Q&A Part 1: Does Low Intensity Cardio Burn the Most Fat? Do High Reps and Bodyweight Exercises Tone Already Developed Muscle?

Q: Does low intensity cardio burn the most fat? Do higher reps and bodyweight exercises actually tone developed muscle?

A: Does low intensity cardio burn the most fat? This is true, sort of. Low intensity exercise burns a higher percentage of fat during the execution, but it’s an ineffective method of fat loss, and this small fact has lead more people astray than almost any other published research. This is a classic case of misinterpretation of results and sensationalizing components without understanding their context. Let me explain; this dates back to studies done in the late 80’s and early 90’s that were examining the mechanisms of adaptation to different intensities of cyclic aerobic exercise. Basically they got a ton of subjects on an exercise bike and had them train at 50, 65, and 80% of max heart rate for 40mins and measured post exercise blood markers as well as breath differential to determine the predominant energy system and fuel source. The aerobic system and their corresponding mitochondria is the only system that can use fat directly as a fuel, so no surprise when the 50% burned the highest ratio of fat to glucose, however, the total amount of fat burned was negligible, 65% burned the highest total amount of fat (but the ratio was slightly equalled) and 80% burned mainly glucose. So from these results it was concluded that to burn the most fat that people should train around 65% max heart rate to burn the highest amount of fat (hence the dawn of the “fat burning zone”). The main problem is that the study design didn’t account for adaptation: the subjects were untrained, and the study only looked at the hour window of the actual training session, not a series of sessions done over several weeks or even 24 hours post exercise. What we found out later was the dirty secret of the 65% and above group is that approximately 3% of the energy demands were supplied by the body’s proteins and over the long run (pun intended) newer studies show that unless you are constantly increasing your distances or frequency, cardio only training actually makes you fatter over time. The mechanism of this change is described in “The Truth about Toning, Part 1” on the Facebook page.

Around this time high intensity intervals were studied with trained and untrained individuals over a period of 8-16 weeks, and although very little fat is burned during the workouts, the mechanisms of adaptation cause more fat to be burned over a 24 hour period and also increase protein synthesis if performed correctly, giving it a 1-2 punch for body composition and fat loss. Very low intensity cardio can be a nice “top up” and a good way to increase overall fat loss and aerobic efficiency, but there’s really no debate over what the more effective method of fat loss is. The real value of low intensity cardio is it’s use in active recovery and increasing the ability to do more high intensity work. Although you will still hear “low intensity cardio burns the most fat (ratio)” and “train in the fat burning zone to burn the most fat (total amount)”; I think we can finally put these to rest. 

Q2: Do high reps and bodyweight exercises actually tone already developed muscle?

A: Ok this one ties right into high intensity interval training. The problem is that we tend to think of things in absolutes. Running is cardio. Bench press (or I should say horizontal pressing) is for muscle growth; however both these exercises fit on a continuum: marathon to sprints. 50pushups to a 500lb bench press. With sprinting you land with 6-8x your own body weight on each limb (1200-1800lbs for a 200lb person) and the energy demand is over 90% anaerobic with the creatine/phosphate system supplying the highest degree of energy – I thought that running was cardio? Where in a set of 50 push-ups you’re going to be relying heavily on the glycolytic/lactic and aerobic systems to produce most of the energy – the same system that is strained during most high intensity intervals. So what are you actually doing with high rep or body weight exercises? High intensity interval training. Does it tone the muscle? That depends on what your definition of toning is, as there is no such thing as toning, just fat loss and muscle gain. So what can you expect from it? Fat loss for sure, but will it build muscle? Only in the untrained for about 12 weeks. Furthermore, not all muscle growth is created equal; the adaptions from high intensity intervals will mainly be enzymatic changes to type 2a muscle – these usually don’t create the lean defined look that most people are after. There’s much more evidence that myofibrillar hypertrophy of type 2b(x) fibers will produce a harder “more toned” muscle. For more about the difference between sarcoplasmic and myofibrillar hypertrophy you’ll have to check out Q&A part 2 coming soon

Made it this far and have your own questions? Comment below or on the Blacksmith Fitness Facebook Page http://www.facebook.com/blacksmithfit and I’ll do my best to answer them in the comments, or if they warrant a longer answer, I’ll make them their own article Look forward to hearing from you all, keep the dialogue going!

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