Not to be a party pooper but trees have different density. Also the army guys have to run while holding it up while the woman can walk slowly, and puting all the weight onto your back is easyer than holding it above your head. And lastly the scots train to do that if you tryed to do it without knowing how to you can hurt yourself. But it is funny.
But I workout a lot... and eat lots of dead animals. I don't iron my shirts and I have even chopped down four trees. I love working on cars as I smoke a cigar and brink beer... maybe I need to move...that might help.
you do understand that the military people lifting the log are doing that after a day(s) worth of intensive training right? And if its a multiple day training session, they are also soaking wet in water and have had maybe 3 hours of sleep