Whole-body Muscle Activity During Baseball Pitching Exercise
Authors: Takata Yasushi , Nakase Junsuke , Shimozaki Kengo , Tsuchiya Hiroyuki 
Published: July 2018

Objectives: Electromyography (EMG) has been used for evaluating skeletal muscle activity during pitching. However, when using EMG, it is difficult to observe the influence of a movement on skeletal muscle activity in deep lying regions of the trunk and extremities. Therefore, at present, only partial investigations into the upper limbs and throwing side have been performed in pitchers. Furthermore, since electrodes and lead wires may interfere with normal motion, it is difficult to conduct experiments that truly replicate a real-world pitching environment. Some studies have utilized 18F-fluorodeoxyglucose- positron emission tomography (FDG-PET) to display cumulative muscle activity during exercise. Glucose metabolism measured by FDG-PET demonstrates a high correlation with intensity of muscle activity and its reliability as an index for measuring muscle activity has been confirmed. This study aimed to evaluate whole body skeletal muscle activity during a pitching exercise by using positron emission tomography-computed tomography (PET-CT). Methods: The study was performed on 10 uninjured, skilled adult pitchers, who were active at a college or professional level (mean ± standard deviation [SD] age, 21.5±3.7 years; height, 175.9±3.4 cm; weight, 74.7±5.2 kg; body mass index, 24.2±1.8). Each participant threw 40 balls at full power for 20 min before 37 MBq of FDG was injected intravenously. Additional 40 balls were then pitched at full power for another 20 min, followed by 25 min of rest in a sitting position. PET-CT images were obtained 50 min after FDG injection. Regions of interest were defined within 72 muscles. The standardized uptake value (SUV) of FDG by muscle tissue per unit volume was calculated, and the mean SUV of the pitchers was compared with that of a healthy adult control group (mean ± standard deviation [SD] age, 28.8±3.5 years; height, 170.4±4.6 cm; weight, 69.6±9.9 kg; body mass index, 23.88±3.0) who restricted exercise and only performed activities of daily living before measuring FDG accumulation. Statistical analysis was performed using a Mann-Whitney test, with a level of significance as p <0.05. Results: Whole-body PET images of the pitchers (Figure 1) show significant increase in glucose metabolism in the muscle groups in the fingers and toes. In addition, the hamstrings on the throwing side and the iliacus, tensor fasciae latae, sartorius on the non-throwing side showed increases in glucose metabolism (Table1). There was however no increase in glucose metabolism either in the rotator cuff or in the trunk muscles. Conclusion: In the present study, we discovered the accumulation of FDG in the relatively small skeletal muscles of the fingers and toes during pitching, and we believe that training these muscles may improve pitching performance. Some muscles of the femoral region showed unilateral accumulation of FDG. We believe this reflects the asymmetric movements performed during pitching. Interestingly, there was little accumulation of FDG in the rotator cuff and trunk muscles, suggesting the possibility that these muscles contribute less to the throwing movement. In conclusion, the whole-body skeletal muscle activity during pitching was investigated using PET-CT and a significant increase in glucose metabolism was observed in muscle groups in the fingers and toes, the hamstrings on the throwing side, and the iliacus, tensor fasciae latae, sartorius on the non-throwing side. [Table: see text]