Functional isometric training involves holding static muscle contractions to build strength without wear and tear on joints. It recruits all muscle fibers at once and can increase strength, particularly in weak ranges of motion. The benefits include maximal muscle fiber recruitment, increased lactic acid tolerance, hypertrophy, injury reduction, improved posture and mental toughness. Isometrics should be periodized and progressed from yielding to overcoming to dynamic efforts to optimize training adaptations over time.