Benefits of Isokinetic Muscle Contraction

Specialized Training for Sports Performance and Rehabilitation

Man using an isokinetic dynamometer
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An isokinetic muscle contraction is one in which a muscle shortens as it contracts but, unlike an isotonic contraction, does so at a consistent rate of speed. It is the rate of speed, in fact, that separates it from other types of muscle contraction and requires a specialized piece of equipment, known as an isokinetic dynamometer, to produce.

Outside of a gym or physical rehabilitation setting, isokinetic contractions are rare. The closest example may be swimming the breaststroke in which water provides constant resistance to the movement of your arms.

Benefits

Despite being uncommon, isokinetic contractions are believed to build muscle mass, endurance, and strength faster than any other type of contraction. They are also used by physical therapists to treat certain injuries, both physical and neurological.

According to a study published in the Journal of Physical Therapy Science, isokinetic training can be used to treat knee arthritis, plantar flexor injuries, and movement disorders associated with stroke and hemiplegia, among other things.

When used for exercise, isokinetic movements allow muscles to exert maximum force within the range of joint movements at a constant speed. The benefits of isokinetic movements vary by the speed (velocity) by which they are performed. Low-velocity exercises generally increase muscle strength, while high-velocity exercises are mainly used for the recovery of muscle endurance following an injury.

Isokinetic Dynamometer

Whether for strength training or rehabilitation, isokinetic contractions require a specialized piece of equipment, known as an isokinetic dynamometer, the controls the resistance placed on a muscle as well as the velocity of the movement.

Most dynamometers are designed for the knees or elbows, but there are some that can be used for wrists, ankles, hip flexors, and other muscle groups. The machines look similar to those found at the gym but are mechanically controlled and able to measure muscle performance on a digital monitor.

Isokinetic dynamometers use hydraulic or motor-controlled instruments pre-set to a specific velocity. To use the dynamometer, your arm or leg would be strapped onto a levered arm with the joint (such as the elbow or knee) placed squarely at the axis. You would then be asked to push as hard as you can against the arm. The dynamometer, in turn, would resist the movement so that the velocity remains constant.

Measuring Performance

The isokinetic dynamometer not only trains a muscle effectively, but it can also be used to track your progress over time.

The rotational force placed on the levered arm, known as torque, is a reliable measurement of muscle performance (i.e., the "strength" of your muscle). By gradually increasing the resistance over time while keeping the velocity the same, you would not only increase your muscle strength but be able to classify those gains with a numeric value. This is especially important for professional athletes.

For example, if you are able to move the levered arm one foot (0.3 meters) with 100 pounds (27.7 kilograms) of force, the torque would be 100 pounds per foot (or 8.31 kilograms per meter). With this baseline value in hand, you can measure changes in performance and determine how effective or ineffective a training program is.

Almost any piece of gym equipment, from stationary bikes to pull-down machines, can be customized for isokinetic training. Most machines are found either in rehabilitation centers and specialized sport training facilities. Professional sports franchises also often purchase them for their players.

Other Types of Contraction

Isokinetic contractions are only one of four types of contraction that move skeletal muscles, enabling mobility and physical movement. The other types of contractions include:

  • Concentric contractions cause muscles to shorten, thereby generating force. They occur during the lifting phase of an exercise, including the upward movement of a push-up, the lifting of a barbell, or the pulling motion of a seated cable row.
  • Eccentric contractions are the counterpart to concentric contractions. Rather than compelling a force, they oppose a force as a muscle lengthens. Examples including lowering yourself during a sit-up, pull-up, or a triceps dip.
  • Isometric contractions are those that do not cause any movement of a joint. Examples include pressing your arms against a stationary wall, holding yourself in a plank position, or doing a wall-sit to build your quads.
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