(Inside Science) -- For today's baseball pitchers, velocity is king. The average speed of a major league fastball in 2019 was 93.4 mph, compared with 90.9 mph in 2008, according to FanGraphs. Such unprecedented speed is changing the game -- and the drive to throw ever faster may also be risking the safety of younger players dreaming of the majors.
"Everyone thinks the harder you throw, the earlier you throw [in age], the better chance you have of being a pro," said Eric Makhni, an orthopedic surgeon at the Henry Ford Health System in Michigan, and the former team physician for the Chicago White Sox.
To throw harder, pitchers from little leaguers to pros have been training with baseballs heavier than the standard 5 ounces. While proponents say heavier balls are safe, doctors like Makhni worry that the extra load may carry too much risk of injury.
Now a recent study with youth players points to a potentially safer alternative: lighter baseballs.
The study, published in the Orthopaedic Journal of Sports Medicine in March, is preliminary and limited. But, "it should start the discussion of whether lighter balls should be implemented instead of overweight balls," said Brandon Erickson, an orthopedic surgeon at the Rothman Orthopedic Institute in New York, who led the research.
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Training programs with weighted balls typically use balls that are both heavier and lighter than normal. And while commercial programs marketed at aspiring ballplayers have proliferated over the last several years, the data as to whether such weighted-ball training works is sparse and varies widely in quality, according to a review paper published last year.
Still, many studies of the practice do show a boost in pitching velocity. One of the most recent, a study with 38 teenage boys published last year in the journal Sports Health, found that 80% of those who trained for six weeks with both heavier and lighter balls could pitch faster by an average of more than 2 miles per hour. But 12% ended up pitching slower, and 67% of those who trained with only standard-weight balls over the same time period also increased their pitching speed, by about 0.7 mph.
"Weighted balls may be effective in enhancing velocity in some, but probably not as much as you think," said Mike Reinold, the senior medical advisor for the Chicago White Sox and a trainer and physical therapist who led the study, at a recent virtual Major League Baseball Injury Conference on weighted balls. "It's not magic."
His study also found that heavier balls did not increase the forces on the elbow and shoulders. That suggests heavier balls help pitchers throw faster not by strengthening their arms and shoulders as was assumed, said Glenn Fleisig, a biomechanist and research director of the American Sports Medicine Institute, and a co-author of Reinold's study. Instead, they found that heavier balls enable players to rotate their arms farther back during the throwing motion, akin to pulling a slingshot farther back.
In Reinold's study, a larger rotation correlated not just with faster pitches, but also with more biomechanical stress and more injuries. Among players who trained with balls of different weights, 24% got hurt either during the program or the following season. None of the players who trained with only the standard ball were injured.
No previous study had assessed injury rates with weighted-ball training. But in the experience of many baseball specialists, overweight baseballs do lead to overuse injury, especially in younger athletes, said Makhni, who's now the team physician for the NFL's Detroit Lions.
Lighter-weight balls, on the other hand, might cause less stress on the elbow, said Erickson, who's also an assistant team physician for the Philadelphia Phillies. So he wanted to see if exclusive use of lighter balls could be not only safer, but also effective at speeding up pitches. Lighter balls, Fleisig explained, can train the arm and shoulders to move faster.
In Erickson's study, 44 ballplayers aged 10 to 17 participated in a 15-week training program that used baseballs weighing 3, 4, and the normal 5 ounces. By the end of the program, 43 participants could pitch faster by an average of 4.8 miles per hour. And, no one got hurt.
"This study adds to our body of knowledge," Fleisig said. But it's not without limitations. "The study would've been better if it also had a control group," he said. Without a comparison group of ballplayers who went through the same training program but with exclusively standard-weight balls, you don't know how much of the velocity increase was due to the lighter balls, or just due to the exercises from the program -- or even simply due to growing taller and heavier.
As for safety, the participants in Erickson's training program could have just gotten lucky, Fleisig said. "It doesn't prove you won't get hurt. It just proves that this group didn't get hurt."
"I don't think it tells you training with lighter balls helps velocity or decreases injuries," Reinold said at the conference. Weighted balls comprised a relatively small part of the study's training program, he said. And to better determine injury risk, you would need to track whether anyone got injured later in the baseball season.
But it's unlikely that an in-season injury could be traced back to a training program, Erickson said. Such an injury could be due to the player's newfound ability to throw harder, or any of the other countless factors and random events during a season. He's now planning another study with a control group of players training with a standard-weight baseball, he said.
With a relative dearth of data on both safety and effectiveness, it's still unclear exactly what role lighter or heavier balls should play in a training program. But most likely, Fleisig said, it will depend on the player and the program. He would recommend a program using both slightly under- and overweight balls, he said. Based on his biomechanics analysis, he hypothesizes that the small variations in ball weight can be a key factor in training the body to throw faster.
But Erickson recommends against throwing overweight balls at all. "Throwing it like a baseball unnecessarily increases the risk of getting an injury," he said.
Makhni agrees. "I would not recommend any weighted ball program for anyone who is skeletally immature -- anyone who's still growing, basically," he said. Training with exclusively lighter balls, however, probably has a low chance of injury.
Overweight balls just aren't worth the risk, he said, especially since there are many other ways to increase velocity, such as improving core strength, range of motion exercises, and overall technique. In fact, one study published this year found that 86% of the energy that drives the elbow comes from the motion of the torso.
Speed shouldn't be everything, either. An array of other skills contributes to a pitcher's success, including accuracy, deception and mental toughness. "Velocity does matter," Fleisig said. "But it does not matter as much as some people think it matters."