In the present study, we explored the relationship between skeletal muscle parameters and mortality risk in a sample of community-dwelling older persons. Our findings showed that body composition measures (in particular, sarcopenia) are not associated with a significantly increased risk of mortality, whereas walking speed confirmed to be a powerful predictor of adverse health-related events.
In a previous study from the Health ABC database (14
), no significant relationship of muscle area and mass with mortality was observed. In contrast, quadriceps and grip strength were strongly predictive of mortality. As noted by the authors, the Health ABC population was not disabled at the baseline. Therefore, the prognostic value of body composition parameters and sarcopenia in older persons with some degree of impairment could not be determined. Our results, besides being confirmatory of this previous study (14
), extend these findings to a wider population of older persons. In fact, our sample is drawn from a heterogeneous, representative population enrolled with no application of exclusion criteria (17
). Moreover, physical performance was the only independent variable of interest significantly associated with an increased risk of mortality, even after the analyses were restricted to participants with biological or clinical markers of frailty.
Because sarcopenia was not a risk factor for mortality, the relationship between walking speed and risk of dying requires further explanations. Sarcopenia is defined on the basis of static measurements of skeletal muscle obtained by different imaging methodologies. On the contrary, walking is the result of multiple interactions existing among several different systems (eg, nervous system, respiratory system, cardiovascular system), in addition to the skeletal muscular apparatus. The harmonic integration of these systems allows the correct explication of the critical subcomponents of walking (eg, motor programming, coordination, execution, energy production and delivery, oxygenation). Consequently, objective measures of physical performance provides a comprehensive assessment of the multiple and complex interactions among the various systems required for optimal physical functioning. Therefore, walking speed may be considered as a more thorough indicator of well-being rather than body composition measures. As a result, it is likely that the increased risk of adverse health events captured by poor physical performance may simply be the ultimate outcome of the accumulation of a broader range of age-related pathophysiological modifications and (sub)clinical conditions.
Our analyses considered the part played by inflammation as a potential explanatory and effect modifier contributing to the relationship between body composition parameters or walking speed and mortality. The irrelevant effect of inflammation on the relationship between physical performance and mortality risk further confirms that walking speed may provide information beyond functional status. Consistent with previous findings (24
), after the inclusion of medical conditions and disease risk factors in the adjusted models, the strength of the relationship between physical performance and mortality remained almost unchanged. This innate link between walking speed and survival is not peculiar of humans but is also common to other species [eg, Caenorhabditis elegans
), Drosophila melanogaster
), mouse (45
), rat (46
)]. This universal feature of physical performance measures may further justify the use of walking speed as a marker of aging or as an objective indicator in the extent of cumulative age-related body changes or disease burden.
Some limitations of the present study need to be mentioned. The InCHIANTI study allows for the adjustment of our analyses for many health- and disease-related characteristics. However, there could be unmeasured factors potentially explaining the observed relationships. The muscle and fat measurements considered in the present study were obtained from tibial pQCT scans. Therefore, our findings may not be applicable to the entire body composition. In our sample population, a limited number of participants (n
= 77) were frail according to the Fried and colleagues’ definition (ie, presence of three or more criteria). Therefore, to avoid the possible lack of adequate statistical power and the consequent risk of false-negative results, we chose to also consider pre-frail participants (ie, presence of one or two frailty criteria) in our restricted analyses. However, we believe this choice did not significantly affect our findings. In fact, although participants with one or two frailty criteria may not be defined as frail, their pre-frailty status still expose them at increased risk for short- and long-term negative health-related events, including mortality (16
In conclusion, our study shows that skeletal muscle measures and sarcopenia are not associated with a significantly higher risk of mortality in community-dwelling older persons. Physical performance (in particular, walking speed) confirms to be a powerful predictor of health-related events, independent of sociodemographics, clinical conditions, and inflammation. The use of physical performance tests in the clinical and research setting should be encouraged to provide a better evaluation of older participants.