Another trend that continues to buzz the fitness industry is metabolic training. A type of very high intensity training, this workout increases your excess post exercise oxygen consumption (EPOC). (Burn more calories when you are not exercising). Metabolic training is really a marketing phrase since all training is metabolic, but the principles behind it are sound. Most people promoting a type of metabolic training (and that includes CrossFit, P90X, Insanity Training, TABATA, HIIT, and many boot camps) are doing resistance or strength training exercises, but it can also involve interval aerobic training.
What is consistent among the different brands is intensity. Metabolic training is HARD. It is a circuit workout involving simple weight training and/or cardiovascular exercises where you work your muscles to fatigue. This will increase your metabolism causing your body to burn more calories during and after the workout. It is an effective way to train, but there are multiple caveats. Working your muscles to fatigue can lead to poor form, which will result injury. In fact, insurers have refused to cover CrossFit instructors, so they have banded together to form a high-risk retention group; a type of self-insurance.
I worry that the fitness industry has gone too far in our endorsement of these programs. They are certainly effective if you want to lose weight or to be in astounding shape, but if your goal is to improve your health and remain injury free, you may want to steer clear. These workouts are most appropriate for those already in shape. If you have any type of chronic joint pain, diabetes, heart disease, arthritis or osteoporosis you are at risk for injury from such extreme training. You may ask how this is different from interval training (see posts from Feb. 13, 2011 and Sept. 30, 2010): It is mostly in degree: Programs advertising metabolic training have you work in the “extremely hard” zone frequently, and for long periods of time. Such extreme training should be balanced with rest days and cycled in with less intense exercise.
I believe the fitness industry needs to reach out more to the inactive, and I fail to see how such intense training will motivate them. I have seen promotions that promise you will workout until you "vomit or cry", and I cannot imagine why they think this is good. I personally prefer my workouts to be pain free, but if you feel you must hurt to get results, metabolic training can deliver.