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PNF Stretching

Flexibility is key for athletes and non-athletes alike. It allows you to move freely and comfortably in your daily life, and can also help prevent injury during exercise. One of the best ways to increase your flexibility is by stretching. However, research suggests that not all stretching techniques are created equal. Proprioceptive neuromuscular facilitation (PNF) stretching relies on reflexes to produce deeper stretches that increase flexibility.

So what is proprioceptive neuromuscular facilitation (PNF)?

PNF stretching is always done in the same pattern: 10-second stretch, 6-second contraction, 30-second stretch. The first stretch should be just to the point of discomfort. The 6-second contraction is an active isometric contraction at submaximal effort (around 20-50 percent of your max effort) against a partner's or other implements resistance. The final 30-second passive stretch should go beyond the range of your first stretch. This style of PNF is called "contract-relax."If you’re still a little confused here’s a real world example using a partner hamstring stretch:

  • Lie on your back with your legs and arms on the floor. Lift one leg and allow your partner to push against it until you feel slight discomfort in your hamstring, and stay in this position for 10 seconds.

  • Next, push with your hamstrings against your partner's resistance for 6 seconds. Think about driving your heel towards the ground.

  • Follow that contraction by relaxing into a passive stretch by your partner for 30 seconds. After the contraction, you should be able to move your muscle into a greater range of motion (ROM) during the passive stretch.

This basic pattern can be implemented by pretty much anyone. However, there are a few variations you can use depending on your flexibility and comfort level:

  • For the first variation, begin your PNF stretch just like you normally do by having your partner stretch your hamstring for 10 seconds. Then, instead of isometrically contracting against your partner, have him or her push against you just hard enough that you can contract and move your leg all the way down to the floor against their resistance. After you've moved your muscle through its entire ROM, you'll move into another 30-second passive stretch.

  • The second variation, referred to as "contract relax agonist contract" (CRAC), calls for you to contract the opposing muscle of the target muscle, or the muscle being stretched. You'll go through the 10-second passive stretch and the 6-second contraction like usual. But as your partner begins pushing your leg into the 30-second stretch, you'll contract your quads to pull the hamstrings into a greater stretch.

Contracting the opposing muscle as the target muscle stretches can actually help increase that muscle's ROM, so you can really get the most out of your stretches.

How does PNF work exactly?

Golgi tendon organs (GTOs) are sensory receptors located within muscle tendons. GTOs respond to changes in muscle tension and provide feedback to your brain to regulate muscle force. Think of it as a safety mechanism: When tension in the muscle reaches levels that could pose a potential risk of injury, GTOs are stimulated to cause the muscle to relax. PNF stretching works because the isometric contraction activates the GTO, ultimately allowing the muscle to lengthen and experience a greater ROM. This technique utilizes "autogenic inhibition," which relaxes a muscle after a sustained contraction is held for 6 seconds. This process allows your muscle to be stretched beyond its initial maximum. PNF can also work through what's called "reciprocal inhibition," which means one side of a joint relaxes to allow for the contraction of the other. Voluntary contraction of the opposing muscle has been shown to reduce activation levels in the target muscle, allowing it to lengthen and achieve greater gains in ROM. While there are multiple PNF stretching techniques, all of them rely on stretching a muscle to its limit. Doing this triggers the inverse myotatic reflex, a protective reflex that calms the muscle to prevent injury. Basically, PNF causes the brain to go ‘I don’t want that muscle to tear’ and sends a message to let the muscle relax a little more than it would normally.

When should you start PNF stretching?

Because PNF stretching may challenge your flexibility beyond your usual ability, it's not a good idea to do it when you're cold. The best time to implement PNF stretching is after you've trained, when your muscles are already warm. One full repetition of PNF for each target muscle is enough to increase your ROM.Start by implementing PNF stretching into your routine twice per week. Because you're challenging your muscles through a larger ROM, they may need a little time to recover before you hit them again, so wait a day or two between bouts of PNF. Whether you use PNF for a few weeks or a year, changes in ROM will occur. The best way to use PNF stretching is to grab a partner. If you have a training partner, then you already have a PNF stretching partner!


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