Yet legs are half of your body and have to be trained in one way or another. Many believe that intensive leg workouts are the key to get over weight-gain plateaus. (Remember those huge guys from the gym that seem to be training legs all the time, everytime you see them? There is a reason for this). Besides you kill two rabbits with one shot as a good planned legs workout makes your heart pump as fast as while doing aerobics: you do cardio and workout at the same time!
If you are a soft-kind person who doesn’t really like training legs or if your goal is not gaining weight (muscles) you can do it the other way around. I have found that doing jogging regularly (twice a week) keeps your legs in a good shape and even improves their strength:
I haven’t been doing legs workouts for some months (Febraury-May 2005), but kept jogging frequently. In this time I lost 6% of my body fat while gaining weight from 80 to up to 89 kg! As I started with legs workouts again I could do same reps in squats with 15% more weight as before! Now if that ain’t an improvement! 
Extra tip: If you like to train first thing first in the morning, like me, you surely know how f******ed up it can be to train your legs… and to go to work/school/etc afterwards. The truth is that leg workouts require twice as much energy as a triceps or biceps workout, for example. That’s why I prefer doing them on the weekend when I can truly relax later.
What you need for jogging: Running shoes
Cost: None, if you already have good running shoes.
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