Jack, a student in BIO 131, is the subject for this lab and has his EMG recorded

Question

Jack, a student in BIO 131, is the subject for this lab and has his EMG recorded during a maximal contraction. To achieve a maximal contraction, he must lift 45 pounds. Six months later, after working out steadily and maintaining a healthy diet, Jack?s muscles are notably bigger. He decides to try to elicit a new maximal contraction (and record the EMG), and is now able to Lift 60 pounds. Questions: 1. (2 Points) Compare the EMG recordings for Jack?s maximal contraction before and after his 6 month training sessions. Circle the correct answer below: a) The EMGs will have the same amplitude b) The before [MG will have a larger amplitude c) The after EMG will have a larger amplitude 2. After his muscle growth, G to look like if he lifted 45 pounds as he did before? : motor unit recruitment. 3. Why were Jack?s muscles notably bigger after his 6 month training period? What caused the increase in muscle size?

Explanation / Answer

1.) c

2.) EMG will have less amplitude because low level of muscle contraction will require less strength that will result in less amplitude.

The functional unit of muscle is the motor unit (MU), which consists of an alpha motor neuron and all fibers innervated by it. Muscle fibers are the structural unit of contraction. One UM can have from 3 to 2000 muscle fibers, depending on the degree of control and strength required by the muscle: muscles that control fine movements and require precise but low strength have fewer fibers per MU, whereas the large muscles that control large rmovements requiring greater strength, may contain 100 to 1000 fibers per MU.

Motor unit recruitment may be defined as "the successive activation of the same and additional motor units with increasing strength of voluntary muscle contraction."The central nervous system can increase the strength of muscle contraction by the following:

Increasing the number of active motor units (ie, spatial recruitment)

Increasing the firing rate (firing frequency) at which individual motor units fire to optimize the summated tension generated (ie, temporal recruitment)

Both mechanisms occur concurrently. The primary mechanism at lower levels of muscle contraction strength is the addition of more motor units, but the firing rate of the initially recruited motor units also increases. When nearly all motor units are recruited, increase in firing frequency becomes the predominating mechanism to increase motor strength.

3.) A range of stimuli can increase the volume of muscle cells. Muscle size increases due to hypertrophic adaptation and an increase in the cross section area of individual muscle fibers. Intensive exercise impacts more on the strength influencing fast twitch type II fibers, therefore the increase in muscle size is accompanied by greater strength.

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