Ever felt that your body gets "stiff" in cold environments or that you lose flexibility as you grow older?

Stiffness and flexibility problems occur due to changes in our muscles.

Professor Shigeru Yamada, who specialises in exercise physiology at Jissen Women's University in Japan, said that "body stiffness is largely influenced by the condition of muscles".

The fibres that make up muscle tissue are arranged in a ladder-like pattern of thick myosin fibres and thin actin fibres.

Each "ladder" is enclosed by a membrane, forming the basic unit of muscle, called a sarcomere. A muscle moves by the expansion and contraction of its many sarcomeres.

Prof Yamada said that "by undertaking exercises such as yoga, that slowly and repeatedly stretch the muscle, the number of sarcomeres increases and the muscle fibres will penetrate the tendons that connect muscle and bone".

Stretching muscle fibres that have plenty of elasticity makes it easier for a person to move his joints.

Conversely, if there is a lack of exercise, the number of sarcomeres gradually drops and the amount of connective tissue, such as tendons, increases.

This makes the body more stiff and he may find it difficult to move as he desires. He may also get injuries more easily.

The person's posture worsens and lower back pain becomes more common. He will also need to make more effort to move his body.

Many people feel stiffer as they get older. Associate Professor Reiko Nogami of Tokyo Gakugei University said that stiffness in the body is believed to be "due to long periods without exercise, rather than the ageing process itself".

She said: "Many young people, such as university students who spend a long time studying for exams, are even stiffer than the elderly."

The tissue that encloses the muscles, called the fascia, also has an effect on flexibility. The fascia takes the form of a mesh, with many layers covering muscle fibres to protect the muscle.

If this mesh is too dense, it can obstruct one's movement.

But if a person exercises or has his muscles massaged regularly, the mesh becomes looser. This makes it easier for him to move around.

Prof Nogami said "the reason that athletes stretch and massage their muscles after practice is not just to recover from exhaustion, but also to increase flexibility".

SECRETS OF STRETCHING

Stretching is an effective means of increasing one's flexibility.

Chuo University assistant professor Ikuko Uratani said the key is to focus on areas that do not usually get stretched, such as the shoulder blades and the back of the thighs.

"If the neck is stretched correctly, this will improve blood flow and you can expect a relaxing effect," said Prof Uratani.

Aim to do two to three sets on each area, making sure that you are not causing yourself pain, he added. Move the muscle gradually as you exhale slowly. Although it is more effective to do this exercise when your body has good circulation - such as after a walk - it can also be done during a break at work. "Try doing a little each day," said Prof Uratani.

THE YOMIURI SHIMBUN/ASIA NEWS NETWORK