Does Resistance Training Make You Less Flexible?

By: Brad Schoenfeld

Reebok One Team

There is a long held belief that resistance training and flexibility are mutually incompatible. Bodybuilders are the poster children for this contention. They’re often called muscle bound—a term that epitomizes a lack of agility (1). The running joke is that bodybuilders are so inflexible that they can’t even lift their arms high enough to comb their hair. Given such stereotypes, it’s no wonder there’s a prevailing sentiment that, if you want optimal mobility then you shouldn’t lift weights.

From a physiologic standpoint, one could make a case for why strength training might impair flexibility. Muscles are encased in a dense sheet of connective tissue called fascia. It has been shown that heavy resistance training causes an increase in these collagen structures. Collagen is a fibrous tissue that has limited stretch capability (in comparison to muscle, which is more elastic), and its strengthening in fascia could conceivably reduce a person’s range of motion (ROM) by binding muscles more tightly. What’s more, the tendons and ligaments also become stronger and thicker when subjected to heavy loads. Hypothetically, by increasing the density of these non-elastic properties, there could be a negative effect on joint mobility.

But while this rationale might sound logical in theory, it simply doesn't translate into practice.

The truth is, studies have repeatedly shown that those who train with weights on a regular basis are at least as flexible as sedentary individuals. In fact, resistance training has actually been shown to be as effective as static stretching for improving joint ROM (2). In effect, lifting weights serves as a form of proprioceptive neuromuscular facilitation (PNF) -- a highly effective flexibility training system whereby a given muscle is contracted and then immediately followed by a lengthening action. Considering the body of research, the common claim that you need to "stretch what you strengthen" has no scientific basis.

Want some real-world proof? The athletic world is replete with examples showing that resistance training has no detrimental effects on flexibility. Consider elite martial artists. They routinely lift weights as part of their conditioning regimens, yet they can throw a roundhouse kick six feet in the air. Or take a look at the well-muscled physiques of Olympic gymnasts. Despite their hyper-muscularity, these competitors regularly perform amazing feats of agility. From baseball, to, golf, to ballet, performance is improved with a properly integrated resistance training program, without any ill-effects. Even bodybuilders, who are often ridiculed for their hyper-muscular physiques, have been known to include full splits in their posing routines.

It is important to note, though, that muscles adapt to the specific range in which they are worked. This is why, from a flexibility standpoint, it’s essential to train through a complete ROM. Full range movements allow the associated joint to approach its stretch capacity. In effect, lifting weights acts as its own form of flexibility training; stretching is already incorporated into the movements.

But just as full range training enhances mobility, restricted movements can hamper mobility. If limited range movements are used on a continual basis, a loss of flexibility can occur. Over time, the repeated use of “half-reps” can cause an adaptation whereby muscles get used to their shortened position and accommodate by assuming this position as their resting length. Unless corrective measures are taken, the muscles remain shortened, impeding joint-related mobility. Take home message: If flexibility is a desired goal, make sure to routinely train throughout a full ROM during exercise performance.

If additional flexibility is desired, specific flexibility exercises can be employed. A combination of resistance exercise and flexibility training is the best way to achieve optimal ROM about the joints. There are a variety of different flexibility exercise strategies to enhance ROM including static stretching, dynamic stretching, PNF, and others. All of them potentially have a place in a well-designed training program. The good news is that you don't need to spend a lot of time stretching. Stretching just a few minutes per joint action every other day has been shown to be just as effective as higher volume flexibility protocols (3). Similarly, evidence shows that low-intensity stretches are just as beneficial as moderate- to high-intensity stretches in improving ROM (4). So neither a lack of time nor intolerance to stretch-induced discomfort is a valid excuse as to why you are inflexible.

The Bottom Line

In final analysis, increasing muscle mass does not necessarily correlate with a decrease in mobility. Provided full range movements are used in performance, resistance training provides a wealth of benefits without any detriment to flexibility; there simply is no downside. Specific stretching exercises can be added for even greater ROM.

Realize that there are limits to just how flexible you can become. Your ultimate potential to increase ROM is dependent on a number of individual factors including genetics, age, gender and others. That said, everyone has the potential to become more flexible provided you have the proper approach and put in the requisite effort.

Finally, understand that increased joint mobility results in decreased stability. Thus, becoming too flexible can actually have a deleterious impact on function and predispose you to injury. Your goal therefore should be to achieve a level of flexibility that allows you to carry out what you need to accomplish throughout the course of your daily life; anything more is superfluous and potentially detrimental.

References

1. Todd T. Historical perspective: The myth of the muscle bound lifter. Natl Strength Cond Assoc J. 1985; 7:37-41.
2. Morton SK, Whitehead JR, Brinkert RH, Caine DJ. Resistance training vs. static stretching: Effects on flexibility and strength. J Strength Cond Res. 2011 Dec;25(12):3391-8.
3. Sainz de Baranda P, Ayala F. Chronic flexibility improvement after 12 week of stretching program utilizing the ACSM recommendations: Hamstring flexibility. Int J Sports Med. 2010 Jun;31(6):389-96.
4. Smith A, Koutedakis Y, Wyon M. A comparison of strength and stretch interventions on active and passive ranges of movement in dancers: A randomised controlled trial. J Strength Cond Res. 2013 Feb 22.

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