How Do You Know if You’re Gaining Muscle When You Strength Train?


How Do You Know if You’re Gaining Muscle When You Strength Train?

It’s easy to tell whether you’re gaining weight. You step on a scale and see the value has changed. If it’s down and you’re trying to lose weight, you do a happy dance! But don’t celebrate so fast. What the scale doesn’t tell you is the type of tissue you’ve lost or gained. Was it body fat, water, or muscle? Of course, you’re training hard with weights and hoping that you’re gaining muscle and losing a little body fat if you have too much. But, how can you really know whether you’re gaining muscle rather than fat?

Weight Training for Muscle Building

When you train with weights, you stress your muscles enough to damage muscle fibers. The injury has to be repaired. So, your muscles go to work mending the torn and stretched muscle fibers. When they do, they lay down new myofibrils, the contractile units within muscle fibers that allow you to flex and proudly display your biceps. More contractile units make your muscles stronger and they’re better able to handle the stress you place on them in the future. In the process, your muscles also, over time, become larger, assuming you’re training properly and supplying your body with the appropriate macronutrients.

It’s not hard to know whether you’re gaining muscle strength. After you’ve trained for a while, you’re able to lift more weight and do more reps than when you started. Progression is one sign that you’ve become stronger. But, how do you know whether you’re gaining muscle size?

Are You Gaining Muscle?

If you’re stronger than you were, you might assume you’ve gained muscle size since muscles become stronger when they’re larger. However, it’s not so clear-cut. Muscles can also become stronger without increasing in size through neural adaptations. In fact, the gains in strength you see during the first 2 to 3 months of training are mostly neural adaptations. These are adaptations that your brain and nervous system make to function better together and they’re independent of gains in muscle size.

What do these neural changes consist of? In response to early training, your nervous system typically becomes better at firing motor units in a synchronous manner. Better synchronization of motor units helps your muscles contract with greater force. Plus, your brain and nervous system become more adept at turning on agonist muscles and turning off antagonist muscles that oppose the contraction of a particular muscle. Therefore, there’s less antagonistic activity opposing the contraction of a particular muscle and the muscle can contract with more force. Your muscles haven’t grown, in the early stages, yet they function better, thanks to your brain, nervous system, and muscles being more in sync.

Now you know why strength isn’t always a good measure of muscle growth. Muscles can become stronger without growing, especially during the first few months of training. So, muscle strength and size aren’t correlated in a one to one manner. Now, let’s look at how you can get a better idea of whether you’re building muscle tissue.

How about the Tape Measure or the Mirror?

You could measure the size of the muscles you’re working using a tape measure. The problem here is you still don’t know whether an increase in the circumference of a muscle is due to a gain in muscle or an increase in body fat. However, if you’re losing weight and seeing an increase in muscle circumference, you probably ARE gaining muscle. Still, using a tape measure is a crude way to measure muscle gains and it’s not extremely accurate due to the fat issue.

How about looking in the mirror? If you’re making significant gains, you might look more defined when you catch your reflection in the mirror and may notice that your clothes fit differently. However, it usually takes significant gains to notice a difference when you see yourself every day. So, this isn’t a very sensitive way to follow gains in muscle size and it’s too subjective.

Is There an Easier Way?

Another approach is to determine your body fat percentage before you begin training. Although it’s not 100% accurate, you can use inexpensive calipers to do this. Even if it’s not completely accurate, you can use it to see how your body fat changes over time. Once you know your body fat percentage, multiply it by your body weight. For example, if you weigh 130 pounds and have a body fat percentage of 20%, the weight of your body fat is 26 pounds

130 X 20% = 26 pounds of body fat

Now, subtract, this value from your total body weight. This will give you the approximate weight of your muscle and all of the lean tissue and water in your body. ( LBM includes muscle, bone, organs, etc.  It’s not just your muscle mass.)

130 pounds – 26= 104 pounds of lean body mass

So, your lean body weight is 104 pounds. You don’t actually know how much of this 104 pounds is muscle and how much is lean body tissue other than muscle but it doesn’t matter. If the value goes up, it will be due to an increase in muscle mass since your other lean tissue doesn’t change significantly over time.

Now, all you have to do at a future point is to check your body fat and weight and plug it into the equations above. For example:

You check your weight in the future and you’re now at 128 pounds and your body fat percentage has dropped to 18%.

128 x 18% = 23.04 pounds of body fat

128 – 23.04 = 104.96 pounds of lean body mass

Subtract the former value for pounds of lean body mass from the current value:

104.96 pounds – 104 pounds = .96 pounds

Congratulations! You gained .96 pounds of lean body mass!

When you weigh yourself, be sure to do it first thing in the morning after urinating and before eating or drinking anything. You want to get the values under standard conditions.

The Bottom Line

Don’t focus TOO much on weighing yourself and checking your body fat percentage obsessively. Concentrate, instead, on whether you’re becoming stronger and how you look and feel. Even if you don’t gain a large quantity of muscle or lose a great deal of body fat, strength training has multiple health benefits, both mental and physical. Most importantly, it helps maintain muscle mass and strength as you age, as well as bone density. Still, it’s nice to know whether you’re building muscle and this calculation will give you a better idea.



Sports Med. 2007;37(2):145-68.


Related Articles By Cathe:

3 Tests that Outperform BMI for Monitoring Obesity & Health Risks

When You Lose Weight, How Much is Fat & How Much is Muscle Loss?

Are Some People Non-Responders to Strength Training?


Related Cathe Friedrich Workout DVDs:

STS Strength 90 Day Workout Program

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Total Body Workouts
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