Does Strength Training Decrease Flexibility?

For the second installment of our myth busting series we are tackling the topic of strength training and flexibility. There is a long held belief that lifting weights decreases one’s flexibility. Couple this belief with the thought that decreased flexibility is a negative adaptation for physical performance, and the hesitation to employ strength training as a means of athletic improvement comes as no surprise. While the strength training/flexibility paradox has stood for many decades, is there any evidence to back up this claim? 

In research comparing the effects of concurrent strength and flexibility training, strength training only, or flexibility training only, researchers found an equal improvement in joint range of motion (flexibility) in the concurrent (strength + flexibility) training group and the flexibility only group. Also worth noting, the strength training only protocol did not positively or negatively affect flexibility following the 12-week training block. These results indicate that joint range of motion (flexibility) can improve equally as much when strength training and flexibility training are combined as when flexibility training is done on it’s own. These results also indicate that strength training in itself does not cause a decrease in flexibility. 

It should be noted that the range of motion employed while executing strength training movements will play a major role on the effect of weightlifting on flexibility. Our tissues adapt to the specific stresses we impose on them. This is known as the SAID principle (specific adaptation to imposed demands). If joints are repeatedly stressed through long ranges of motion while carrying out weightlifting sessions, the tissue (muscle and connective tissue) surrounding the joints will ‘know’ that the range of motion being used should be maintained. If shorter ranges of motion are employed for long periods of time, the tissue will likely adapt to this stress, and joint range of motion (flexibility) will likely be compromised. The concept of training quality is discussed in greater detail here. 

In summary, strength training in itself does not cause a decrease in flexibility, but if joint range of motion is a concern strength training should be accompanied by a flexibility program. Also, it is always important to maintain proper movement mechanics when carrying out a strength training program to ensure optimal strength and movement related improvements. 

 

References 

Morton, S. K., Whitehead, J. R., Brinkert, R. H., & Caine, D. J. (2011). Resistance training vs. static stretching: Effects on flexibility and strength. Journal of Strength and Conditioning Research, 25(12), 3391-3398. 

Nobrega, A. C., Paula, K. C., Carvalo, A. C. (2005). Interaction between resistance training and flexibility training in healthy young adults. Journal of Strength and Conditioning Research, 19(4), 842-846.