Chi Pang Wen and colleagues (Oct 1, p 1244)1 report on the minimum amount of physical activity necessary for reduced mortality and extended life expectancy. Compared with individuals in the inactive group, those in the low-volume activity group reportedly had a 14% reduced risk of all-cause mortality and a 3-year longer life expectancy. We agree that any additional physical activity is worthwhile, but the reported decline in all-cause mortality and increase in life expectancy are not compatible. On the basis of the 2009 Taiwan life tables, and using Wen and colleagues' mortality hazard ratios for the low activity group compared with the inactive group, we estimate that the life expectancy extension at age 30 years is 1·85 years for men and 0·96 years for women. Wen and colleagues therefore overestimate by 38% for men and 223% for women.