Stretching and muscle growth: can stretching increase muscle growth?
By Coach Hunter Bennett
Stretching has always been used to increase flexibility. But can it also improve muscle growth?
Stretching and muscle growth: a history
The was an abundance of research in the 1970s showing that stretching stimulates the physiological pathways that cause muscle growth. This led to some interesting research in animals exploring this topic further.
For example, a study published in 1985 examined the effects of weighted stretching in quails.
They attached weights weighing ~25% of the birds’ bodyweight to their right wing. They then observed changes in muscle mass over a one-month period and compared it to the muscle growth in the left wing (which remained unweighted).
And the results were astounding.
Muscle mass increased by an absurd 318% after 28 days of stretching.
This demonstrated that stretching can cause huge increases in muscle growth when applied in prolonged periods.
But there is a caveat here.
A load of 25% of bodyweight is large. And having it attached every minute of every day is unrealistic.
This is the equivalent of an 80kg male carrying a 20kg dumbbell around with him 24 hours per day to increase arm size.
It’s just not going to happen.
However, this did provide enough reason to explore this topic in humans…
Stretching and muscle growth in humans
A recent review of the literature investigated the results of ten studies looking at stretching and muscle growth in humans.
They found that, across ten studies, only three saw significant increases in muscle size. The other seven saw no significant change.
However, there was a something those three studies did that the others didn’t.
They used a form of weighted stretching, where the stretch was enhanced by an external load (like the birds in our early research). This might suggest for stretching to increase muscle size, it needs to be done under load, or under intense settings.
What do I mean by intense?
Well, let me draw your attention to a study published in 2022 (after that review was completed).
This study had over fifty participants. Each participant had one leg undergo a stretching intervention, and one that did nothing (as a control).
For the stretching intervention, each person used a device that locked the foot in place while pulling the ankle up, which stretched the calf. The participants then adjusted the incline of the device to achieve a stretch that was rated as an 8 out 10 (in terms of discomfort).
They then held this stretch for a full hour. This was repeated every single day for six weeks.
Yep, you read correctly – an hour a day for six weeks.
Importantly, the calf muscle of the stretched leg saw an average increase in size of 15%. The control leg saw an average increase of 2%, demonstrating a notable difference,
Which provides strong evidence that stretching can indeed cause muscle growth under intense settings (i.e., under load, and with long stretching protocols).
However, it is important to note that in all these studies, stretching was the only intervention.
And let’s face it, if you want to build some muscle, you are not going to only stretch. You are also going to weight train.
Weight training, stretching, and muscle growth
Several studies have explored the effect of stretching combined with weight training on muscle growth.
Stretching before weight training and muscle growth
One study had participants perform stretching before weight training and saw worse muscle growth that did weight training alone.
They thought this may be because, in the short term, heavy stretching can reduce strength and power. As a result, stretching before training may reduce the number of reps you can perform at a given weight, reducing the training stimulus.
Stretching on alternate days and muscle growth
Another study had people stretch on opposite days to weight training and compared it to a group that only did weight training. They found that the increases in muscle size were the same between groups, suggesting no positive or negative impact.
If you want to improve flexibility, stretch on the days you don’t strength train it won’t impact your gains in any way.
Inter-set stretching and muscle growth
A recent study had people perform a loaded calf stretch between sets of calf raises, as part of a 90 second rest period. They compared this to a group who only did the calf raises and did nothing for their 90 second’s rest.
They found that the addition of stretching increased muscle growth more than weight training alone.
This design has been repeated in two different studies (one and two) using different exercises. Although their results lean towards stretching between sets being slightly better for muscle growth, the findings were not statistically significant (which means we cannot be confident in this).
So, where does this leave us?
Stretching and muscle growth: the take home
Stretching alone is unlikely to improve muscle growth unless using high loads and holding them for long durations. And even then, this may only work in untrained individuals.
Stretching before training is probably a bad idea.
Doing loaded stretching between sets might cause small improvements in muscle growth.
All of which suggests that if you like stretching, then you can do it on your rest days or between sets of weights. But you shouldn’t expect to have any real effect on those gains.
Want to get big?
Keep it simple and lift heavy – no need to overcomplicate it.