In this day & age where I almost feel the odd one out for not being a triathlete, I thought this clip was interesting. Its something I have thought about for a while now particulalry after having kids and personally juggling time between exercise & valuable time with my family...Short clip below about the "exercise wdows" although worth checking out the full article at the link; 

http://tinyurl.com/6g9w87q

The exercise widow often wakes to an empty bed—a sure sign of a morning workout—and may find dinner plans spoiled by a sudden avoidance of anything heavy before a night run. Hoping for an hour of television or catching-up before bedtime? Forget it: All that early-morning exercise takes its toll. Mr. Waxman arrives home from the office after his children, ages 11, 10 and 8, have eaten dinner, and he hits the sack before they do. "I'm out of gas by nine o'clock," Mr. Waxman says.