8. Isolating Muscle Groups. How can you fit in separate exercises for your biceps, triceps, deltoids and lats when you only have 30 minutes to work out?
For body-builders, concentrating on two or three muscle groups per session might be fine, but this doesn't work for the average person. There's not enough time to get to all the muscle groups in three 30-minute sessions a week.
Instead, says Pillarella, choose exercises like squats and push-ups that target several muscle groups at once. You'll get a better workout in less time and you'll also be training more functionally (mimicking the way you use your body in daily life).