There are four principles that should form the basis of most weight resistance programs. For best results training should involve overload and progressive resistance with careful attention going to arrangement of the program and the specificity of its effects.
Muscular strength is the most effectively developed when the muscle or muscle group is overloaded - that is, the muscle is exercised against resistance exceeding those normally encountered. If an individual is accustomed to bench pressing 150 pounds on a regular basis then a resistance of 155 pounds or more is required for muscular strength and growth to occur. The use of resistance that overloads the muscle stimulates the physiological adaptations that lead to increased muscular strength and development.
Overloading a muscle during exercise is your way of telling the body that the current muscular strength and development is not enough. Therefore, it needs more. An overload can be applied to muscles two ways;
1. Application of a resistance or weight greater than can be lifted for one repetition (strength).
2. Forcing a muscle group to repeatedly lift a load or weight over an extended period of time (endurance).
For example, if an individual can only curl 55 pounds 2 times, then they have two options to improve strength and development.
1. The individual can force their bicep muscles to lift 60 pounds one to two times (strength) or,
2. The individual can train to lift 55 pounds 4 times (endurance). Either way the muscle is forced to overcome a resistance that it is not normally accustomed.
Resistance Principle Progressive
Throughout a weight-training program, the work load (overload) must be increased periodically to continue muscle overload. A gradual increase in resistance or maximal repetitions will ensure further improvement in strength or endurance. It is important this increase be gradual. To much too soon may injure the musculoskeletal system. Nonetheless, it's important to understand that a muscle must encounter progressively increasing overloads. Many individuals will continue to exercise with the same resistance (weight) at the same number of repetitions for weeks, even months. By exercising against a resistance that is encountered time after time with no overload, the muscle will adapt and no gains will occur.
The Principle of Arrangement of Exercise
A weight-training program should include exercises for all major muscle groups. For optimal efficiency during weight-training, the exercises in a weight resistance program should be arranged so that the larger muscle groups are exercised before the smaller ones. Smaller muscles tend to fatigue sooner and more easily. Therefore, in order to ensure proper overload of larger muscle groups, they should be exercised first. The larger let muscles should, for instance, be exercised before the smaller arm muscles.
The development of muscular fitness is specific to the muscle group that is exercised, the type of contraction and training intensity. This simply means, that to increase the strength of the elbow flexors (biceps), exercises must be selected that involve the concentric and eccentric contraction of that muscle group. This also applies to increasing strength for improving a specific sports skill (i.e. soccer kick; baseball throw). This means that not only must the specific muscle be exercised for improvements, but the exercises will be most effective if the pattern of the movements is simulated. This "motor-skill" specificity not only applies to specific skills or movements, but also to overall conditioning of muscles. For example, the professional skier who is in excellent condition to ski, may not have the strength or endurance to run a marathon (and vice-versa). Although in both activities the same muscle groups are used, the movement patterns they produce are quite different.