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Aging and Bones a study

At baseline, men were stronger than women, and within gender, blacks were stronger than whites. However, specific torque (strength per unit mass) was lower in blacks than in whites (Table 1). All race and gender groups of participants lost a significant amount of their leg lean mass and strength over 3 years (Table 2). The absolute strength decline (Δ leg torque) was almost 2-fold greater in men compared to women (p <.001). Within the same gender, blacks lost about 28% more strength than whites (p =.001). The proportional loss of strength (% Δ leg torque) was greater in men than in women but was similar in blacks and whites. The changes in leg lean mass showed a similar pattern; men lost more leg lean mass than women, and blacks lost more leg lean mass than whites in both absolute

and proportional terms.

The annualized rates for strength declines were 3.42% and 4.12% in white and black men and 2.65% and 2.97% in white and black women, respectively (Figure 1). These rates of strength declines were almost 3 times greater than the rates for loss of leg lean mass, which were about 1% per year throughout gender and race. The specific torque was also decreased in men and women, ranging from −5.43% to −8.61% over 3 years across groups (Table 2). However, there were no gender or racial differences in the proportional changes of specific torque (% Δ specific torque), suggesting that the loss of strength was similar across gender and race after controlling for the loss of lean mass.


Baseline weight and measures of muscle mass, including total lean mass, leg regional lean mass, and thigh muscle cross-sectional area, were significantly correlated to changes in strength (Table 3). However, baseline measures of fat mass, including total body percent fat, total fat mass, leg regional fat mass, and muscle attenuation as a marker of muscle fat content, were not associated with changes in strength. Strength declines were greater among participants with higher initial strength (Table 3), although the changes in lean mass were similar between quartiles of baseline strength (Figure 2).

The bivariate correlations between changes in body composition parameters and changes in strength are also summarized in Table 3. Absolute and relative changes of weight (Δ weight and % Δ weight) were significantly associated with strength decline


in both men and women (p <.001). The changes in total and leg lean mass were significantly associated with changes in strength. However, the changes in total and leg fat mass were generally not associated with changes in strength. Men and women who lost more than 3% of their body weight over the 3 years (N = 263 for men and N = 270 for women) lost significantly more leg lean mass and strength than did those who either maintained (N = 492 for men and N = 457 for women) or gained (N = 174 for men and N = 224 for women) weight (Figure 3). However, participants who gained weight had no advantage over participants who were weight stable in either preventing or attenuating the strength decline, despite slight increases in their leg lean mass.

As shown in Table 4, for all men and all women, higher baseline strength, lower baseline leg lean mass, greater loss of leg lean mass, and increasing age were associated with greater strength decline. However, baseline leg lean mass and changes in leg lean mass together explained only about 5% of the changes in strength over 3 years in both men and women. The results were further stratified by the direction of lean mass change (loss or gain of leg lean mass) because the association of Δ lean mass and Δ strength appeared to be nonlinear. Strength declined as a function of lean mass in participants who lost their lean mass, but there was no association between Δ lean mass and Δ strength in p


articipants who gained lean mass (Table 4). Therefore, there was no gain in strength in participants who gained weight or lean mass. These associations remained after controlling for weight and weight loss and further adjusting for potential confounders including smoking status, physical activity, education, family income, and health status.





Summary

The loss of strength in these older men and women was much more rapid than the concomitant loss of muscle mass, suggesting a significant decline in the quality of muscle. Additionally, individuals who maintained or even gained lean mass were not able to significantly prevent their loss of strength. Although it may be important to preserve lean mass to prevent strength decline in old age, a considerable amount of the age-dependent strength decline is not explained by the loss of muscle mass alone. Therefore, we can put forth an alternative hypothesis that, in addition to muscle quantity, muscle quality may be an important determinant of loss of strength with aging. Further studies are required to identify other risk factors for the decline in strength with aging so that more targeted interventions can be planned to prevent or slow the decline, thus maintaining the overall function of older men and women.

Source:https://academic.oup.com/biomedgerontology/article/61/10/1059/600461


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