Human Physiology with Vernier 18 - 1 Computer 18 EMG and Muscle Fatigue Voluntary muscle contraction is the result of communication between the brain and individual muscle fibers of the musculoskeletal system. A thought is transformed into electrical impulses which travel down motor neurons (in the spine and peripheral nerves) to the neuromuscular junctions that form a motor unit (see Figure 1). The individual muscle fibers within each motor unit contract with an “all or none” response when stimulated, meaning the muscle fiber contracts to its maximum potential or not at all. The strength of contraction of a whole muscle depends on how many individual fibers are activated, and can be correlated with electrical activity measured over the muscle with an EMG sensor. Regular exercise is important for maintaining muscle strength and conditioning. The most common form of non-aerobic exercise is isotonic (weight training). In isotonic exercise, the muscle changes length against a constant force. In isometric exercise the length of the muscle remains the same as greater demand is placed on it. An example of this is holding a barbell (or suitcase) in one position for an extended period of time. Muscle fatigue occurs with both forms of exercise. In this experiment, you will use a Vernier Hand Dynamometer to measure maximum grip strength and correlate this with electrical activity of the muscles involved as measured using the Vernier EKG Sensor. You will see if electrical activity changes as a muscle fatigues during continuous maximal effort. Finally, you will observe the results of a conscious effort to overcome fatigue in the muscles being tested. Figure 1 Important: Do not attempt this experiment if you suffer from arthritis, or other conditions of the hand, wrist, forearm, or elbow. Inform your instructor of any possible health problems that might be exacerbated if you participate in this exercise.
18 - 2 Human Physiology with Vernier Computer 18 OBJECTIVES In this experiment, you will Obtain graphical representation of the electrical activity of a muscle. Correlate grip strength measurements with electrical activity data. Correlate measurements of grip strength and electrical activity with muscle fatigue. Observe the effect on grip strength of a conscious effort to overcome fatigue. MATERIALS computer Vernier Hand Dynamometer Vernier computer interface Vernier EKG Sensor Logger Pro electrode tabs PROCEDURE Select one person from your lab group to be the subject.
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