The interaction of force and repetition on systemic inflammatory cytokine response in a rat model

In this paper, we describe the effects of force and repetition on systemic inflammatory responses in a voluntary rat model of repetitive reaching and handle pulling. Specifically, we examine the interaction of force and repetition on serum cytokine expression, which we believe may be a response to fatigue failure damage in musculoskeletal tissues. Young adult, Sprague-Dawley rats performed a handle-pulling task for 12 weeks at 4 different repetition and force levels: 1) low repetition with low force (LRLF), 2) low repetition with high force (LRHF), 3) high repetition with low force (HRLF), and 4) high repetition with high force (HRHF). Force x repetition interactions were observed at week 12 for serum cytokines including TNFalpha (p = 0.003), IL-1alpha (p < 0.0001), and IL-1beta (p < 0.0001). The pattern of interaction observed with serum cytokines in this study mirrors the force-repetition interaction observed in epidemiological studies of musculoskeletal disorder risk (Gallagher and Heberger, 2013).