just as the article which I cited suggest,for western women above 40,their squat ability may decrease as aging. For those who above 50,very few of them can make full squat. if you only interview the women who above 40,you may find that their difficulty to squat will increase as they get older,but if you only interview the women under 40,the opposite might be correct, if my suggestion of peak age is correct. also,if you interview women in some colonies in Asia, you may find that younger women ten