September has rolled around, bringing the high-stakes chapter of the baseball season that separates true title contenders from pretenders. With the trade deadline behind us, rosters refreshed by late-season deals, and playoff spots on the line, managers are leaning on their pitching staffs harder than ever. It is the time of year when a single frayed arm can derail an entire pennant run—and when the physical toll on modern pitchers shifts from an academic debate to a season-defining reality.
For the past few seasons, that dynamic has carried a ticking variable: the pitch clock. Introduced in 2023 to trim downtime, the rule requires pitchers to throw within 15 seconds with empty bases and 20 seconds with runners aboard—a notable drop from the previous average pace of roughly 22 seconds. While the clock succeeded in shaving nearly half an hour off game times, it also raised immediate red flags among players, coaches, and orthopedic surgeons who feared that reduced rest between throws would trigger a surge in arm injuries.
Recent research, however, complicates that narrative—and the leading scientific expert on pitching biomechanics remains doubtful that the pitch clock was ever the injury culprit it was painted to be.
What the Data Shows—and Why the Skeptics Aren’t Buying the Panic
A study published in the Orthopaedic Journal of Sports Medicine tracked the 200 highest-volume MLB pitchers across four seasons (2021–2024), spanning two years before and two years after the clock’s implementation. Surprisingly, the data defied popular expectations. Rather than rising, the percentage of elite workload pitchers landing on the injured list fell from over 50% prior to the rule change to under 40% afterward. Additionally, the average time before a pitcher’s first injury stretch extended from 143 days to nearly 161 days, with survival analysis indicating a 31% reduced likelihood of injury over a given stretch under the clock.
Dr. Glenn Fleisig, a biomechanist at the American Sports Medicine Institute whose research helped shape MLB’s Pitch Smart guidelines, remains unpersuaded that the clock deserves credit for protecting arms. When asked if two post-clock seasons altered his stance, his response was direct:
“Nothing has changed, not at all.” Fleisig treats velocity and pace as entirely separate issues. “These are two separate issues: the pitch clock and velocity. But if we’re just talking about the pitch clock, I think the data continue to show that the pitch clock has had no effect on injury rates, either positive or negative.”
Interestingly, pitchers weren’t throwing fewer pitches to get these numbers; total batters faced actually increased while total pitch counts and per-inning efficiency held steady. The study’s authors theorized that shorter pauses between throws might keep forearm muscles warm and engaged, reducing the risk of acute damage caused by constant cooling and re-engaging under max effort. Elbow-specific injuries—specifically those requiring Tommy John surgery—dropped during the clock’s first two years before ticking up slightly in 2024, though without reaching statistical significance over the whole sample.
Pitching Ninja analyst Rob Friedman sees an invisible physiological tax embedded in the faster pace, even if it hasn’t sparked a massive wave of Tommy John surgeries. In Friedman’s view, the clock robbed pitchers of their ability to manually control their own recovery tempo.
“A veteran pitcher could step off, walk around the mound for 30 seconds, collect himself and essentially create his own recovery period. There’s much less room for that now.”
While pitchers have adapted using tactical deep breathing, calculated mound visits, or asking for fresh baseballs to buy extra seconds, the physical burden remains immense.
“Modern pitching is incredibly high effort,” Friedman observed. “There aren’t many ‘take a pitch off’ fastballs anymore.” Unlike past eras where starters paced themselves early to save their best stuff for late innings, today’s arms “have to be ready from pitch one because hitters are trying to do damage on every pitch.”
Inside the Elbow: The Mechanics of Breakdown
To understand how fatigue damages an arm regardless of the clock, it helps to examine the mechanics of a UCL (ulnar collateral ligament) tear. Fleisig breaks down the delivery process starting at max external rotation—the layback position where the shoulder is cocked back, the ball faces skyward, and the arm prepares to accelerate forward.
During that peak strain, three primary structures protect the inner elbow joint: the ulnar collateral ligament itself, the surrounding bone structure, and the flexor-pronator forearm muscles. In a healthy, fresh arm, that stress is distributed roughly equally among those three elements, keeping UCL strain within tolerable limits. Once fatigue sets in, the system breaks down. When forearm muscles tire and fail to absorb their share of the load, that extra stress transfers directly to the ligament, pushing tension past structural thresholds and causing tears.
Laboratory studies confirm this fatigue process. Research out of Detroit’s Henry Ford Hospital monitored pitchers over simulated six-inning starts while measuring torque and speed pitch by pitch. The results were remarkably consistent: self-reported fatigue rose steadily, medial elbow torque spiked significantly after the third inning, and velocity naturally drifted down. High-effort fastballs consistently generated the greatest torque on the joint.
Spotting the Subtle Red Flags
When an exhausted starter is navigating a high-stakes September inning, what visible signals indicate an arm is working on borrowed time? Biomechanical tracking technology installed in MLB parks allows teams to monitor key mechanical indicators of fatigue, such as a shortening stride distance, a front knee that fails to firm up efficiently upon foot contact, an overly upright trunk that lacks forward flexion, and a dropping throwing elbow that falls below the natural shoulder line.
Fleisig pointed to a set of biomechanical tells that professional clubs can now track through the ball- and body-tracking systems installed in every MLB stadium: a shortening stride, a front knee that no longer straightens the way it should on landing, a trunk that stays more upright instead of flexing forward, and a dropped throwing elbow. Normally, he explained, “the throwing elbow should be aligned with that shoulder line… When a pitcher is fatigued, a lot of times he’ll drop his elbow below that imaginary line.”
From an analytical perspective, Friedman notes that watching radar gun readings alone can be misleading, as velocity is often the last thing to drop. The truer warning signs are subtle and systemic, including a loss of pitch movement and life where fastballs lose ride or breaking balls flatten out, drifting release points and altered delivery routines, or a loss of command across the entire pitching mix simultaneously.
When a pitcher loses fastball shape, breaking ball depth, and release consistency all at once, it reveals far more than a simple two mile-per-hour dip on a single heater. Yet, as Friedman points out, identifying fatigue on the field remains part art and part science, as every pitcher expresses physical drain differently.
Why Major Leaguers Don’t Map to Teenagers
One reason pitch-clock deployment hasn’t triggered an explosion of pro injuries comes down to how workloads are managed at the elite level compared to youth baseball, where Fleisig’s Pitch Smart guidelines strictly limit exposure. In amateur ranks, scientific evidence directly links heavy pitch volume to injury risk.
In Major League Baseball, that linear relationship is harder to isolate—not because high workloads are harmless, but because modern teams actively intervene before catastrophic failure occurs. When a major league pitcher shows biomechanical strain or fatigue, managers pull him. Professional baseball rarely lets athletes pitch to the point of complete exhaustion, creating a controlled environment that disrupts traditional injury data.
Stuff vs. Survival: The Modern Dilemma
Underlying both the pitch clock debate and biomechanical science is a central dilemma: the technology designed to protect pitchers is the same technology driving them to push their bodies harder than ever. Pitchers can adjust a grip, review tracking metrics instantly, and optimize their movement to chase max velocity and spin—a process that rarely moves in reverse. Once an athlete learns to throw 98 miles per hour with elite movement, telling them to dial it back to 94 miles per hour in the late innings is a tough sell.
That relentless drive for elite performance runs directly into human biological limits. Human ligaments haven’t evolved as fast as pitch-design tech. Consequently, modern workload management has expanded far beyond basic pitch counts to encompass long-toss volume, bullpen stress, sleep metrics, and subjective athlete feedback. Balancing elite pitch design with human physical endurance remains an ongoing challenge across the sport.
What It Means for the Stretch Run
The pitch clock isn’t a primary driver of pitching injuries; high velocity and maximum effort are, with fatigue serving as the catalyst that turns strain into ligament tears. The clock simply compresses that physical stress into tighter time windows.
For postseason contenders leaning heavily on their pitching staffs down the stretch, the challenge remains clear. Navigating the final stretch of the season won’t come down to watching the seconds on a pitch clock—it will be measured in torque, innings, and the subtle mechanical changes that signal a fading arm long before an MRI confirms it.
Endnotes
First, Lavi A, Johnson M, Ibrahim T, et al. “Pitch Counts and Injury Incidence in Major League Baseball: Responses to Pitch Clocks and Defender Rule Changes.” Orthopaedic Journal of Sports Medicine, January 2026.
Second, Okoroha KR, Meldau JE, Lizzio VA, et al. “Effect of Fatigue on Medial Elbow Torque in Baseball Pitchers: A Simulated Game Analysis.” 2018.
Third, Sonne MW, Keir PJ. “Major League Baseball pace-of-play rules and their influence on predicted muscle fatigue during simulated baseball games.” Journal of Sports Science, 2016.
Fourth, Yang SC, Wang CC, Lee SD, et al. “Impact of 12-s rule on performance and muscle damage of baseball pitchers.” Medicine & Science in Sports & Exercise, 2016.
Fifth, MLB pitcher injury report, cited in theScore, “MLB pitching-injury study knows the causes, but solutions may be elusive,” 2025.
Sixth, Langs S. “What the standings on August 1st mean for teams in the pennant race.” MLB.com, August 1, 2026.
Seventh, “MLB playoff picture on Aug. 7, 2026.” MLB.com, August 7, 2026.
Eighth, Glenn Fleisig, biomechanist, American Sports Medicine Institute, interview with the author, 2026.
Ninth, Rob Friedman, pitching analyst and consultant, interview with the author, 2026.