Oliver et al. (2021) published a study to determine whether pitching a simulated softball game causes changes in the long head of the biceps tendon (LHBT) and whether those changes are related to pitching mechanics. Twenty-three female youth softball pitchers (average age 12 years) participated in the study. Before and immediately after throwing a simulated game of about 61 pitches, researchers used ultrasound imaging to measure the size of the biceps tendon. Motion capture technology was also used to record pitching mechanics, including trunk movement, stride length, center of mass, and shoulder joint forces. The researchers compared mechanics and tendon measurements before and after pitching and examined whether pitchers who developed greater tendon swelling also showed different movement patterns.
They found:
Biceps Tendon Changes
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Longitudinal biceps tendon thickness increased significantly after the simulated game (p = 0.006).
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The increase suggests an acute inflammatory response to pitching.
Even one game can produce measurable changes in the biceps tendon.
Pitch Speed
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Average pitch speed decreased from:
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46 mph in the first inning
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45 mph in the last inning (p < 0.001).
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Pitchers threw slightly slower as the game progressed.
Overall Mechanics
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There were no significant changes in:
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Shoulder kinetics
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Stride length
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Center of mass
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Most trunk movements
between the first and last inning.
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Most pitching mechanics remained consistent over one simulated game.
Trunk Rotation
Pitchers whose transverse biceps tendon thickness increased showed:
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Less change in trunk rotation at the start of the pitching motion.
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Pitchers without tendon thickening demonstrated greater changes in trunk rotation throughout the game.
Limited trunk rotation was associated with greater tendon changes.
Trunk Flexion
Pitchers whose tendon thickness increased also showed:
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Decreased trunk flexion at ball release.
Pitchers whose tendon thickness did not increase showed:
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Increased trunk flexion at ball release.
Less forward trunk flexion may increase stress on the biceps tendon.
Shoulder Forces
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No significant relationship was found between:
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Shoulder joint moments
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Biceps tendon changes.
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Mechanical positioning appeared to be more important than shoulder kinetics in this study.
Implications: The authors concluded that even one simulated softball game can cause measurable swelling of the long head of the biceps tendon in youth pitchers. This finding suggests that the tendon experiences enough stress during pitching to produce an acute inflammatory response, even when no injury is present. The study also found that pitchers who developed greater tendon changes tended to use less trunk rotation at the beginning of the pitch and less trunk flexion at ball release. These movement patterns may reduce the contribution of the core and force the shoulder and biceps tendon to absorb more stress. Although the changes in pitching mechanics were relatively small, they may become more important over repeated games and long seasons. The authors suggest that coaches should monitor trunk mechanics because changes in trunk movement may be an early sign of fatigue and increased injury risk. They also note that this study supports the need for pitch-count guidelines in youth softball since repeated pitching could increase tendon stress and eventually contribute to overuse injuries. The study was limited because it measured only one simulated game and did not directly assess fatigue, so future research should examine multiple games and tournament workloads.
Key Takeaways
This study provides strong evidence that:
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One game of pitching can produce measurable biceps tendon swelling.
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Reduced trunk contribution (less rotation and less flexion) is associated with greater tendon changes.
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The biceps tendon may serve as an early indicator of shoulder overload, even before pain develops.
Important Biomechanics Connection
This paper fits the kinetic-chain model well:
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Efficient trunk rotation and forward trunk flexion help transfer energy from the lower body to the arm.
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When trunk movement decreases, the shoulder and long head of the biceps tendon must absorb more of the workload.
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The observed tendon thickening likely represents an early response to increased mechanical stress, which, if repeated over many games or tournaments, could contribute to overuse injuries.
Also…
Every one of us works with women athletes which means this recent podcast on Perform by Dr. Andy Galpin is an absolute must listen. The podcast is with Dr. Lauren Colenso-Semple and discusses the differences in training men and women. Please check it out.
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