High Reps And Fat Loss: Do High Reps Get You Leaner And Prevent Muscle Loss During A Fat Loss Phase?

Question: I heard that weight training protects your muscles during a fat burning phase. If I perform 50 reps using a light weight, will it protect my muscles from decreasing when I'm on a diet? If I perform, say, 100 reps, using 40% max weight, my muscles feel the same as if I had just used 80% of my max weight for 10 reps... what's the difference?


Answer: You asked "do light weights protect your muscles?" The direct answer is no. The type of resistance and repetition scheme that builds the muscle is also the best way to keep it. It's actually a common error to switch over to light weights and high reps during a fat loss program, thinking that high reps burn more fat.

It's OK, and probably a good idea to do some high rep work - some people do a "pump set" after their heavy sets, for example - but to drop all your 6, 8, 10, and 12 rep sets in favor of high reps (15-20+) and light weights is a mistake.

You mentioned the "feeling in your muscles." You are probably feeling a "burn" which is the build up of lactic acid. However, wouldn't it be better to judge your workout effectiveness based on your change in body composition, strength, muscle size, and body appearance rather than on how much it burns or fatigues you? Which is your goal, to improve your physique and strength or to get a burn?

Another way to look at it is if you can do 50 or more repetitions with a weight, then the weight is so light that you're not really doing the type of weight training that builds strength or muscle, you're training for muscular endurance or strength-endurance. You could even say that you're doing cardio with extra resistance.

A beginner may notice some muscle development or "tone" when they first start a weight training program, even a purely high rep program, but you won't get continued increases in muscle size or muscle strength with low weights and high reps, especially if high reps are done exclusively.

Including high rep weight training is fine. In fact, your muscles probably respond best from using a variety of rep ranges rather than one. But I'd suggest looking at the higher rep endurance work as ancillary to your primary workouts with lower reps and heavier weights.

While the burn you mentioned may feel the same when comparing a set of 100 reps to 10 reps, there's a very different training effect produced by using different repetition brackets, especially on such an extreme example of 100 reps versus 10 reps.

Our muscles do not know the difference between 10 reps and 100 reps or five sets versus 3 sets - our muscles only know how hard and how long they have to contract. This is not recent, revolutionary training breakthrough - it's just a common training variable called "time under tension."

We use rep "brackets" like 8-12 to target an appropriate time under tension range for muscle hypertrophy, and setting a target for time under tension seems to work very well even though it's not a direct approach. Here is a list of basic training goals with rep brackets and appropriate time under tension stats:

Strength: 1-5 repetitions X 4 seconds = approx. 5-15 seconds
Hypertrophy: 8-12 repetitions = approx. 30-45 seconds
Endurance: 25-50 repetitions = approx. 1-2 minutes
Cardio: 50-100+ repetitions = approx. 3-30 minutes

With that said, it is very important to monitor your time under tension, or make sure that you are lifting within the correct rep ranges for your goals. If you want to build muscle or maintain muscle during a fat loss phase, you should stay within the hypertrophy recommendations above. Anything more than that, and you are changing the type of training effect on your muscular system.

From a strength training perspective, anything over 12 reps is either endurance or cardiovascular work. The optimal approach is to use the time in your weight training sessions to develop strength, muscle size and or muscular conditioning - not for extra endurance and cardio benefits.

Of course, cardio and endurance training have their place in a fat loss program, but they can't replace heavier weight training and should be considered separately.

For more information, this article goes further into the physiological effects of the different rep ranges:

Last but not least, whether you lose muscle while in a caloric deficit is also a function of proper recovery from your workouts and good lifestyle (low stress, proper sleep), as well as the magnitude of the calorie deficit (calories should not be cut too severely), and protein intake (there is new research that just came out recently confirming once again that sufficient protein intake during a calorie deficit helps protect lean body mass).

We thank Mr. Venuto for his contribution in our blog.