1.min-1) for senescent rats vs young adult rats rest and at all comparable treadmill grades and speeds except for 5% grade, 25 m.min-1 and 10% grade, 20 m.min-1. In addition, resting VO2 was significantly lower (P < 0.05) in old rats when compared with young rats. Thus, we conclude that the oxygen cost of treadmill running is lower for 24-month-old rats than in 4-month-old rats except at higher work levels.

Aging↗
PubMed1992

Cigarette smoking, steroid hormones, and bone mineral density in young women.

There are few studies of the effect of smoking on bone density in young women. The reported antiestrogenic effect of smoking could be a mechanism for a possible effect of smoking on bone. We measured bone mineral density (BMD) by dual-energy X-ray absorptiometry (whole body, proximal femur, lumbar spine), and serum levels (mid-follicular phase) of testosterone (T), estradiol (E2), sex hormone-binding globulin (SHBG), and cortisol in 52 women (25 smokers, 27 nonsmokers) aged 20-35 years. The two groups did not differ significantly in age, height, weight, or the sum of eight skinfold thicknesses. The mean number of cigarettes smoked per day and the number of years of smoking were 16.9 and 12.9, respectively. There were no significant differences in BMD between smokers and nonsmokers at any site. For both smokers and nonsmokers, SHBG and the free androgen index (T/SHBG) made significant contributions (P less than 0.005) to the variance in BMD at all sites except the lumbar spine. The free estradiol index (E2/SHBG) contributed to whole body BMD (P less than 0.05). For all subjects, there were significant inverse relationships between SHBG and BMD (P less than 0.002), and positive relationships between T/SHBG and BMD (P less than 0.02) for all sites except the lumbar spine. These data suggest that moderate smoking in young women is not associated with low BMD at any site. However, smokers had lower free estradiol and higher SHBG, both of which have been related to increased bone loss in older women.

Adult↗
PubMed1992

Opiate receptor blockade by naltrexone and mood state after acute physical activity.

Acute mood changes occur with various forms of physical activity. Increased levels of endogenous opioids (endorphins) in response to exercise may mediate activity-induced shifts in mood state. Thirteen female and six male aerobics class participants aged 20-46 years received the opiate receptor antagonist naltrexone and a placebo in randomized, double-blind crossover fashion on two separate occasions at the same 75-min high-intensity aerobics class. Mood states were assessed before and after each class, which were spaced 5 days apart, using the Profile of Mood States questionnaire (POMS), a mood adjective checklist, and a Visual Analogue Scale (VAS) which measured mood in relation to several emotional extremes. Mood changes over the course of each aerobics class were compared in the naltrexone and placebo groups. For men and women, significant differences between conditions were observed in overall mood by both the POMS (P less than 0.005) and VAS (P less than 0.02). There were significant differences between conditions for most subscales of each mood instrument (P less than 0.05); with the placebo, mood states became calmer, more relaxed and pleasant, tending away from depression, anger and confusion. Positive mood shifts did not occur when subjects were preloaded with naltrexone, suggesting that activity-generated mood changes are mediated through endorphinergic mechanisms.

Adult↗
PubMed1992

Sex hormones and adipose tissue distribution in premenopausal cigarette smokers.

Androgen dominance is associated with android (abdominal) adiposity and increased health risk. Cigarette smoking has an anti-estrogenic effect in women and recent evidence has linked cigarette smoking with abdominally-localized adipose tissue. The relationship between cigarette smoking, endogenous sex steroid levels and adipose tissue distribution in women has not been examined. We assessed anthropometric indicators of fat distribution and serum levels of estradiol, testosterone and sex hormone-binding globulin (SHBG) in 56 women aged 20-35 years (27 cigarette smokers and 29 non-smokers). Free estradiol and testosterone were estimated. Endocrine and anthropometric variables were adjusted for overall fatness. Cigarette smokers had significantly higher mean serum levels of SHBG than non-smokers (63.38 nmol/l and 57.85 nmol/l, respectively; P less than 0.01); there were no differences in serum estradiol, testosterone or estimated free levels of these sex steroids. Cigarette smokers had a more android distribution of adipose tissue: significantly greater waist-to-hip ratio (WHR) (P less than 0.01), greater waist-to-thigh ratio (WTR) (P less than 0.02) and smaller thigh girth (P less than 0.05). Waist and umbilical girths were greater in cigarette smokers (P less than 0.0002), but there was no difference in the sum of central skinfold thicknesses (abdominal, iliac crest and supra-spinale). A significant interaction (P less than 0.05) of cigarette smoking with serum testosterone levels was observed in effects on WHR; the relative impact of serum testosterone upon abdominal adiposity was greater in cigarette smokers than in non-smokers. The results suggest that in premenopausal women, cigarette smoking promotes android adiposity by increasing abdominal fat deposition and decreasing femoral fat deposition via interactive effects with sex steroids. The results also suggest an effect of cigarette smoking on serum SHBG, independent of effects on androgen/estrogen balance.

Abdomen↗
PubMed1991

The incidence of fracture of the proximal femur in two million Canadians from 1972 to 1984. Projections for Canada in the year 2006.

Reported increases in the number of fractures of the proximal femur in Europe are greater than can be explained by demographic changes alone. This trend was assessed in Canada by examining hospital discharge records from the provinces of Saskatchewan and Manitoba from 1972 to 1984. The annual number of first fractures of the proximal femur in persons older than 50 years of age increased 59.7% in women and 42.2% in men during this time period. In most of the five-year age groups the percentage of increase in the number of fractures exceeded the percentage of increase in population of that age group. Annual age-specific incidences (by five-year age groups) increased exponentially with age, doubling every six years, and reached a maximum value of 4% in women older than 90 years of age. Annual age-adjusted incidences increased significantly over the study period in men and women. For the whole of Canada in 1987, it is estimated that there were 13,193 first fractures of the proximal femur in women and 4610 in men, and that in the year 2006 these will rise to 22,922 and 7846, respectively. The actual increase will be considerably greater if the age-specific incidences continue to increase as they have from 1972 to 1984. The gradual decline in physical activity, which contributes to bone loss, may be one etiological factor of this trend during the last half century.

Age Factors↗
PubMed1990

Anthropometric estimation of muscle mass in men.

Twelve male cadavers (aged 50-94 yr) were subjected to comprehensive anthropometry, dissection, and weighing of all skeletal muscle. Correlation coefficients of limb girths with total skeletal muscle mass (MM) were high: forearm r = 0.96, mid-thigh r = 0.94, calf r = 0.84, and midarm r = 0.82. These increased when limb girths were corrected (by subtracting pi times the skinfold thickness) to estimate muscle girth. For dimensional consistency, variables in the regression analyses included the product of stature and the square of each corrected girth. For the six unembalmed cadavers, this yielded a three-girth equation for MM (r2 = 0.93; SEE = 1.56 kg), which was then validated using data from the embalmed cadavers. It predicted MM with an SEE of 1.58 kg and r2 = 0.93. Because the values of these SEEs were similar, we pooled the subjects from the two groups to generate the final estimation equation: MM = STAT (0.0553CTG2 + 0.0987FG2 + 0.0331CCG2) - 2445 (SEE = 1.53 kg, r2 = 0.97), where STAT is stature (cm), CTG is thigh circumference corrected for the front thigh skinfold thickness (cm), FG is the uncorrected forearm circumference (cm), and CCG is the calf circumference corrected for the medial calf skinfold thickness (cm). Despite the limitations of the cadaver sample, the proposed equation appears to provide the best estimate of skeletal muscle mass to date, in that it is the only cadaver-validated equation and it gives values that are consistent with all known dissection data.

Aged↗
PubMed1989

Predicting maximal oxygen uptake from treadmill testing in trained and untrained women.

This study was conducted to develop an equation to predict maximal oxygen uptake from exercise time during a standardized treadmill test in women aged 29 to 75 years before and after aerobic training. Treadmill tests were administered to 181 women with measurement of maximal oxygen uptake, and an equation predicting maximal oxygen uptake was derived: maximal oxygen uptake (ml.kg-1.min-1) = 10.34 + 1.29 (exercise time), r = 0.88, standard error of the estimate = 2.1, p less than 0.0001. Thirty-three women were retested after 6 and 12 months of aerobic exercise training. Maximal oxygen uptake was predicted from the equation developed and compared with the measured values at 6 and 12 months. The predicted and measured maximal oxygen uptake values after training were not significantly different. These results indicate that it is possible to predict maximal oxygen uptake for clinical purposes with a single equation from exercise time in untrained and trained women across a wide range of ages.

Adult↗
PubMed1989

Epidemiology of fractures of the distal end of the radius in children as associated with growth.

We determined the annual incidence of fracture of the distal end of the radius for patients of all ages and both sexes in the province of Saskatchewan, using two data sets: data on hospital admissions for 1970 through 1984, and data on physician billing for 1978 through 1985. The rate of occurrence of this fracture in children, by age and sex, was compared with longitudinal data on the velocity of growth that was collected during the same time for children from the same population. We compared the incidences of the fracture with the results of studies on the levels of activity in children and adolescents during growth. We also compared the age-specific incidence of the fracture in children with the incidence in adults. For both data sets, the age at the peak incidence of fracture of the distal end of the radius almost perfectly matched the age at which peak velocity of growth in height occurs for boys and girls. For girls, the peak incidence occurred between the ages of 11.5 and 12.5 years and for boys, between 13.5 and 14.5 years; these ages corresponded to the mean peak velocity of growth at 11.9 years for girls and 14.3 years for boys. The age-adjusted incidence of the fracture in male subjects was highest at fourteen years and was not exceeded by that in female subjects until fifty-three to fifty-four years.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Effect of exercise on glucose metabolism in postmenopausal women.

A cross-sectional study was conducted to examine the effect of treadmill and muscle resistance training on glucose tolerance and insulin levels in a group of 25 normal-weight, naturally menopausal women. Subjects trained 20 minutes three times per week for at least 6 months to 70% to 85% of maximum heart rate on a treadmill, or to maximum effort for all major muscle groups on Nautilus equipment. A nonexercising age-height-weight--matched group was monitored as a control. All three groups were of above-average fitness for age as measured by aerobic capacity during initial testing. The treadmill group significantly increased its maximal oxygen uptake over the training period. Glucose tolerance and insulin response, measured as areas under the curve after a 75 gm oral glucose load, were improved in both exercise groups compared with controls, with more marked improvement in the treadmill group. The only difference achieving statistical significance was the insulin levels 30 minutes or less after glucose ingestion, representing the first phase of insulin release. Long-term exercise training that increases aerobic power thus maintains normoglycemia with lower insulin values than in otherwise physically fit postmenopausal women.

Aged↗
PubMed1988

Physiological responses to walking with hand weights, wrist weights, and ankle weights.

To compare the blood pressure (BP) responses to exercise with 1.36 kg (3.0 lb) hand-held weights (HW), wrist weights (WW), and ankle weights (AW), 12 sedentary males (20.8 +/- 1.2 yr) completed three randomly assigned treadmill exercises at 75% maximum heart rate (HR) reserve. Systolic and diastolic BPs among HW (181.2 +/- 21.9 and 73.2 +/- 7.9 mm Hg), WW (180.1 +/- 27.2 and 71.0 +/- 10.1 mm Hg), and AW (183.8 +/- 26.8 and 71.7 +/- 7.8 mm Hg) were not significantly different (P greater than 0.05). When compared to exercise with no weights (NW), only the diastolic BP for HW was significantly different (+4.4 mm Hg, P less than 0.05). To evaluate the energy cost of exercise with HW, WW, and AW, subjects completed a fourth exercise at constant treadmill speed (6.3 +/- 0.3 km.h-1) and grade (6.3 +/- 1.4%). Oxygen uptake and HR responses were greater (P less than 0.01) for HW (30.4 +/- 0.8 ml.min-1.kg-1; 160.6 +/- 4.0 beats.min-1), WW (30.4 +/- 0.9 ml.min-1.kg-1; 159.7 +/- 4.6 beats.min-1), and AW (29.0 +/- 0.7 ml.min-1.kg-1; 154.6 +/- 4.4 beats.min-1) than for exercise with NW (26.6 +/- 0.7 ml-min-1.kg-1; 147.0 +/- 3.8 beats.min-1). Oxygen uptake and HRs for HW and WW were greater than for AW (P less than 0.05). Ratings of perceived exertion (Borg scale for NW (11.7 +/- 1.8), HW (12.1 +/- 2.0), WW (12.2 +/- 1.8), and AW (12.3 +/- 1.8) were not significantly different (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Osteoporosis, calcium and physical activity.

Sales of calcium supplements have increased dramatically since 1983, as middle-aged women seek to prevent or treat bone loss due to osteoporosis. However, epidemiologic studies have failed to support the hypothesis that larger amounts of calcium are associated with increased bone density or a decreased incidence of fractures. The authors examine the evidence from controlled trials on the effects of calcium supplementation and physical activity on bone loss and find that weight-bearing activity, if undertaken early in life and on a regular basis, can increase the peak bone mass of early adulthood, delay the onset of bone loss and reduce the rate of loss. All of these factors will delay the onset of fractures. Carefully planned and supervised physical activity programs can also provide a safe, effective therapy for people who have osteoporosis.

Animals↗
PubMed1987

The skinfold: myth and reality.

The interest in skinfolds, given the easy accessibility of the subcutaneous layer and its non-invasive nature, has led to a proliferation of 'skinfold' applications and formulae. To obtain data to investigate body composition methods, particularly the use of skinfolds, two separate cadaver dissection studies were undertaken, allowing for the analysis of data from 32 cadavers with more than 2500 data per cadaver. In addition, 40 elderly 'living' subjects of the same age range were compared with the cadaver population and no significant macro-morphological differences were found. The available data have clearly demonstrated that skinfold compressibility is by no means constant. Adipose tissue patterning by assessment of skinfold thickness using calipers and incision confirms significant sex differences but emphasizes the neglected importance of skin thickness. It appears that the best adipose tissue predictors are different from those used in general. Also the problem of estimating body fat content by skinfold is compounded by the fact that two identical thicknesses of adipose tissue may contain significantly different concentrations of fat. Skinfolds are significantly related to external (subcutaneous) adipose tissue. However, the relation to internal tissue is less evident and the relation with intramuscular adiposity is unknown.

Adipose Tissue↗
PubMed1987

Bone dynamics: stress, strain and fracture.

Bone is a dynamic tissue whose functional mass is controlled by the balance between the endocrine drive towards bone resorption and the mechanically-engendered drive towards bone formation. Strain is the key intermediate variable between loading forces and bone remodelling. Animal studies have shown that static loading of bone has no osteogenic effect; bone loss occurs as if there were no loading at all. However, dynamic loading, that is, cyclic change in internal strain, is strongly osteogenic, with relatively few cycles required for maximum effect. However, if a sufficient number of cycles is applied, repetitive loading can cause stress fractures. This number decreases as internal strains increase. Thus strain redistribution within bone, as caused by muscle fatigue or improper sports equipment, is a significant cause of fracture.

Aging↗
PubMed1987

Developmental issues and their resolution for gay and lesbian adolescents.

The primary developmental task for homosexually oriented adolescents is adjustment to a socially stigmatized role. Although the individual homosexual adolescent reacts with diversity and great resilience to societal pressures, most pass through a turbulent period that carries the risk of maladaptive behaviors that may affect adult performance. Despite individual variation, certain issues have been found to concern most homosexual adolescents. Empirical data from the Institute for the Protection of Lesbian and Gay Youth, Inc. in New York City suggests that isolation, family violence, educational issues, emotional stresses, shelter, and sexual abuse are the main concerns of youth entering the program. If not resolved, the social, cognitive, and social isolation may extend into adulthood, and anxiety, depressive symptoms, alienation, self-hatred, and demoralization may result. In a non-threatening supportive environment that provides accurate information and appropriate peer and adult role models, many of the concerns are alleviated and internalized negative attitudes are either modified or prevented from developing. The authors discuss the effects of prejudice and the impact of negative societal attitudes on the developing social and personal identities of homosexual youths.

Adolescent↗
PubMed1985

Prediction of body fat by skinfold caliper: assumptions and cadaver evidence.

A series of assumptions required for use of skinfold calipers for the estimation of human body composition is examined in terms of direct evidence from the measurement and dissection of 6 male and 7 female cadavers. Skinfold compressibility showed significant inter-subject and inter-site differences with the highest values (64.7 percent and 63.8 percent) at the spinale and biceps sites and the lowest (33.6 percent and 34.4 percent) at the front thigh and medial calf. Skin thickness as a percentage of skinfold thickness was highest at the subscapular site (28.1 percent). Adipose tissue patterning showed great variability, indicating the importance of using skinfold caliper readings from a variety of different sites including upper limb, lower limb and trunk. Further sources of error include variability in fat content of adipose tissue (estimated at 20 percent in our sample) and in the internal and subcutaneous fat deposition. Recommendations for the use of skinfold calipers to assess adiposity and monitor change are made in the light of these findings.

Adipose Tissue↗
PubMed1984

Stimulation of mitochondrial pyruvate metabolism and citrulline synthesis by dexamethasone. Effect of isolation and incubation media.

Hepatic mitochondria isolated in 0.3 M-sucrose or 0.3 M-mannitol from rats treated for 3h with dexamethasone displayed stimulated rates of pyruvate carboxylation and decarboxylation and citrulline synthesis when compared with organelles from control animals. Mitochondria isolated in mannitol also displayed elevated rates of pyruvate carboxylation and decarboxylation when compared with those isolated in sucrose, and this stimulation was shown to be independent of the lengthy isolation procedure. Citrulline synthesis proceeded at similar rates in mitochondria isolated in either sugar. The concentration of exchangeable adenine nucleotides was identical in mitochondria isolated in sucrose or mannitol, suggesting that those prepared in the former sugar are not more permeable to metabolites than those prepared in the latter. The matrix volume of mitochondria isolated in mannitol was greater than that of mitochondria isolated in sucrose, and the effect of mannitol on pyruvate metabolism was mimicked by swelling the organelles in hypo-osmotic sucrose. Measurements of the extra-matrix volume by using [14C]sucrose or [14C]mannitol suggest that mannitol can permeate mitochondria to a greater extent than can sucrose. The possibility that mannitol elicits its effect by entering the mitochondrial matrix and so initiating swelling is discussed.

Adenine Nucleotides↗