What does overload mean?
The overload principle refers to the workload or demand put on the body. The demand strains the body systems (cardiovascular, muscular, respiratory) in a good way. The body systems respond to the demand by adapting. This means that the heart will pump more blood, the muscles will become firmer and stronger, and the lungs will supply more oxygen. When you want to increase your fitness level or your strength, you have to provide this demand on your body systems to see them improve.