Research Review Shorts: Does Stretching Actually Cause Muscle Growth?
Depending on who you ask, you’ll hear a wide range of narratives surrounding stretching’s impact on performance and muscle growth. A 2022 study now gives us more concrete evidence that stretching can actually have a positive effect on both muscle size and strength.
Over the past 20 years, views on stretching have changed more than most other fitness-based topics.
The popular opinion as of recent is that stretching is useless at best (if not counterproductive). Arguments include the ideas that stretching doesn’t actually reduce injury risk and even hinders performance and muscle growth.
However, when you actually dig into the research on stretching, an interesting, nuanced picture emerges.
For example, intense stretching immediately before exercise might reduce muscle growth, but light stretching between sets may actually increase muscle growth.
Similarly, intense, long-duration stretching right before an exercise test may reduce force and power output, but longitudinal stretching interventions may actually increase strength over time.
In short, stretching isn’t all good or all bad – whether it helps or hinders you largely depends on the timing, intensity, and duration of your stretching sessions.
A recent study by Warneke et al. sought to look further into the possibility that stretching interventions can cause hypertrophy, or muscle growth.
In this presently reviewed study took 52 subjects who were randomized into two groups: a stretching group and a non-stretching control group. Furthermore, the legs of the subjects in the stretching groups were randomly divided within-subject: one leg underwent the stretching intervention, and the other leg served as a non-stretching control leg.
The muscle being stretched and thus measured was the gastrocnemius or main calf muscle.
The stretching intervention was quite intense. Each subject used an orthotic device that locked the foot in place while pulling the ankle into dorsiflexion. From there, they sat upright in a chair, propped their leg up on another chair of the same height, and stretched their calf for a full hour. The stretching intervention lasted for six weeks, and subjects stretched their calf for a full hour every day.
- Gastrocnemius thickness increased substantially in the stretching legs of the stretching group (+15.3%), while the non-stretching legs experienced a much smaller increase (+2.1%).
- Isometric and dynamic strength increased significantly more in the stretching leg of the stretching group (+16.8%) than in the non-stretching leg of the strength group (+1.4%).
- Changes in flexibility followed a similar pattern. Knee-to-wall test performance increased substantially in the stretching leg of the stretching group (+13.2%), while all other groups and conditions experienced small reductions in performance (reductions of 0.8-2.4%).
Interpretation & Takeaways
This study demonstrates that static stretching with sufficient intensity and volume can directly cause hypertrophy in humans. While this isn’t a completely novel finding (Simpson and Panidi previously observed similar effects), the results of this study are stronger and more conclusive than those observed in prior research.
This is a pretty important finding, because it places the idea of stretch-mediated hypertrophy on firmer evidentiary grounds. Furthermore, this study confirms that longitudinal stretching interventions can directly increase dynamic strength and isometric force output.