In school, for seniors, you can do normal gym class or do conditioning.
Conditioning is where you go to the weight room everyday.
You can hop on a treadmill, use the fitness machines or do some weightlifting. I seriously thought about it since I really wanted to be lazy for a period a day. I then decided that I liked trying the new sports better and stuck to gym. I am thankful because I never realized how good of a workout you can get from different sports. My last year of highschool was pretty eye opening. I ended up trying really hard no matter the sport that was offered. I liked playing tennis because the cardio work out was intense. Volleyball was amazing since you are always in a crouch position. My legs would kill after that class. I even enjoyed playing football because it was a good arm workout. Now as an adult, I do different sports as a work out. Frequently I will call a friend up to play tennis. Sometimes on my own I will kick a soccer ball around to get a good cardio workout in. I am a part of my office baseball league and frequently do pick up basketball games in my town. I prefer doing this than going to a gym. It is so boring lifting free weights or running on a treadmill. Playing a sport tricks you into being physically fit. I also get a more balanced workout since most sports use more than one muscle. I also am more likely to stretch when I do a sport.