Does Stretching Actually Lengthen Muscles?


Does Stretching Actually Lengthen Muscles?

Do you stretch before or after a workout? If you don’t, you probably feel a tad guilty. After all, stretching does so many good things, or so they say. You often hear claims that stretching reduces the risk of injury and improves flexibility. Another common belief is that when you stretch, you actually lengthen the muscle you’re trying to stretch. Is there any truth to this? Let’s look at this issue more closely and also confirm or dispel other myths and facts about stretching.

Does Stretching Lengthen Muscles?

It’s a common belief that when you stretch a muscle, it becomes longer in length – but does it really? Your muscles are attached at one point on a bone and end at another point. Stretching doesn’t change those two attachment points – so how can you lengthen a muscle just by stretching it? The truth is you don’t actually change the length of the muscle permanently. Instead, when you stretch you soften your body’s protective response, or stretch reflex. It’s this protective reflex that keeps you from overstretching a muscle and causing injury.

How does the stretch reflex work? Within muscle fibers are proprioceptors called muscle spindles. These receptors send sensory input to your brain to tell it what state your muscle is in. For example, the muscle spindles monitor muscle length. If you stretch a muscle quickly, it activates the muscle spindles. The muscle spindles, acting through a sensory nerve, send input to your brain. The brain then sends a message back, through a motor nerve, telling the muscle to shorten so it won’t be overstretched and potentially injured. This is called the stretch reflex.

How does this relate to stretching? When you elongate a muscle in a slow, controlled manner, as when you stretch, it’s not perceived as a threat and the stretch reflex isn’t activated. As a result, you can extend the muscle further than you would normally be able to. The goal of a good stretch is to get the muscle to relax a little more by bypassing the stretch reflex. Although the muscle may be more relaxed and extended, it’s only temporary.

If you could see inside a muscle fiber during a stretch, you’d see the fibers are stretched too. The thick and thin myofilaments that overlap when a muscle contracts expand and the degree to which they overlap decreases up to a muscle’s maximum length at rest. At this point, the stretching action is transferred to the connective tissue that surrounds the muscle. As you hold the stretch, it helps realign fibers in the connective tissue. That’s why a nice stretch is therapeutic for some types of injuries with muscle scarring.

Not All Stretches Are Created Equal

In general, stretches come in three main varieties: static stretches, ballistic stretches, and dynamic stretches. A fourth one called proprioceptive neuromuscular facilitation stretches, or PNF is sometimes used in neuromuscular rehab programs. We won’t discuss this one since you also need a partner to do it.

Static stretches are the classic stretch you see people do after a workout. It’s where you slowly stretch the muscle out, slow enough so that you don’t activate the stretch reflex. You then hold the stretched position for 30 seconds or so before relaxing. In contrast, ballistic stretches involve movement of the muscle during the stretch. An example would be bending over to touch your toes and bouncing up and down as you stretch. Most trainers don’t recommend ballistic stretching because the bouncing movement can abruptly activate the stretch reflex and lead to muscle injury.

Dynamic stretches are those that mimic the movements of the workout you’ll be doing. For example, leg swings and shoulder circles are examples of dynamic stretches. Notice that these movements are fluid and don’t involve bouncing like ballistic stretches do. Dynamic stretches not only increase blood flow to the muscles you’ll be working but they also raise your core body temperature and get your heart rate up prior to exercise.

Which Stretch Should You Do?

Avoid ballistic stretching. The risk of injury is higher and they offer no benefits that you can’t get from dynamic stretching. Dynamic stretching is the preferred form of stretching prior to a workout and it can double as a warm-up. It’s best to avoid static stretching prior to a workout as some studies show static stretches can reduce strength for as long as an hour after a static stretching session. That’s not what you want before a strength-training session. Static stretching may also reduce muscle power and explosive muscle power. So, save the static stretches for the end of your workout.

Does Stretching Prevent Injuries?

You’ve probably heard that one reason to stretch is to lower your risk of injury, yet there’s not a lot of evidence to support this idea. Studies that do show a reduction in injuries are usually ones where the participants also did a warm-up. At one time, experts believed that jumping straight into exercise without stretching caused muscle spasm and stretching, by increasing blood flow, could prevent spasms. However, this idea didn’t hold up to scrutiny and is no longer valid.

In 2008, a review of 364 studies concluded that static stretching does not reduce overall injury rates. When you also consider that static stretching may reduce performance in strength and power exercises, there’s no reason to do static stretching prior to exercise. Stick with dynamic stretches.

The Bottom Line

Dynamic stretching before a workout increases blow to your muscles and gets you prepped for training. It also gets your joints moving through their entire range of motion and eliminates tightness. Save the static stretching for when your workout is over and you’re cooling down to avoid any reduction in strength and power capabilities.



Journal of Applied Physiology, 89, p. 1179–1188
Journal of Strength and Conditioning Research, 2006, 20(3), 492–499
Int J Sports Phys Ther. 2012 Feb; 7(1): 109–119.
The Impact of Stretching on Sports Injury Risk: A Systematic Review of the Literature. Stephen Thacker, Julie Gilchrist, Donna F. Stroup, C. Dexter Kimsey.
Res Sports Med. 2008: 16 (3): 213-31.


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Should You Stretch Before a Workout and What Type Should You Do?

What to Do to Help Your Muscles Recover After a Workout

Does Stretching Really Increase Flexibility?

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