Lack of time is the number one reason people give for not exercising. Not getting results once they do start exercising is reason number two. Interval training is a great solution for both of these common problems.
Interval training mimics sports' start-and-stop motions. A standard interval training protocol involves alternating rounds of high- and low-intensity. High-intensity intervals are typically performed above the lactate threshold, which is about 100 percent total effort. The high-intensity round is then followed by a low-intensity recovery period that allows the body to buffer and clear lactic acid from the blood. The general prescription for interval training is to employ 3- to 5-minute rounds with a work to rest (W:R) ratio of 1:1. An example would be to perform a 30 second sprint and then rest 30 seconds, repeat four more additional times. This would add up to 5 minutes of total training time, 2:30 of running and 2:30 of resting.
Studies have compared interval training to steady state, traditional cardio. One study by Tremblay and others compared an endurance-trained group versus an interval-trained group for 20 weeks. Although the endurance group worked out much longer than the interval group, the interval group saw nine times the reduction in body fat compared to the endurance group.
The reason why people can spend significantly less time training and experience better results can be explained in part by Exercise Post Oxygen Consumption (EPOC). Scientifically speaking, EPOC is the recovery of metabolic rate back to pre-exercise levels. It can require several minutes of light exercise, several hours of hard intervals and anywhere from 12 to 24 hours, or even longer of prolonged and exhaustive exercise. What this basically means is how many additional calories your body will burn after the exercise session in order to return your body to normal. Working out at a higher intensity means more metabolic disturbance, and more energy that your body will need to bring it back down to normal. The body needs to replenish muscle glycogen contained in the muscle that's been depleted during the workout. It needs to restore the blood lactate levels to normal and bring down the heart rate and body temperature. This is a major source of energy expenditure. It's the result of exercise, but it occurs during rest, and EPOC is frequently ignored in most calculations of energy expenditure. Other factors that contribute to the success of interval training are an increase in anabolic hormones, increasing the body potential to uses fat as a primary energy source.
For most people a 1:1 work to rest ratio is a bit much. Most people new to interval training respond better to a 1:2 or 1:3 work to rest ratio. This allows for a little more rest to make sure the trainee is fresh and able to perform the work at or close to 100 max effort. If there is not enough rest time the interval training program can turn into more of an aerobic training program because the trainee is not able to give max effort and thus won't receive the benefits of EPOC. For those who are less fit a 1:4 ratio would be a good place to start with the goal to eventually get to a 1:1. High intensity interval training can offer more health benefits than traditional cardiovascular exercise and it takes less time. It's efficient and can fit in almost any fitness program, making it a great choice for anyone looking to improve their health and fitness.
Impact of exercise intensity on body fatness and skeletal muscle metabolism.Tremblay A, Simoneau JA, Bouchard C.Metabolism. 1994 Jul;43(7):814-8.