Fatigue of the Dynamic Stabilizers of the Medial Elbow in Baseball Pitchers.

Background: The flexor carpi ulnaris and flexor digitorum superficialis are thought to provide dynamic stability to the medial elbow during pitching. High medial elbow stress during pitching fatigues these dynamic stabilizers of the medial elbow. This fatigue of dynamic stabilizers could leave the ulnar collateral ligament more vulnerable to the stress of pitching.

Purpose/hypothesis: The purpose of this study was to identify the onset of fatigue in the dynamic elbow stabilizers during a pitching performance. It was hypothesized that middle finger (MF) and ring finger (RF) fatigue during a pitching performance would occur earlier and be more substantial than grip and 3 finger grip fatigue.

Study design: Descriptive laboratory study.

Methods: Eighteen baseball pitchers (age, 17 ± 4 years) threw 4 innings of a simulated game (16 pitches per inning plus 5 warm-up pitches per inning). Before the game and after each inning, MF flexion, RF flexion, and grip strength were recorded. A standard full grip (FG) and a modified 3-finger grip (3FG) test were employed. Fatigue was classified as marked (>20% loss), moderate (10%-20% loss) or minimal (<10% loss).

Results: MF strength was greater on the dominant versus nondominant hand (7%; P = .04). There was no hand dominance effect for the other 3 tests (RF, P = .15; FG, P = .79; 3FG, P = .90). The fatigue responses differed significantly between tests (P < .001). After the fourth inning, MF fatigue (21%) was greater than RF (7%; P < .001), FG (5%; P < .002), and 3FG (5%; P < .001) fatigue. MF fatigue was evident early and was progressive. After the first inning, 4 pitchers (22%) had marked MF fatigue and 3 (17%) had moderate MF fatigue. By the end of the fourth inning, 10 pitchers (56%) had marked MF fatigue and 6 (33%) had moderate MF fatigue. By contrast, only 5 pitchers (28%) had marked RF fatigue after 4 innings, and only 3 pitchers (17%) had marked FG or 3FG fatigue. Pitchers with high valgus elbow torque during pitching had greater MF fatigue than pitchers with lower elbow valgus forces (22% vs 10%; P = .045).

Conclusion: By the end of the fourth inning, 10 pitchers (56%) had marked MF fatigue and 6 (33%) had moderate MF fatigue. MF fatigue may be indicative of medial elbow dynamic stabilizer fatigue in pitchers.

Clinical relevance: We recommend finger flexor strength training to help support the medial stabilizers of the elbow during pitching. In the future, MF fatigue testing could be an "in-game" measure of pitcher fatigue.