I added box jumps & hopping up stairs to my workouts. i really enjoy them. i'm 40 & 250 lbs. should i set a limit to prevent injury? doing 5x10 4 days

Whoa: Jumping at a weight of 250 pounds translated to 500 # of force through the knee. This is not a good idea. When you get your weight down to normal there is less concern. Weight training to build muscle will help strength and weight loss. Jumping may be added for sports specific training, or for agility, but not for weight loss. See a professional for personal training if you want help

Too much: watch the stress on your joints. Find another work out~ how about trampoline, less impact, keeps you jumping?

Scale it back: 4 times a week is probably a bit much. I would scale it back to 1-2 times per week to give your muscles a chance to adapt, so they are able to bear the load instead of your joints. It is all in technique as well. Make sure you are landing with knees and ankles flexed so the impact is absorbed by your muscles instead of your knees and back.