INTERNAL VALIDITY OF THE PHYSICAL-ACTIVITY INDEX OVER 26 YEARS IN MIDDLE-AGED AND OLDER MEN

OBJECTIVE: To determine the internal validity of the physical activity index (PAI). DESIGN: Three time periods over a 26-year period (1965/6 8 examination, n = 7911; 1980/82 examination, n = 2054; 1991/93 examin ation, n = 3425). SETTING: Honolulu, Hawaii. PARTICIPANTS: Middle-aged to older Japanese-American men. MEASUREMENTS: PAI, other physical act ivity measures, body mass index (BMI), tricep skinfold thickness, subs capular skinfold thickness, and HDL cholesterol. RESULTS: PAI level wa s associated significantly with levels of other physical activity meas ures at all time periods. Higher PAI level was associated with lower B MI at the baseline examination (1965/68), lower subscapular skinfold t hickness at the 1965/68 and 1980/82 examinations, lower tricep skinfol d thickness at all examinations, and higher HDL cholesterol at the 198 0/82 examination. Change in PAI level from 1965/68 to 1980/82 was asso ciated with change in BMI, subscapular, and tricep skinfold thickness levels, but there were no significant associations between change in P AI level and change in BMI, skinfold thicknesses, or HDL cholesterol l evels from 1980/82 to 1991/93. CONCLUSION: PAI level is a relatively v alid estimate of overall daily energy expenditure that may be an accep table general measure across the middle-to-late stages of life. The PA I may also be sensitive enough to discern a shift toward less physical demanding activities as a population becomes older, although further studies should be conducted to better determine its validity in older populations.