Muscle mass of competitive male athletes

The recent publication of the first validated equation for the estimation of muscle mass (MM) in men has made possible a comparison of MM in athletes from different sports. Limb girths and skinfold thicknesses were measured in 62 male athletes (aged 17-38 years) and 13 non-athletic males (aged 22-36 years). The MM (g) was calculated from the equation MM = S(0.0553 Gt2 + 0.0987 Gf2 + 0.0331 Gc2)-2445, where S is stature, Gt is the mid-thigh girth corrected for the front thigh skinfold thickness, Gc is the maximum calf girth corrected for the calf skinfold thickness and Gf is the uncorrected maximum forearm girth (all in cm). The athletes were classified as gymnasts (n = 10), basketball players (n = 10), body-builders (n = 10), track and field power athletes (n = 12), track and field long sprinters (n = 10) or distance runners (n = 10). The MM means ranged from 38.4 kg for the distance runners to 58.7 kg for the body-builders. Both body-builders and basketball players had significantly greater MM than gymnasts, long sprinters, non-athletic males and distance runners (P < 0.01). Also, MM was greater in track and field power athletes than in distance runners (P < 0.05). The MM as a percentage of body mass (%MM) ranged from 56.5% in the non-athletic group to 65.1% in the body-builders; body-builders scored higher than basketball players (P < 0.05), distance runners (P < 0.01) and the non-athletic group (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

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.

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.

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.

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)

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.

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)

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.

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.