Benefits
Increased muscle mass: Muscle mass naturally decreases with age, but strength training can help reverse the trend.
Stronger bones: Strength training increases bone density and reduces the risk of fractures.
Joint flexibility: Strength training helps joints stay flexible and can reduce the symptoms of arthritis.
<span>There is not such thing as a universally accepted standard of flexibility because there's no material that is taken as a reference point. You can't say it's twice the flexibilty of rubber or twice the flexibilty of bamboo or anything similar because no official reference points have been established in the SI system.</span>
The answer can be both increase in self-esteem and increase in aggression. All of the research generally points to increase of self esteem because during puberty self awareness is very prominant which increases self esteem. I would be safe and go with self esteem. I hope this helps.