When you’ve been going at it in the gym, few things top the rush of casually admiring a fresh pump in the mirror. Interestingly, flexing is good for more than just an ego boost, it can boost gains, too.
Does flexing your biceps stand up to heavy dumbbell curls for increasing muscle strength and size? Predictably, no. Flexing is not the most efficient way to build muscle. Nor should it be on the top of your priority list if you’re looking to increase strength or hypertrophy (growth).
However, flexing can significantly increase newbie gains, and it offers some unique benefits (even to veteran lifters) that might earn it a specific spot in your routine. Here’s the down low.
Does Flexing Build Muscle?
Yep, flexing builds muscle. Every time you flex a muscle, your muscle fibers temporarily contract and shorten—a phenomenon more accurately described by the term muscle contraction.
For example, when you flex your bicep, your muscles first contract concentrically, shortening your muscle fibers and creating tension in your bicep as you curl your hand towards your shoulder. Then, your muscles contract isometrically (or a contraction without movement) as you hold your flexed bicep in place.
While there isn’t much research on the long-term strength adaptations of flexing, there’s loads of scientific evidence that concentric and isometric contraction are good options for building strength and size (1). In other words: by simply flexing any muscle, you can build it.
How Effective is Flexing for Building Muscle?
Flexing can certainly help build muscle. One study found that after 12 weeks of performing five sets of ten reps of a four-second isometric bicep flex (where participants focused on mindfully flexing both their biceps and triceps), young, healthy adults were able to significantly increase both muscle strength and size in their biceps and triceps (2).
You might be thinking: ‘Surely, I shouldn’t sub in mere bicep flexing for bicep curls or quad flexing for leg extensions’. And, you’re absolutely correct. Flexing is a tool that can and should be used to boost your results in the gym or to rehabilitate an injury when a full range of motion isn’t available to you; but, it shouldn’t be the bread and butter of your workouts.
Why? Flexing isn’t your best option for increasing muscle strength and size. Eccentric contraction (when your muscles lengthen as they lower a load) generates the most force at a lower metabolic cost (1, 3, 4). This means movement patterns that involve activating a muscle through a full range of motion have the most potential for increasing muscle hypertrophy. Unfortunately, when you simply flex a muscle, eccentric contraction doesn’t come into play.
Plus, when it comes to increasing muscle strength, load might be the most important factor. You can build strength whether you use high-load training (like lifting a relatively heavy, loaded barbell) or low-load training (like bodyweight exercise or light dumbbells); however, most research supports a dose-response relationship between load and strength (4). Which is just a fancy way of saying, the heavier loads you lift, the more strength you’ll gain. And on the load spectrum, flexing your muscles lands somewhere on the bottom.
Benefits of Flexing Your Muscles
So, what is flexing good for? Flexing isn’t the most efficient way to gain strength or hypertrophy, but it still comes with a list of advantages. Here are the biggies.
Even though flexing isn’t the best for building muscle, it does a decent job in the strength-building department. According to one study, which involved holding isometric contractions simultaneously flexing the biceps and the triceps with the elbow at a 90-degree angle, participants improved isometric force production in the biceps by 12.5 percent and triceps by 14 percent (2). That isn’t nothing.
Although, it’s important to note that since flexing only focuses on building isometric strength, the strength you build when flexing doesn’t fully translate to functional exercises that involve activating a muscle through a full range of motion.
What isometric strength is good for is building muscular strength in one specific position. For example, practicing planks to reinforce your neutral spine position (which will help you in nearly every exercise). It can also be great for increasing strength at the sticking point of an exercise—i.e. just after starting a biceps curl, where the mechanical tension is highest and the weight feels the heaviest—helping you break through plateaus.
Improve mind-muscle connection
Have you ever done hip thrusts, but felt like you weren’t really targeting your glutes? Building your mind-muscle connection can help with that. Mind-muscle connection is a conscious and deliberate muscle contraction—or, the ability to flex or create tension in a muscle you’re trying to work.
Just thinking about activating a muscle while working out can increase your effectiveness at targeting that specific muscle. For example, one study found that focusing on activating a specific muscle group during a lift, rather than the overall outcome, led to greater hypertrophy of that muscle (5).
But if you have a weak mind-muscle connection with a particular muscle group, you might not know how to isolate it. In that case, it’s nearly impossible to bring that muscle up to speed unless you improve your mind-muscle connection.
That’s where flexing comes in. Practice flexing specific muscle groups that are lagging or you’re struggling to connect with. It’ll significantly improve your ability to activate and control specific muscle groups on command—meaning you’ll get more out of every rep during your gym sessions.
Strengthen muscles during and after injuries
If you’re suffering from an injury that makes moving a joint painful, such as arthritis, or an ACL or rotator cuff tear, isometric exercises can help build strength without needing to move the joint. For example, after an ACL reconstruction, quad strength in the injured leg is an important factor in assessing when someone is ready to return to sports (6). You can build quad strength without even moving your leg by flexing your quad with your leg fully extended.
How to Flex to Build Muscle
How to incorporate flexing into your sessions? Here are our favorite ways.
Flex weak muscle groups
Got a lagging muscle group (like small calves) but don’t want to head to the gym for a focus session? Flex your muscles at home to build strength and mind-muscle connection so your time in the gym is more effective. Isolate a specific muscle group by running through intentional sets of flexing with an isometric hold.
Flex between sets
During a strength workout, rest periods between sets are essential to give your cells time to re-up their energy stores. Thus, cutting a rest period short, or activating those muscle groups during that time can reduce the performance of your primary exercise.
Despite this, one study found that doing a 30-second maximal isometric quadriceps contraction followed by a 90-second rest in between sets of back squats and leg presses increased muscle hypertrophy in the quads when compared to taking a full two-minute rest break without a quad contraction (7).
The study authors note flexing between sets might be an effective way for those interested in increasing hypertrophy without increasing total training duration. However, it might have a detrimental effect on overall strength gains, so it’s really only worth experimenting with if hypertrophy is your number one goal.
Flex antagonistic muscle groups
Antagonistic resistance training involves tensing the muscle opposite to the one you’re directly working on to provide even more resistance on the muscle you’re aiming to work; for example, flexing your triceps while performing a biceps curl.
One study found that activating both the biceps and triceps during an unweighted biceps curl increased biceps strength 11.6 times more than performing biceps curls as normal (8).
Work on building your mind-muscle connection in antagonistic muscle groups and mindfully activate them during your workouts, and you might see more gains.