My research follows two primary lines of investigation: 1) Factors that contribute to pain heterogeneity including: sex, psychological traits, genetics, activity level, etc. To study this question, we use experimental pain models in humans: intramuscular infusion of an acidic phosphate buffer into the anterior tibialis muscle, cold pressor task (hand immersion in ice water), or isolated muscle fatigue (isometric contraction to failure). We also utilize surveys of pain perceptions and self-reported personality responses. In particular we are focusing on why women appear to have a higher risk of referred pain with the muscle pain model (~80%) whereas men are less likely to experience referred pain (~45%) despite similar local infusion-site pain. 2) Strength and fatigue research: We are working with the Virtual Soldier Research (VSR) group to develop mathematical models of normal strength and fatigue, using both static and dynamic strength indices. In addition we are studying whether clear differences in fatigue with aging, by muscle group, or between sexes exist, and the potential interactions between these variables.