An acute throwing episode decreases shoulder internal rotation

Area of Science:

• Sports Medicine
• Biomechanics
• Orthopedics

Background:

• Throwing athletes often experience decreased glenohumeral internal rotation (GIR) and total arc of motion (TAM).
• The recovery timeline for GIR after throwing and the influence of pitching role remain unclear.
• External rotation (GER) may increase post-throwing, but its dynamic is less understood.

Purpose of the Study:

• To quantify rotational changes in the shoulder after a single throwing episode.
• To determine if these rotational changes return to baseline before the next throwing session.
• To investigate whether pitching role (starter vs. reliever) affects the magnitude of rotational change.

Main Methods:

• Forty-five pitchers (starters and relievers) participated in the study.
• Glenohumeral internal rotation (GIR) and external rotation (GER) were measured at five time points: pre-throwing, immediately post-throwing, and 24, 48, and 72 hours later.
• Total arc of motion (TAM) was calculated by summing GIR and GER.

Main Results:

• GIR significantly decreased from baseline and remained below baseline even 72 hours post-throwing.
• GER showed minimal changes, while TAM decreased by 72 hours.
• Although relievers exhibited greater absolute GIR, GER, and TAM, the degree of change over time did not differ between starters and relievers.

Conclusions:

• Glenohumeral internal rotation (GIR) is significantly affected for at least 72 hours after a single throwing episode.
• Pitching role does not influence the short-term (72-hour) changes in shoulder rotation after throwing.
• Conditioning and recovery strategies are recommended to mitigate post-throwing GIR deficits, and measurement timing within the pitching cycle is crucial for GIR studies.