Three principles that explain why high-intensity training is so effective

Advocates of high-intensity training (HIT) rave about the constant variety and lack of boredom in the workouts while being amazed at the results the programs deliver. Devotees often have dramatic changes in both body composition—especially fat loss—and performance that they never gained with more traditional weight or cardio programs. Far from being a mystery, however, the performance and aesthetic benefits people gain with HIT can be explained through a few scientifically researched mechanisms.

“While the science can get complicated and expansive, it is worth understanding some key concepts and mechanisms behind why HIT is so effective,” says certified strength and conditioning specialist Dan Trink, director of training operations at Peak Performance in New York City. In his book, High-Intensity 300, Trink offers three principles that explain why HIT proves to be an efficient and results-driven approach to training:

1. Excessive post-exercise oxygen consumption (EPOC). Trink admits this concept can be difficult to understand but explains that after either resistance training or cardiorespiratory training—or a combination of both—the body continues to need oxygen at a higher rate than before exercise began. This need for oxygen occurs so that the body can get back to homeostasis, or its typical resting metabolic rate. Repaying the oxygen debt caused by training requires additional energy expenditure. “What this means, in a nutshell, is that you will continue to use energy in the form of burning calories well after your exercise session is over,” Trink says. “High-intensity workouts drive up the effect of EPOC even more because you are creating a larger oxygen deficiency during the intensified effort of this type of training.”

The bottom line, according to Trink, is that the greater the intensity of the workout, the greater the EPOC. Therefore, the greater the energy expenditure, or calories burned, during and after the workout. He points out that this afterburn can last for 36 hours post-workout, so people should not underestimate just how powerful it is.

2. Building and maintaining lean mass. Many of Trink's workouts focus on building strength or gaining muscle mass, with a component of resistance—such as barbells, kettlebells, dumbbells, machines, or even body weight—included in every program. He points out that the prevailing thought used to be that if you wanted fat loss, the majority of your training had to be centered on traditional long, slow cardio activities such as jogging or cycling. While those activities still have some value when looking for fat loss, he believes they pale in comparison to resistance training because resistance training builds lean muscle tissue. “Lean muscle not only helps you gain strength but is also metabolically active, meaning that it takes a lot of energy to maintain muscle and keep it functioning,” he explains. “So, essentially, the more muscle mass you have, the more calories you can consume without gaining additional body fat."

3. Exercise density. Density is simply the amount of work performed in a given time. In the case of Trink's system, that amount is 30 minutes or less in each workout. “By packing more work into a shorter time, you drive up your work capacity, which is critical for cardiovascular health and sport performance,” he stresses. “Ever notice that it is the athlete who can give the greatest effort in the fourth quarter or final rounds who is usually the most successful?”

In High-Intensity 300, Trink offers the ultimate in exercise efficiency, helping people get the most work done in the least time while delivering optimal body composition and performance results. The book features 300 workouts that can each be completed in just 30 minutes.