For a muscle to become stronger, it must be worked harder than it would be in everyday activities. When it is, we say that the muscle has been overloaded. To achieve this degree of muscle work, we must decide on the type of exercise required, and its duration, frequency of use and intensity. These are called the training variables (see table 3.1), and altering any of them will change the overall work intensity. The total amount of work is often expressed in sets and reps and, together, the description of an exercise using these variables is commonly referred to as training volume. For example, heavy weight training is clearly harder than light jogging (exercise type), while slow walking is easier than fast walking (intensity). Performing a trunk curl exercise every hour throughout the day is harder than performing it every other day (frequency), and performing 10 repetitions is easier than 100 repetitions (duration). Performing the trunk curl everyday for 3 sets of 10 repetitions gives a larger training volume than performing it three times each week for 2 sets of 12 repetitions.

When we are trying to strengthen the abdominal muscles, the type of exercise will dictate the type of strength we will build up. There are three major sorts of strength, termed isometric, concentric and eccentric. Isometric strength occurs when we tense a muscle and hold it tight. It is the type of strength needed to hold a joint still and to stop it moving, so is important to stability. Concentric strength occurs when a muscle is shortening and speeding up a movement. It is the type used when we pick something up, for example. Eccentric strength is exactly the reverse. During eccentric activity, the muscle begins to lengthen and is gradually ‘let out’. It is the type of activity used when lowering a weight in a controlled fashion, or when leaning over a desk to put a book down.

The three types of muscle work can be further illustrated when standing up and sitting down in a chair. As we stand up, the thigh muscles are tightening and working concentrically. If we stop ourselves just short of full standing and hold the position, the same muscles work isometrically. As we slowly lower ourselves down again back into the chair, the muscles are working eccentrically. All three
types of muscle work are important to the abdominals, and so all three are used in this programme.

The intensity (how hard), duration (how long) and frequency (how often) of exercises used in an abdominal training programme is also important: too little exercise will fail to achieve the results we want; too much will lead to overtraining, leaving us stale and possibly leading ultimately to injury. The intensity and duration of exercise are dictated by the type of muscles we are using. The abdominal muscles work mainly to tense and hold the trunk steady during everyday activities. To do this, the muscles will require endurance, so that they can continue to work for long periods. This may be achieved by working the muscles at slightly less than half of their maximum strength. When the muscles contract, we try to build up the length of time they can hold the contraction until eventually we can hold the abdominal muscles tight for a duration of 30 seconds or so.

Where the abdominal muscles are used in sport, in addition to their role of supporting the trunk by holding it tight, they may be used in dynamic actions to move the trunk rapidly. In this case, the muscles must be trained for power and speed. It is important to note that the supporting (stabilising) function of the abdominal muscles is always re-trained first. Only when this has been achieved, and an athlete has good control of trunk alignment and movement, should power movements begin. The restoration of good support in the trunk forms the foundation upon which other types of training may be built.

The frequency of practice will change as we progress through the programme. This is because initially the intention is to learn correct exercise technique. When learning technique, we aim for a high number of short practice bouts to help concentration. For foundation movements most exercises are practised twice daily at first. The only exception is abdominal hollowing which is practised regularly throughout the day during everyday activities. Once the techniques of the exercises have been mastered, the number of practice bouts reduces and the exercises become harder (intensity increases). Harder exercise will require a longer recovery period, therefore exercises are practised every other day, with a full day in between to allow the muscles to recover.

When a muscle is strengthened, its make-up actually changes. The muscle becomes larger and tighter, and there are alterations in the chemicals it contains. In addition, the way the brain controls the movement itself becomes smoother and more coordinated. All of these changes constitute what we call the training adaptation. In other words, the changes which the body makes are a direct result of the training itself. The exact adaptation will closely reflect
the type of exercise which has been used, so we say that the muscle adaptation is ‘specific’ to the demands placed upon it.

An example from general sport may make this clearer. Imagine two people who run marathons. They want to reduce their times and go for a ‘personal best’. If one person trains by running long distances and the other by running short sprints, who will be more successful in reducing their times? The answer is the person who runs distances. This type of training more accurately reflects the actions required during marathon running. Marathon runners need endurance. Short sprints will build mainly strength and speed and so, although the person using sprint training is getting fitter, the fitness is not the type required for the final marathon race. His body has changed (adapted) but these changes do not closely match those needed for running the marathon, they are not truly ‘specific’.

When training the trunk muscles, the same principles of specificity apply. We need to know what function the trunk muscles perform and then tailor our training programme to improve this function. We have already seen that trunk muscle function falls broadly into two categories: support (stabilisation) and movement.