Credit: Photography by Corey Sorenson
If you’ve been a CrossFitter for any significant length of time, you’ve been instructed — repeatedly — about the benefits of stretching. In fact, assuming you’re a good CrossFitter and you listen to your coaches, you have likely felt the effects of improving mobility before training. But we’re willing to bet that even if you’re the best CrossFitter, you also can remember a day when you came in a bit late to the box and jumped into the WOD, having shirked a proper warm-up and stretch. Bad idea, wasn’t it?
The reason some athletes tend to bypass stretching is not necessarily because they believe it isn’t important but rather because they simply get bored with it. And the reason they get bored with stretching tends to be because they’re asked to do the same static and dynamic stretches over and over again, day in and day out. WODs change daily; stretching routines never seem to.
Furthermore, the stretching technique that is most effective, most interesting and variable is very likely the one technique you don’t perform. Often, coaches don’t ask athletes to perform this type of stretch because they don’t understand it themselves, despite its surge in popularity thanks to mobility experts like Kelly Starrett. It’s called proprioceptive neuromuscular facilitation stretching, and it’s perfectly suited to CrossFit not only because of its benefits but also because it requires a partner.
To be completely clear, PNF is not so much a type of stretching as it is a technique that combines passive stretching with isometrics in order to bring about maximal range of motion in a joint. Developed in the 1940s as a method of rehabilitating stroke victims, PNF techniques are the result of work by Herman Kabat, a neurophysiologist, and his assistants Margaret Knott and Dorothy Voss, who combined their understanding of functional movement with theories of motor control, motor learning and neurophysiology.
The term “proprioceptive neuromuscular facilitation” actually refers to several stretching techniques in which a muscle group is passively stretched, then contracts isometrically against resistance while in the stretched position, and then is stretched again through the resulting increased range of motion. And it has consistently been shown to be more effective than other forms of stretching to increase flexibility.
Researchers from William Paterson University in New Jersey developed and tested a self-administered version of the stretch to compare it to static stretches. Study participants were put into one of two groups — static or self-PNF hamstring stretches — for the six-week study. For both the static stretches and the self-PNF testing, volunteers placed one foot on a chair about 20 inches in height while keeping the other foot on the floor. The static stretch group simply held a stretch for the entire 40 seconds. (This study used 40 seconds, though most PNF techniques employ 30-second holds.) The self-PNF group performed a static stretch on the chair for 15 seconds followed by a 10-second hamstring isometric contraction in which they contracted their hamstrings by pushing into the chair to 90 percent of maximum effort. They then followed with another 15-second static stretch.
Researchers found a significant difference in range of motion of the hip after the PNF stretching compared to the static stretch. PNF stretching helps prevent knots and realigns muscle fibers and connective tissue after the microscopic damage that’s triggered by a vigorous workout.
How It Works
When a muscle isometrically contracts, there is tension but no movement, but on relaxation, that muscle is able to stretch beyond its initial maximum length and thereby increase the associated joint’s range of motion. PNF takes advantage of this brief opportunity by immediately subjecting the muscle to a passive stretch.
There are three physiological factors that enable enhanced range of motion following an isometric contraction. First, the muscle spindles — specialized receptors in the muscle that protect against rapid, forceful and damaging movements — learn to reset their comfort zone to accommodate a greater muscle length. That is, with regular PNF stretching, the muscle spindles learn to exert their protective tension later, allowing the muscle to achieve a longer length. Second, during the isometric contraction, the muscle’s fibers contract against resistance, and because the tension is held for a period of time, the fibers fatigue. During the subsequent passive stretch, it’s more difficult for the fatigued muscles to contract and resist the stretch. And third, another specialized set of protective cells in the muscle, called the golgi tendon organ, is activated by the contraction. The golgi tendon organ then inhibits contraction of the muscle (to keep it from tearing against potentially damaging resistance).
These three factors together enable a kind of vulnerability within the muscle immediately following an isometric stretch. PNF stretching techniques take advantage of this vulnerability and the muscle’s increased range of motion by using the window of time immediately following the isometric contraction to train the stretch receptors to adapt to the new increased range of muscle length.
PNF techniques can be performed for virtually any muscle group and are quite varied. There are even dynamic and ballistic PNF stretching techniques (such as the hold-relax-swing and the hold-relax-bounce). However, athletes should be careful and only employ such higher-impact techniques after proficiency has been shown.
In addition, there’s one other caveat. Because PNF involves muscle contraction, it may be best employed on days when the athlete is not attempting a one-rep max in a movement in which the muscles being stretched are most active.
When employing the PNF technique, athletes should perform each stretch three times for a given muscle group (resting 20 seconds between each repetition). PNF stretching should be performed for a given muscle group no more than once per day (ideally, no more than once per 36-hour period).
The hold-relax technique is the mainstay of PNF stretching and is generally considered the model for other variations. Lie on your back with your hands resting at your sides and with a partner kneeling, facing you. Keeping it as straight as possible, lift one leg up in the air and have your partner stabilize your knee (preventing hyperextension or pressure against the knee joint) with a palm cupped gently over the kneecap. Your partner will grip your ankle and gently assist by providing a small amount of force to the back of the thigh in order to maximize the stretch (a “passive” stretch). Keep your hips down, and once you reach a point of mild discomfort, signal your partner to stop applying pressure and hold that stretch for 10 seconds. Then try to extend at the hips (force your leg back down) while your partner resists and holds your leg in that position; there should be no movement. Hold this isometric contraction for six seconds and then relax while your partner moves your leg farther up toward your torso in a second passive stretch, holding that stretch for 30 seconds. The final position should be greater than the initial stretched position.
If you’d like to take PNF stretching further, here are two advanced variations to try with the hamstrings as examples.
This technique begins in the same way as the standard PNF stretch — with a passive stretch that is held at the point of discomfort for 10 seconds. At this point, when you apply resistance in hip extension (forcing your leg back down), your partner applies some resistance but allows the leg to move slowly down toward the ground in a controlled manner. This resisted movement should take about six seconds and be tense and slow. Once your leg touches the floor, you raise your leg back up and your partner again immediately applies a passive stretch, ending in a stretch beyond the degree of the first one and maintaining it for 30 seconds.
Hold-Relax With Agonist Contraction
This technique is identical to the standard PNF stretch above throughout the first two stages (initial passive stretch and isometric contraction). However, in the third stage, instead of just a passive stretch being employed for 30 seconds, more force is added to the movement from the agonist.
The agonist in a movement is the muscle group that’s the prime mover. In the standard hamstrings PNF stretch, one might tend to think the agonist is the hamstrings because that is where you feel the stretch, but no. The movement employed here is hip flexion (decreasing angle of the hip joint); therefore, the agonist is the hip-flexor group. So you benefit here not just from the assistance of your partner but also from the strength of your hip flexors (including your rectus femoris).
This variation can be difficult to perform, and concentration is key. After the six-second isometric contraction, while your partner takes your leg farther, focus on contracting your quads (you will notice your knee straighten) and your hip flexors. Squeeze them hard. You will see a marked difference between the initial passive stretch and the final stretched position.
Lie facedown on the floor, bending one leg so that you are as close as you can come to full knee flexion (i.e., try to get your heel to touch your butt). Kneeling behind you, have your partner gently stabilize your lower leg (to prevent excessive force to an already flexed knee) by holding your leg at the ankle with one hand and place the other hand under the bent knee on the floor. Slowly, your partner should raise your bent knee off the floor. (With the slight pressure from your partner’s stabilization, three of your quadriceps muscles are already maximally stretched because they only cross the knee joint. However, the rectus femoris crosses the hip and the knee and therefore also can be stretched with movement at the hip. That’s why this stretch can be used to increase range of motion at both joints.)
After you reach a point of mild discomfort, hold that position for 10 seconds. Now, keeping your ankle back near your buttocks (fully flexed, with the assistance of your partner), contract your quads against resistance with two different movements: knee extension, as if you were kicking your foot outward; and hip flexion, as if you were pulling your bent knee straight back down to the floor. Your partner resists both movements while you stay in isometric contraction for six seconds. Following that contraction, your partner can maximize the knee flexion (if it was not already fully flexed) and the hip extension by (a) pressing your ankle to your buttocks and (b) pulling your bent knee upward to a new position, holding that for 30 seconds.
Hip Adductors (Groin)
Sit in a stable position with your legs bent and the bottom of your feet flat against each other and pulled in close to you. Your knees should be out to the sides, and you should be able to grab your feet. If you are in the correct position, your groin muscles will feel tense. Your partner kneels behind you and applies pressure to your knees downward for 10 seconds, stretching the adductors. After this passive stretch, forcibly contract the adductors against your partner’s resistance. Allow no movement and stay in that isometric tension for six seconds. Following the isometric stretch, your partner again applies a passive stretch and maintains the new position for 30 seconds. (Be careful here; these muscles do not need much force to be stretched.)
Sit on the floor in a stable position with your legs crossed in front of you. With your partner standing behind you, raise your arms up to your sides. Your upper arms should be parallel to the floor, and keeping a slight bend in your elbow, your hands should be about the level of your ears. Your partner takes hold of your forearms, and being careful not to apply pressure against the elbow joint, slowly pulls your arms behind you and slightly upward until you feel mild discomfort. After a 10-second stretch, pull your arms directly forward as if performing a chest-flye exercise in an isometric contraction against your partner’s resistance. No movement should occur. Hold this for six seconds. Then immediately relax and allow your partner to passively stretch your arms back farther for 30 seconds.