Human and animal experimental models of acute and chronic muscle pain: intramuscular algesic injection

Intramuscular injection with algesic substances has defined the nature of local and referred muscle pain, provided insights into the genetic basis for pain sensitivity, revealed interactions between muscle pain and motor function, and identified biologically based sex differences. Endogenous algogens have contributed significantly to the understanding of peripheral mechanisms while more aggressive exogenous agents have revealed central neural mechanisms, particularly those related to activation and neuroplastic changes involved in the maintenance of chronic muscle pain. Future studies utilizing intramuscular injections would benefit from strategies that bridge results obtained in animal experiments with data from human clinical and experimental muscle pain studies.