Does Flexing Build Muscle? (Answer May Surprise You)

March 15, 2022

What if that flexing you do in the mirror before you shower each day could build muscle and make you stronger? I’d beg to guess you’d be showering multiple times a day for more chances to get flexing!

Flexing does build muscle, especially within untrained individuals. However, regular lifters may not see the same gains in muscle size but can still benefit from flexing.

If you lift regularly, what other benefits can you take from flexing other than building bigger muscles?

Does Flexing Build Muscle?

Based on one study to date, flexing can build muscle. This study took healthy young adults over 12 weeks performing 10 x 4-second isometric contractions of the arm with 4 seconds of muscle relaxation for five total sets three times per week [1].

After 12 weeks, the size of the biceps and triceps increased by 4%! Simply by holding their arm at 90° at their side (the halfway position of a bicep curl) and tensing the biceps and triceps as hard as possible.

How is this possible if you’re not lifting weights? Isometric exercise has been studied extensively regarding strength and hypertrophy. While flexing at long muscle lengths is better for building muscle, isometric flexing at short muscle lengths still makes gains, as evidenced by this study.

It’s not how hard you flex either that enhances muscle growth. It comes down to volume. The duration of the set and how many sets you do will push muscle growth to the next level [2].

A good example is a 4 x 30-second isometric contraction resulting in more significant muscle growth than 4 x (10 x 3 seconds) even though volume is equated [3].

So, holding your flex longer, performing more sets, and doing it more often can be the icing on the cake in addition to your weight training routine.

Hidden Benefits Of Flexing Muscles

Does Flexing Burn Calories

The potential to build muscle while flexing is not the only benefit, with many hidden benefits often overlooked.

Improve The Mind Muscle Connection

The mind-muscle connection may seem like broscience spouted by bodybuilders on YouTube. But research backs up these claims. For example, just thinking about squeezing the muscle during an exercise led to twice the muscle growth of the biceps and quadriceps [4].

The mind is THAT powerful. So powerful in fact that imagining (not doing) 52 x 5-second maximal contractions of the wrist extensors five times per week while in a cast attenuated the loss of strength from 4 weeks of immobilization [5].

Think about that for a second (no pun intended). Thinking about doing reps can reduce the decline in strength loss when stuck in a cast. When performing an exercise, thinking about squeezing the muscle (e.g., thinking about the biceps during a curl) can double the muscle growth.

Flexing a muscle is like doing mind-muscle connection practice. As the great Dave Tate has said (I’m paraphrasing), “if you can’t flex the muscle, you can’t isolate it.” Meaning if you can’t flex your muscle without any load, how will you train that muscle in isolation with weights?

So, if you have a lagging body part or struggle to feel a muscle work during an exercise, start flexing in the mirror, and you’ll see it carry over to the gym.

Get Stronger

A second hidden benefit to flexing is the ability to get stronger. For example, using the same 10 x 4-second isometric contractions with 4 seconds of muscle relaxation protocol, subjects improved isometric force production by 12.5% for the biceps and 14% for the triceps in just four weeks [6].

The same authors found a 13% increase in biceps strength and a 27% increase in triceps strength in a different cohort of subjects [1]. But there’s another method of flexing that can make you strength gains that doesn’t involve static flexing.

It is known as antagonistic resistance training. That is, tensing the opposite muscle to provide resistance for the muscle you are working. For example, tensing your biceps and triceps and then slowly performing the curling motion.

Doing this increased biceps strength by 5.8% after six weeks [7]. However, we must take results from these studies with a grain of salt as they are all untrained subjects. If you’ve been lifting weights consistently for years, you probably won’t see such huge gains in strength.

Does Flexing Burn Calories

Can Flexing Alone Build Muscle

A hard flexing session will burn calories. But your reason for flexing shouldn’t be to burn calories as that is not the primary goal of the exercise. Instead, use flexing for the benefits listed above, such as building muscle, getting stronger, and improving the mind-muscle connection.

If your goal is to burn calories, there are many more efficient ways to do so through various cardiovascular activities.

Can Flexing Alone Build Muscle?

It seems flexing alone can build muscle, especially if you are untrained. However, if you’ve been lifting weights for a while, flexing alone instead of lifting weights probably won’t build extra muscle as the stimulus won’t be as intense as lifting.

Instead, look to incorporate flexing within your training or daily routine. I’ve got some ways to do this below!

How To Use Flexing To Build Muscle

Flexing in the mirror before your shower isn’t the only way to build muscle. Here’s how you can use it to your advantage.

In Between Sets

While performing exercise during your rest periods will reduce the performance of your primary exercise, it can enhance muscle growth to a greater extent. Doing a 30-second maximal isometric contraction of the quadriceps in between sets of back squats increased muscle growth [8].

However, this one study seems to be isolated to the quadriceps and not other muscle groups. It’s worth experimenting with, however, for short training blocks.

Stand Alone Home Flexing

Flexing at home on your rest days can be a way to add extra volume to your training week. Choose a lagging body part you want to target and use the protocol listed in this article. Flex those muscles three times per week, and you’ve got an extra boost without heading to the gym!


Within untrained individuals, flexing does build muscle. Three times a week of flexing with a total of 200 seconds of flexing per session is enough to make small gains in muscle size. But there are hidden benefits to flexing, such as getting stronger and improving the mind-muscle connection, so don’t sleep on flexing in the mirror!


1. Maeo, S., Yoshitake, Y., Takai, Y., Fukunaga, T., & Kanehisa, H. (2014). Neuromuscular adaptations following 12-week maximal voluntary co-contraction training. European Journal of Applied Physiology114(4), 663-673.

2. Oranchuk, D. J., Storey, A. G., Nelson, A. R., & Cronin, J. B. (2019). Isometric training and long‐term adaptations: Effects of muscle length, intensity, and intent: A systematic review. Scandinavian journal of medicine & science in sports29(4), 484-503.

3. Schott, J., McCully, K., & Rutherford, O. M. (1995). The role of metabolites in strength training. European journal of applied physiology and occupational physiology71(4), 337-341.

4. Schoenfeld, B. J., Vigotsky, A., Contreras, B., Golden, S., Alto, A., Larson, R., … & Paoli, A. (2018). Differential effects of attentional focus strategies during long-term resistance training. European journal of sport science18(5), 705-712.

5. Clark, B. C., Mahato, N. K., Nakazawa, M., Law, T. D., & Thomas, J. S. (2014). The power of the mind: the cortex as a critical determinant of muscle strength/weakness. Journal of neurophysiology112(12), 3219-3226.

6. Maeo, S., Yoshitake, Y., Takai, Y., Fukunaga, T., & Kanehisa, H. (2014). Effect of short-term maximal voluntary co-contraction training on neuromuscular function. International journal of sports medicine35(02), 125-134.

7. MacKenzie, S. J., Rannelli, L. A., & Yurchevich, J. J. (2010). Neuromuscular adaptations following antagonist resisted training. The Journal of Strength & Conditioning Research24(1), 156-164.

8. Schoenfeld, B. J., Grgic, J., Contreras, B., Delcastillo, K., Alto, A., Haun, C., … & Vigotsky, A. D. (2020). To flex or rest: does adding no-load isometric actions to the inter-set rest period in resistance training enhance muscular adaptations? A randomized-controlled trial. Frontiers in physiology, 10, 1571.

About the Author

I am a professional strength & conditioning coach that works with professional and international teams and athletes. I am a published scientific researcher and have completed my Masters in Sport & Exercise Science. I've combined my knowledge of research and experience to bring you the most practical bites to be applied to your training.

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