As a personal trainer, I hear this question all of the time. After all, you want to make sure your workouts are producing results, but the last thing you want to do is hurt yourself. So, how hard should you be pushing your body so that your health increases instead of decreases?Let’s Talk Heart RateIf you’re doing cardiovascular exercise, your target heart rate should be somewhere between 65 and 85 percent of your maximum heart rate. What is your maximum heart rate? Simple. Just take 220 and subtract your age. For example, if you are 40 years old, your maximum heart rate is 180 beats per minute (which is 220 minus 40). Then, take that number and multiply it by .65 (117) and then .85 (153) to get your target heart rate zone, which is 117 to 153 beats per minute. One of the best ways to monitor your heart rate while working out is to wear a monitor. This makes knowing whether you are in “the zone” completely effortless. However, if you don’t have one or can’t afford one, just take your pulse every 10 minutes or so and see where you stand. If your heart rate is too low, work out a little harder. If it is too high, slow down a bit so you are in a safe zone.What About Muscles?Working your muscles is a little different as, although this type of exercise will raise your heart rate a little bit, it isn’t the same as cardio. So, how do you know if you’re working out hard enough with your resistance training?You want to feel a slight achiness or tension in your muscle, but never pain. And if you feel something pop or snap, that isn’t a good sign either. Remember it is always better to start small and then increase your resistance as this is the safest.Admittedly, there are several other methods that will tell you if you are working out hard enough. What one do you use?