Introduction
Flexibility training or stretching is a conditioning factor that comes closer to mythology than sport science. What we see going on as stretching is often nothing more than an organized act of controlled contortion. We stretch because someone tells us we have to, everyone is doing it so no one stops to ask why, when and how. Newer studies are starting to question more and more the effects of stretching. The following theory, anatomical and physiological information will give you a beginning critical base for understanding stretching.
Anatomy and Flexibility
Passive body structures - joints
- ligaments
Active body structures - muscles including tendons
Flexibility is dependent on many factors which may we may or may not be able to change.
- Age: We lose flexibility with age
- Gender: Women are generally more flexible than men
- Genetics: Shape of joints and bones, muscle tension, hormone levels, muscle fiber type.
- Time of day
- Temperature
- Fitness level and type of sport or work
- Psyche (stressed or relaxed)
We need to distinguish between normal mobility, hyper mobility and hypo mobility.
Normal Mobility
Hyper Mobility
Hypo Mobility
With regard to the norm, it is important to keep in mind that there are individual differences in body type, etc., so there should always be an assessment of the individual athlete and the demands of his/her sport before designing any kind of stretching program. (For example, a gymnast needs to be hyper flexible for his/her sport but for the runner it has been proven that running economy suffers it the athlete is hyper flexible.)
Muscular Imbalance (MIB) and Muscular Dysharmony (MDH)
To be able to stand upright with a good relaxed posture and to look smooth and coordinated during running or any other activity, we need to have a muscle system that works optimally and economically together.
MIB describes an imbalance in the horizontal plane, that is, an imbalance between opposing muscles. For example, the hamstrings are the muscles that bend the knee and the quadriceps are the muscles that extend the knee. These muscles need to have a similar tension and strength to maintain a balance. Such opposing muscles are termed Agonist and Antagonist. While you bend your knee the hamstrings are the agonist muscles and the quadriceps are the antagonist muscles. Another example would be the abdominal and the back muscles. Muscular Imbalance may be developed by improper training. For example, strength training that is focused on developing the abdominal muscles (6 pack) while ignoring the back muscles. This situation may be aggravated by bad posture (sitting all day in a slouched position will tend to shorten the abdominal muscles and stretch the back muscles) or by repetitive work with overload of first the muscle and later the actual joint. The continuously overstretched muscles of the lower back will lose tension and therefore the ability to protect and move the back properly. At the same time, the trained abdominals will shorten and will often change in metabolic activity (too high tension causes oxygen deficit and change of fiber type). These changes will eventually lead to loss of performance and injuries.
MDH describes an imbalance in the vertical plane (a weakness in a muscle chain). Such an imbalance is developed after an injury requiring a cast, where one muscle in a chain loses its strength. The purpose of rehabilitation is to eliminate injuries due to such MDH and an athlete should never go back into competition until rehabilitation is complete. Returning to competition too early can initiate a cycle of re-injury until the problem becomes chronic.
Both MIB and MDH will show up as:
A Performance Loss
B Tension Change (muscle length)
Performance loss can occur due to an imbalance at the knee as in the above example. A shortened antagonist does not allow the agonist to develop the full strength for motion because it uses much of its strength to overcome the resistance of the antagonist. For example, shortened hamstrings will not allow the quadriceps to develop full power for kicking a ball.
The overuse of a muscle can produce a change in the muscle’s metabolic activity. A too high tension will reduce blood flow which will reduce the amount of oxygen supplied to the muscle. This changes the work time of the muscle (anaerobic activity) which may finally even change the fibers doing the work. For example, the back muscles of a rower has STF fibers but constant overuse will increase the muscle tension and therefore reduce the oxygen supply for these muscles, promoting a switch to the use of FTF fibers. This may completely change this athlete’s performance without anyone realizing why!
These changes in performance (strength) or muscle length may be Functional or Structural.
Functional Change from Stretching
The sarcomere is the basic contractile unit of a muscle.
Structural Change from Stretching
A: Normal physiological muscle length
B: Structural shortening of the muscle (decrease in the number of sarcomeres)
C: Structural lengthening of the muscle (increase in the number of sarcomeres)
SummaryTo produce an effective training plan it is necessary to assess each athlete and design a program appropriate for the individual not a whole group. This applies to flexibility as well as to endurance and strength. Before beginning on a stretching program we have to be sure that the muscle we stretch really has one of the above problems. It may be that an antagonist is too weak, requiring strengthening, rather than stretching the agonist.
Before beginning on a stretching program and even before testing muscle length it is important to make an anatomical assessment of body symmetry. (Leg length, joint symmetry, etc.)
Once we decide to stretch we have to plan how often and the appropriate technique for each individual athlete. As with all conditioning factors, we have to re-assess over time whether the athlete is making the desired progress and adjust the program accordingly.
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