Which of these techniques measures muscle tension as an index of pain?

Question

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Electromyography (EMG) can be used to measure the electrical activity in muscles, which increases with muscle tension, providing an index of pain. Thermography (B) measures skin temperature changes and is not specific to muscle tension. Blood flow in the temporal artery (C) and heart rate (D) are related to physiological changes associated with pain but are not direct measures of muscle tension.

Which of These Techniques Measures Muscle Tension as an Index