A lower leg peripheral quantitative computerized tomography (pQCT) was performed in all participants by means of a recent generation device (XCT 2000, Stratec, Pforzheim Germany) to evaluate calf muscle cross-sectional area. Data presented here were derived from standard 2.5-mm-thick transverse scans obtained at 66% of the tibia length, proximal to the anatomic marker. Previous studies demonstrated that this is the region with the largest outer calf diameter, with little variability across individuals (29). The total dose of radiation administered to the participants was <1 mrem. The cross-sectional images obtained from the pQCT were analyzed by using the BonAlyse software (BonAlyse, Jyvaskyla, Finland; http://www.bonalyse.com). Different tissues in the analysis were separated according to different density thresholds: a density value of 35 mg/mm3 was used to separate fat from muscle tissue, and 180 mg/mm3 to separate muscle from bone tissue. To assess walking ability, we collected both subjective and objective information. The subjective evaluation consisted of asking participants to estimate the maximum distance they could walk without difficulty. The interviewer provided examples of distances taken from real life. For instances, for the participants living in Greve in Chianti, 1 km was exemplified as the distance between the municipal building and the local hospital. Based on responsec, we categorized participants into able or unble to walk 1 km without stopping, feeling fatigued, or developing symptoms. To measure walking speed, two photocells connected to a recording chronometer were placed at the beginning and the end of 4-m course established at the site clinic. Participants were instructed to stand with both feet touching the starting line and to begin walking at their usual pace after a verbal command. The time between the activation of the first and the second photocell was recorded. The average of two walks was used to compute a measure of walking speed. The coefficient of variation between duplicate trials was 5.2%, and only in 3.7% of the participants did the second measure differ by >20% from the first one. Use of aids (canes or walkers) was allowed for this test. The 4-m walk test has been used extensively in previous studies, and its concurrent and predictive validity and its sensitivity to change have been confirmed in large epidemiological studies (17,18,23,24). For the purpose of this analysis, low walking speed was defined as walking slower than 0.8 m/s. After exclusion of those who where unable to walk, this value approximately identified the lowest quintile of the speed distribution in our population.
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