Question

Lifting the four loads in ascending order produces larger EMG signals as the loads get heavier.

1. Discuss how you think the EMG signals for each load might change if the loads were lifted in descending order, or in random order.

2. Explain your answer with reference to the underlying physiological mechanisms associated with muscle strength, motor unit activity, and muscle fatigue.

Answer 1

1) The amplitude of EMG will increase with increase in load up to a maximum limit for that muscle. Beyond the maximum limit, the amplitude of EMG remains constant. If loads were lifted, the amirude of EMG will remain same till a threshold point after which it begin to decrease. If the loads were lifted in descending order, the decrease in EMG amplitude follows a uniform decrease in slope and when the loads were lifted randomly, the decrease in EMG amplitude will not be uniform.

2) Each load recruites a different number of motor units according to its strength. The amplitude of EMG increases in proportion to the number of motor units recruited. Muscle fatigue occurs after a threshold level beyond which increase in load does not increase the amplitude of EMG.