What if you could achieve the benefits of a 3 hour bike ride with just 30 minutes of training? What if you received the same endurance adaptations of an 18 mile run during a simple 20 minute session? No, I’m not talking about blood doping or ‘roids. I’m referring to HIT.

HIT stands for “High Intensity Interval Training”. If you’ve done it, you know it, because you never quite forget a HIT session. If you haven’t yet been introduced to this highly time efficient and fitness effective form of training, then by all means, keep reading.

Let’s examine what happens in the body in response to traditional endurance training.

• Improved muscle oxidative capacity. This means that the mitochondria enzymes, the machinery of the tiny powerhouses in your muscle cells, become faster and more efficient at converting oxygen into energy.
• Altered substrate utilization. The body changes its primary exercise fuel, or substrate, to contain a lower percentage of carbohydrate and a higher percentage of fat. This is also known as “enhanced lipid oxidation”.
• Increased glycogen storage. Your carbohydrate stores amplify, up to 20% over normal, un-trained values.

Wouldn’t it be fantastic if we could achieve these same aerobic adaptations via shorter bouts of more intense training? This question has been posed several times by researchers, who have conducted various studies that inspected the effect of HIT compared to traditional endurance training.

HIT is somewhat broadly defined and basically would include any repeated efforts of brief, intermittent exercise performed at a high work intensity. These efforts can last from a few seconds up to several minutes, and are separated by a longer period of rest or low-intensity exercise. Intensityranges from 175% VO2 max intensity (typical for shorter 10-30 second bouts) to 85% VO2 max intensity (typical for longer 3-4 minute bouts).

Let’s take a look at some of the important and interesting pearls from HIT studies:

• A series of 48 ten second high-intensity sprints with 40 seconds recovery after each (8 minutes of total work), achieved similar mitochondrial enzyme improvements as four 12.5 minutes efforts at a moderate intensity (50 minutes of total work).
• Over the course of three 30 second all-out sprints with 4 minutes of recovery, individuals were observed to progress towards increased fat utilization with each sprint.
• Over two weeks, performed three times per week, a workout that simply involved four 30 second “all-out” sprints with four minutes of recovery after each (2 total minutes of work) nearly doubled cycling time to exhaustion at approximately time trial pace (from ~30 minutes up to ~60 minutes).
• Fat oxidation in women was significantly improved by performing an exercise sessions that involved ten 4 minute efforts with 2 minute recoveries (a bit higher volume in this study!).
• Five 30 second high-intensity efforts with 4 minute recoveries, performed 3x/week (10 minutes total training time), resulted in similar aerobic adaptations as a single 40-60 minute low to moderate-intensity session performed 5x/week (4.5 hours total training time).
• Finally, one interesting study looked at what type of HIT training was most effective in well-trained cyclists, and concluded that twelve 30 second efforts with 4.5 minutes rest or eight 4 minute efforts with 1.5 minutes rest produced the highest potency for inducing aerobic training adaptations.

I personally liked the idea of four 30 second “all-out” sprints with four minutes of recovery after each, so I performed this workout on the indoor trainer over the weekend, in lieu of a 2 hour bike session. So I grabbed my iPod and sweat towel, sucked down a cup of coffee, and prepared for a short, sweet, slightly painful exercise session.

My goal was 450-500 watts for each 30 second sprint. In no time flat, I experienced a revelation. With just 18 minutes of training, I was cooked, wasted, destroyed and any other violent adjective we avid exercisers might use to refer to the fact that we just completed a fantastic and highly effective workout.

As I draped myself over the handlebars and gasped for breath, I realized that I had the same feeling I might have after a three hour brick session, or a 75 minute open water swim, or a cage fight with lions.

This HIT concept might just save me a few hours this winter, and a fair share of indoor trainer boredom. For your endurance training purposes, it might just be worth looking into...