The Impact Of Experimentally-Induced Muscle Pain on the Performance of Single-Limb and Whole-Body Exercise Tasks

Exercise-induced pain (EIP), which is often accompanied by fatigue, has been suggested to have a limiting or regulatory role during endurance performance, with the ability to tolerate or overcome pain a determinant of success. Despite this, the potential impact of EIP on endurance performance is not well understood, partly because prior research investigating this relationship has employed methods of pain induction that are inappropriate in representing the transmission and experience of EIP.

The focus of this thesis was to investigate the role of EIP on exercise performance through the experimental induction of muscle pain using a model that closely replicates the experience of naturally occurring EIP. There were two overarching main aims of this thesis which were addressed in four experimental studies. The first aim was to investigate and confirm the hypertonic saline model as a suitable experimental method of muscle pain induction to investigate the fatigue-pain relationship. The second aim was to apply the hypertonic saline model to evaluate the impact of EIP on exercise tasks relevant to endurance performance.

When combined with muscle contraction, hypertonic saline injected into the vastus lateralis induced a muscle pain that felt like naturally occurring EIP of a greater contraction intensity (Study 1). Applied both unilaterally and bilaterally at rest, is was found that this method is unlikely to directly elicit a confounding response that may influence exercise performance (i.e. exercise pressor reflex) (Study 3). When applied to exercise, the increased muscle pain from the hypertonic saline impaired both the accuracy of single-limb isometric torque reproduction (Study 2) and time to task failure performance (i.e. an accelerated progression of fatigue) in both single-limb (Study 1) and whole-body exercise tasks (Study 4).

In summary, the findings of this thesis provide evidence and advances understanding of the potential limiting impact of EIP on endurance performance tasks. This thesis also has practical application in providing a novel experimental model that can be applied in future investigations of experimental muscle pain and the fatigue-pain relationship.