Go hard or go home?

espnW's resident coach helps you reach your full fitness potential.

No doubt you know at least one person who is currently obsessed with either P90X or Insanity -- the workout DVDs that promise to get your butt into tip-top shape in a mere months. The thing that separates these DVDs from others is they are balls-to-wall crazy extreme hard. We're talking the kind of hard that will leave you crying, throwing up ... or both.

I get some masochistic thrill from doing these types of torturous workouts -- I teach spin class, after all -- and I also appreciate that they incorporate intervals (bouts of high-intensity efforts followed by short rest periods). That said, when clients ask me whether they should take on these types of crazy-hard workouts, the answer isn't simple.

The thing is, high-intensity interval training, while fantastic for boosting speed and improving other areas of fitness and athleticism, isn't the holy grail of workouts. This is mainly because you're body can't handle them consistently without risking injury, and because they leave out a major component of your performance arsenal: endurance.

Here are four things to keep in mind before you dive into any high-intensity interval-training program:

1. If you do this type of workout every day you will stop progressing.
At some point, going hard on a daily basis will lead to overtraining -- where your cardio capacity, strength and coordination stop progressing ... and even begin to regress (ugh). You need to give your body time to recover between workouts, with rest days or longer, easier efforts. Think: a leisurely 30- to 40-minute jog around your neighborhood.

2. Interval training alone will not help you complete a marathon -- or rule your sport.
To have the cardio capacity to make it to the finish line or the final minutes of your soccer game or tennis match, you absolutely positively need to incorporate longer endurance workouts into your routine. While a hard-core 20-minute workout every day has some fitness benefits, you will certainly flameout long before you hear the game-ending buzzer if you don't incorporate longer, less intense workouts (even if you dread them).

3. Interval training doesn't necessarily burn mega calories.
Yes, it's true that you burn more calories per minute interval training compared to endurance workouts. However, if you are someone who's looking to lose a few pounds so you can be more competitive in your sport or generally feel more fit, remember that a 20-minute hard-core interval workout will not equal the same caloric output as a 60-minute moderately challenging endurance-based workout.

4. It won't stoke your metabolism.
I've overheard clients at the gym saying that interval training somehow magically jacks up your metabolism long after your workout has been completed. Though I wish this were true, there is absolutely no research of statistical significance that has confirmed this.

So, bottom line? High intensity interval training is an important tool when it comes to improving athletic performance, VO2 max and overall fitness. However, as with most things (ranging from watching the "Jersey Shore" to drinking wine) it needs to be done in moderation. For best results, whether you're a fitness fanatic or amateur athlete, go hard three days a week and let endurance take care of you on the other three.

And, if you're looking for a killer routine, check out this Tabata interval workout inspired by soccer phenom Ali Riley.