Stretching, Force Relaxtion, and Creep - How Stretching Can Cause Ligament Damage

Ligaments are a type of connective tissue that contributes greatly to the structural integrity of the body. Ligaments are known for tying bones together and are particularly important because they contribute significantly to joint stability.

 Ligaments of the Shoulder

Ligaments rupture after they are stretched too much. Generally, this is the result of a traumatic collision. However, ligaments can be over-stretched and weakened simply by overzealous stretching due to their unique properties.

First off, ligaments exhibit a trait known as force relaxation (1). When ligaments are stretched and the stretch is held at a given length, the ligament will stretch out and slowly give less and less resistance to the force. As a result, holding a moderate intensity stretch for a long period of time can potentially result in more ligament lengthening than a brief intense force.

Secondly, ligaments also exhibit creep (1). When a ligament is stretched with a constant force, and the force is maintained, it is continually stretched. Once a ligament reaches a given length (dependent on the ligament), failure occurs. When a ligament fails (torn, ruptured, or stretched beyond its capacity) it is irreversibly damaged.

Sometimes, stretching can result in ligament damage based on the properties of force relaxation and creep. Here is how it plays out:

1. A stretch is being held that is putting stress on the ligament. The ligament begins to stretch out and provide less and less resistance (force relaxation).

2. The person stretching feels like they can go further (since the ligament is resisting less) and he increases the stretch back to the same force he used at the start. Since the force is being maintained, the ligament continues to stretch (creep).

3. As this pattern continues, eventually the ligament can be stretched too far.

A ligament may can be deformed without tearing or rupturing it. This may result in joint instability due to less contribution from the damaged ligament. Though ligaments can heal, they have a poor blood supply and generally never reach pre-injury levels of strength. Since serious ligament injury does not heal well, both ligament tears and significant joint instability are oftentimes treated surgically.

Solution

The first thing you should do is that when you stretch, make sure you are actually "feeling it" in the muscle rather than in the ligamentous tissue. For example, when stretching the hamstrings, you want to feel it actually in the hamstring rather than behind the knee. Bend the knee some until you hit the target spot. If you are stretching out the external rotators of your hip, make sure you actually feel it around your hip rather than in your knee.

Secondly, save the static stretching for after a workout. Ligaments can handle more load and are more resilient when warmed up. Additionally, extra blood and fluid in the target area as a result of working out will make it easier to stretch.

At the end of the day, its important to remember that ligaments only can handle ~10% change in length before undergoing permanent damage, while muscle length is largely regulated by neural activity. This is why I like Z-Health so much - improving proprioception is much more effective than stretching for decreasing excessive muscle tension.

References

1. Enoka, R.M. (2002). Neuromechanics of Human Movement. Champaign: Human Kinetics.