Isotonic exercises are the most common type of activity or form of muscle work used during fitness programs, workouts, and routines.  ‘Iso’ means no change, while ‘tonic’ applies to the tension or tone of the muscle. Thus an isotonic movement, exercise, or contraction happens when the tension on a muscle, muscles, or muscle group, remains constant ‘Iso’ but the length changes or there is movement in a joint, joints, and the muscle(s).

Isotonic differs from an Isometric exercise when the muscle length, or the ‘metric’, does not change ‘Iso’ against a constant resistance, or there is no movement of joints or muscles. Planks and their variations are good examples of Isometric exercises. Almost all exercises and day-to-day activities involve components of Isotonic muscle work; running, weight lifting, resistance bands, bicycling, swimming, racquet sports, basketball, and rowing.

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The benefits of Isotonic exercises

include increased metabolism, weight loss, increased strength, sports performance, speed, agility, and muscle endurance, improved bone density, reduced risk of Type II Diabetes, osteoporosis, and heart disease, rehabilitation from injury, and stress reduction. There are two components to Isotonic exercises: Concentric and Eccentric muscle activation.

Concentric muscle activation

occurs during the shortening part of an Isotonic movement or contraction when the tension on a muscle increases while the muscle SHORTENS, such as the upward part of a biceps curl, the work performed by the quadriceps while climbing stairs, or when lifting any load.

Concentric exercises reduce the angle at a joint, are commonly voluntary, accelerate movement, the amount of force the muscle generates is not necessarily its maximum, but enough to complete the movement.Eccentric muscle activation, sometimes referred to as negative training, occurs during the lengthening part of an Isotonic movement or contraction when the tension on a muscle increases as the muscle LENGTHENS.

Lowering a weight, going down stairs and hills, the downward part of a squat, and sports that require opposing forces, braking, speed, or deceleration such as tennis and pitching a ball require extensive eccentric work.  The tension on the muscle may be more than the muscle generates, may be involuntary, and often responsible for injury and delayed muscle soreness.

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