The effects of fitness-type exercise on iron status in adult women.

To determine if compromised iron status results from fitness-type exercise, 24 women from a 35-min, 4-day/wk aerobic exercise class provided blood samples at wk 0, 6, and 13. Hb increased from wk 0 to wk 6 (p less than 0.001), and decreased from wk 6 to wk 13 (p less than 0.001). Hematocrit did not change from wk 0 to wk 6, but decreased from wk 6 to wk 13 (p less than 0.005). Ferritin concentrations were lower at wk 6 and 13 (p less than 0.01 and p less than 0.05) than initially. No changes in these measures were detected among 11 sedentary control subjects. Intakes of iron, ascorbic acid, protein, and energy were comparable between exercise and sedentary groups. Decreased resting and recovery step test heart rates indicated improved aerobic fitness in exercising subjects from wk 2 to wk 11. Thirteen weeks of aerobic exercise class did not induce iron deficiency anemia. Decreased plasma ferritin concentrations suggest a compromise in iron stores which appears to be stabilized after 6 wk.

Height-normalized indices of the body's fat-free mass and fat mass: potentially useful indicators of nutritional status.

Expressing fat-free mass (FFM) and body fat mass (BFM) as percentages of body weight or by weight is unsatisfactory. For example, tall patients with protein-energy malnutrition (PEM) can exhibit values for FFM and BFM similar to those of shorter well-nourished individuals. To obviate such difficulties, we propose use of height-normalized indices, namely, a FFM index [FFM (kg)/height (m)2, or FFMI] and a BFM index [BFM (kg)/height (m)2, or BFMI]. We calculated these indices in a reference population of 124 healthy young men and in 32 nonobese young men (from the Minnesota Study) before, during, and after experimental semistarvation. When values for FFMI and BFMI falling below the reference cohort's 5th percentile cutoff point were used as a criterion for PEM, these indices, together with basal oxygen-consumption rate, diagnosed PEM in 27 of the 32 Minnesota Study subjects after 12 wk of semi-starvation. These findings indicate that FFMI and BFMI may be useful in nutritional assessment.

Preexercise meal composition alters plasma large neutral amino acid responses during exercise and recovery.

This study was designed to determine the effect of ingesting three preexercise meals on energy metabolism during exercise and recovery and to relate metabolic perturbations to subjective and objective measurements associated with central fatigue. Twelve subjects consumed isoenergetic meals consisting of oat, wheat, or corn cereals 90 min before cycling. A fasting trial served as the control. Blood samples and cognitive function, perceived hunger, and sleepiness measurements were obtained before and after feeding and during recovery when self-selected food intake was also measured. After meal ingestion, plasma insulin was lower for oat than for wheat or corn whereas the ratio of tryptophan to large neutral amino acids (LNAAs) for corn was less than for all others. During exercise, the tryptophan-LNAA ratio increased from preexercise values for the fasting and wheat trials, but exercise performance was unaffected. During recovery, tryptophan:LNAA increased from postexercise values in fasting trials. Also, hunger and fatigue ratings were greater in fasted subjects, but self-selected food intake measured at the end of the recovery period was not different among groups. We conclude that preexercise meal consumption affected tryptophan:LNAA before, during, and after exercise, but these changes were not sufficient to alter physical and cognitive performance.

Total-body electrical conductivity (TOBEC): relationship to estimates of muscle mass, fat-free weight, and lean body mass.

A comparison of methods for estimating body composition (BC) of 12 subjects was made by using fat-free weight from total-body electrical conductivity (FFWT), muscle mass from 3-methylhistidine excretion (MM3MH) and creatinine excretion (MMCRE), fat-free weight from hydrostatic weighing (FFWBD), and lean body mass from whole-body potassium counting (LBMK). Data were analyzed for day-to-day variability and regression analyses were applied to compare the different methods of measuring BC. Mean values (+/- SEM, kg) for the estimates were 53.9 +/- 3.5 (FFWT), 26.9 +/- 2.9 (MM3MH), 25.3 +/- 2.5 (MMCRE), 53.2 +/- 3.6 (FFWBD), and 52.8 +/- 3.5 (LBMK). Regression analyses revealed that TOBEC estimates of fat-free weight had an adjusted r2 (+/- SEE, kg) of 0.95 +/- 2.2, 0.50 +/- 7.9, 0.95 +/- 1.8, and 0.88 +/- 4.0 for MM3MH, MMCRE, FFWBD, and LBMK, respectively. It was concluded that TOBEC is a potentially reliable method for estimating the muscle mass within the fat-free compartment, as well as fat-free weight and lean body mass.

The physical activity scale for the elderly (PASE): evidence for validity.

We assessed the validity of the Physical Activity Scale for the Elderly (PASE) in a sample of sedentary adults (56 men, 134 women, mean age +/- [SD] 66.5+/-5.3 years) who volunteered to participate in a randomized controlled trial on the effect of aerobic conditioning on psychological function. Construct validity was established by correlating PASE scores with physiologic and performance characteristics: peak oxygen uptake, resting heart rate and blood pressure, percent body fat, and balance. The mean PASE scores were higher in men than in women (men = 145.8+/-78.0; women = 123.9+/-66.3, P<0.05), and in those age 55-64 years compared with those age 65 years and over (55-64 = 144.2+/-75.8; 65 and over = 118.9+/-63.9, P<0.05). PASE scores were also significantly higher in those who did not report a chronic health condition (cardiovascular disease, hypertension, cancer, or recent surgery). PASE scores were significantly associated (P<0.05) with peak oxygen uptake (r = 0.20), systolic blood pressure (r = -0.18) and balance score (r = 0.20). No significant associations of PASE score and diastolic blood pressure, resting heart rate, or percent body fat were noted. These results provide additional evidence for the validity of the PASE as a measure of physical activity suitable for use in epidemiology studies on the association of physical activity, health, and physical function in older individuals.

Sex and training differences in human growth hormone levels during prolonged exercise.

Human growth hormone (hGH) levels were measured during rest, prolonged treadmill exercise at 60% maximum O2 uptake (VO2max), and immediate recovery in four groups of subjects (n = 7/group), ages 21-30 yr, classified as male runners (MR), female runners (FR), male controls (MC), and female controls (FC) to determine whether sex differences in the hGH response are related to resting 17 beta-estradiol (E2) and/or cardiorespiratory endurance (CRE). Glucose (Glc), E2, and hGH levels were determined from serial blood samples taken from an intravenous catheter. Glc did not change significantly during exercise, but different trends for the runners (increases) vs. controls (decreases) resulted in higher (P less than 0.01) postexercise levels in the runners. Resting hGH was higher (P less than 0.05) in the FRs and FCs than the MRs and MCs, respectively, and continued to be higher in the FCs (vs. MCs) during the first 30 min of exercise. The MRs achieved higher peak hGH levels and exhibited higher values than the MCs throughout exercise and recovery. There were no statistically significant training differences in the females. The strongest predictors for peak hGH were absolute work load and group (runners vs. controls), both of which combined accounted for 32-36% of the variability (P less than 0.01) in hGH response. Significant sex-related variables (sex, resting E2) accounted for 11-19% of the variability in peak or percent change in hGH, with E2 having a positive effect at rest but a negative effect during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of arm training on central and peripheral circulatory function.

The purpose of this study was to examine the effect of endurance arm training on metabolic and circulatory function during arm and leg exercise. Thirty-eight females (aged 18 to 35 yr) participated in the study, with 19 subjects in the training group and 19 in a control group. Both a specific and general training response was observed at the conclusion of the 5-wk training period. As a result of training, during peak arm exercise, significant increases (P less than 0.05) were observed for oxygen uptake (VO2), ventilation, cardiac output, stroke volume, arterial-venous oxygen difference, cumulative work, and total performance time. During peak leg exercise following arm training, significant increases (P less than 0.05) were observed for VO2, ventilation, cardiac output, cumulative work, and total performance time. Standardized partial regression coefficients were used to examine the relative influence of the metabolic and circulatory components which define VO2. Prior to training during arm work, the arterial-venous oxygen difference accounted for the largest proportion of variance in VO2; but after training, stroke volume contributed the largest portion of variance. On the other hand, during leg exercise, stroke volume accounted for the largest portion of variation in leg VO2 both before and after arm training. The data suggest that endurance arm training as prescribed in this study elicits significant circulorespiratory function adaptations to support improved performance in both arm and leg work. Further, the findings suggest both a specific and general training effect, with the more dominant effect specific to arm work.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of total body water fluctuations on estimation of body fat from body density.

The purpose was to investigate the possibility that variability in body weight in females due to water retention causes differences in body density (Db) values determined by hydrostatic weighing (HW). Determination of total body water (TBW) and Db were concurrently measured in seven females who experienced considerable fluctuations in body weight (1.5-4.5 kg) and seven males, ages 19-24. Females were measured when they felt they were at their lowest (LO) and highest (HI) body weights (BW) during a menstrual cycle. Males were randomly tested approximately 3 wk apart. Mean values of selected variables were compared in the LO vs HI testing sessions by paired t-tests. Significant mean differences were found in the females (P less than 0.01) for the following variables: BW (kg) (LO = 58.9, HI = 61.1), Db (g.cc-1) (LO = 1.0430, HI = 1.037), and percent body fat (%BF) as determined by HW alone (LO = 24.8%, HI = 27.6%). Variables significant at the P less than 0.05 level were TBW(l) (LO = 33.6, HI = 35.1) and %TBW of the fat-free body (LO = 74.5, HI = 75.9). However, changes in TBW could not entirely account for observed changes in Db. Only mean BW (kg) was significant (P less than 0.01) in the males (LO = 74.3, HI = 74.6). It is concluded that changes in TBW can in part result in significantly different Db values obtained from HW in females who did experience perceptible changes in BW during a menstrual cycle. The remaining differences may be due to changes in fat and protein content or methodological errors.

Methodological factors and the prediction of body fat in female athletes.

The effect of skinfold caliper, investigator technique, and various skinfold prediction equations on estimates of body fatness was investigated using college-age female basketball players. Four skinfold calipers, four investigators, and five prediction equations from the literature were selected for study. Skinfolds were obtained on 16 athletes for each of five sites by all four investigators using each caliper. Triceps and subscapular skinfolds showed less variation among investigators (mean differences of 1-4 mm) as compared to suprailiac, abdomen, and thigh skinfolds (mean differences of up to 5-6 mm). Differences among investigators were less using the Harpenden and Holtain than for the Lange and Adipometer calipers. All three sources of variation--caliper, investigator, and prediction equation--contributed significantly to the variability in estimates of mean fat content of this sample, which ranged from 14.1-28.1% depending on which of the 80 caliper-investigator-prediction equation combinations (four calipers, four investigators, and five equations) was used. Using any one prediction equation, the range in mean percent fat due to the 16 caliper-investigator combinations was 7%. The results illustrate the need for standardization of skinfold sites, caliper, and prediction equations for reliable estimation of body composition in a specific population.

Effects of oral contraceptives on hormonal and metabolic responses during exercise.

This study examined the influence of oral contraceptives (OC) on GH and PRL responses and on energy substrate utilization during prolonged submaximal exercise in moderately active women (21-30 yr). Eight women taking OC (OC) and eight women with normal menstrual cycles (C) performed a standardized treadmill test of 90 min at 50% maximal oxygen uptake. Blood samples were withdrawn from an indwelling venous catheter during a 2-h rest period, at 10-min intervals during exercise and at 3 and 15 min of recovery. Serum concentrations of glucose, GH, PRL, E2, and P4 were assayed. Carbohydrate and fat utilization were estimated from respiratory exchange ratios. Basal serum levels of GH, PRL, and glucose were not significantly different (P greater than 0.05) between OC and C. OC had significantly higher (P less than 0.05) serum GH levels than C at 10 and 20 min of exercise, but the integrated areas for GH responses were not different (P = 0.059). Serum PRL levels significantly decreased (P less than 0.05) during exercise, and PRL responses were similar for the two groups. OC exhibited significantly lower blood glucose levels (P less than 0.05) during exercise and utilized significantly lower total grams of carbohydrate (P less than 0.05) during exercise than C. In conclusion, OC use was associated with enhanced GH responses, lower glucose levels, and diminished carbohydrate utilization during prolonged exercise. These results indicated that OC users demonstrated a greater carbohydrate-sparing ability than eumenorrheic women, which may be related to the contra-insulin effects of GH. The lower blood glucose levels, however, suggest the sparing of carbohydrate may act to compensate for decreased hepatic glucose output, similar to animal data.

Isometric intermittent endurance of four muscle groups in men aged 20-74 yr.

Muscular endurance of upper and lower extremities may provide a more practical measure of muscle function related to normal daily activity than measures of strength, especially with the elderly. Maximal isometric intermittent endurance of the finger flexors, thumb abductors, dorsiflexors, and plantar flexors were characterized by peak force, impulse, percent total impulse, and percent force decrement in men aged 20-74 yr. Volunteers (N = 153) were placed into appropriate 5-yr age groups: 20-24, 25-29, ..., 70-74 yr. The intermittent endurance task consisted of 11 consecutive, 2-s maximal contractions, each separated by 3-s rest. Age group differences within each 2-s interval as well as differences in endurance were determined by ANOVA, and after adjusting for differences in body composition, by ANCOVA. The lower extremities had the greatest declines in absolute measures of force within each 2-s interval, and declines occurred earlier than previously reported. When values were expressed as percent change over the entire endurance task, there was generally no age group difference in force or impulse; however, there were significant muscle group differences. In conclusion, declines in absolute measures of force occurred at different ages depending on the muscle group; however, relative measures of muscular endurance were maintained for all age groups but varied by muscle group location.

Estimation of minimal weight of adolescent males using multicomponent models.

The purpose of this study was to determine whether the estimation of minimal weight (the body weight at which 5% of the weight is fat) of adolescent males could be improved by accounting for differences in hydration state and bone mineral content. Improvement was defined as a larger value for minimal weight and a smaller standard deviation compared to minimal weight estimated from body density. Forty adolescent males (mean age +/- SD, 15.5 +/- 1.4 yr) were measured for height, weight, body density (hydrostatic weighing), total body water (deuterium oxide dilution), and bone mineral content (single photon absorptiometry). Twenty-two adult males (mean age +/- SD, 23.6 +/- 2.2 yr) were measured as a reference group. Percent body fat and minimal weight were calculated from the body density (MWD), body density adjusted for total body water (MWDW), and body density adjusted for body water and bone mineral content (MWDWB). Repeated-measures ANOVA was used to test for differences between the methods and for trends in the data. The results showed a slight but nonsignificant increase in minimal weight for the adolescent group when body water and bone mineral data were added. The means +/- SD for MWD, MWDW, and MWDWB values of the adolescents were 54.6 +/- 9.0 kg, 54.8 +/- 8.6 kg, and 55.4 +/- 8.4 kg, respectively. It was concluded that the multicomponent methods, which accounted for hydration and bone mineral status, did not significantly improve the estimates of minimal weight of adolescent males compared to the single component method, i.e., minimal weight from body density.

Lower thermic effect of a meal post-exercise in aerobically trained and resistance-trained subjects.

Despite the abundance of literature concerning the thermic effect of a test meal (TEM) at rest in trained and untrained subjects, there is little information available concerning the TEM post-exercise. Therefore, it was the purpose of this study to examine the metabolic response to a 763-kcal meal prior to 30 min of exercise at 50% VO2max, in aerobically trained (AT, N = 8), resistance-trained (RT, N = 8), and untrained (UT, N = 8) subjects. Mean (+/- SEM) VO2max was 60.7 +/- 2.3 ml.kg-1.min-1, 52.9 +/- 2.2 ml.kg-1.min-1 and 51.1 +/- 2.2 ml.kg-1.min-1, for the AT, RT, and UT groups, respectively. Mean (+/- SEM) percent fat was 13.7 +/- 1.2, 12.7 +/- 1.9, and 16.9 +/- 1.4 for the AT, RT, and UT groups, respectively. Post-exercise VO2 was measured by indirect calorimetry every half hour, on two nonconsecutive days (post-absorptive (PA) post-exercise and post-prandial (PP) post-exercise) for 3 h. The total TEM (post-exercise PP VO2 minus post-exercise PA VO2) was 4.86 +/- 1.62, 5.22 +/- 1.80, and 9.36 +/- 5.08 I for the AT, RT, and UT groups, respectively. The TEM post-exercise was significantly lower (P less than 0.05) for the AT and RT groups compared with the UT group. Respiratory exchange ratio (R) differed significantly only during the PA post-exercise condition, with the AT group exhibiting significantly lower (P less than 0.01) values compared with the RT and UT groups. PA post-exercise R for the RT group was not significantly different (P = 0.09) from the UT group.(ABSTRACT TRUNCATED AT 250 WORDS)

Isometric muscle force production as a function of age in healthy 20- to 74-yr-old men.

Typically, previous studies have focused on one muscle group, the finger flexors, and only one aspect of muscle function, strength, when assessing age-related muscle force production characteristics. In the present study, the maximal voluntary isometric contraction force-time curves of five muscle groups (right hand finger flexors, right thumb abductors, right forearm extensors, right leg dorsiflexors, and right leg plantar flexors) were assessed in men, ranging in age from 20 to 74 yr. One hundred fifty-three volunteers were placed into appropriate 5-yr age groups: 20-24 (N = 14), 25-29 (N = 15), 30-34 (N = 16), 35-39 (N = 13), 40-44 (N = 16), 45-49 (N = 11), 50-54 (N = 16), 55-59 (N = 12), 60-64 (N = 17), 65-69 (N = 13), and 70-74 (N = 10) years. Muscle function was characterized by a number of force-time parameters, including strength, time, rate, and impulse. The data were analyzed both with and without consideration of the influence of physique and body composition. The results indicated that there were significant age group differences in the ability to produce maximal force (strength) (P less than 0.05), to generate maximal rates of force production (P less than 0.05), and in the total forces generated (impulse) (P less than 0.05), with an overall and in the total forces generated (impulse) (P less than 0.05), with an overall decline with increasing age.(ABSTRACT TRUNCATED AT 250 WORDS)

Substrate oxidation and GH responses to exercise are independent of menstrual phase and status.

The purpose of this study was to determine the extent to which growth hormone (GH) and energy substrate utilization are influenced by basal sex steroid levels during prolonged submaximal exercise across menstrual phase and status. Also the 17 beta-estradiol (E2) and progesterone responses during prolonged exercise were compared according to menstrual phase and menstrual status. Six amenorrheic (AMc) athletes and seven eumenorrheic (EUc) athletes ran at 60% VO2max for 90 min and serial blood samples were taken at rest, every 10 min throughout exercise, and 5 and 15 min post-exercise. The EUc athletes were tested in the early follicular phase (EF) (days 3-5), the late follicular phase (LF) (days 14-16) and the mid-luteal phase (ML) (days 22-25). The incremental GH response to exercise, measured by area under the curve, was consistent with previous reposts and was not altered according to menstrual phase or status (EF-37.5 +/- 11.5, LF-61.9 +/- 11.5, ML-48.1 +/- 12.8 micrograms.1-1.90 min-1). Furthermore, carbohydrate and fat utilization during exercise were not influenced by basal sex steroid levels associated with menstrual phase or status. The incremental E2 response to exercise in AMc athletes was significantly smaller than seen in EUc athletes (AMc-208.1 +/- 44.0, EF-383.0 +/- 116.4, LF-204.7 +/- 84.1, ML-45.1 +/- 18.4 pmol.1(-1).90 min-1), although the pattern of release is similar between groups. In conclusion, GH levels and substrate utilization are independent of both menstrual phase and status; hence, menstrual phase has no negative ramifications on metabolism during exercise. Amenorrhea does not result in metabolic consequences during prolonged exercise by influencing substrate utilization.

Age-related patterns in body composition for men aged 20-79 yr.

Fat-free body mass has been reported to decline by 30% between the ages of 30 and 70 yr, whereas body weight increases until age 50 yr. This study examined the age-related patterns in body composition, specifically its two components, fat-free body mass and fat mass, in 157 men aged 20-79 yr. Total body composition was assessed by hydrodensitometry and subcutaneous fat was measured with skinfolds. Approximately 15 men were tested in each of the 12 5-yr age groups (20-24, 25-29, 30-34, ... 75-79 yr). Body density, as determined by underwater weighing, was lower successively from the youngest to oldest age groups; men below age 40 yr had significantly higher (P < 0.01) body densities than the older men. Although there was a gradual decline in fat-free body mass with increasing age, there was not a significant age group effect until age 70 yr. Fat mass gradually increased with increasing age; men above age 40 yr had significantly higher (P < 0.01) total body fat when compared to the younger men. Subcutaneous body fat was similar at the distal limb locations for each age group; however, the proximal trunk locations, especially the abdomen, demonstrated significantly (P < 0.01) higher skinfold thicknesses with increasing age. In conclusion, fat-free body mass was maintained to a later age than previously reported; thus, the age-related decline in body density could be attributed to an age-related increase in body fat.

Contributions of exercise, body composition, and age to bone mineral density in premenopausal women.

The purpose of this cross-sectional study were to determine whether exercisers have greater bone mineral density (BMD) than nonexercisers, whether aerobic dancers have greater BMD than walkers, and to determine the contributions of energy expenditure, body composition, and dietary factors to spine and femur BMD. Measurements were obtained on 93 eumenorrheic women (walkers N = 28; aerobic dancers, N = 34; nonexercisers, N = 31) ages 25-41 yr; lumbar spine and proximal femur BMD, body composition, physical activity, and nutrient intakes. Mean height, weight, and body mass index and median age and calcium intakes were similar for the three groups. Mean (+/- SD) values of the spine, total femur, and femoral neck BMD, respectively, were: walkers (1.092 (+/- 0.098), 0.947 g.cm-2), dancers (1.070 (+/- 0.124), 0.990 (+/- 0.104), 0.908 (+/- 0.106) g.cm-2), and nonexercisers (1.020 (+/- 0.112), 0.887 (+/- 0.073), 0.792 (+/- 0.089) g.cm-2) multiple regression analyses indicated that exercise contributed to spine (P = 0.018), total femur (P =0.012), and femoral neck (P < 0.0001) BMD, whereas type of exercise (aerobic dance vs walking) did not (P > 0.05). Total femoral BMD was influenced by exercise (P = 0.012) and energy expenditure (P = 0.023), while vertebral BMD was influenced by age (P = 0.0067), body weight (P = 0.017), and exercise (P = 0.018). These findings suggest that walking and aerobic dance exercise may provide physically active premenopausal women with greater lumbar and femoral BMD than sedentary females.

Concept of chemical immaturity in body composition estimates: Implications for estimating the prevalence of obesity in childhood and youth.

This paper estimates the prevalence of obesity in 6-8-year-old children, 13-15-year-old youth, and 18-19-old adults by using skinfold data of the National Nutrition and Health Examination Survey. Obesity is defined as above 25% fat in males and above 32% fat in females. Skinfold equations used to estimate the fat cotent at each age were based on a multicompontent approach that used body density, body water, and bone mineral. The prevalence of obesity in the U.S. population was found to be much lower in children than in youth and young adults and to increase from 1 in 20 in childhood to 1 in 5 in adulthood.

Differences in the subcomponents of fat-free body in relation to height between black and white children.

The individual subcomponents of fat-free body (FFB) in relation to height were investigated in 131 white (N = 85) and black (N = 46) males (MW, MB) and 108 white (N = 63) and black (N = 45) females (FW, FB), aged 8 to 18 years. Bone mineral content (BM), bone width (BW), and bone mineral index (BMI) were measured using photon absorptiometry; total body water (TBW) was measured by deuterium dilution; body density was measured by hydrostatic weighing, correcting for residual lung volume; and estimates of lean body mass (LBM) were made from total body potassium (40 K spectroscopy). The subcomponents of the FFB-BM, BW, BMI, TBW, and K-were regressed on the log of height to determine the exponent of the independent variable (Ht) that would most accurately predict the dependent variables (BM, BW, BMI, TBW, K) within gender and race. Regression equations were derived for each of the variables used to represent a subcomponent of the FFB on Ht. Significant (P < .05) racial differences were found in BW, with the MB having wider bones than the MW. Significant racial differences were observed in BMI with FB demonstrating a greater difference across height than FW. Racial differences in BM and TBW approached significance within the female sample. At heights greater than the mean of a typical pubescent child, the males had higher values for each of the variables, except for BMI, than did the females. The lower BMI values observed in males indicated that the rate at which male bones grow in width was greater than their rate of mineralization. Within the male sample, blacks had higher bone mineral than whites with the magnitude of these differences dependent on the variable under consideration. Within the female sample the blacks had greater amounts of BM and BMI in relation to height, while the whites had a greater amount of K. Therefore, the magnitude of the differences between blacks and whites in the subcomponents of the FFB are dependent on gender, stature, and the particular subcomponent of the FFB under consideration.

Maximal voluntary isometric force production characteristics of six muscle groups in women aged 25 to 74 years.

The age-related force production characteristics of six muscle groups in 143 women aged 25-74 years were examined. Measures of maximal force (MFR) were obtained on the finger flexors (FF), thumb extensors (TE), forearm flexors (FAF), forearm extensors (FAE), dorsi flexors (DF), and plantar flexors (PF) utilizing a linear voltage differential transducer. The subjects were categorized by age into ten 5-year groups. The magnitude of decline across age in MFR ranged from 36.2% (FAE) to 45.1% (PF). There were differences among muscle groups in the age at which a significant decline in MFR was first detected. The earliest drop off in MFR was observed in FF and FAF (45-49 years), while the latest significant decline across age was noted in FAE (65-69 years). Since the magnitude of maximal force decreases with age, and because these characteristics can not be entirely explained by age-related decrements in fat-free mass, it appears that the quality in addition to the quantity of senescent muscle tissue may be compromised. However, the magnitude of decline in maximal force is dependent upon the muscle group considered. © 1992 Wiley-Liss, Inc.