Illustration of a skinny guy flexing his arms to build muscle.

Does Flexing Build Muscle? Yes, But It’s Not What You Think

I came across this fascinating story about Charles Atlas years ago when I was writing an article about training for muscle size. If you don’t know, we’re a muscle-building site for skinny guys, and Charles Atlas was the first person to mass-market a workout program specifically designed to help skinny guys bulk up.

His story is much more interesting than I expected. First of all, it’s a flexing program. You buy the guide, and then you do a flexing routine at home. The “dynamic resistance” from flexing is supposed to stimulate muscle growth. There’s nothing wrong with that idea in theory, but does it actually work?

There have been studies measuring muscle growth from flexing, too. We can look at the results of a recent one.

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Illustration of a skinny lifter using collagen to build muscle.

Does Collagen Help Build Muscle? A Quick Research Overview

Collagen is a popular “anti-aging” supplement for maintaining skin elasticity, keeping our joints strong, and helping our connective tissues recover. So far, the research has shown that collagen does indeed offer all of those benefits, in a small way—probably (study, study).

Lifters often run into nagging aches and pains in their joints and tendons. Supplementing with collagen seems like a reasonable way to improve recovery. That raises an obvious question: what about muscle growth? Does collagen help build muscle?

Jacinto and colleagues tried to answer that question by comparing whey protein against collagen protein, then seeing which yielded more muscle growth. It’s a neat study. Let’s delve into it.

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Illustration of a bodybuilder doing cardio after lifting weights, but he's losing all his muscle mass.

Does Cardio Kill Muscle Gains?

Cardio can kill muscle gains. We’ve known this for many decades. It’s common knowledge among lifters and shows up in studies. Most recently, a study found that cardio cut muscle growth in half. We’ll go over the nuance of that study in a moment.

That isn’t normal, though. Most people who combine weight training with cardio build muscle just fine. The latest meta-analysis found that cardio didn’t interfere with muscle growth at all (meta). In fact, I’ve noticed the opposite.

If you’re clever, you can use cardio to build more muscle. We’ll go over some interesting research. It’s something I’ve seen with clients, too. The guys who get the best results are often the ones who get fit while they’re bulking up.

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Illustration of a skinny guy who gained weight by eating more calories.

How Many Calories Do You Need to Gain Weight? (With Calculator)

You’ll often hear that the number of calories you need to gain weight depends on your age, sex, height, weight, activity level, and metabolic health. That works well if you’re overweight like everyone else. It works less well if you’re starting off thin and trying to become muscular, neither of which is typical.

If you’re trying to gain weight or build muscle, you can forget most of those factors. They’re for estimating how lean and muscular you are. If you lift weights, you can be lean and muscular at 20 or 50, so those proxies won’t do you much good. If you have a rough idea of your body-fat percentage, you can be much more accurate.

The other thing to consider is how fast you’re trying to gain weight. If you’re bulking leanly, you’ll need fewer calories. If you’re bulking more aggressively, you’ll need more.

So, I’ve made a simple calorie calculator that will ask you all these questions and spit out an estimate. Once you have that estimate, we can talk about what to do with it.

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Illustration of a skinny man building muscle.

The Newbie Gains Guide for Skinny Guys

If you’re new to lifting weights, you can build muscle incredibly fast. Lifters call this phenomenon “newbie gains.” Most men can gain over 20 pounds of muscle during their first year alone. Skinny guys can often do even better.

We specialize in helping skinny guys build muscle, and we’ve worked with over 10,000 clients over the past decade. We do this all day, every day, with clients ranging from everyday desk workers to professional and Olympic athletes. There are methods to get incredibly consistent newbie gains. But there’s a catch.

Although most new lifters build muscle quickly, some “hardgainers” fail to gain any muscle whatsoever. What’s going on here? Why are some guys able to build a lifetime of muscle in a single year, whereas others spend an entire lifetime unable to build a single year’s worth of muscle?

In this article, we’ll explain what newbie gains are, how they cause such rapid rates of muscle growth, how to take advantage of the phenomenon, and how to avoid becoming a “hardgainer.”

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Illustration of a skinny guy doing an aggressive bulk, building muscle as quickly as he can.

Aggressive Bulking: How to Build Muscle FAST

If you’re a skinny guy desperate to build muscle fast, I get it. I remember hungering not for food but for muscle. I was too eager to heed any of the many warnings. I gained weight as fast as I possibly could. And to my great surprise, it worked.

I gained 20 pounds in 3 months. Then I helped my skinny roommate bulk up even faster. He gained 30 pounds in 3 months. Since then, we’ve helped thousands of other skinny guys do the same. Under the right circumstances, aggressive bulking can work incredibly well.

Not everyone should bulk fast. The stars need to align just so. You need to be skinny and naturally lean. You also need to be ready to bulk properly—to follow a good workout program, eat a nutritious bulking diet, and live a lifestyle that supports muscle growth.

If that sounds like you, good. Let’s delve into the thick of it.

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Illustration of a tub of weight gainer powder.

The Best Bulking Supplements for Skinny Guys

Over 5,000 shares and 500 comments later, here’s our revised supplement guide for skinny guys trying to build muscle in time for last summer. We’ll cover supplements that speed up muscle growth, such as creatine. We’ll review supplements that help skinny guys bulk up, like mass gainers. We’ll talk about pre-workout supplements, too.

When talking about supplements, we use research, personal experience, and over a decade of full-time coaching experience. We’ve each gained seventy pounds (naturally). We’ve also helped over 10,000 skinny guys bulk up with our Bony to Beastly Bulking Program. Marco has a degree in Health Sciences, and he’s trained hundreds of clients, ranging from everyday desk workers all the way up to college, professional, and Olympic athletes.

We don’t sell supplements. There are no affiliate links.

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Illustration of a skinny guy bulking up and becoming muscular. Illustrated by Shane Duquette from Bony to Beastly.

The Skinny Beginner’s Guide to Bulking

In this guide, we’ll teach you how to bulk up, even if you’re a skinny beginner. This is the method we’ve used to help over 10,000 skinny guys build muscle, with clients ranging from deskworkers to Olympic athletes. It’s also the method Marco and I used to gain over 60 pounds each.

We kept this guide as simple and practical as possible. But bulking is what we do. We’ve written articles about every aspect of building muscle. You can follow the links as deep as you want. There’s no bottom.

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Illustration of a skinny beginner doing a 3-day full-body workout routine to build muscle and bulk up.

The 3-Day Full-Body Workout Routine for Beginners

3-day full-body workout routines are usually best for beginners. They’re the best for building muscle, gaining strength, getting leaner, mastering your exercise technique, and improving your health.

Once you reach an intermediate level, full-body workouts are still great, but 4-day and 5-day routines start to offer some advantages. That isn’t because 3-day routines become too easy, though. Rather, they get too hard.

In this article, we’ll also give you a workout routine you can follow or build from. It’s designed to get you bigger, stronger, healthier, and better looking. Customize it as much as you want. We’ll show you how.

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Illustration showing a skinny guy who bulked up like a Hollywood actor.

Hollywood Bulking Transformations ARE Realistic for Skinny Guys

There are a ton of articles talking about how Hollywood body transformations are unrealistic. There’s some truth in that. Most guys are overweight. For them, even just dieting down to a healthy body-fat percentage can be surprisingly difficult.

Most Hollywood transformations are coming at it from the other side, though. From the naturally skinny side. From our side. These actors aren’t losing a dramatic amount of fat, they’re building an impressive amount of muscle, and they’re doing it suspiciously fast.

Many of us can do that, too.

Let’s dive into it.

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