What do stretching, yoga, and squatting all have in common? They help you become more flexible.
But surely stretching is superior, right? Recent research challenges that assumption.
A recent systematic review — a study that reviews all the published research on a given topic to determine themes — compared the impact of stretching and resistance training on flexibility. The review included 11 research trials.
The trials differed significantly. Some compared healthy and unhealthy populations while others compared sedentary and active people. The stretching protocols differed as well, with some focusing on static stretching and others focusing on dynamic stretching, each trial consisting of different volumes and frequencies. The benefit of the variety is the many ways one can stretch are covered.
When looking at general themes and pooling the data together, the results were clear: strength training is as effective as stretching for improving flexibility.
Flexibility and strength are linked
The review builds on previous research questioning the value of stretching. If stretching is enjoyable, by all means, continue to stretch, but it is not necessary to improve flexibility.
Strength training leads to similar flexibility improvements with the added benefits of improving cardiovascular and metabolic health, building muscle, and increasing bone mineral density.
Does this mean any strength training will improve flexibility?
As a physical therapist, I have seen strong people who can barely reach down and touch their knees and people who can simulate the shape of a pretzel but barely do a pushup. When it comes to fitness combinations, there is no standard.
This is a narrow viewpoint, however. There will always be exceptions to the rule. If you take a step back and look at the body of research as a whole, reduced flexibility is associated with muscle weakness.
Our body adapts to the stresses placed on it. If someone is inactive, their body will respond with a deteriorating cardiovascular system, diminished muscle bulk, and restricted mobility.
Conversely, if we exercise and remain active, our body adapts to the demands placed on it.
How does weight training improve flexibility?
Baseball pitchers have extreme mobility in the shoulder external rotation and limited internal rotation because of regular throwing. Gymnasts are flexible because of the constant activity, not because of pre-routine stretching. The same is true for weight training.
Keep in mind, weight training does not guarantee universal flexibility. Traditional bodybuilding and recreational lifting have been shown to reduce shoulder mobility. Why? Again, it’s about the demand placed on the body.
When you lift weights, what range do you work through? If your overhead work is primarily inclined press and dumbbell overhead press, it is unlikely you will have great shoulder mobility. If you only squat to parallel or focus on the Smith Machine and leg press, you will struggle with full depth squats.
Is this a problem? Only if you want to achieve those extreme ranges of motion. However, it’s not just the motion you routinely adopt that matters, the load applied matters too.
Flexible with load only
Another consideration is how and when you are measuring flexibility. Let’s use the overhead squat as an example.
The image on the left is how most people look when performing an overhead squat without weight. Once a load is added, our ability to brace and place tension through the bar allows for improved mechanics. Even some Olympic athletes have similar differences when comparing loaded and unloaded overhead squats.
You will find your mobility improves when external resistance is added. Even mechanics improve provided you are not maxing out and hitting fatigue. Whether it is a complex movement like a power clean or a full-depth squat, adding resistance improves the quality of movement.
Context matters
When people think about flexibility, they often think of complicated yoga poses or the dreaded sit and reach test from high school P.E. class. Flexibility comes in many forms, however.
Static stretching is largely a short-term effect and only improves flexibility for the specific stretches you perform.
If you want to improve flexibility, consider the reason why. If it is for general health, flexibility isn’t going to do much for you. If it is for a specific task — yoga poses, squat depth, weightlifting — then you need to perform the specific task many times for your body to adapt.
Strength training isn’t only about getting big and strong. Strength training teaches our body how to move, builds resilience, and helps us adapt to the physical demands of life.