This week, our fitness blog delves deeper into the benefits of PNF stretching.
As discussed in our previous blog, there are three different ways a personal trainer can apply PNF stretching:
- CRAC (Contract, Relax, Antagonist, Contract)
- CR (Contract and Relax)
- HR (Hold and Relax)
and each way will work best on different muscle groups.
Using muscles in pairs
During CRAC, muscles will be used in pairs. For example, if a personal trainer asks a client to carry out a hamstring stretch, they will start by lifting their leg until they feel tension in the hamstring. Once the tension subsides, they will use their hip flexor – the muscle on the opposite side – to increase the range of motion. Employing the opposite muscle in this way is known as reciprocal inhibition: as the hip flexor is contracting, the hamstring has to relax. This method is called CRAC.
CRAC stretching and the hamstrings
The CRAC training method is particularly effective for the hamstrings, as many people have tightness in this muscle, and when they lift a leg to the point where they can feel tension in the hamstring, usually around 50-60°, the hip flexor is still within its range of motion to be able to pull the leg up.
CRAC is not suitable for all stretching exercises that a personal trainer sets for a client. For example, with a quad stretch, the fitness instructor would ask the client to lie face down, bend one leg and push the heel towards the backside until they feel tension in the quadriceps. If the protocol for CRAC was being followed, the client would be asked to pause and then pull the heel further to heir backside. However, this wouldn’t be possible, as the hamstring muscle will have gone past its functional range of movement.
In other words, for CRAC PNF stretching, a muscle must have an opposite muscle with an equal or higher range of movement.
Incorporating CR and HR into a training programme
CR and HR can be used on any other muscles. A few examples might be:
CR stretching requires the joint and the muscle to move during the stretch. It is not classed as an isometric exercise, which means that it’s suitable for those with high blood pressure who want to carry out stretching exercises. It can also be beneficial for developing flexibility and strength through a range of motion, as well as being suitable for someone working around an injury, as they can carry out the movement within a range that is comfortable and then return to the starting position, all without placing any stress on the injured area.
As CR stretching keeps an individual within a comfortable range of movement, once the client is used to the stretching exercise, their personal trainer may want to move them on to Hold and Relax.
The benefit of HR is that once a client has reached a point of tension in a stretch, they will then need to hold that position and push down through the muscle in an isometric fashion, which puts a lot more tension through the Golgi tendon organs and through the muscle spindles, giving a bigger stimulus and increasing the autogenic inhibition. HR is not as suitable for clients with high blood pressure, as it is an isometric exercise.
