When it comes to cardio, intense Intervals always produce better results for fat loss than moderate intensity-long duration aerobic exercise (steady-state). Everyone I knew who made the switch to an interval or sprinting program greatly increased fat loss. A recent study found, “Despite its lower energy cost, the decrease in the sum of six subcutaneous skinfolds induced by an interval training programme was 9-fold greater than the group performing 30–45 minutes of sustained aerobic exercise”(2) Now there is some controversy with this study, but overall there is a consensus that this concept holds true.
Why does this occur? From a calorie standpoint interval programs burn the same or less calories than longer sustained aerobic exercise. In the end calories in-calories out is what matters, right? In most cases yes, but there is a major hormonal difference between the two training programs.
Sprints or interval training has a much more anabolic hormonal effect. Anabolic meaning building, growing, and synthesis of cells. This is a much better environment for your body post workout than being in a catabolic state. Catabolic meaning the breakdown of tissues, cells, and use of energy. With intervals there is a bigger increase in growth hormone (GH), insulin-like growth factor 1 (IGF-1), and testosterone (T). These anabolic hormones will promote muscle gain as well as fat loss resulting in a leaner versus skinnier look.
With sustained aerobic activity there is little increase in anabolic hormones. In addition to this, there is a much bigger increase in Cortisol, commonly referred to as the stress hormone. Although very much needed, Cortisol can wreak havoc on the body if it stays elevated in excess magnitude or duration. This makes sustained aerobic activities like distance running very catabolic and stressful on the body. The result is a decrease in both muscle and fat if weight loss occurs.
I’ve experienced first hand how distance running burns off muscle as well as fat. Over the past few years I decided to improve my distance running thus I ran 3-5 times a week, 3-6 miles a run. Although I kept up an intense lifting regimen, I still lost significant muscle. I ended up at my goal “lean” weight, but was 2-3% fatter than in previous years at the same weight. Of course, I did become a better runner. Aside for one session of interval training a week, I stopped running. With the absence of running and a consistent lifting program I soon dropped 1% body fat in just a few weeks.
So if you want a better shot at decreasing your body fat percentage perform intense intervals for cardio. If you want to be smaller and flabbier then keep doing the same boring 30-45 minutes of steady-state cardio.
1) Marcus C.C.W. Elliott, Phillip P. Wagner, and Loren Chiu, Power Athletes and Distance Training, Physiological and Biomechanical Rationale for Change. USC Sports Med 2007, vol 37, issue 1. Retrieved from: http://www.spartascience.com/publishedresearch_assets/Power%20athletes%20and%20distance%20training%20physiological%20and%20biomechanical%20rationale%20for%20change.pdf
2) Tremblay A, Simoneau JA, Bouchard C. Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism 1994; 43 (7): 814-8 Retrieved from: http://www.sciencedirect.com/science/article/pii/0026049594902593
3)Shawn Talbot, PH.D., FACSM (2007) The Cortisol Connection - Why Stress Makes You Fat and Ruins Your Health - And What You Can Do About It.
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