There are two types of muscle tissue in the human body, they are involuntary muscle and voluntary muscle, (the heart muscle is composed of involuntary AND voluntary muscle tissue). Involuntary muscle is found in your internal organs such as in your digestive system, your intestines for instance regularly pushes ingested food along from your oesophagus to your rectum, it is called involuntary because you don’t need to think about it for it to work, it does so automatically in a healthy body. Voluntary muscle on the other hand requires conscious thought for it to work like when your legs move when you are walking and it is this muscle that is conditioned through exercise.

There are two types of voluntary muscle, they are type I slow twitch (red muscle fibre) that operates at low intensity but with greater endurance. Type II fast twitch  (white muscle fibre) operates with greater force but with much shorter duration. Type I and type II muscle fibres use different energy sources within the body. Red muscle fibre (type I)  for instance uses more oxygen, it is used in aerobic exercise and can be sustained for hours at a time like when you walk. White muscle fibre (type II) on the other hand is anaerobic and uses another energy process , it can be sustained only for short periods but with much more force. White muscle fibre is used in short bursts of strenuous activity like sprinting or lifting heavy weights. 

A long distance runner will have more red muscle fibre than a sprinter who has a greater ratio of white muscle fibre. White muscle fibre gets bigger when exercised, a successful body builder can be expected to be white fibre dominant. We tend to inherit these traits from our parents. Sports like football and rock climbing will use both, in continuous low intensity body movements interspersed with short high intensity muscle action.

Good blood circulation helps and is helped by muscles in action, the amount of oxygen consumed by a working muscle can increase 20-50 times more than a relaxed idle muscle. A flexed muscle not only uses more blood it’s shape changes because of the way it’s various fibres interlock.

Apart from your red and white muscle fibre ratio the actual size and strength of your muscles is determined by how much you exercise, your diet, neurology, hormone levels or presence of artificial growth promoters like anabolic steroids.

Your muscles are the motors of your body’s movements and posture, we cannot even breathe without them.

About 40% of average body mass is voluntary muscle and most of the rest of our mass is composed of involuntary muscle.

Stress stiffens muscle because when we are stressed the body primes itself for a flight or fight response by flooding your skeletal (voluntary) muscle with extra blood. This creates added strength to save yourself even if you are not actually in physical danger.

During short contractions your jaw muscles are strongest while the muscles of your thigh and butt are stronger in longer contractions. When muscles are stretched the interlocking myosin and actin fibres in your muscle are relaxed and help restore full extension to your joints.

When muscle strength is even between the front and back of your body and between the left and right sides of your body your posture will be upright and straight.

Other body tissues respond well to massage too but muscles respond best. It is easy to forget what it’s like to feel normal, it is too easy to attribute your aches and pains to aging alone. It is how you feel after some regular massage that tells you how young you can still feel.