Will the Insanity Workout Make You Lose Muscle?


I get asked this all the time. Will I lose muscle if I do the Insanity Workout? As with most questions, there’s an annoying answer: it depends. What are the variables? They’re your current body composition, your goals, and how you approach nutrition. Let’s take a quick look at what the Insanity Workout is designed to do, and then see how you can tweak that to best suit your needs.

First of all, what is the Insanity Workout? What did Shaun T design it to do? If you do the Insanity Workout ‘correctly’, what should the end results be? The Insanity Workout is a form of Threshold Training, where you operate just under your absolute maximum for up to forty five minutes, cycling through three or so sets, each composed of 4 exercises that are repeated 3 times. Thus it’s a form of interval training, which while not quite HIIT, is still absolutely intense. The exercises are a mixture of calisthenics, plyometrics, traditional cardio and sports drills. It’s designed to help you develop explosive power, to rev up both your aerobic and anaerobic engines, to help you burn a large number of calories, and to improve your flexibility, endurance and general sports performance.

Now, an athletic person who is capable of maintaining a high level of intensity for an extended period of time could easily burn up to 1,000 calories doing an Insanity Workout. Most people won’t be able to sustain that level of intensity, and can expect to burn half or less of that in the beginning. The result is that you’re burning calories, and those calories have to come from somewhere. That means you’re drawing energy either from your own reserves, or your nutrition.

The Insanity Nutrition plan is designed to help promote weight loss. It sets your caloric intake at a deficit, ensuring that you get high quality food but not enough that you maintain your current weight. Thus, if your goal is to lose weight, combining the Insanity Workout with the Nutrition Plan will ensure that you do so.


Now, everybody wants to burn fat and gain muscle. Unfortunately, the truth is that the mechanisms that promote those processes are generally opposed. Your body burns fat when it thinks it is running out of fuel; you need to convince it that you are in danger of not getting enough calories through nutrition to make it dip into its fat stores. On the other hand, you body needs to think that energy sources are plentiful for it to begin investing in building muscle. Building muscle is an incredibly expensive thing to do, and your body will only do this when there are plenty of calories to fuel it. What’s the up shot? It’s very hard to convince your body that you are starving and have plenty of fuel at the same time, resulting in fat loss and muscle gain.

What does this mean for you? You need to decide what your goals are. If you want to burn fat, you have to understand that you will not be building muscle. With the correct nutrition, you can conserve what you already have, but not gain muscle. If you want to gain muscle, you have to accept that you won’t be burning fat. Think of it as a sliding scale, with fat on one side and building muscle on the other. Where you position yourself on that scale will determine the ratio of what’s happening in your body, but you can’t do both.

Think of it this way: professional body builders go through cycles. On their off-seasons, when they’re not competing on stage, they stuff their faces and gain a ton of muscle and fat, swelling up into big, fat bears. Then, when it’s time to start getting ready for competition, they start cutting, and lean out. They change their diets, drop weight, hold onto their muscle, but burn away the body fat. One season is gain muscle, the next is lose fat. They can’t and don’t try to do both at once.

So say you simply want to lose weight. You’re body fat percentage is high, you’ve not worked out in some time, and you want to lose those love handles. Then simply follow the Insanity Workout as is. Follow the diet, do the exercise, and you’ll lose body fat and probably a little lean muscle mass as well. But the key will be the amount of fat you lose, which will make you happy.

If, however, you are an athlete, say a basketball player who wants to conserve his physique even as he prepares for his next season, then you don’t want to just lose fat as quickly as you can. Instead, you need to tailor your diet to maintain your lean muscle mass even as your body adapts to the rigors of the Insanity Workout. The way to do this is to carefully figure out the correct amount of calories you need, and ensure a diet high in carbs so as to have a readily available source of fuel. Discussing the kind of nutrition you would need to follow goes way beyond the scope of this blog post, so I won’t get into it here, but the take away is this: if you want to accrue the benefits of the Insanity Workout without losing muscle mass, you need to get your diet right. You’ll lean out, you’ll get all the benefits, but you’ll conserve your physique and walk away ripped. Not bigger, but ripped.

So there you have it. What happens when you do the Insanity Workout depends on what you eat, and what your goals are. You can go for total fat loss, or you can try to conserve what you already have, and lose less.




  1. Nuno Fernandes says:

    I’ like to get your program but I’ve tried to buy it on your website but than I realize that because I’m living in China I’m not able to get it shipped here. There’s any other way to get it here! Let me know because I’m really interested!


  2. La-Donna says:

    I’ve been doing Insanity for a while now and will begin the recovery week before too long. While I’m proud of myself for doing these tough workouts and have every intention to finish Insanity, I’m not happy with my results so far. Since starting I’ve gained a couple of pounds and while I’m hoping this is just muscle gain, I haven’t heard of this happening to anyone else.

    I’m 5’6 and a bit, and at the end of Insanity I hope to go from 136 lbs to 130…I think that’s a realistic goal. After reading this article, I guess the problem is my diet. I couldn’t tell you how many calories I consume, but I don’t think it’s a crazy amount. I guess I need to cut back?

    I have noticed more definition in my arms, back, legs and abdominals (although they’re covered with enough fat right now that I only see them while working out).

    Any feedback would be appreciated, and thank you for the informative articles.

  3. DHruszko says:

    To La-Donna, I know this is late but it’s normal for that to happen. I’ve been doing insanity and lifting daily for 3 weeks now and haven’t lost or gained for than a pound (it usually fluctuates) but I’m seeing alot more definition and size difference. I lost 2 inches on my waist and my chest has gotten a little smaller. I’m taking a thermogenic called Oxyelite Pro and it gives me alot more energy during insanity and gets my heart rate up nice and quick and gets me sweating a bit more so I really end up feeling well exercised at the end of each session. And the reason you only see the definition while working out is most likely water weight. Stay away from foods high in sodium and take a thermogenic if you’re not sensitive to caffeine (they make various strengths). Sorry this was such a late response lol.

  4. I have just completed P90X but I still have some fat to lose. I am worried that if I do Insanity I will lose the muscle that I have already gained. Is the concept more, if I do Insanity I will not gain/lose muscle but burn fat? Thanks for your time.


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