The effects of exercise and training
In these health-anxious times, exercise offers some reassuringly simple prescriptions. A daily dose of organised activity, whether it be jogging, Pilates, pumping weights in the gym, or brisk walking is generally seen as the cornerstone of a healthy lifestyle. Doctors, dietary consultants, personal trainers, journalists and, of course, the fitness industry form a chorus of support for the benefits of regular exercise.
Much of this is perfectly justified. A reasonable amount of daily exercise is essential to the preservation of a healthy human body. Muscles which are not exercised waste away; those which are vigorously and regularly exercised gain in strength and bulk. Yet few people have any detailed idea about the effects of exercise on muscles or general body health.
One of the key points is that the red and white fibres in muscles are quite differently affected by exercise. Excessive development of white fibres can lead to a physique which is ideal for the weight-machine but leads to an inability to sit at a computer for more than a half-hour without backache. A proper balance between red and white muscles fibres is necessary for general health and well-being.
The aim of this paper is to set out the basic facts about muscles, how they do their job and how they are affected by exercise and training. It is short on detailed prescriptions because people are different and want different things from their exercise programmes. Instead, it provides the information for people to make their own judgements on what they want to achieve and how to go about it. Healthy living is not about chasing exercise and other fads but about understanding how one’s body works and taking responsibility for how one uses it.
The skeletal muscles
There are around six hundred skeletal muscles in the body and their role is to generate force or movement. They are called skeletal because they are connected at one or both ends to a bone in the skeleton. It is these muscles which are affected by exercise and training.
The skeletal muscles are often referred to as striated because, under a microscope, they show alternating light and dark transverse bands, giving them a striped or striated appearance. They are also referred to as the voluntary muscles because they are, to a greater or less extent, subject to conscious or voluntary control.
Each skeletal muscle contains hundreds to thousands of elongated cells called muscle fibres. The number of fibres varies according to the size of the muscles. The smallest muscle in the body, the tensor tympani in the inner ear, contains only a few hundred fibres. The first lumbrical muscle, in the back of the hand, contains about 10,000 fibres and the medial gastrocnemius, one of the big calf muscles contains over a million.1
These fibres are capable of contraction and relaxation and vary in length from 2 mm to about 300 mm.2 They vary in diameter from 10 to 100µm (micro metres or millionths of a metre) in diameter,3 with an average of around 50µm.4 This is about the diameter of a human hair.