The size of motor units can vary from as few as 4 or 5 muscle fibers to as many

Question

The size of motor units can vary from as few as 4 or 5 muscle fibers to as many as 2000. The strength of a muscle Contraction depends on the number of motor units stimulated. If the muscle contracts slowly and with little force, relatively few motor units have been activated. If the muscle receives more frequent nerve impulses, additional motor units are activated and the muscle contracts faster and with more power. The activation of increasing numbers of motor units is called motor unit recruitment. Rest forearm of your dominant side comfortably on the laboratory bench with your palm directed superiorly. Grasp a 2.25-kg (about 5-lb) dumbbell or another object of similar weight that is easy to hold. Flex your forearm with the minimum amount of force (muscle tension) required to lift it. Keep your elbow on the bench at all times. Repeat step 2 several times, increasing the force of contraction with each lift. On the last turn, lift the dumbbell by applying peak muscle tension. Describe your results in terms of motor unit recruitment.

Explanation / Answer

according to the activity the movement of the hand while lifting the dumble at the begining is slow that means the activitation of motor neurons is less and the motor unit recruitment is low and due to to the continuous lifting of the dumble and more frequent nervre impulses in the hand more motor neourons are activated. on the last turn by applying peak muscle tension the more more neurons are activated as the flexibility is upto 2000 and so the motor unit recruitment with be high.

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