We investigated the relationship between CSA of FPMs and MEJS in healthy baseball players on each side and aimed to contribute to the development of FPMs training methods for pitching elbow injuries.
Fourteen male university baseball players with no history of throwing elbow disorders were included in this study. MEJS (mm) was measured under 2 conditions, resting and ball grasping, using an ultrasonography (SONIMAGE MX1, KONICA MINOLTA, Japan) under 30 N valgus stress. The CSA of the FPMs (mm²) was measured for flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor digitorum profundus (FDP) and pronator teres (PT). Narrowing rate of MEJS was defined as the difference between the MEJS of the resting and ball grasping conditions at 30 N load was divided by the MEJS of the ball grasping condition. Pearson's correlation coefficients were conducted to calculate the relationship between the CSA of each FPMs on the throwing and non-throwing sides. Furthermore, multiple regression analysis was performed with the narrowing rate of MEJS as the dependent variable and each FPMs as the independent variable.
On the throwing side, a significant positive correlation was found between the narrowing rate of MEJS and the CSA of FDS and FDP (r=0.75, p0.01; r=0.50, p0.05). On the non-throwing side, there was a significant positive correlation between narrowing rate of MEJS and CSA of FCU, FDS and FDP (r=0.48, p0.05; r=0.55, p0.05; r=0.46, p0.05). Narrowing rate of MEJS was significantly associated with the CSA of FDS on the throwing side (β=0.82, p0.01).
The results of this study showed that the contribution of the FCU was absent and that of the FDS was relatively greater on the throwing side compared to the non-throwing side. In players with throwing elbow disorders, repetitive throwing can be supposed to cause ulnar neuropathy and muscle atrophy of the FCU. The results of the present study suggest that the contraction force to narrow the MEJS was reduced in relation to the CSA of the FCU on the throwing side in healthy athletes. This indicates that FDS developed as an adaptation to pitching and pitching may cause a reduction in muscle function, such as contraction of the FCU, that precedes changes in muscle morphology.
The development of FDS is an adaptation of healthy players, and there is a possibility that it can help to replace the loss of function of FCU.
Ultrasonography
Throwing elbow disorders
