Dynamic Exercise and how to muscle work

A dynamic muscle contraction causes joint movement and excursion of a body segment as the muscle contracts and shortens (concentric contraction) or lengthens under tension(eccentric contraction).

Dynamic Exercise—Concentric and Eccentric

concentric exercise

 shortening of the muscle occurs as an external force (resistance) is overcome, as when lifting a weight.

 eccentric exercise

lengthening of the muscle as it attempts to control the load, as when lowering a weight.

Eccentric contractions also act as a source of shock absorption during high-impact activities.

During concentric and eccentric exercise, resistance can be applied in several ways: 

   (1) constant resistance,such as body weight, a free weight, or a simple weight pulley system; 

(2) a weight machine that provides variable

    resistance;

   (3) an isokinetic device that controls the

      velocity of limb movement.

 Isokinetic devices

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A combination of concentric and eccentric muscle action is evident in countless tasks of daily life, 

→such as walking up and down inclines, 

→ascending and descending stairs,

→ rising from a chair and sitting back down,

→ or picking up or setting down an object

Eccentric trainning benifical more then concentric trainning 

Eccentric training, in particular, is thought to be an essential component of a rehabilitation or conditioning program to reduce the risk of musculoskeletal injury or reinjury during activities that involve high-intensity deceleration and quick changes of direction.

Regimens of exercise that emphasize eccentric loading,such as plyometric training (stretch-shortening drills) or fast-velocity, eccentric isokinetic training.

Muscle Work

When a load is lowered, the force exerted by the load is controlled not only by the active, contractile components of muscle but also by the connective tissue in and around the muscle. In contrast, when a weight is lifted, 

only the contractile components of the

     muscle lift the load. 

With a concentric contraction, greater numbers of motor units must be recruited to control the same load compared to an eccentric contraction,

suggesting that concentric exercise has less mechanical efficiency than eccentric exercise. 

Consequently, it requires more effort by a patient to control the same load during concentric exercise than during eccentric exercise. 

As a result, maximum resistance during the concentric phase of an exercise does not provide a maximum load during the eccentric phase.

Velocity of exercise.
 The velocity at which concentric or eccentric exercises are performed directly affects the force-generating capacity of the neuromuscular unit.

At slow velocities with a maximum load, an eccentric

contraction generates greater tension than a concentric

contraction.

At slow velocities, therefore, a greater load

(weight) can be lowered (with control) than lifted.

 As

the velocity of exercise increases, concentric contraction

tension rapidly and consistently decreases, 

whereas

eccentric contraction forces increase slightly but then rapidly

reach a plateau under maximum load conditions

Energy expenditure.

 Eccentric exercise consumes less oxygen and energy stores than concentric exercise against similar 

 loads. 

Therefore, the use of eccentric activities

such as

downhill running may improve muscular

endurance 

more efficiently than similar concentric activities because

muscle fatigue occurs less quickly with eccentric exercise.

Cross-training effect. 

Concentric and eccentric training has been shown to cause a cross-training effect, that is,a slight increase in strength in the same muscle group of the opposite, unexercised extremity

Exercise-induced muscle soreness. 

Repeated and rapidly progressed eccentric muscle contractions against resistance are associated with a significantly higher incidence andseverity of delayed-onset muscle soreness (DOMS) than

   resisted concentric exercise.

Dynamic Exercise—

Constant and Variable Resistance

Dynamic constant external resistance (DCER)

 exercise is a form of resistance training where a limb moves through a ROM against a constant external load, provided by free weights such as a handheld or cuff weight,  weight machines, or pulley systems.

Variable-Resistance Exercise

Variable-resistance exercise, a form of dynamic exercise, addresses the primary limitation of dynamic exercise against a constant external load (DCER exercises). 

Specially designed resistance equipment imposes varying levels of resistance to the contracting muscles to load the muscles more effectively at multiple points in the ROM.

The resistance is altered throughout the range by means of a weightcable system that moves over an asymmetrically shaped cam, by a lever arm system, or by hydraulic or pneumatic mechanisms. How effectively these machines vary the resistance to match muscle torque curves is questionable.

Dynamic exercise with elastic resistance products

(bands and tubing) can also be thought of in the broadest

sense as a variable-resistance exercise because of the

inherent properties of the material and its response to

stretch.

Isokinetic Exercise

Isokinetic exercise is a form of dynamic exercise in which the velocity of muscle shortening or lengthening and the angular limb velocity is predetermined and held constant by a rate-limiting device known as an isokinetic dynamometer .

The term isokinetic

refers to movement that occurs at an equal (constant) velocity.

Characteristics of Isokinetic Training

Constant velocity. →

 The velocity of muscle shortening or lengthening is preset and controlled by the unit and remains constant throughout the ROM.

Range and selection of training velocities.

 Isokinetic training affords a wide range of exercise velocities in rehabilitation from very slow to fast velocities.