Physical activity declines during adolescence, but the underlying reasons remain unknown.

Considerable evidence suggests that the loss of strength and muscle mass appear to be inevitable consequences of aging. Moreover, aging is associated with an increase in body fat. This study examined whether increased physical activity could prevent or reverse the losses of strength and skeletal muscle mass as well as the gain in fat in older adults. Eleven men and 31 women completed a randomized trial consisting of either a physical activity (PA; n = 22) or successful aging health educational control (SA; n = 20) group. Isokinetic knee extensor strength and computed tomography-derived midthigh skeletal muscle and adipose tissue cross-sectional areas (CSA) were assessed at baseline and at 12 mo following randomization. Total body weight and muscle CSA decreased in both groups, but these losses were not different between groups. Strength adjusted for muscle mass decreased (−20.1 ± 9.3%, P < 0.05) in SA. The loss of strength was completely prevented in PA (+2.5 ± 8.3%). In addition, there was a significant increase (18.4 ± 6.0%) in muscle fat infiltration in SA, but this gain was nearly completely prevented in PA (2.3 ± 5.7%). In conclusion, regular physical activity prevents both the age-associated loss of muscle strength and increase in muscle fat infiltration in older adults with moderate functional limitations.

Lower ambulatory performance with aging may be related to a reduced oxidative capacity within skeletal muscle. This study examined the associations between skeletal muscle mitochondrial capacity and efficiency with walking performance in a group of older adults. Thirty-seven older adults (mean age 78 years; 21 men and 16 women) completed an aerobic capacity (VO₂ peak) test and measurement of preferred walking speed over 400 m. Maximal coupled (State 3; St3) mitochondrial respiration was determined by high-resolution respirometry in saponin-permeabilized myofibers obtained from percutanous biopsies of vastus lateralis (n = 22). Maximal phosphorylation capacity (ATP_max) of vastus lateralis was determined in vivo by ³¹P magnetic resonance spectroscopy (n = 30). Quadriceps contractile volume was determined by magnetic resonance imaging. Mitochondrial efficiency (max ATP production/max O₂ consumption) was characterized using ATP_max per St3 respiration (ATP_max/St3). In vitro St3 respiration was significantly correlated with in vivo ATP_max (r² = .47, p = .004). Total oxidative capacity of the quadriceps (St3*quadriceps contractile volume) was a determinant of VO₂ peak (r² = .33, p = .006). ATP_max (r² = .158, p = .03) and VO₂ peak (r² = .475, p < .0001) were correlated with preferred walking speed. Inclusion of both ATP_max/St3 and VO₂ peak in a multiple linear regression model improved the prediction of preferred walking speed (r² = .647, p < .0001), suggesting that mitochondrial efficiency is an important determinant for preferred walking speed. Lower mitochondrial capacity and efficiency were both associated with slower walking speed within a group of older participants with a wide range of function. In addition to aerobic capacity, lower mitochondrial capacity and efficiency likely play roles in slowing gait speed with age.

The present study examined lifestyle and behavioral correlates of the change in total testosterone over 13 years in 66 men aged 41–61 years who were former participants of the Multiple Risk Factor Intervention Trial (MRFIT) at the Pittsburgh, Pennsylvania, center. The authors also determined in these men if changes in total testosterone are related to changes in cardiovascular disease risk factors. The mean total testosterone level was 751 (standard deviation, 248) ng/dl at baseline and decreased by 41 (standard deviation, 314) ng/dl during follow-up. The correlation between measures was r = 0.44 (p <0.001). In multivariate analysis, higher type A coronary-prone behavior score, greater pack-years of cigarette smoking, and the MRFIT special intervention group were associated with larger decreases in total testosterone. Age, body weight, weight change, leisure time activity level, and alcohol intake were not related to the change in total testosterone. The decrease in endogenous testosterone was associated with an increase in triglycerides and a decrease in high density lipoprotein cholesterol in multivariate analysis controlling for obesity and other lifestyle covariates. There was little relation between change in testosterone and change in total and low density lipoprotein cholesterol or blood pressure. This longitudinal study confirms a gradual decline in total testosterone levels with advancing age in older men and provides evidence that lifestyle and psychosocial factors are related to this decline. Decreases in endogenous testosterone levels with age in men are associated with potentially unfavorable changes in triglycerides and high density lipoprotein cholesterol.

TOTAL JOINT replacements for the hip and knee are among the most common surgical procedures in the United States. Rehabilitation is essential to minimize disability after surgery, yet pressure on clinicians to reduce length of stay has limited the use of hospital rehabilitation services. Most patients can be discharged directly home in 5 to 7 days if they are medically stable and have completed a postoperative rehabilitation program.¹ Those who were significantly older, lived alone, and had an increased number of comorbid conditions were at high risk for requiring further inpatient rehabilitation services before returning home.² However, there are no practice parameters to determine how best to treat high-risk patients who are unable to go directly home after joint replacement surgery.