Depending on the goal of the exercise, the exertion can be maximal, or sub-maximal.
Isometrics was first brought to the modern public’s attention in the early days of physical culture, the precursor to bodybuilding. Many of the great bodybuilders of the day used and incorporated isometrics into their training regimes. Perhaps the most famous of the isometric advocates was Charles Atlas. In his course he advocated a series of dynamic tension exercises which included isometrics. He had learned these exercises from the "Conscious Evolution" Course of Alois P. Swoboda. Atlas said "everything he knew he learned from A.P. Swoboda". Isometrics fell out of favor as it was discovered that many of the principal advocates were using steroids to enhance their gains. Charles Atlas' methods of self-resistance did not have traditional resistance limits as weight exercises do, as the tissue exercising against can provide greater resistance as it develops in tandem. His system was flawed in that there was no method of measuring progression; users were not motivated by measurable progress as assessment of increases in strength was subjective and lacked an empirical means of demonstrating progress.
In addition, there is a role for isometric exercise in the rehabilitation of people with joint disease, particularly where there are strong reasons to avoid bearing weight through a joint such as recent major joint surgery. One such example is isometric exercising of the Quadriceps Femoris Muscleof the thigh for people with disorders of the knee, or the muscles supporting the shoulder girdle for people with disorders of the shoulder joint
Isometric exercises have some differences in training effect as compared to dynamic exercises. While isometric training increases strength at the specific joint angles of the exercises performed and additional joint angles to a lesser extent, dynamic exercises increase strength throughout the full range of motion. Generally speaking however, people who train isometrically don't train through a full range of motion as the strength gained at the training joint angle is where they require it. While dynamic exercises are 5% better at enhancing the twitch force of a muscle than isometric exercises, isometrics are 32% better than dynamic exercises at increasing maximal muscle power.
Muscle strength training and weight loss from a combined isometric exercise and dietary program.(Clinical report)
Mar 01, 2007; ABSTRACT While many studies have examined the effect of diet and dynamic exercise on muscle strength and weight loss, none have...
US Patent Issued on Feb. 19 for "Isometric Exercise Apparatus and Storage Rack Therefor" (Canadian Inventor)
Feb 20, 2013; ALEXANDRIA, Va., Feb. 20 -- United States Patent no. 8,376,917, issued on Feb. 19."Isometric Exercise Apparatus and Storage Rack...