“When it comes to bringing baseball players back to the mound after they’ve had throwing injuries, sports medicine professionals generally rely on common practice that has been passed down via coaches and players for decades,” explained Neal S. ElAttrache, MD. “However, the rehabilitation and throwing progression can significantly affect the return-to-play process, so we decided to examine some of these traditional throwing programs and see if they make sense from a scientific standpoint.”

Dr. ElAttrache is the senior author of “Biomechanical Comparison of the Interval Throwing Progression and Baseball Pitching,” which was presented by lead author Nicholas R. Slenker, MD, during the 2014 AAOS Annual Meeting.

The researchers used a quantitative motion analysis system to analyze the throwing motions of 29 healthy college baseball pitchers and calculated mean values for humeral internal rotation torque (HIRT) and elbow valgus load (EVL) for each throw type. Because these are both bending moments, they were normalized (nHIRT and nEVL) to body weight and height to compare kinetics across pitchers of different body types.

After a warm-up, the participants threw from flat ground to a catcher at distances of 60 feet, 90 feet, 120 feet, and 180 feet. All flat-ground throws were at full effort. After a 5-minute rest, participants then then pitched fastballs to the catcher from a mound at three different perceived efforts: 60 percent, 80 percent, and 100 percent.

“When to make the transition from throwing on flat ground to throwing off the mound has been debatable,” explained Dr. ElAttrache. “A common practice in pitching rehab is to have the player throw from flat ground for as long as possible, but how does that affect the forces on the shoulder and the elbow? Does putting the pitcher on the mound too early put the repair or the recovering injury at increased risk?”

Biomechanical stresses
“Throwing from even the shortest flat-ground distances demonstrated essentially identical biomechanical stresses when compared to pitching full-effort from the mound,” reported the researchers. “Despite these similar stresses on the shoulder and elbow, throwing from the flat ground showed significantly decreased ball velocity when compared to throwing from the mound, indicating a lower throwing efficiency from flat ground.”

The research team found statistically significant differences for both nHIRT and nEVL as the intensity of the throwing effort from the mound increased. However, they found no statistically significant differences in either nHIRT or nEVL across all flat-ground distances and no statistically significant differences in either peak HIRT or peak EVL when comparing full-effort pitching to flat-ground throws at any distance.

The researchers did note that longer flat-ground throws (180 feet) showed significantly different kinematics and biomechanical patterns when compared with pitching from the mound, while shorter flat ground throws had patterns similar to those of pitching.

“We found that variable effort pitching off the mound was associated with significantly lower stresses on the shoulder and elbow during partial-effort throws, illustrating the importance of these throws during the recovery and rehabilitation process,” said Dr. ElAttrache.

“Despite lower velocity, we noted that flat-ground throwing at distances as short as 60 feet produced similar biomechanical stresses on the upper extremity when compared with pitching full-effort from the mound. There was no increase in shoulder or elbow stress with increasing distances from the flat ground, likely because the pitchers began using a ‘crow-hop’ approach (extra step before pitching) for longer distances,” he continued.

Although the authors noted several limitations to their study—including the limited number of distances tested, the use of only healthy pitchers, and the use of a minimal number of pitches (3 at each distance and effort level), they also pointed to their use of shorter distances frequently employed in rehabilitation programs and their use of newer generation motion capture cameras that enabled them to conduct the study at an outdoor field in broad daylight.

“The mechanical advantage to throwing from a mound or using the crow-hop may be protective during rehabilitation and training throws. In light of this, we suggest that pitchers who undergo rehab may wish to consider switching to mound work earlier in the throwing program and that fielders consider using a crow-hop approach at shorter distances,” they concluded.

Additional authors include Orr Limpisvasti, MD, and Karen J. Mohr, PT.

Disclosure information: Dr. ElAttrache—Arthrex, Inc; Dr. Slenker and Ms. Mohr—no conflicts; Dr. Limpisvasti—Ossur, CONMED, Linvatec.

Peter Pollack is electronic content specialist for AAOS Now. He can be reached at ppollack@aaos.org

Bottom Line

• This biomechanical analysis of healthy college baseball pitchers was designed to measure stresses on the shoulder and elbow during throws from flat ground and pitches from the mound.
• Partial-effort pitching from the mound demonstrated significantly lower stresses on the shoulder and elbow compared to pitching at full effort.
• Stresses on the shoulder and elbow were similar between flat-ground throws and pitches from the mound, but ball velocity was significantly decreased.
• Protective strategies for rehabilitation after injuries may include partial-effort pitching, throwing from an incline (mound), and using ‘crow-hop’ footwork on flat ground.