As physical therapists, we’re often recommending that patients achieve a particular level of mobility and flexibility as part of their journey towards performing their daily functional tasks pain-free. Additionally, we’re big proponents of participating in activities to improve general strength.
One common misconception that patients often have is they see flexibility and strength as a sliding scale, wherein they perceive an improvement in one attribute as leading to a drop in the other.
Strength training does not reduce flexibility when performed through a full range of motion. In fact, it can improve flexibility by increasing joint mobility and muscle length. Strength and flexibility can be developed simultaneously.
In this article, we’d like to discuss this misconception, where it comes from, the kernels of truth it contains, and hopefully lay this myth to rest for our patients.
Short Answer: No, strength training doesn’t reduce flexibility
Whether we’re talking about traditional “strength training” using barbells and machines, or we’re talking about specialized strength-building exercises like those you’d learn in a physical therapy clinic, becoming stronger does not reduce flexibility on its own.
What’s more, it’s even been shown that strength training can improve flexibility: this 2021 meta-analysis of 15 studies concluded that based on available research, strength training and stretching provide similar improvements in range of motion (ROM).
Similarly, a 2023 meta-analysis including 55 studies stated in its results:
“Resistance training increased range of motion … there were no significant differences between resistance training versus stretch training.”
The results of these studies speak for themselves: not only does strength training not reduce flexibility, if done properly, it will improve flexibility.
Why becoming stronger makes you more flexible
This is counter-intuitive to a lot of folks, so we’d like to discuss some of the reasons we think this is the case:
By definition, strength training is “stretching under load”
When strength training, we’re taking a muscle group or muscle groups through a full range of motion under load. During the lowering, or eccentric, portion of the lift, we’re stretching the muscle to it’s natural limit, and during the raising, or concentric, portion of the lift, we’re shortening the muscle to its natural limit.
What this means is that lifting weights, using cables, or using machines is stretching!
Strength training involves a full range of motion
Recent research has suggested that the end range (stretched portion) of each particular lift is the portion that leads to the greatest hypertrophy and strength improvements in that lift. This means that in order to get the most out of each exercise, we focus on the stretched portion of the exercise by default.
It’s been hypothesized that this effect results from a phenomenon known as “sarcomere addition,” whereby a muscle grows by adding length, though this is still up for debate.
Increased strength means increased control
When we grow stronger in a particular movement or a particular muscle group, we improve the level of control we have over the end ranges of that particular muscle group. For instance, as we grow stronger on a lunge, we have increased control over our balance and control in a bent single-leg position (with the quadriceps “stretched”).
This allows folks who are stronger to relax and have confidence in these unusual positions, leading to improved ranges of motion, practically speaking.
Where this myth comes from
We think that, on some level, this myth simply originates from the fact that it seems intuitive that a stronger muscle would be “tighter” and have less range of motion. Note that it’s really only in the last few years that we’ve gotten good aggregate data on this topic. In the past, the science simply wasn’t there.
Additionally, it’s often true that folks who are very dedicated to strength training aren’t particularly concerned with mobility beyond the requirements of their particular sport, leading to the perception that people who are less flexible have more strength.
Couple this with the image of the bodybuilder that we all carry around in our mind’s-eye, often described using terms like “muscle-bound.”
Over the years, athletic coaches have let go of the misguided idea that lifting weights makes athletes slower, less flexible, or otherwise negatively affects their performance. However, there are still large swaths of the general public that haven’t let go of our old ideas about the potential downsides of becoming stronger.
Kernels of truth
After examining the evidence, we hope we’ve been able to lay this misconception to rest. However, there is one kernel of truth we’ll discuss before we completely write off this notion:
We’ve written elsewhere on our site about the phenomenon known as adaptive shortening, whereby muscles and connective tissues become shorter over time if they aren’t utilized through their full ranges of motion.
While we don’t think that strength training in general will shorten muscles, we do think that we’re much less likely to receive these range of motion improvements if we aren’t actually emphasizing range of motion during our resistance training sessions.
What this means from a practical standpoint is that we should bias our strength training towards using a full range of motion, emphasizing the “stretched” portion of our exercises rather than simply pursuing heavier weights.
It might mean we need to load a little less weight on various exercises, leaving our egos at the gym door.
The other way around: Does flexibility reduce strength?
A similar superstition we hear from the other side of this debate is that one can become too flexible and negatively affect muscular strength. Let’s discuss that here:
A 2023 meta-analysis of 35 studies concluded:
- “When stretching was added to RT [resistance training] interventions, the main analysis indicated no significant effect.”
- “… moderator analysis indicated that performing stretching before RT sessions has a small but negative effect.”
In short, flexibility training before engaging in strenuous resistance training can negatively affect strength for that particular session, but being flexible doesn’t have a major deleterious effect on strength over the long term.
Being strong and flexible
There are numerous paths to becoming stronger, some of which we have our patients engage in during their course of physical therapy treatment. In general, we advocate for the quality of life improvements that come from becoming stronger (see our full article on how much exercise we really need).
Additionally, improving our flexibility and mobility is one of the primary levers we pull in the pursuit of helping our patients lead functional and injury-free lives.
The point in bringing all of this up is that we can lay to rest the notion that we’ve got to have one or the other. Training to improve our strength won’t necessarily make us less flexible, and vice versa.
We know that as we age, we’ll naturally incur reduced muscle strength and flexibility; there’s no need to help the process along by neglecting one attribute due to the belief that it will hinder the other.
A good mixture of both will provide you with the functional abilities you need to continue to live a happy, healthy, independent life for many years to come!
