Why Lifting Weights Can Make You More Flexible

Oct 5

4 min read

"Stretching might not be the only way to increase flexibility and ROM. While resistance training (RT) is generally associated with increased muscle cross-sectional area, force generation and neural adaptations, RT has demonstrated increased flexibility in a variety of joints and muscles" [1-2]

(Yes, really. And here's a yoga routine built around it.)

The myth: "Lifting makes you stiff"

Many people picture weightlifters as muscle-bound and unable to scratch their backs. The research says otherwise. When strength exercises are done through a full range of motion, they improve flexibility as much as dedicated stretching.

A 2021 systematic review and meta-analysis (Afonso et al., Healthcare) found that strength training and stretching produced similar gains in range of motion, with no meaningful difference between them. A 2023 meta-analysis (Alizadeh et al., Sports Medicine) reached a similar conclusion. Earlier, Morton et al. (2011, Journal of Strength and Conditioning Research) found that resistance training and static stretching improved flexibility comparably, but only resistance training also improved strength.

How strength training improves flexibility

1. You get more comfortable with stretch (stretch tolerance)

This is the best-supported mechanism. In a classic review, Weppler and Magnusson (2010, Physical Therapy) argued that much of the short-term flexibility gain from stretching comes from the nervous system tolerating more stretch, not from the muscle becoming physically longer. The muscle isn't necessarily changing. Your brain is simply turning down the alarm. Strength training through a long range likely trains this same tolerance, since you repeatedly load the muscle in a lengthened position and teach your nervous system it is safe there.

2. Muscle fascicles may get longer

Eccentric training in particular seems to add sarcomeres (the tiny contractile units) in series, lengthening the fascicles. This has been shown in animal and human studies, for example Blazevich et al. (2007, Medicine & Science in Sports & Exercise) and Potier et al. (2009, European Journal of Applied Physiology). Longer fascicles can mean a muscle that tolerates and permits more length. Research on hamstring injury (Timmins et al., 2016, British Journal of Sports Medicine) also links shorter fascicles with higher injury risk. Note that this adaptation is better documented for eccentric training than for flexibility specifically.

3. Strength in the stretched position

Being flexible only helps if you can control the range. Strength at long muscle lengths gives your joints stability at end range, which makes the nervous system more willing to "allow" you to go there.

4. Stiffness and tissue properties

Changes in tendon and connective tissue stiffness may play a role, but the evidence here is mixed.

What the studies on eccentric training show

Nelson and Bandy (2004, Journal of Athletic Training): in high school males, both eccentric hamstring training and static stretching improved hamstring flexibility.
Aquino et al. (2010, Manual Therapy): strength training in the lengthened position improved hamstring flexibility comparably to stretching.

Both findings point to the same conclusion: eccentric or lengthened-position strength work is a legitimate flexibility tool, roughly equal to stretching. Neither shows it is clearly superior.

What about holds under 60 seconds?

Short holds (15 to 45 seconds) are well supported. Static stretching studies commonly use 15 to 60 seconds per hold, 2-3 sets, and the total weekly time under stretch per muscle appears to matter at least as much as hold length.

A simple yoga approach- from me

Alternate slow, controlled movements, such as lowering gradually into a lunge or forward fold, with static holds of 30 to 45 seconds in a similar posture. Keep the stretch firm but comfortable, and build up gradually. Expect some muscle soreness at first. It is suggested to hold the static stretches less than 60 sec to avoid performance detrimants.

The bottom line

Resistance training, particularly slow eccentric and lengthened-position work, improves flexibility about as well as stretching, and it builds strength too. Pairing it with short static holds is a well-reasoned, evidence-consistent approach. It just hasn't been proven to be the best one.

References (please verify before publishing)

Afonso J, et al. (2021). Strength training versus stretching for improving range of motion: a systematic review and meta-analysis. Healthcare, 9(4), 427.
Alizadeh S, et al. (2023). Resistance training induces similar adaptations of muscle strength and range of motion compared with stretching: a systematic review and meta-analysis. Sports Medicine, 53, 601–618.
Morton SK, et al. (2011). Resistance training vs. static stretching: effects on flexibility and strength. Journal of Strength and Conditioning Research, 25(12).
Weppler CH, Magnusson SP (2010). Increasing muscle extensibility: a matter of increasing length or modifying sensation? Physical Therapy, 90(3), 438–449.
Nelson RT, Bandy WD (2004). Eccentric training and static stretching improve hamstring flexibility of high school males. Journal of Athletic Training, 39(3), 254–258.
Aquino CF, et al. (2010). Stretching versus strength training in lengthened position in subjects with tight hamstring muscles: a randomized controlled trial. Manual Therapy, 15(1), 26–31.
Blazevich AJ, et al. (2007). Training-specific muscle architecture adaptation after 5-wk training in athletes. Medicine & Science in Sports & Exercise, 39(1), 1–9.
Potier TG, et al. (2009). Changes in the architecture of the vastus lateralis after eccentric training. European Journal of Applied Physiology.
Timmins RG, et al. (2016). Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football. British Journal of Sports Medicine, 50(24), 1524–1535.
Behm DG. The science and physiology of flexibility and stretching: implications and applications in sport performance and health. Routledge; 2018. [Ref list]