Maximum Grip Strength Is Not Related to Bone Mineral Density of the Proximal Femur in Older Adults

In the past decade there have been numerous publications reporting a significant and direct relationship between handgrip strength and bone mineral density (BMD) of the proximal femur in older adults. The present report challenges the appropriateness of the methods, and thus the conclusions used in these studies. Specifically, these studies failed to control for the concomitant influence of body weight on both BMD and muscle strength. In the present study, maximum handgrip strength was measured using a conventional hand-held hydraulic dynamometer. Bone mineral density of the proximal femur was measured using dual-energy X-ray absorptiometry (DXA). Using allometric scaling, the influence of body weight on the value of maximum handgrip strength was removed for the data of the women. A small, but significant relationship between BMD of the proximal femur and maximum handgrip strength was found that accounted for about 6% of the total variation. The relationship between BMD of the proximal femur and unscaled maximum handgrip strength was not significant for the men. The findings diminish the confidence in a protective effect of skeletal muscle on some nonadjacent skeletal structures and suggest that these relationships may benefit from being revisited. The results highlight the utility of allometric scaling in analyses in which the relationship between a physiological variable and a body dimension variable can be nonlinearly and simultaneously influenced by other body dimension variables that are not considered in the analysis and therefore are statistically uncontrolled. Received: 21 October 1997 / Accepted: 22 September 1998     

Older Age and Higher Body Mass Index Are Associated With a More Degraded Trabecular Bone Score Compared to Bone Mineral Density

Trabecular bone score (TBS) may detect subjects with a more degraded microarchitecture but whose bone mineral density (BMD) reflects normal or osteopenia. The purpose of this study was to evaluate whether age and body sizes were associated with the discordance between BMD and TBS. We analyzed BMD and TBS in 1505 Korean women over 40?yr of age who had no history of osteoporotic fractures or conditions that affect bone metabolism. We considered 3 groups to have TBS values that reflected a more degraded TBS than their BMD values: (1) normal BMD but partially degraded TBS, (2) normal BMD but degraded TBS, and (3) osteopenia but degraded TBS. We compared subjects in these 3 groups with other subjects in terms of age and body sizes, and used multivariable logistic regression to analyze the odds ratios (ORs) for the occurrence of a more degraded TBS than their BMD level using age and body mass index (BMI). One hundred sixty subjects (10.6%) were found to have a more degraded TBS than their BMD level; these subjects were older, heavier, and had higher BMIs than the other subjects. Age (OR: 1.038, 95% confidence interval: 1.020–1.057, p <?0.001) and BMI (OR: 1.223, 95% confidence interval: 1.166–1.283, p <?0.001) were statistically significant in the multivariable analysis for the occurrence of this feature. Women with a more degraded TBS than their BMD level are older and have higher BMIs than the other subjects. It may be helpful to consider the possibility of trabecular bone degradation when clinically evaluating fracture risk in patients who are older or who have high BMIs with normal BMD or osteopenia.     

A 3-Year Longitudinal Study of the Effect of Physical Activity on the Accrual of Bone Mineral Density in Healthy Adolescent Males

It has previously been suggested that physical activity predominantly influences the accumulation of bone density before puberty. The purpose of the present study was to examine the effect of physical activity on the accumulation of bone mass in male athletes between 16 and 19 years of age. The cohort studied consisted of 12 badminton players (aged 16.1 ± 0.5), 20 ice hockey players (aged 16.1 ± 0.5), and 24 age-matched controls (aged 16.1 ± 0.6). The bone mineral density (BMD, g/cm²) of the total body, spine, dominant and nondominant humerus, head and femoral neck was measured twice with a 3-year interval by dual energy X-ray absorptiometry (DXA). In addition, at the femoral neck, volumetric bone mineral density (vBMD, mg/cm³) was estimated. At baseline, the athletes as a whole group had significantly higher BMD at the total body (P = 0.03), dominant (P = 0.006) and nondominant humerus (P = 0.009) and femoral neck (P = 0.007) compared to the controls. At the 3-year followup, the athletes had significantly higher BMD at all sites (total body; P = 0.003, spine; P = 0.02, dominant humerus; P = 0.001, nondominant humerus; P = <0.001, femoral neck; P = 0.001) except for the head (P = 0.91) compared with controls. The athletes also had higher vBMD at the femoral neck compared with the controls (P = 0.01). Furthermore, to be an athlete was found to be independently associated with a higher increase in nondominant humerus BMD ( = 0.24; P < 0.05) and femoral neck BMD ( = 0.30; P < 0.05) compared with the controls, during the study period. In summary, these results suggests that it is possible to achieve continuous gains in bone mass in sites exposed to osteogenic stimulation after puberty in males by engaging in weight-bearing physical activity.     

A Comparison of Bone Mineral Density and Muscle Strength in Young Male Adults with Different Exercise Level

The aim of this study was to investigate any differences in bone mass at different sites between young adults subjected to a high physical activity and a group of young adults with a low level of physical activity. In addition, we compared the relationship among bone mass, muscle strength, and body constitution in these two groups. The reference group consisted of 20 men, age 24.6 ± 2.3 years, not training for more than 3 hours per week. The ice hockey players consisted of 20 players, age 23.4 ± 4.9 years, from an ice hockey team in the second highest national Swedish league, training for about 10 hours per week. The groups were matched according to age, height, and weight. Areal bone mineral density (BMD) was measured in total body, head, humerus, spine, pelvis, femur, femoral neck, Ward's triangle, trochanter, femur diaphysis, proximal tibia, and tibia diaphysis using dual energy X-ray absorptiometry. BMD was significantly higher in the total body (8.1%), humerus (11.4%), spine (12.7%), pelvis (12.4%), femoral neck (10.3%), femur (7.4%), proximal tibia (9.8%), and tibia diaphysis (7.5%) in the high activity group. Fat mass was significantly lower in the high activity group (18.7%). The high activity group also had a significantly higher lean body mass (5.4%) and a significantly higher isokinetic muscle strength of the quadriceps muscle compared with the reference group. In the reference group, there was a general strong independent relationship between muscle strength of the thigh and all BMD sites, except for the head, tibia diaphysis, and proximal tibia. Furthermore, in the same group, body mass index (BMI) independently predicted pelvis BMD. On the contrary, in the high activity group, muscle strength did not predict any BMD site at all. In the same group, body constitutional parameters (weight, height, and fat mass) independently predicted pelvis BMD, and BMI was shown to be an independent predictor of humerus BMD. The differences in BMD between the groups seem to be site-specific and may be associated with the type and magnitude of loading during off season training and preferentially during ice hockey. High physical activity seems to weaken the relationship between BMD and muscle strength. Hence, impact forces may be of greater importance in regulating bone mass than muscle strength in itself in highly trained athletes. Received: 15 October 1997 / Accepted: 1 November     

Correlation of Bone Density to Strength and Physical Activity in Young Men with a Low or Moderate Level of Physical Activity

The objective of this study was to evaluate the relationship among bone mineral density (BMD), physical activity, muscle strength, and body constitution, in young men with a low or moderate level of physical exercise. Another aim was to investigate whether the head is unaffected by physical activity. The subjects consisted of 33 Caucasian healthy men, mean age 24.8 ± 2.3 years. BMDs of the total body, lumbar spine (L2-L4), femoral neck, Ward's triangle and trochanter, humerus, and head were measured using dual-energy-X-ray absorptiometry (DXA). Bivariate correlations were measured among the different BMD sites and age, weight, height, body mass index (BMI), fat mass, lean body mass, amount of physical activity (hours/week), hamstrings strength, and quadriceps strength. Significant predictors were found for all BMD sites except the head. Using all these variables, only 6% of the variation in BMD of the head could be explained, whereas 46% (total body), 31% (humerus), 17% (lumbar spine), 38% (femoral neck, Ward's), and 41% could be explained for the trochanter. Physical activity and muscle strength were found to be independent significant predictors of BMD of the total body and the sites at the proximal femur. These results suggest that at the time of peak bone mass attainment, physical activity is an important predictor of the clinically relevant proximal femur in young men with a low or moderate level of physical activity. Furthermore, since head BMD was not related to the level of physical activity, we suggest that head BMD may be used as an internal standard, to control for selection bias, in studies investigating the effect of physical activity on bone mass. Received: 5 February 1996 / Accepted: 24 September 1996