There are a wide variety of interval programs out there and research shows that they yield different results based on how they stress the body to adapt. For example, a recent study showed that an interval model called 30-20-10 was highly effective at improving health markers and performance in recreational runners, but it probably isn’t the best method for fat loss because it’s not intense enough to generate high levels of lactate or growth hormone.The 30-20-10 model has trainees perform four 5-minute intervals in which they jog for 30 seconds, run at a moderate intensity for 20 seconds, and sprint for 10 seconds, and then repeat. After doing the program for 7 weeks, trainees improved performance on a 1,500 meter run by 21 seconds and by 48 seconds on a 5 km run. They also decreased their systolic blood pressure by 5 mm Hg and improved cholesterol levels.

Body composition wasn’t measured, but there was no change in muscle pump activity, indicating that although the program improved performance and health, it wasn’t metabolically taxing enough to produce significant fat loss or muscle development.

In comparison, a 20-minute sprint interval program that used 60 intervals of all-out 8-second sprints followed by 12 seconds recovery on a ergometer cycle resulted in 2 kg fat loss and 1 kg muscle development in untrained men. The same program produced 2.5 kg fat loss in women. Note that the difference between this program and the 30-20-10 method is that for each minute trained, trainees sprint all out for a total of 24 seconds, compared to only 10 seconds with 30-20-10. The greater time spent working at maximal intensity is the difference in metabolic stress for fat loss.

For trained individuals or athletes, more demanding programs may be necessary.  Studies suggest longer all-out intervals will elevate growth hormone to produce fat burning.

For instance a very demanding 1 to 1 interval-to-rest program has produced significant fat loss and performance enhancement in trained athletes. This program used four 4-minute intervals with a 30-second sprint and 30-second jogging recovery.

Another model that allowed participants to lose 9 times more body fat than a steady-state aerobic program used 10 sprints of 15 seconds each increasing to 15 sprints of 30 seconds each as trainees began to adapt. The recovery period was based on heart rate—once it returned to 120 beats per minute the next interval was performed.

A third model that produced a significant 2 kg loss of body fat in trained runners included two interval protocols alternated for four sprint sessions a week: Ten intervals of 30-second  all-out sprints with 90-seconds active rest and 6 intervals of 2-mintue maximal intensity sprints followed by 90 second active rest. The maximal intensity sprints were performed at the maximal running speed achieved during a treadmill stage test to exhaustion, so they weren’t at the maximal speed that the trainees could run.

The take away is that you must program interval training to reach your goal and if that goal is fat loss, near maximal intensity sprints in the 30 second range to produce lactate buildup are ideal. Rest periods should be active rather than passive, and 1 to 2 or 1 to 3 work-to-rest intervals have proven effective for eliciting a growth hormone response for fat loss.

11/29/2012 9:07 AM  

charlespoloquin.com