Contractions During PNF Stretching

Q: Many texts encourage maximal (100%) isometric contractions when performing PNF stretching. However, in your stretching article(link article here), you recommend to "use only about 25% force during a PNF stretch." Who's right?

A: The simple answer would be "I am right ... just do as I say and don't ask questions!", but that would seem too arrogant so let me try a different approach. First of all, there is no right or wrong in this case - there are pros and cons to everything. As I mentioned in my Stretching For Strengthening article, the benefits of submaximal contractions during PNF stretching include ease of application and less discomfort/fatigue. Here's an example. Picture a 100 lb. female trainer performing just about any PNF stretch on a 300 lb. male lineman. If he gives her a maximal contraction, she's going flying across the room! On the other end of the spectrum, if you use PNF stretching to restore ROM in a rehabilitative setting, maximal contractions are contraindicated. For scientific evidence, take a look at this abstract:

Effect of submaximal contraction intensity in contract-relax proprioceptive neuromuscular facilitation stretching.

Feland JB, Marin HN.
Br J Sports Med. 2004 Aug;38(4):E18.
Brigham Young University, RB-120A, Provo, UT 84602, USA.

OBJECTIVE: To determine if submaximal contractions used in contract-relax proprioceptive neuromuscular facilitation (CRPNF) stretching of the hamstrings yield comparable gains in hamstring flexibility to maximal voluntary isometric contractions (MVICs).

METHOD: Randomised controlled trial. A convenience sample of 72 male subjects aged 18-27 was used. Subjects qualified by demonstrating tight hamstrings, defined as the inability to reach 70 degrees of hip flexion during a straight leg raise. Sixty subjects were randomly assigned to one of three treatment groups: 1, 20% of MVIC; 2, 60% of MVIC; 3, 100% MVIC. Twelve subjects were randomly assigned to a control group (no stretching). Subjects in groups 1-3 performed three separate six second CRPNF stretches at the respective intensity with a 10 second rest between contractions, once a day for five days. Goniometric measurements of hamstring flexibility using a lying passive knee extension test were made before and after the stretching period to determine flexibility changes.

RESULTS: Paired t tests showed a significant change in flexibility for all treatment groups. A comparison of least squares means showed that there was no difference in flexibility gains between the treatment groups, but all treatment groups had significantly greater flexibility than the control group.

CONCLUSION: CRPNF stretching using submaximal contractions is just as beneficial at improving hamstring flexibility as maximal contractions, and may reduce the risk of injury associated with PNF stretching.

One more thing on PNF stretching that I learned awhile back from Kate Fletcher at the Institute of Sport Medicine & Wellness Centre in Etobicoke, Ontario. After the submaximal contraction, rest for a second or two to allow the muscle to relax before moving it into the new range. At this point, ease back a touch to take the edge off of the stretch and repeat the process until full range of motion has been achieved.