Validity of Pitch Velocity and Strike Percentage to Assess Fatigue in Young Baseball Pitchers

Although coaches chart pitch velocity (PV) and strike percentage (SP) to assess pitcher fatigue levels, the validity of these tools has not been quantified in young pitchers. The purpose of this study was to compare PV and SP across levels of perceived fatigue in young pitchers. Data describing PV, first strike percentage (SP1st), total strike percentage (SPT) and perceived fatigue (PFL) throughout a simulated performance were recorded for 14 pitchers. Differences within PV, SP1st, and SPT were compared across PFLs utilizing repeated measures analysis of variance. PF was the independent variable and PV, SP1st, and SPT were the dependent variables. Results indicated no differences in PV across fatigue levels. SPT increased significantly from PFL 0 to PFL 1 (p = 0.0250). SP1st also increased significantly between PFL 0 and PFL 1 (p = 0.0040) before decreasing significantly for PFL 2 (p < 0.001). These results indicate that the tracking of PV may not be a valid tool for assessing fatigue. However, tracking both SP1st and SPT may be valid tools for assessing fatigue and may provide coaches with evidence of the onset of fatigue.