Because I SAID so

It is also one of the driving factors behind a concept known as periodization.

The term periodization was first coined several decades ago and refers to changes in training over time. There are many models of periodization but all models basically dictate changes in training style or different phases of training.

For example, someone training to be a long distance runner may start out with a base-building phase where they simply focus on gaining more distance week after week. Later, they will go through a phase of tempo training where shorter, faster runs that focus on pace and perhaps even weight training is performed. There may be a stamina phase focused on strenuous parts of the run such as going up hills.

Each phase focuses on a particular element of training. The reason why these phases are different is the SAID principle. An easy way to understand the SAID principle is to look at your workouts as a blueprint. Every time you train, you are creating a blueprint of how you would like your body to respond to the training. In the days after training and during recovery the body will adapt by following that blueprint.

The SAID principle is perhaps best illustrated in the differences between a long distance runner and a sprinter. Both individuals may train vigorously for their activities, but the sprinter's training won't help them run longer distances just as the distance runner's longer runs won't help them sprint faster. The body adapts to each form of training in an entirely different fashion.

The sprinter is producing larger muscles (hypertrophy) as well as faster and stronger muscles. Their training stimulates a particular type of muscle fiber that can generate great amounts of force but will fatigue very quickly. The long distance runner, on the other hand, will increase the amount of blood vessels in their muscles (to improve flow of oxygen) while gaining organelles inside the cells such as mitochondria and myoglobin that help the muscles utilize oxygen as an energy source.

While a sprinter can run long distances and vice versa, the body actually responds better to training when one adaptation is the main focus. An individual that trains for sprints during one month and then distance running for another month will achieve greater results than someone else who trains for both at the same time over the same period. When you are sprinting (short, anaerobic activity) and distance running (long, aerobic activity) at the same time, the blueprint is confusing and the body will not maximize its adaptation.

The take-home lesson is that while there may be several areas of training you wish to focus on, the SAID principle tells us to take those areas and stage them in our training. When training with weights, you may want to train with lighter weights (flexibility and range of motion) for a period of time, then switch to moderate weights (hypertrophy and muscle gain) and finally do a phase of heavy weights (strength). Focusing on each goal in a separate phase of training over time will produce better results over al than trying to achieve them all at once.

All phases of training can complement each other. While lifting weights may not increase your endurance and help you run longer distances, it can reduce the risk of sustaining an injury on those long runs. Strong muscles will help protect your joints. Focus on various areas of training and remember that each phase should have a specific goal or focus. Doing this will help you better reap the benefits of SAID.