A study published this year by a Portuguese team was met with great fanfare by anti-stretching zealots, who claimed that it demonstrated strength training is as effective as stretching for improving range of motion. But, of course, we can't exactly blame them for saying that because the title of the article they were sharing was "Strength training is as effective as stretching for improving range of motion: A systematic review and meta-analysis." You can read that version of the paper by clicking here.
In essence, the authors claimed that resistance training through a full range of motion is as good for improving flexibility as stretching. Unsurprisingly, some people took this as confirmation for their anti-stretching bias and proceeded to share it with proclamations about how traditional stretching is a waste of time. Some even went as far as to claim the article proved strength training is more effective than stretching, which was just dumb considering its title.
However, that article version was a preprint, which means it had not yet passed the peer review process. Peer review is a method of checking the quality of an article before being published in a journal. It's a long and comprehensive process, and it isn't uncommon to see preprints heavily amended in response to feedback from reviewers.
That's exactly what happened with the article mentioned above. You can see the peer-reviewed, published version of the article by clicking here.
Most notably, the authors changed the title to "Strength Training versus Stretching for Improving Range of Motion: A Systematic Review and Meta-Analysis."
Also notable was the removal of this passage, which appeared in the preprint version: "Since ST [strength training] generates ROM similar to those obtained with stretching, clinicians may prescribe smaller, more time effective programs when deemed convenient and appropriate, thus eventually increasing patient adherence rates."
Furthermore, the peer-reviewed version featured the inclusion of this passage: "However, the heterogeneity of study designs and populations precludes any definite conclusions and invites researchers to delve deeper into this phenomenon."
And also this passage: "If future research confirms that ST generates ROM gains similar to those obtained with stretching, clinicians may prescribe smaller, more time-effective programs when deemed convenient and appropriate, thus eventually increasing patient adherence rates."
In short, while the data collection methodology was sound, the peer-reviewed version of the article did not confirm that strength training is as effective as stretching for improving range of motion. Much more research is needed on the subject.
Understand that I'm not saying strength training is not effective for improving flexibility. On the contrary, I think it should be the cornerstone of every flexibility training programme, and flexibility and strength go hand-in-hand.
But does research support the idea that strength training is as effective as stretching for improving flexibility?