If you want to gain muscle, do aerobic exercise to warm up fully first. If you want to lose weight, I suggest you do some stretching exercises or something to exercise your muscles (to avoid injury). You can walk slowly on the treadmill for 10 minutes, and then run for more than 30 minutes (moderate heart rate). Don't stop or sit down to rest immediately after running. You need to walk slowly 10 minutes to rest. I wish LZ early success in losing weight ~!