Which of the following refers to a static muscle contraction?

Type of muscle contraction?

• When a basketball player lands back on the court following a dunk they contract their quadriceps to resist the knee flexion torque caused by the impact of the landing and slow the speed of the landing. If the player is contracting their quadriceps while their knee flexes, what type of contraction is this? It's not concentric.

• Answer:

  A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle cell (called a muscle fiber) lengthens or shortens. Locomotion in most higher animals is possible only through the repeated contraction of many muscles at the correct times. Contraction is controlled by the central nervous system comprised of brain and spinal cord. The brain controls voluntary muscle contractions, while the spine controls involuntary reflexes. For voluntary muscles, contraction occurs as a result of conscious effort originating in the brain. The brain sends signals, in the form of action potentials, through the nervous system to the motor neuron that innervates the muscle fiber. In the case of some reflexes, the signal to contract can originate in the spinal cord through a feedback loop with the grey matter. Involuntary muscles such as the heart or smooth muscles in the gut and vascular system contract as a result of non-conscious brain activity or stimuli endogenous to the muscle itself. Other actions such as locomotion, breathing, chewing have a reflex aspect to them; the brain will start the contractions, but continuation of the movements can become reflexive. There are three general types of muscle contractions: skeletal muscle (voluntary and involuntary) contractions heart muscle (involuntary) contractions smooth muscle (involuntary) contractions. Skeletal and cardiac muscle are called striated muscle because of their striped appearance under a microscope which is due to the highly organized alternating pattern of A band and I band. For skeletal muscles, the force exerted by the muscle is controlled by varying the frequency at which action potentials are sent to muscle fibers. Action potentials do not arrive at muscles synchronously, and during a contraction some fraction of the fibers in the muscle will be firing at any given time. Typically when a human is exerting a muscle as hard as they are consciously able, roughly one-third of the fibers in that muscle will be firing at once, but various physiological and psychological factors (including Golgi tendon organs and Renshaw cells) can affect that. This 'low' level of contraction is a protective mechanism to prevent avulsion of the tendon - the force generated by a 100% contraction of all fibers is sufficient to damage the body.