Training Principles
When designing a resistance and / or cardiovascular training programme, there are a number of factors to consider. However, before considering these factors, there are several fundamental principles I would like to explain:

Adaptation:
Any type of resistance, cardiovascular, flexibility or Proprioception training has only one goal; adaptation. Adaptation is simply any anatomical or physiological change that occurs in the body, such as getting stronger, losing fat or increasing muscle size. This is an evolutionary ability of animals to adapt to changes in their environment in order to survive. In the case of fitness training, the change in the environment may be lifting a weight. Lifting the weight will cause stress to the bones, muscles and connective tissue of the affected area. The body will adapt to this stress by trying to protect or strengthen the area; laying down more collagen in the bones and connective tissue, and strengthening the muscles fibres within the muscle. Thus if the weight is lifted again at a later date, the body will not be put under as much stress. This is an example of the body trying to maintain homeostasis, or equilibrium.

Overload:
When a weight is lifted, it must be heavy enough to elicit a change in the body. Exactly how heavy will depend on what the body is used to at that moment. The stress, in this case the weight, must be above a certain threshold or the adaptation will not occur. The term overload simply means that the stress must be above the normal, or habitual, level in order to get a subsequent change. Overload can be achieved by altering the intensity, duration, type or frequency of an exercise.

Specificity:
Any change or adaptation in the body's muscles, organs and systems will be very specific to the type of training (stress) undertaken. This is the principle of specificity and means that if an athlete wants to improve their running, they must run. Swimming will elicit many generalized improvements in their cardio-respiratory system, which may improve the athlete's running fitness. However, for the best results, the athlete should undertake running training.

Reversibility, Recovery and Overtraining:
The principle of reversibility states the any adaptation that occurs in the body is non-permanent. This is sometimes referred to as the "use it or lose it!" syndrome. Any adaptation can return to a genetically determined, pre-training state if the stress is not maintained or developed properly. The aspect of recovery becomes very important in relation to this. Sufficient rest or recovery between stresses, or training sessions, must be allowed for adaptation to occur. Adaptation will only occur during the inter-training recovery periods. How much recovery is sufficient, will depend on the type, duration and intensity of training, and the level of the athlete. Sufficient recovery is essential in order to prevent overtraining, which is defined as an acute syndrome resulting in fatigue with a plateau or decrease in performance. Short-term overtraining has been called overreaching.

Progression and Periodisation:
To avoid any plateaus or decrease in performance, the principles of progression and periodisation should be applied. Progression means that when an overload is applied it should be gradually and sufficient enough to elicit an adaptation, but it should not be excessive. Excessive stimulus is counterproductive since it will lead to overreaching and maybe overtraining. Excessive post-training muscular soreness lasting up to 7-11 days after resistance training is a prime example of excessive stimulus being applied.

Periodisation is planned progression and manipulation of the training variables over a prolonged period of time. Varying the intensities and types of training in phases or cycles can cause greater improvements in performance and decrease the risks of overtraining and injury.

Training Variables
To vary the training stimulus, there are a number of variables, which can be manipulated:

Duration:
The duration refers to the amount of time dedicated to exercise session. The type of exercise and fitness level of the individual largely dictates this. The amount of time the individual is willing to dedicate to training must also be taken into account.

Intensity:
The intensity is the amount of effort put into each repetition; it can be increased either by adding to the weight lifted or the running speed. When training for strength, power or speed, the intensity is high. However, training for aerobic endurance calls for lower intensities and longer duration.

Frequency:
Frequency refers to the number of training sessions per week, month or year. Beginners typically start with a three times a week schedule with a day's rest in between. Competitive athlete may train up to twelve times a week.

Mode:
The mode or type of training may also be manipulated, as long as the specificity of the adaptation
does not move away from the training goal. This can be done by changing the aerobic exercise from running to cycling, or the resistance exercise from lateral raise to a shoulder press.