Scientists rate workout intensity as a percentage of maximum heart rate (MHR). If you want to, you can track your heart rate by wearing a heart rate monitor, or checking your pulse. I found that a more simple way is to pay attention to your body. When you’re at 60-75% of your maximum, you feel like the happy face in the beginning of the video below. Most of this long-slow training is in this range. Here, you feel great, you’re relaxed, and you could keep going for a long time. Notice that at 75-85%, the smile flattens out into a look of determination. You’re not talking…you’re focused! You are on a mission! At 85-95%, you start making your battle-cry face! You can only keep this pace up for a few minutes.
Somewhere between your happy face and your battle-face grimace is your lactate threshold. That’s the point where your muscles are producing more of a waste product (called Lactic Acid) than they can clear away, and you start to feel the burn. As lactic acid builds, the burn gets worse, until you finally feel like you are going to collapse, and you have to stop. Your lactate threshold is what keeps you from training harder and burning more calories (see the video below).
Steady training in the happy face pace never stretches that limit, and it doesn’t increase. But, when you push yourself to the grimace-range a few times a week, several exciting things happen. First, it raises the calorie count of your workouts. Second, it tunes your aerobic system and trains you to clear lactic acid better, so in time, you can comfortably work harder and burn more calories…even on your slow days! Third, it raises your metabolism for several hours afterward, which means more calories up the chimney! Lastly, those high intensity bursts can significantly increase the number of muscle-fibers in play. On average, about 50% of your muscles are composed of fast-twitch fibers, which are only activated as you move into higher-intensity ranges. Intervals switch on those fibers, and eventually they stay switched on for a while, even after you slow back down. This improves muscle tone and further improves your calorie-burning efficiency.
3. Strength Training To Build New Muscle
Strength training does a lot of great things for your body…including increasing bone density, improving your posture, adding contour, and once again, devouring calories. Each new pound of that shapely muscle automatically hikes up your metabolism.