070: What is the Difference Between PNF and Contract-Relax Stretching? Is One More Effective Than the Other?

This post originally appeared as a response to a question posted on the knowledge-sharing website Quora.

PNF and contract-relax are two names for similar methods that fall under the same banner of flexibility training: static active stretching. The term, which authors of research papers throughout the scientific literature utilise, describes the nature of motion and muscle activity. Static refers to a state in which no acceleration is present - the joint is motionless or stationary since humans always display changing rates of velocity during movement - and active refers to the presence of muscular contractions driven by chemical energy. In simpler terms, the joint is not moving, and the muscles crossing it are contracting. Both PNF and contract-relax stretching use alternating isometric muscular contractions with periods of relaxation to elicit further increases in joint range of motion (ROM), i.e., flexibility. An isometric contraction is one during which muscle length does not change; the joint angle does not change either. The term isometric stretching, popularised by one of my mentors Thomas Kurz in his landmark text 'Stretching Scientifically,' is used interchangeably with PNF, contract-relax, and static active stretching.

PNF is an acronym for proprioceptive neuromuscular facilitation. Herman Kabat, a clinical neurologist, is often credited with coining the name during his work with stroke patients in the 1940s. Contract-relax has been used both as a specific method within the PNF approach and as a synonym for PNF. They work the same way: 1) A muscle stretches to the point of discomfort (or slightly before this point if the pain is clinically significant); 2) the muscle being stretched contracts isometrically; 3) the muscle relaxes and stretches again. A leading hypothesis is that isometrically contracting stretched muscles activates autogenic inhibition pathways, which subsequently reduces muscle tension through stimulation of Golgi tendon organs. The result: the person feels less resistance to the stretch and can lengthen the muscle further.

There is little data to support the greater effectiveness of PNF vs contract-relax, or vice versa, mainly because they are essentially the same thing. Most research teams tend to focus their study designs on establishing the effectiveness of static active stretching compared to other methods of flexibility training, including static passive stretching, dynamic active stretching, and resistance training ("loaded stretching"). Results vary depending on the sex, age, and training status of samples. However, all stretching methods increase flexibility, and static active stretching is very effective. It also has the added benefits of being very safe (it is easier to control muscular tension in isometric contractions than in dynamic contractions) and increasing strength throughout the ROM. Getting stronger at longer muscle lengths not only makes accessing one's flexibility without a warm-up ("cold flexibility") more effortless, but it also facilitates greater neuromuscular control and joint health. Static active stretching should be a staple component in any flexibility training programme, regardless of the name it is given.