TNF and inflammatory response: This model proposes that excessive musculoskeletal stress (two or three training sessions per day for several weeks) in combination with insufficient recovery (sleep, nutrition, psychological down time) leads to chronic musculoskeletal inflammation and the release of the following pro-inflammatory cytokines: interleukin-6 (IL-6), interleukin-1-beta (IL-1β), and tumor necrosis factor-alpha (TNF-α).