Strength training and flexibility: truth vs. hype

Resistance training has become a critical component in the sports preparation of athletes of all types. However, that certainly wasn’t always the case. Prior to the general acceptance of strength training in sport, the common belief was that resistance training, and lifting weights in particular, would lead to ‘muscle-bound’ athletes. For this reason it wasn’t just that resistance training wasn’t performed, it was actively avoided.

Persistent fears

Over time, it has become apparent that resistance training provides a net benefit to performance, and even if resistance training does promote inflexibility, the argument is that including it still allows athletes to accomplish their goals. However, many athletes have noticed that resistance training actually has the opposite effect, working to improve joint range of motion. For instance, athletes who participate in the sport of weightlifting demonstrate incredible flexibility throughout the entire body, even while lifting tremendously large loads on a daily basis.

Yet despite these anecdotes, and as resistance training becomes a key component of sports preparation, these fears still persist. The typical person - even the typical athlete - still has the perception that resistance training impairs flexibility, even though the opposite seems to be true. Fortunately, the research literature examining the impact of resistance training on joint range of motion is accumulating. So much so, that a group of researchers decided to analyze all of the data to determine the impact of resistance training on range of motion once and for all.

The research

One of the challenges with scientific research in the exercise and sports performance field is that many similar, yet differently structured studies are performed related to a specific topic. And because of the importance of context in all training related outcomes, the results of these studies can often differ slightly, leading to a lot of confusion. This is especially true when it’s not readily apparent why these differences occur. However, once a significant body of literature emerges, it becomes possible to use certain statistical analyses to determine parse out the subtleties involved.

As resistance training is a topic that has been widely studied across many contexts, an international research group decided to use these statistical strategies to determine the impact of resistance training on range of motion⁽¹⁾. They used 55 different studies in their final analysis. Because these studies were all different in small ways, they were able to analyze the impact of sex, prior activity levels, age, frequency of training, and duration of training.

They also performed multiple comparisons between different types of training. They compared the impact of resistance training on range of motion to a control group. They compared resistance training to stretch training. And they compared resistance training and stretch training to stretch training alone. The goal was to get a nuanced perspective on the impact of resistance training on range of motion, rather than just a simple yes or no answer.

What they found

The results were crystal clear. Contrary to the perception of many, resistance training positively impacts joint range motion, rather than hinders it (see figure 1). It does so in a manner that is equally effective as stretch training, as no differences were found between the protocols. The same result was found when the combined application of resistance training and stretch training was compared to stretch training alone.

Interestingly, it does not appear that sex or the type of contraction influences whether resistance training enhances range of motion. Likewise, differences in age, training frequency, or the duration of training had no impact on outcomes. Further, positive results were found at every joint studied, so it does not appear that these results are limited to specific joints or specific muscles. In plain English, no matter your sex, age, training habits or muscles trained, strength training will increase your joint range of movement – not decrease it.

Figure 1: Effect of resistance training on joint range of motion