Flex for Success
We thought we'd tackle a topic that happens to a lot of people. You get a small injury and stop training altogether. There are many ways to train around an injury. Today we’re going to talk about flexing. Yes — there is actual scientific research showing that just contracting your muscles (i.e., isometric “flexing” or static muscle tension) can lead to increases in muscle size and strength, not just in theory but in controlled studies.
Key Scientific Findings on Muscle Size from Flexing/Isometric Training
1. A human study found muscle growth from repeated flexing without external load. Researchers at the University of Mississippi had subjects perform four sets of 20 muscle-flexing movements with no added weight and compared that to conventional arm curls at 70 % of the subjects’ 1-rep max. After six weeks, both the flexing group and the traditional lifting group experienced similar increases in muscle size in the biceps. However, strength gains were larger with actual weights. This study concluded that mechanical tension in the muscle–even without external resistance–can stimulate hypertrophy if the muscle is actively and intensely contracted.
2. Isometric training increases lean muscle mass. This study looked at older adults doing isometric quadriceps training (static contractions) over six months. Results showed significant increases in lean muscle mass (4–5 %) compared with controls who didn’t train. The study concluded that sustained tension via static holds can produce measurable muscle growth.
3. Isometric strength training produces adaptations in muscle structure. Animal research on isometric contraction training also found increases in muscle fiber size and cellular markers associated with hypertrophy, suggesting similar mechanisms apply across species.
Why This Works (Mechanism)
Muscle growth is largely driven by mechanical tension and recruitment of muscle fibers, and this can be produced by flexing your muscles.
Static contraction (flexing) still generates mechanical tension in the muscle fibers even if there’s no movement.
When tension is high enough (especially taken near fatigue), the muscle senses a need to adapt — signalling pathways that trigger protein synthesis and muscle growth.
Studies indicate that this tension is a primary driver of muscle hypertrophy, whether through dynamic lifts or static holds.
How To Do It
Our suggested protocol involves three sets of flexing for 15 seconds. Repeat this four times throughout your day. (This is even something you can do at a work desk.) Flex a different set of muscles each day.
For example:
Legs
While standing and keeping legs perfectly straight, squeeze your leg muscles by giving max pressure to straightening your legs. Do this three times for 15 seconds, with 15-second rests between sets. You will feel “the pump” increasing throughout these sets, until your muscles feel close to cramping. Here is a video that gives a great overview of different isometric exercises:
https://youtu.be/96T2Uuls3yk?si=4dGj635QsAy_djgK
Most injuries involve the joints. Isometric exercises are a great way to keep your muscles strong without having to go through full ranges of motion that may cause pain. It’s a great way to work around pain instead of pushing through it–which will only make an injury worse. So start flexing today!
Until next time
Scott and Lennart