By Jennifer Copley (Last Updated 19 June 2009)
PNF techniques, originally developed as a form of physical therapy, make use of isometric muscle contractions during stretching.
PNF is a highly effective way of increasing both strength and flexibility, and only one stretch for each muscle group per session is required.
Some PNF techniques can be applied alone, using hands, a towel, the wall, or the floor to supply resistance, but doing the techniques incorrectly carries a risk of injury, so working with an experienced partner is advised.
There are a number of different PNF techniques, but two of the most popular are contract-relax and contract-relax-agonist-contract.
With contract-relax (also known as hold-relax), the muscle is stretched, contracted, relaxed, and then stretched a little further. For example, a partner gently stretches the hamstrings (muscles at the back of the thigh) by slowly raising the stretcher’s leg into position and then holding it steady while she resists, attempting to force her leg back down to the floor, thus contracting the target muscle. Recommended times for this contraction vary from one expert to the next, ranging from 4-15 seconds, with more experts recommending lower times of 4-6 seconds.
The hamstrings are then relaxed for up to 3 seconds, after which the partner moves the leg into a more intense stretch position, extending the range of motion slightly, and holds for 10-15 seconds. The rationale is that the first stretch will promote a relaxation response in the muscle, which will enable a further subsequent stretch.
The CRAC technique is the same as CR, except that the opposing muscle group (in the case of the hamstrings, this will be the quadriceps), is actively contracted after the contraction of the target muscle is relaxed. The full sequence is as follows:
- The partner raises the stretcher’s leg into the stretch position.
- The stretcher contracts his hamstrings, attempting to bring his leg back down to the floor for 4-15 seconds while the partner holds it in place.
- The stretcher relaxes his hamstrings, takes a deep breath, then exhales and contracts his quadriceps (the muscles at the front of the thigh) to deepen the hamstring stretch, and holds this contraction for a few seconds (there is also disagreement among the experts as to how long this second contraction should be held, with most favouring low times of 4-6 seconds).
While some athletic advisers recommend following up with an additional passive stretch, other experts maintain that no passive stretch is required after the second contraction and that implementing one may even increase the risk of injury.
Research indicates that the CRAC technique is the most effective for increasing range of motion, and has the added benefit of enhancing active flexibility. An example of active flexibility is the ability to hold a kick in the air for a few seconds without any support.
PNF can also be performed using bouncy ballistic movements, but this is a risky strategy. Some professional dancers and athletes use this technique, but for someone who does not have extremely well-developed muscle control, strength, and flexibility, there is a high risk of injury.
To avoid injury when implementing a PNF stretching program:
- Consult a doctor before beginning.
- Work with a skilled, experienced partner.
- Don’t engage in PNF stretching directly before athletic pursuits requiring strength or explosive movements because, like static and passive stretching, it can temporarily decrease muscle force production.
- Warm up with 5-10 minutes of aerobic activity before stretching.
- Use only about 20% of the maximum force possible when contracting muscles – research indicates that maximum effort is unnecessary for increasing range of motion and may cause injury.
- Rest for at least 20 seconds between stretches.
- Leave 36 hours or more between PNF stretching sessions – PNF stretching only needs to be done once or twice a week.
- PNF stretching can raise blood pressure, so those with high blood pressure should avoid it.
- Like isometric stretching, PNF stretching is not recommended for children or teenagers as the risk of injury is higher for those who are still growing.
- Alter, M.J. (1998). Sports Stretch. Champaign, IL: Human Kinetics.
- Appleton, B. (1998). “Stretching and Flexibility.”
- Bradley, P.; Olsen, P.; & Portas, M. (2007). “The Effect of Static, Ballistic, and Proprioceptive Neuromuscular Facilitation Stretching On Vertical Jump Performance.” Journal of Strength & Conditioning Research, 21(1), 223-226.
- McAtee, R.E., & Charland, J. (2007). Facilitated Stretching. Champaign, IL: Human Kinetics.
- Neporent, L.; Schlosberg, S.; & Archer, S.J. (2006). Weight Training for Dummies. Wiley Publishing, Inc.
- Sharman, M., & Cresswell, A. (2006). “Proprioceptive Neuromuscular Facilitation Stretching: Mechanisms and Clinical Implications.” Sports Medicine, 36(11), 929-939.
- Weerapong, P.; Hume, P.; & Kolt, G. (2004). “Stretching: Mechanisms and Benefits for Sport Performance and Injury Prevention.” Physical Therapy Reviews, 9(4), 189-206.