Grip Strength And Fat Mass Discriminate Older Adults Based On Risk For Mobility Related Disability

PURPOSE: As aging is associated with a loss of muscle quality (force/unit muscle tissue), recent studies have suggested that using grip strength/body mass index (BMI) may be a more robust indicator of age-related impairment of muscle function than grip strength alone. This study tested whether grip/BMI could better discriminate older adults (OA) from younger adults (YA) or OA of different disability risks than grip or grip directly normalized to forearm muscle mass METHODS: In the present study, we evaluated measures of total and regional body composition (via DXA), and grip strength in 85 older adults (OA; 78.4 ± 6.7 yrs; 56 Women) categorized by isokinetic leg strength as being low, moderate or high risk for mobility-related disability as well as a group of 26 healthy, young adults (YA; 78.4 ± 6.7 yrs; 14 Women) Differences between older adults (OA) and younger adults (YA) were assessed via a 2 x 2 (age group X sex) ANOVA, with Bonferroni post-hoc tests. Differences among disability-grouped OAs were evaluated with 3 X 2 (group X sex) ANOVAs, with Bonferroni post-hoc tests. RESULTS: Grip, grip/BMI and grip/LTM all showed significant effects of age and sex (all P < 0.006) when comparing OA to YA, but only grip showed an age X sex interaction (P = 0.032). Grip and grip/BMI were reduced in W vs. M in both age groups, while grip/LTM was greater in women. Among older adults, all three grip measures showed significant effects of group and sex (all P < 0.001) with no interactions. Again, grip and grip/BMI were higher in M, while grip/forearm LTM was higher in W. Grip/BMI was significantly different among all 3 groups in W and in M it was higher in the low risk vs. the moderate and high risk groups. The grip/LTM was the least discriminating among groups, with significant differences observed between the high-risk group and the low and moderate risk groups in W only. CONCLUSIONS: Grip strength/BMI was better than either grip alone or grip/LTM at discriminating among the mobility-disability groups. Interestingly, no measure of total or regional LTM differed across the mobility-disability groups, but total FM and percent body fat were both significantly different across all groups, suggesting that normalizing to BMI reflects negative effects of fat mass accumulation vs. positive effects of muscle mass. Supported by: NIH R01AG044424