Which is better to lose fat and get lean?

It seems that every couple of years, there is a new method or product that offers to solve your weight and fat loss problems, in as little time as possible.  This is great if you are a fat loss and exercise marketer, but for the average gym goer, this can be a bit overwhelming.  Just as the low carb group has come, and largely gone, when it comes to fat loss, a new group has arrived on the scene recently: the interval crowd.  

Also, as a precursor and dislaimer, be sure to consult with a physician and only implement any workout plan if you are healthy enough to do so.  If you are severely overweight, the overall intesnsity of your workouts should be fairly low, and interval training should be ignored until you are physically capable of handling it.

What is interval training?

Interval training is exactly what it sounds like, working hard for a certain time period, then working or resting for another time period.  You repeat these intervals over a 20-30 minute general time frame and call it a workout.  The idea is that you are working hard, getting your heart rate extremely high for only a few seconds to a minute, and then get to back off for another time period.  Often, the work to rest ratio is somewhere around 1:2 or 1:3.  As an example on the stationary bike: sprint hard for 30 seconds, rest for 1 minute or 90 seconds.  

Over a 20 minute session, at a 1:2 ratio, that workouts out to a 1200 second session (20 minutes x 60 seconds) with only about 10 minutes of actual work being done.  The rest is either spent at complete rest, or at a very easy pace where benefits are minimal.  

A potential negative of interval training is whether the cardiovascular system is up to par to handle the recovery requirements of a strenuous interval session.  A few weeks of brisk walking with an elevated heart rate etc. will help to develop some positive adaptations and improve overall work capacity.

 Working at an elevated heart rate with an under trained heart and lungs is unproductive, and potentially dangerous. 

A Word About Steady State Training

Steady state training gets a bad rap from a number of people, and often for legitimate reasons.  The naysayers complain that it is boring (for many this is true), makes you slower (kind of true), or is sub optimal for fat loss (not really true).  Using a similar example from above of a short 20 minut session, instead of 10 minutes of work, you will complete 20 minutes of work, assuming that you keep your pace fairly steady, as the name implies.

Assuming that the interval trainee reaches a heart rate of 180 beats per minute (BPM) during the work interavals, and that the steady state trainee maintains a heart rate between 150-170, the trade off in terms of fatigue and work completed indicates that the steady state trainee would benefit more.  

What About "Slow Twitch" vs. "Fast Twitch" Muscle Fibers?

One of the big knocks on steady state work is that the lower intensity engages slow twitch muscle fibers while neglecting the fast twitch fibers.  As a very general description, slow twitch fibers lack explosive power are aerobic in nature meaning they rely on oxygen to function, and in general are not capable of significant overall strength and growth.  They do resist fatigue well though.  Think a 5k runner .  Fast twitch fibers rely primarily on anaerobic mechanisms for fuel and are powered primarily by ATP (adenosine triphosphate).  While fast twitch fibers have greater capacity for growth and power, they fatigue very quickly.  A decent example here would be a Olympic Weightlifter.  

Side note: Many will use the example of the way an average sprinter looks compared to a marathoner.  What they don't often mention though, is that sprinters do far more lower intensity work to develop work capacity and technique than you would think.  In turn, distance runners do a little bit of speed work to help cover their bases for when they need to break away from the pack or make a dash to the finish line.  The methods are similar, but the training volumes and  ratios of work are very different.  In short, sprinting won't give you a professional bodybuilder physique.

So, Which Method Should You Use?

In a conditioning sense, doing more slow twitch work may spare the fast twitch fibers for more appropriate work.  However, most people don't want or don't have the time to spend an hour or more on a treadmill, on the asphalt or bike.  Likewise, many people may benefit, especially those with athletic aspirations, from some sprint and speed work.  

A compromise may be to do an extended steady state workout two or three days per week, with an interval session another two days per week.  There is no real reason to neglect either style of training.  Mixing the two is great for your psyche as well as for your physique.