Tired Bodies, Tired Ligaments

The pitch clock was introduced to MLB in 2023 with the goal of fixing the league’s timeliness problem. Entering that season, game lengths were at an all-time high, averaging three hours and ten minutes. The sluggish pace made it difficult for fans to sit through, and a common complaint was that baseball was becoming “too slow” and “boring.” By placing a limit on the amount of time pitchers could take between each pitch, the league aimed to shorten game times and set a faster pace of play to keep fans engaged.

Initially, the pitch clock was set at 15 seconds with the bases empty and 20 seconds with runners on base. If a pitcher does not “begin their throwing motion” before the clock strikes zero, the batter is awarded a ball. Likewise, the batter has to be “ready to hit” and looking at the pitcher before the clock reaches the eight second mark. If the batter fails to comply, they are charged with a strike.

It was an immediate success for the marketability of the game. The pitch clock cut average game times to two hours and 40 minutes in 2023. After its successful debut season, the pitch clock was shortened in 2024. The league reduced the runners-on-base time to 18 seconds, while simultaneously introducing a new 30-second time limit between batters. So far this season, average game time has fallen to two hours and 36 minutes.

These changes irked the MLBPA, which expressed concerns that a device feared to be causing increased pitcher fatigue was being accelerated without proper guardrails. 

How significant has the injury epidemic become? If the 2024 rate were to hold true throughout the season, 607 pitchers would miss time with an injury. As of June 3, 2024, 617 pitchers have recorded at least one inning of work this season, and 221 of them — or 36% — have sustained an injury.

If more than a third of employees at a manufacturing plant were to miss time because of workplace injury, the plant would likely be forced to shut down until it could guarantee safer working conditions. While a professional sports league like MLB operates under different regulations, the rate of employees missing time due to injury remains startling.

The problem is not new, either. Over the last 20 years, pitching injuries have been increasing at a steady rate. According to MLB.com’s Mark Feinsand, between the 1995 and 1999 seasons, pitchers spent a combined 11,668 days on the injured list. In 2023, they tallied a combined 31,558 days on the injured list. 

Since the introduction of the pitch clock in 2023, that rate has spiked, lending credence to the MLBPA’s claims that it has a direct impact on pitcher health. Between the 2021 and 2022 seasons, there were 1,173 pitching injuries; the 2023 and 2024 seasons are on pace to register 1,258 pitching injuries. While there was a slight drop in overall injuries in 2023, the severity of the injuries increased, and more pitchers were sidelined with UCL injuries than in years past.

Not only has the rate of injuries increased, but the severity of injuries also continues to climb. In 2020, the average injured list designation for a pitching injury was 23 days, while in 2023 and 2024, post-pitch clock introduction, the average length of an injured list stint climbed to 32 and 29 days, respectively.

Interestingly, injuries are also impacting pitchers across the age and experience spectrum. According to the data from 2020 to 2024, variables such as age, service time (number of years logged at the MLB level), and career innings pitched have little correlation with a pitcher’s risk of injury — even though older pitchers with more arm mileage are typically thought of as being prone to missing time.

In fact, the most common age bracket for pitcher injuries in 2024 is 25 to 29, which many consider to be the prime of a pitcher’s career. Sixty-five — or 42% — of the 155 injured pitchers are in this range. Another 9% are aged 20-24, while 30-34-year-olds make up 24% of the injured group.

It all begs the question: What is causing the increased rate of pitching injuries, and is the pitch clock to blame?

Experts in the medical field, baseball coaches and baseball trainers interviewed for this story all share a common consensus: while the pitch clock may be contributing to the recent spike in injuries, the crux of the problem lies with baseball's culture itself, where a variety of factors are causing pitchers to place more stress on their arms than ever before.

Since the sport’s inception, pitching in competitive baseball has experienced its share of changes and advancements. But in the past quarter-century alone, pitching at the game’s highest level has evolved at an extraordinary rate. Pitchers are throwing 2.3 miles per hour faster on average in 2024 than they did in 2008, and they’re throwing 0.8 miles per hour faster in 2024 than they did as recently as 2020. Slider velocity is up as well, 1.8 miles per hour faster in 2024 than in 2008.

While those differences may seem trivial, just a one- or two-mile-per-hour bump in velocity could make all the difference for a pitcher trying to break into the big leagues, especially when MLB teams are clearly putting a premium on throwing hard.

“The evolution of pitching in general, in the last five or six years, has become very heavily velocity focused,” said Kevin Tyrrell, head baseball coach at the University of Chicago. “And now there's so much information out there and so many training programs that can get you to throw 100 miles an hour if it's in there. I don't think human beings are designed to throw a baseball 100 miles an hour.”

As technology has advanced, so too have training methods for young athletes. New enterprises like Driveline and Tread Athletics have developed and marketed offseason training programs intended to increase a pitcher’s velocity at a dramatic rate, primarily through the use of weighted balls — or Plyo Balls.

These brightly colored plastic balls, weighing anywhere from 100 to 1500 grams, are thrown by pitchers at high and low intensities. The balls on the light end of the spectrum, weighing less than a standard-use baseball, train arm speed while the heavier balls train the generation of muscle force. The combination of a faster arm speed and the ability of an athlete’s muscles to generate more force significantly increases the ceiling of a pitcher’s velocity output.

Weighted ball training has become common practice at baseball programs across the country. Even younger athletes, who may lack access to the technology through a school or club team, have the ability to purchase and use it at home.

According to David Marmon, head sports performance coach for the University of Illinois Chicago baseball team, more and more young pitchers are getting swept up in the alluring results that modern training models can offer. 

“Starting at a young age, kids are just enamored with this idea that, ‘I have to be able to throw 90 to 100 miles an hour, and I'm willing to do whatever it takes to be able to do that,’” Marmon said. “There's less focus on having a wide range of different types of pitches and being able to manage the game better.”

What’s unique about baseball, and pitching specifically, is that a little league baseball player can view their steps to achieve an ultimate goal — to pitch in MLB — as a checklist of attributes they must acquire. It’s different from a sport like football, where an athlete can run extremely fast, catch at an elite level and have the ability to memorize a playbook overnight, but if they lack elite size and stature, their chances of going pro are relatively miniscule. 

Not so with baseball. If a pitcher has the ability to throw in the mid- to upper-90s and a breaking ball with 20 inches of break before they turn 22, there’s a strong possibility that they’ll generate interest from MLB scouts — no matter their size. 

In his role working with and supporting Division I athletes, Marmon knows well the impact that a “checklist” mentality can have on pitchers at the high school and college levels. He cites that aggressive approach to “chasing velocity” as one of the main drivers behind the wear and tear that young pitchers are increasingly experiencing.

Although the potential benefits of these types of programs are tantalizing for pitchers seeking to gain every advantage they can on the mound, it can come at a cost, especially for middle school and high school-aged athletes who may lack proper muscular strength and whose bodies are still developing. 

“It's the best way [to increase velocity], but it's also very dangerous,” Tyrrell said. “Guys can get carried away with building velocity to the point where it causes UCL damage, shoulder damage, or both. It's not surprising, but it is necessary, unfortunately, because you're not going to get drafted throwing 91 anymore. You're not going to crack a big league roster throwing 93. It just doesn't happen. So in order for you to get to that level, which is the absolute goal, you make sacrifices and take risks.”

Even for pitchers who are already playing professionally, the financial incentive to throw harder and exert themselves in training off the diamond looms large.

“It's becoming what pays dollars in MLB, throwing a hundred miles an hour,” said Jacob Ranalli, a Doctor of Physical Therapy and clinic manager at Chicago-based Athletico Physical Therapy. “How many of these pitchers were sitting at 95, and then go into these offseasons like, ‘Wow, I can bump my salary by a million dollars just by hitting the gym every day and throwing as hard as I possibly can’ — as opposed to trying to lengthen that out over the season. Now you got guys just going for as hard as they can on the fastball, especially these relief pitchers. And what that's doing to them over time, we're just starting to see the effects of it.”

It doesn’t end at velocity, either. Pitch tracking devices, like TrackMan and Rapsodo boxes, have also grown in popularity over the last decade, helping pitchers “design” throws and add more movement into their repertoire.

TrackMan training sessions have become known in baseball circles as trips to the “pitching lab” where athletes work like mathematicians to develop the best offspeed and breaking pitches they can physically throw. These technologies allow pitchers to analyze minute details of their breaking balls and make adjustments to their throwing motion to garner a more competitive pitch profile. 

Desired results are often acquired by changing the grip used on a specific pitch or installing mental cues to alter the way a pitcher releases the ball out of their hand. In some cases, pitchers will go as far as to change their arm slot, or the angle from which they throw the baseball. 

While this is generally viewed as safe, it can change the way stress is dispersed throughout the body and arm. A fully developed physique can typically handle the changes in stress dispersion, but an arm that is still developing may not be able to withstand the shock of a new biomechanical motion through continued exertion. It’s part of the reason why youth pitchers typically aren’t cleared to begin throwing breaking balls in competition until they reach the age of 13.

Just like velocity training, pitch design for movement comes with a similar set of risks and rewards.

“When you change somebody's arm angle for pitch design purposes, there is inherent danger,” Tyrrell said. “Sometimes it works great, sometimes it's more efficient. But sometimes if they have too high a volume too early, or are throwing weighted balls and exerting their arm from an angle that they're not used to throwing, that can obviously result in injuries.”

Another cultural factor contributing to the recent trend of pitcher injuries is the growing specialization movement among youth athletes, which is increasingly causing burnout for elite young pitchers. 

In past generations, it was common for young athletes to play three or even four sports during their developmental years. But now, many specialize in a single sport at an early age in order to develop skills year-round and stay ahead of the curve in today’s ultra-competitive youth sports environment.

For Ranalli, this “lack of diversity” in sports participation can have unintended consequences for young pitchers who aren’t spending enough time developing certain muscle movements inherent in other sports.

“If you're pitching all the time, you're taking away from the time that you're playing a different sport, such as basketball, and working on cutting,” Ranalli said. “In the rehab process, if somebody is lacking lateral hip strength to push off the mound, they're going to generate a lot of that force either through the obliques in their torso, or they're going to make up for that torque through their shoulder and rotator cuff muscles, simply from a lack of hip strength.”

It is not uncommon for an aspiring baseball player to play their usual spring season for two teams — little league and club —  while also playing in a fall and summer league, followed by a rigorous offseason training program. More playing, more development, more pitching. It’s a double-edged sword. They will develop faster with more repetition and opportunity while simultaneously putting more and more stress on their arm. 

“When I was growing up, everyone played for one team,” Ranalli said. “You played during the summer, maybe the spring, and then you played your other sports. Now, a lot of the athletes I see are playing spring ball, summer ball and a fall ball league now, too. They take about three weeks off, and they're right back to training for their summer team or travel team. They're playing nine, ten, even 11 months out of the year.” 

That same ultra-competitive environment thrives in the Major Leagues. To be the best in the game, a pitcher must train the most and work the hardest. Many pitchers who used to spend an offseason solely in the weight room now throw high-intensity bullpen sessions in a pitching lab throughout their six months away from the game.  

The nature of throwing a baseball at high velocities, with the high spin rates required to create the desired movement, without any offseason rest, puts tremendous stress on an arm and only heightens the risk for injury. It’s a formula that’s increasingly being followed at all levels of the game.

But with so much on the line, and because the checklist to reach the major leagues is advertised as realistically attainable, players are willing to accept major injury as a cost of doing business in order to rise to the top of the sport.

“They're like, ‘Oh, it's not a matter of if, it's a matter of when it's going to happen,’” Marmon said. “And then you get it done and have more life and longevity in the elbow. Which to me is just insane. The whole mindset behind it to me just seems absolutely preposterous. But it's the culture of the sport, right?”

As pitchers at all levels continue to experiment with different arm angles and new training programs that test the limits of their throwing power, their bodies are feeling the impacts of fatigue.

And more often, the elbow is the body part that’s being put in harm’s way.

Of the more than 2,100 injuries that have occurred in MLB since the 2020 season, 412, or nearly 1 in every 5 injuries, have been elbow-related — the most of any type over that span.

While shoulder injuries have been almost as common, injuries to the elbow are much more likely to cause serious damage that can keep pitchers sidelined for longer periods of time — mainly due to the relative vulnerability of the UCL.

“The root of the problem is the nature of the sport itself,” Marmon said. “The act of pitching. That loaded external rotation, driving with your lower half and having your upper half falling behind it. Biomechanically, the weakest link in that chain is going to be the elbow.”

Since 2020, MLB pitchers have undergone a total of 24 shoulder surgeries, representing a mere 6% of all shoulder injuries over that span. Meanwhile, there have been 172 elbow surgeries performed on major league pitchers in the past four years, representing 42% of all elbow injuries, and 8% of total injuries. The vast majority of those elbow surgeries are for UCL reconstruction — known popularly as Tommy John.

First performed on the eponymous MLB pitcher in 1974, UCL reconstruction is a surgical technique in which the torn or ruptured ligament is replaced with either a donor tendon or a tendon from another part of the patient’s body. It restores function to the UCL, which is located on the inside of the elbow and connects the upper arm to the forearm.

Tommy John has become one of the most common procedures in the sport of baseball, and it’s especially common among the game’s elite pitchers, who are at particular risk of suffering from UCL damage because of the repeated stress they place on the ligament while playing.

“It’s usually attritional,” said Dr. Michael Chiu, a Chicago-based orthopedic surgeon who specializes in sports medicine, referring to the type of UCL injury that usually leads to Tommy John surgery. He explained that a pitcher’s frequent, high-intensity throwing motion can create “valgus stress” on the elbow, creating microscopic tears, fraying or partial ruptures in the ligament over time. But with UCL reconstruction, a pitcher’s arm can be brought “back to a proper, functional level.”

The procedure’s effectiveness, which has increased over the past several decades with advancements in medical knowledge and surgical techniques, is why it’s still the go-to remedy for athletes who want to return to the playing field as soon as possible. And for professional pitchers with around-the-clock access to high-level athletic trainers and top-of-the-line rehab facilities, the road back to the diamond is one that is growing increasingly easier to navigate.

“Professional athletes make it look sexy,” said Ranalli. “They make it look like you can be back in like nine months no problem, [and] you're actually throwing five miles an hour harder than before surgery.”

But that’s not the case for most pitchers. The standard return-to-play time following UCL reconstruction surgery is still 12 to 18 months in most cases. It’s an uncomfortable, monotonous ordeal that lower-level athletes, who lack the same financial incentives as their professional counterparts, may struggle to complete.

“It's a long recovery,” Ranalli said. “And not one that feels great. Rehab is boring. Rehab is really boring in those first three months. It is literally just making sure you're keeping your forearm muscles somewhat alive. Not even strong, just honestly active enough to write a pen.”

Although traditional Tommy John surgery is still by and large the industry standard for UCL reconstruction, a new variation of the procedure is beginning to gain traction, primarily because of its shorter recovery time.

The internal brace, a surgical technique first introduced roughly a decade ago, stabilizes the existing but damaged ligament by using a tape-like suture called a biocompatible polymer brace. Instead of grafting and replacing the damaged ligament like in Tommy John, the brace is woven into the ligament to support its repair during the subsequent healing process, allowing for a more aggressive recovery timeline that can range anywhere between 4 to 6 months.

Based on MLB injury data reviewed for this story, only seven pitchers were listed as having undergone a UCL internal brace surgery, five of which had the procedure done this year. That includes Strider and Boston Red Sox starter Lucas Giolito. There is no mention of it occurring before the 2022 season.

“[Internal brace] has been growing in popularity because it’s pitched as more of preserving your own anatomy,” said Chiu, who agreed that patients who undergo the procedure are able to get back to pitching sooner.

But he cautioned that, while promising, the technique is not effective for all UCL injuries. Athletes with avulsions, or damage at either end of the ligament, are the best candidates for internal brace surgery. If it’s a mid-substance tear, Chiu said, “it's not going to work as well.”

While Chiu believes it’s “too early to say” for certain whether the pitch clock is the driving force behind the growing number of MLB pitcher injuries, the data suggest that elbow surgeries — whether Tommy John, internal brace or other kinds — have been more frequent in recent seasons.

In fact, the share of overall pitcher injuries that have resulted in elbow surgery has risen in each of the past four seasons. In 2021, 5.2% of all pitcher injuries were elbow surgeries. In 2023, that figure grew to 8.7%. And so far in 2024, 13.1% of injuries have been elbow surgeries.

This trend, although it was on an upswing before the pitch clock’s formal introduction in 2023, appears to fit with the assertion that the pitch clock is correlated with increased burnout among MLB pitchers. With athletes throwing harder and with more movement than ever before, giving them shorter rest between pitches could be taking a toll.

As Ranalli explained, if a pitcher’s muscles are getting more fatigued over the course of an outing and are unable to assist with the deceleration portion of the pitch movement, the explosive forces they’re generating “have to go somewhere.” And increasingly, it’s ligaments like the UCL that are bearing the brunt of that force.

“You can have the strongest muscles in the world, but when you're talking [about] some of the forces that these guys are decelerating [at] coming off a fastball, it doesn't matter how big your muscle is,” Ranalli said. “The ligaments and the bone still have to hold those muscles where they're at.”

As the data indicates, powerful muscles are winning out in this internal battle of forces at the ultimate expense of the less sturdy ligaments. But Ranalli isn’t ready to blame it all on the pitch clock just yet.

“I really think it's multifaceted,” he said. “It's not just, ‘Oh, they implemented the pitch clock and the injuries went up.’ I think that it's been an iceberg building for years of [pitchers] getting less and less diverse with their motion.”

A rollback of the pitch clock won’t change the underlying causes of pitcher injuries, but an extension in the rest time between pitches may help ease the transition into the new pitch clock era. 

The fact remains that faster games are more engaging for fans, and more profitable for MLB, meaning the pitch clock isn’t going away anytime soon. If the league were to implement any further changes, it’s likely the pitch clock would be shortened, not lengthened. 

“We have to train them to adapt to the demands of their sport,” Marmon said. “So when the pitch clock changes, you then need to change your training mechanism. Whether it's how you throw a bullpen, how you throw to live batters, how you're running your metabolic conditioning with your pitchers. It needs to mimic the demands of the sport.”

Perhaps this is just an adjustment period, and pitchers’ bodies are reacting to a significant change in the way they are being asked to perform. Without a larger sample, there is no way of knowing how the most athletic and gifted baseball players in the world will adapt over time. 

“I think the pitch clock exacerbates it a bit, but I don't think it's going anywhere,” Tyrrell said. “Human beings, as you've seen — the bodies will adapt. They're just not adapting as quickly as the rules are changing yet. It's not out of the question that the injury numbers go down in the near future because people are used to the circumstances.”

Aside from the pitch clock, moving forward baseball must consider what it values in its sport. The cost of many professional pitchers throwing at velocities previously unimaginable is an exciting draw for a game that desperately craves more eyeballs, but it also means more frequent injuries — for both those already in MLB and others looking for a way in.

“I think a lot of these subpar athletes will get caught up in the injury barrage because they're chasing what high-level athletes are capable of doing,” Marmon said. “We're basing training protocols off what freaks and phenoms can do. We're telling average guys that throw 88, ‘You could be this guy too.’ The reality is that's probably not the case. You're setting them up for disappointment and injury.”