1) body composition: a lot of teens (especially girls) are worried about how much fat there is on their bodies compared to muscle bone and others.
2) muscular endurance: i believe most teens don't address this because building up muscle endurance takes a lot of time and a lot of teens don't have time to build up that endurance.
3) it is easy to go for a quick jog in the morning or evening but because a lot of teens find it hard to find time to go the gym maybe having a set of hand weights would encourage daily exercise resulting in better muscular endurance.
i hope this helps <3