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This study tested the hypothesis that activation of nociceptive muscle afferent fibers would be linked to an increased excitability of the human jaw - stretch reflex and whether this process would be sensitive to length and velocity of the stretch .
 nociceptive muscle
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 nociceptive muscle