To assess age and gender differences in muscle strength, isometric, concentric (Con), and eccentric (Ecc) peak torque was measured in the knee extensors at a slow (0.52 rad/s) and fast (3.14 rad/s) velocity in 654 subjects (346 men and 308 women, aged 20-93 yr) from the Baltimore Longitudinal Study of Aging. Regression analysis revealed significant (P < 0.001) age-related reductions in Con and Ecc peak torque for men and women at both velocities, but no differences were observed between the gender groups or velocities. Age explained losses in Con better than Ecc peak torque, accounting for 30% (Con) vs. 19% (Ecc) of the variance in men and 28% (Con) vs. 11% (Ecc) in women. To assess age and gender differences in the ability to store and utilize elastic energy, the stretch-shortening cycle was determined in a subset of subjects (n = 47). The older women (mean age = 70 yr) showed a significantly greater enhancement in the stretch-shortening cycle, compared with men of similar age (P < 0.01) and compared with younger men and women (each P < 0.05). Both men and women showed significant declines in muscle quality for Con peak torque (P < 0.01), but no gender differences were observed. Only the men showed a significant decline in muscle quality (P < 0.001) for Ecc peak torque. Thus both men and women experience age-related losses in isometric, Con, and Ecc knee extensor peak torque; however, age accounted for less of the variance in Ecc peak torque in women, and women tend to better preserve muscle quality with age for Ecc peak torque. In addition, older women have an enhanced capacity to store and utilize elastic energy compared with similarly aged men as well as with younger women and men.

To determine the differences between arm and leg muscle quality (MQ) across the adult life span in men and women, concentric (Con) and eccentric (Ecc) peak torque (PT) were measured in 703 subjects (364 men and 339 women, age range 19-93 yr) and appendicular skeletal muscle mass (MM) was determined in the arm and leg in a subgroup of 502 of these subjects (224 men and 278 women). Regression analysis showed that MQ, defined as PT per unit of MM, was significantly higher in the arm ( approximately 30%) than in the leg across age in both genders (P < 0.01). Arm and leg MQ declined at a similar rate with age in men, whereas leg MQ declined approximately 20% more than arm MQ with increasing age in women (P

Bilateral asymmetry in the structure of the second metacarpal was examined in relation to functional hand dominance in a large, clinically nonselected, healthy population sample from the Baltimore Longitudinal Study of Aging. Bilateral bone measurements were made from anteroposterior hand radiographs of a total of 992 individuals, 609 males and 383 females, with an age range of 19-94 years. Hand dominance was determined on the basis of personal impression. Total width and medullary width at the midshaft of the second metacarpal were measured to 0.05 mm using a Helios caliper. These two measurements were used to derive cortical thickness, cortical bone area, periosteal (total) area, medullary area, percent cortical area, and the second moment of area in the mediolateral plane. In both right and left-handed individuals, statistically significant side differences were found in the calculated bone areas and the second moment of area, with the dominant hand being larger. Cortical thickness did not show significant side-related differences for either handedness. These results show that functional handedness leads to periosteal and endosteal expansion of the second metacarpal cortex on the dominant side, increasing bone strength without increasing cortical thickness. This is the first time this pattern of asymmetry has been reported in left-handers as well as right-handers. Our results argue for the primacy of environmental (mechanical) effects in determining bilateral asymmetry of limb bone structural properties.

Muscle mass and strength losses during aging may be associated with declining levels of serum testosterone (T) in men. Few studies have shown a direct relationship between T and muscle mass and strength. Subjects were 262 men, aged 24-90 yr, from the Baltimore Longitudinal Study of Aging, who had T and sex hormone-binding globulin sex hormone-binding globulin (SHBG) measurements, from which the free T index (FTI) was calculated (T/SHBG) from serum samples collected longitudinally since 1963, total body fat mass and arm and leg fat-free mass (FFM) by dual-energy X-ray absorptiometry and arm and leg strength by dynanomometry. Mixed-effects models estimated T and FTI at the time of mass and strength measurements. Age, total body fat, arm and leg FFM, T, and FTI were significantly associated with concentric and eccentric strength. FTI, not T, was modestly, but directly, related to arm and leg strength after fat, arm and leg FFM, height, and age were accounted for and indirectly through body mass. FTI is a better predictor of arm and leg strength than T in aging men.

Advancing age, rather than declining serum levels of IGF-I, appears to be a major determinant of life-time changes in body composition and BMD in women and men.

A causal role in age-related bone loss has been attributed to alterations in vitamin D status, the bone mineral regulating hormones, and/or renal function. We assessed biochemical parameters of bone metabolism and renal function in healthy subsets of young and old men (n = 191) and women (n = 120) and evaluated the relationships between these parameters and bone mineral density (BMD) in the radius, spine, and femur. There were no significant associations between BMD at any site and serum 25-OHD, 1,25-(OH)2D, PTH, or creatinine clearance in either young men or in young or old women, after controlling for age. In old men, however, lower radius BMD was significantly related to higher PTH and higher 1,25-(OH)2D and marginally related to lower 25-OHD values. In young men, there were unexpected but significant associations between lower femoral neck BMD and higher serum osteocalcin and urinary calcium/creatinine excretion after age adjustment. In old women, lower spine and radius BMD was also significantly correlated with higher serum osteocalcin. In this healthy, vitamin D-replete population, there were significant cross-sectional declines in BMD in the femur in young and old men and at all sites in old women. Elevated remodeling may be an important feature that contributes to reduced femoral BMD in young men and reduced spine and radius BMD in old women. However, compromised renal function or levels of 1,25-(OH)2D or elevated PTH appear to be neither necessary nor relevant as determinants of osteopenia in the spine or femur in these normal, healthy men and women.

Testosterone precursors do not enhance adaptations to resistance training when consumed in dosages recommended by manufacturers. Testosterone precursor supplementation does result in significant increases in estrogen-related compounds, dehydroepiandrosterone sulfate concentrations, down-regulation in testosterone synthesis, and unfavorable alterations in blood lipid and coronary heart disease risk profiles of men aged 35 to 65 years.

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