The exercise in this book are not arbitrary. The come from EMG studies. EMG devices are used to measure how active a muscle group is during exercise. The level of activation, expressed as a percentage, determines how effective an exercise is. Before researchers test the exercised muscle, the subjects first perform an isometric contraction by contracting the muscle as hard as possible – usually without a load (weights). This is known as the maximal voluntary isometric contraction MVIC, so the value will be 100%. This is called normalization. Another normalization method is via performance of the actual movement at various angles, these are angles in which the muscle contracts the hardest.
Consequently, the researchers use the highest readouts after checking different angles from the movement being tested as their MVC (maximal voluntary contraction). Recall isometric means the muscle did not change length, so it’s static hence MVIC. As a result the two normalization methods are called static-MVIC and dynamic-MVC (Kellis E et al.)