Impact of 12-s Rule on Performance and Muscle Damage of Baseball Pitchers

INTRODUCTIONA recent US Major League Baseball (MLB) rule change requires baseball pitchers to deliver pitches within 12 s. PURPOSESTo examine the effect of three between-pitch rest intervals on throwing performance during a simulated seven-inning game and muscle damage during postgame recovery. DESIGNA randomized counterbalanced study. METHODSSeven intercollegiate pitchers threw 15 pitches per inning for seven innings with rest interval trials of 8, 12, and 20 s between pitches and 5 min between innings. Pitchers threw aimed fastballs at their best effort. Trials were separated by ≥2 wk. RESULTSProgressive decreases in pitching speed and accuracy below baseline (first inning of 20-s trial) occurred after fourth inning during the 8-s and 12-s trials, but not the 20-s trial. Plasma creatine kinase elevated 48 h later for the 8-s and 12-s trials (+105% and +75%, P < 0.01), but not the 20-s trial (+26%, no significance). A transient interleukin (IL)-6 surges immediately after the game for the 8- and 12-s trials (+265%, +128%, P < 0.01) above baseline. IL-6 reversed below the level of 20-s trial at 48 h after game, whereas IL-10 increased significantly above the level of 20-s trial. CONCLUSIONSUnder the same pitching load, decreasing rest interval from 20 to 12 s or less results in an early-onset performance loss during a game and increases in muscle damage and inflammation for more than 2 d after a game. Our data do not favor the current rule change in concern of keeping musculoskeletal health of pitchers.