THE SPORT METHOD:
Specificity. Progression. Overload. Reversibility. Technique.
Specificity: To develop a particular fitness or skill component, you must perform exercises designed specifically for that component; this is the broad principle of specificity. Weight training will develop muscular strength but will not be very effective in improving flexibility. A well-rounded exercise program includes all components of fitness designed to improve different parts of the body or towards specific sport activities.
Progression: Progression and Overload are typically mentioned together. We like to look at these individually. Progression is critical since exercising at the same levels will not provide adaptations and can lead to a plateau.
Overload: We've mentioned this before, but it is a critical component of training; Your body is adaptive. Skeletal muscle is adaptive. You have to challenge a muscle to do more than it currently can in order for it to adapt. Progression alone can, perhaps, increase muscular endurance, but without overloading the muscle groups you may not increase muscular strength.
Reversibility: Again, the body is adaptive. You can adapt to high levels of exercise, and you can also adapt to lesser levels of exercise (particularly with cardio). Muscular gains can take a little longer to lose. Cardio and cellular fitness levels can decline more quickly. Maintenance requires a planning.
Technique: Focus on form. Proper form and technique, whether weightlifting, running, stretching etc. prevents injury and improves results. Technique includes proper warm up and proper cool down, both of which are essential to a quality fitness program.