Introduction Motor unit recruitment is the sequential activation of motor units to perform a certain task. In this lab we examined motor unit recruitment and muscle fatigue by electromyography (EMG) with dynamometry (DYN). When the motor unit in the muscle is activated signals are then generated, which result in muscle contraction. The impulse generated are a bit weak, yet can still be detected by the electrodes, EMG and is coupled by a measurements of power, DYN. When all the motor units reach its maximum strength the muscles will fatigue.
Finally, the objectives of this lab were to determine the maximum clench strength for the right and left hand. To observe, record and correlate motor unit recruitment with increase power of skeletal muscle contraction. As well, as to record the force produces by the clenching muscles and integrated EMG during fiber recruitment and inducing fatigue. Methods The lab equipment included a hand dynamometer, electrodes lead set and the computer program. We placed three electrodes to each forearm of the subject. First we began with the subject’s dominant forearm.
We recorded a cycle clench-release-wait, holding for two seconds and releasing for two seconds before beginning the next cycle. This is when the subject began to increment force as assigned (10, 20, 30 kg). Then the subject clenched the hand dynamometer with maximum force until the maximum displayed forced on the screen decreased to more than 50% then we suspended the recording. Then we connected the electrodes to the subject’s non-dominant forearm. Next we repeated the same steps as mentioned for the subject’s dominant forearm.
Finally, we analyzed the data by using the I beam cursor to measure the CH 1 (Force) mean, CH 3 (EMG) p-p and CH 40 (integrated EMG) mean for both the dominant and non-dominant forearm fore increasement segments. Finally, we measured the CH1 value and CH 40 delta T value for both forearms using the maximum force segment. We then calculated the 50% maximum clench forge for both the dominant and non-dominant forearm. Results During segment 1 and segment 3 data the clenched dynamometer recorded motor unit recruitment of force (kg) in increments (10, 20 and 30kg). At assigned force of 10kg the subjects clench force was 8. 4 kg, at 20kg the clench force was 17. 26kg and 30kg the clench force was 28. 14kg for the dominant forearm. The raw EMG from the dominant forearm started from 0. 65mV (10kg), 1. 69mV (20kg) and 28. 14mV (30kg). The integrated EMG value in the dominate forearm began with 0. 12mV then rose to . 196mV. The non-dominant arm rose but then failed to reach the last assigned force, 30kg. The clench force values reached 9. 44k for 10kg, for the17. 61kg for the clenched force 20kg, and only reached 23. 22kg for the fore clenched increment of 30kg. The raw EMG value for the non-dominant forearm began at 2. 1mV then increased to 2. 97mV and ended up at 3. 73mV. Integrated EMG began at 2. 89mV then dropped to 0. 36mV and ended at 0. 44mV. During Segment 2 and 4 muscles fatigue was measured with maximum clench forge (kg) for both dominant and non-dominant forearms. The dominant forearm had a maximum clench force of 28. 30 kg and the time of fatigue was 42 mV-s with a 14. 15 kg of force. While the non-dominant forearm maximum clench force was 19. 07 kg and time of fatigue of 24. 77mV-s with a 9. 54 kg of force. Discussion In this lab we correlated motor unit recruitment with increase power of skeletal muscle contraction.
From our data there was a correlation between grip strength and EMG, as the power increased the EMG also increased. Furthermore, the EMG is much greater at 30kg than 10 kg, as more motor units are recruited to conduct a more powerful contraction. During segment 1 and 3 we expected the subject’s dominant forearm had a higher EMG mean value than the non-dominant forearm, yet in the10kg and 20kg the non-dominant forearm had a higher mean value. Yet, the subject’s non-dominant arm did not reach the last 30kg force, while the dominant forearm reached a higher mean.
Showing that the sensory impulses for the subject’s non-dominant forearm recruited motor units have a more reliable clench force. In segments 1 and 4 we looked at muscle fatigue, when the energy supply does not meet the demand of the muscle. Form our data we observed that the dominant forearm had a greater clench force than the non-dominant forearm. As well, the dominant forearm took longer to fatigue at a 50% max clench force. Typically, as muscles begin to fatigue, less motor units will be firing which decreases the frequency of EMG signal.