There is still some confusion about whether or not lifting weights causes a decrease in flexibility and unlike my previous fact or fiction posts, this one does not have a definitive fact or fiction response. It is more accurate to say that lifting weights can decrease your flexibility, but it doesn’t have to. It is certainly possible to lift heavy weights as your primary form of exercise and increase your flexibility at the same time. However, another person could follow a similar exercise program and lose flexibility.
There are a number of factors that determine if lifting weights will decrease your flexibility or not, but the most significant one is probably stretching. If you lift weights and consistently follow a good stretching routine, then you will most likely not have any problems with losing flexibility. On the other hand, if you do not stretch at all, there is a good chance you will lose flexibility when lifting weights.
Technically, the act of lifting weights does result in slightly shortened muscles, but this also happens during most other type of exercise as well. When your muscles contract, they end up being a little shorter than before the contraction started, especially when you contract your muscles very strongly, such as when lifting heavy weights. This shortening is only temporary as long as your muscles are stretched back to their normal length after your workout is finished.
If you lift weights or contract your muscles during other activities and do not stretch at all, then your muscles will stay in a partially shortened position. The amount of muscle shortening after each workout is so small that you will not notice anything, but it will become significant over time. After exercising without stretching for an extended period of time, you will have a decrease in flexibility and probably an increase in stiffness or pain as well. To keep things in perspective, this muscle shortening also happens with people who don’t exercise at all, so decreases in flexibility can’t all be blamed on exercise.
One of the most common reasons for muscle shortening and flexibility loss is sitting for extended periods of time. If you sit all day, your hip flexors and other muscles will lose flexibility, because a muscle kept in a shortened position will tend to stay in a shortened position, even if it is not being actively contracted. As a side note, muscle shortening and flexibility losses from sitting are also major causes of low back stiffness and pain. Again, this shortening can be prevented by stretching or even just getting up and moving around at regular intervals.
Muscles kept in a shortened position and muscular contractions can both lead to a loss of flexibility but they are not the only problems. With regards to lifting weights, another factor that affects flexibility is the range of motion of the exercises. Specifically, when people lift weights using short ranges of motion, it makes it more likely for flexibility decreases to occur.
Performing exercises through only a portion of your full range of motion simultaneously keeps the muscle contracted and in a shortened position, so it basically combines the previously discussed issues that decrease flexibility. If you perform a lot of short range of motion exercises and do not stretch, you have a definite recipe for losing flexibility. In addition, constantly exercising a muscle through only a partial range of motion encourages muscle imbalances and/or weakness in the non-exercised range of motion.
On the other hand, performing weight training exercises through a full range of motion can actually improve your flexibility, especially if you currently have poor flexibility. As previously stated, keeping or moving your muscles in ways that do not utilize their full range of motion will eventually lead to losses in flexibility, but the opposite is true as well. Moving or exercising your muscles in ranges of motion greater than what your muscles usually experience, but still within normal limits, encourages muscle lengthening and flexibility increases.
When looking at all of this information together, the issue of whether or not lifting weights will decrease your flexibility becomes clear. From a practical standpoint it is fiction, because you don’t have to worry about lifting weights reducing your flexibility as long as you have good lifting habits, including performing exercises with correct form through their entire range of motion. Finally, and probably most importantly, regardless of whether you lift weights, do other types of exercise, or don’t exercise at all, stretching is essential for maintaining and improving flexibility.