4. The faux pas Coasting on your cardio
The facts Sticking with the same aerobic workout can sabotage your results as much as pushing too hard. To truly boost your fitness (which enables you to burn more calories with less effort), you need to venture outside your comfort zone a couple of times a week, to the point where you're somewhat winded and can feel your heart pounding.
The fix Instead of zoning out or doing moderate-intensity cardio all the time, mix in some high-intensity intervals twice a week. For instance, after warming up for 10 minutes on the treadmill, increase the speed or incline for 30 seconds to 1 minute, then recover with 1–3 minutes of easy-to-moderate exercise. Keep alternating for 10–20 minutes, then cool down. You also may want to do longer high-intensity intervals -- say, 5 minutes -- where you don't push quite as hard as you do on the shorter ones.
5. The faux pas Lifting the wrong amount of weight
The facts If you lift weights that are too light, you won't see improvements in strength, tone or bone density. If you lift weights that are too heavy, you'll compromise proper form, increasing your injury risk. You'll also be forced to recruit additional muscles, for instance, using your entire body to complete a biceps curl, thus cheating the targeted muscles of a good workout.
The fix For the most significant strength building, perform 4–6 repetitions per set; for more moderate strength building, perform 8–12 repetitions per set, choosing weights heavy enough that you struggle through your final few reps, but not so heavy that your form falls apart. If you get to your final rep and feel that you could perform another one, increase the weight by 5–10 percent. You may find that when you've considerably increased the amount of weight you're using, you'll drop to fewer reps, which is fine, as long as your targeted muscles are fatigued by the final rep. Don't worry: Lifting to fatigue will not leave you with monstrous muscles.