An Interval Throwing Program for Baseball Pitchers Based upon Workload Data

Abstract

Background Interval throwing programs (ITP) have been used for decades to enable baseball pitchers to return to competition after injury or surgery by gradually applying load to the throwing arm. Past programs have been based on personal experience; however, advances in our understanding of the biomechanics and workloads of throwing allow for a more modern data-based program to be developed. Hypothesis/Purpose To 1) develop a updated ITP for rehabilitation of modern baseball pitchers based upon biomechanical and throwing workload data, and 2) compare the updated program with a past program to determine differences in chronic workload and acute:chronic workload ratios (ACWR). Study Design Cross-sectional study Methods Workloads (i.e. daily, acute, chronic, and ACWR) for the original ITP were built from the prescribed throwing schedule. Elbow varus torque per throw was calculated based upon a relationship between elbow varus torque and throwing distance. Throw counts, daily/chronic/acute workloads, and ACWR were calculated and plotted over time. A new ITP was built to model current pitcher’s throwing schedules and gradually increased ACWR over time. Results The original ITP had a throwing schedule of 136 days, final chronic workload 15.0, and the ACWR above or below the “safe” range (i.e. 0.7 – 1.3) for 18% of the program with a peak of 1.61. The updated ITP was built to consist of a 217-day schedule, final chronic workload of 10.8, and deviated from the safe range for 9% of the program, with a peak of 1.33. Conclusion The newly created ITP is more familiar to modern baseball pitchers while exhibiting a more gradual buildup of chronic workload than traditional ITP programs. This ITP may be used to return baseball pitchers back to competition as safely and efficiently as possible, and potentially with less risk of setbacks or reinjury. The ITP may be used following common injuries or surgeries to the throwing shoulder and elbow, such as Tommy John surgery, while also serving as a basis for future development of shorter duration ITPs. Level of Evidence 2c

Author Response - Letter to the Editor Concerning: "An Interval Throwing Program for Baseball Pitchers Based upon Workload Data”

“…We agree that elbow throwing torque magnitudes reported in Reinold et al 1 and nearly two dozen other peerreviewed studies 2,3,5-21 using the IMU are consistently less than elbow torque magnitudes reported by camera-based motion capture studies. However, we challenge the letter's implication that differences between the two technologies show that motion capture data are correct and IMU data are incorrect.…”

“…While there may be multiple ways to quantify intensity, using an interval throwing program that does not consider workload is shortsighted. As explained in our study and furthermore in this response, the updated interval throwing program presented in Reinold et al 1 is based upon reliable biomechanical data and workload management to safely and efficiently rehabilitate pitchers back to pitching after shoulder and elbow injuries.…”

“…In their letter, Wong et al made several statements that we find are not supported by science and may be misleading to the reader. The letter states that Reinold et al 1 "utilized an unvalidated inertial measurement unit (IMU) device" because "multiple scientific studies" [2][3][4] have "clearly demonstrated that this particular IMU device is not valid for accurately measuring elbow arm stress." The letter points out that elbow torque magnitudes from the IMU sensor reported by Reinold et al 1 are significantly less than torque magnitudes reported by "gold standard" motion capture systems.…”

“…The letter states that Reinold et al 1 "utilized an unvalidated inertial measurement unit (IMU) device" because "multiple scientific studies" [2][3][4] have "clearly demonstrated that this particular IMU device is not valid for accurately measuring elbow arm stress." The letter points out that elbow torque magnitudes from the IMU sensor reported by Reinold et al 1 are significantly less than torque magnitudes reported by "gold standard" motion capture systems. In summary, they state elbow torque magnitudes are different when measured with IMU than when measured with camera-based motion capture, and therefore IMU data are wrong.…”

“…The biomechanical model developed in Dowling et al 5 and used in Reinold et al 1 calculates workload based upon within-subject changes in elbow torque for different types of throws. Because IMU and motion capture data are correlated, the chronic workload graphs for the interval throwing programs presented in these studies would likely be remarkably similar to what is shown even if motion capture data had been used; simply, the magnitude of chronic workload would be on a different scale.…”