eccentric contraction

Examples of eccentric contraction in the following topics:

• Types of Muscle Contractions: Isotonic and Isometric

  • Isotonic muscle contractions can be either concentric or eccentric.
  • An eccentric contraction results in the elongation of a muscle while the muscle is still generating force; in effect, resistance is greater than force generated.
  • For example, a voluntary eccentric contraction would be the controlled lowering of the heavy weight raised during the above concentric contraction.
  • An involuntary eccentric contraction may occur when a weight is too great for a muscle to bear and so it is slowly lowered while under tension.
  • An isotonic concentric contraction results in the muscle shortening, an isotonic eccentric contraction results in the muscle lengthening.

• Impacts of Exercise on Muscles

  • Exercise involves a series of sustained muscle contractions of either long or short duration depending on the nature of the physical activity.
  • Muscle soreness, once thought to be due to lactic acid accumulation, has more recently been attributed to small tearing, or micro-trauma, of the muscles fibers caused by eccentric contraction.
  • With repeated cycles of eccentric contraction this soreness will be reduced.

• Creatine Supplementation

  • Exercise resulting in eccentric contractions at high loading can cause muscle soreness, indicative of muscle tearing, and reduced or impaired muscle function.
  • This is specifically caused by eccentric exercise altering muscle ultrastructure and sarcoplasmic reticulum functioning.
  • Creatine supplements, when used in the short-term, can increase performance during high intensity anaerobic exercise that requires short bursts of muscle contraction.
  • Phosphocreatine is an important source of energy-rich phosphate groups that can be added to available ADP to resynthesize ATP for muscle contractions.
  • Molecular structure of phosphocreatine donates the high energy phosphate group to ADP and acts as a short-term energy pool for muscle contractions.

• Exercise-Induced Muscle Damage

  • Exercise damages muscles due to eccentric and concentric muscle loading and often results in delayed onset muscle soreness (DOMS).
  • Exercise damages muscles due to eccentric and concentric muscle loading.
  • Resistance training, and particularly high loading during eccentric contractions, results in delayed onset muscle soreness (DOMS).
  • Acute inflammation of the muscle cells, as understood in exercise physiology, can result after induced eccentric and concentric muscle training.
  • Participation in eccentric training and conditioning, including resistance training and activities that emphasize eccentric lengthening of the muscle such as downhill running on a moderate to high incline, can result in considerable soreness within 24 to 48 hours, even though blood lactate levels, previously thought to cause muscle soreness, were much higher with level running.

• Interactions of Skeletal Muscles

  • Skeletal muscle contractions can be grouped based on the length and frequency of contraction.
  • The time between the stimulus and the initiation of contraction is termed the latent period, which is followed by the contraction period.
  • At peak contraction the muscle relaxes and returns to its resting position.
  • After contraction the muscle relaxes back to a resting level of tension.
  • If the frequency of these contractions increases to the point where maximum tension is generated and no relaxation is observed then the contraction is termed a tetanus.

• Velocity and Duration of Muscle Contraction

  • Skeletal muscle contractions can be broadly separated into twitch and tetanic contractions.
  • In a twitch contraction, a short burst of stimulation causes the muscle to contract, but the duration is so brief that the muscle begins relaxing before reaching peak force.
  • If the stimulation is long enough, the muscle reaches peak force and plateaus at this level, resulting in a tetanic contraction.
  • Twitch contractions are short in duration.
  • Tetanic contractions, which are long in duration, reach peak force and plateau.

• Mechanism and Contraction Events of Cardiac Muscle Fibers

  • The gap junctions spread action potentials to support the synchronized contraction of the myocardium.
  • In cardiac, skeletal, and some smooth muscle tissue, contraction occurs through a phenomenon known as excitation contraction coupling (ECC).
  • The actual mechanical contraction response in cardiac muscle occurs via the sliding filament model of contraction.
  • The pathway of contraction can be described in five steps:
  • This removal of the troponin complex frees the actin to be bound by myosin and initiates contraction.

• Abnormal Contractions of Skeletal Muscle

  • Involuntary muscle contractions are referred to as spasms, and can be due to abnormal activity of the nerve or the muscle.
  • In medicine, a spasm is a sudden, involuntary contraction of a muscle, a group of muscles, or a hollow organ, or a similarly sudden contraction of an orifice .
  • There are a variety of other causes of involuntary muscle contractions, which may be more serious, depending on the cause.
  • Examples of spasms include muscle contractions due to abnormal nerve stimulation, or abnormal activity of the muscle itself.
  • Spasmodic muscle contraction may be due to a large number of medical conditions, including the dystonias.

• Onset of Labor

  • Pre-labor, also called prodromal labor, consists of the early contractions and labor signs before actual labor starts.
  • In contrast, Braxton Hicks contractions should be infrequent, irregular, and involve only mild cramping.
  • When the contractions of labor begin, the walls of the uterus start to contract through stimulation by the release of the pituitary hormone oxytocin.
  • The contractions cause the cervix to widen and begin to open.
  • As contractions become closer and stronger the cervix will gradually start to dilate.

• How Skeletal Muscles Produce Movements

  • Muscles exist in groupings that work to produce movements by muscle contraction.
  • Agonist muscles produce the primary movement or series of movements through their own contractions.
  • Contraction will move limbs associated with that joint.
  • In this sense, the bone acts as a lever with the attached muscle fiber's contraction, driving movement.
  • Synergists are useful because they fix certain joints to allow a range of contractions, in contrast with the sheer power of an agonist contraction that limits the range of possible movements.