A 2022 study published in The Journal of Applied Biomechanics examined the acute biomechanical effects of weighted baseballs ranging from 85 to 198 grams in 26 collegiate and professional pitchers. Researchers O'Connell and colleagues used motion capture to track how different implement weights influenced throwing kinematics and joint kinetics during a single session. What they found provides valuable insight into how experienced throwers can use weighted balls as a training tool, ball weight significantly altered pitch velocity and arm speed, but it did not increase the measured shoulder or elbow joint kinetics during the acceleration phase. Specifically, elbow varus torque and shoulder internal rotation moment, the primary forces measured during the concentric acceleration of the throw, remained statistically unchanged across implement weights. Lighter balls produced higher rotational velocities in the pelvis, shoulder, and elbow, while heavier balls slowed those segments down.

This finding suggests that experienced throwers can modulate their mechanics to maintain consistent joint loading during the acceleration phase even when implement weight varies dramatically. But here's a critical distinction that often gets overlooked, the study measured concentric phase kinetics, the forces generated while accelerating the ball forward. It did not measure eccentric deceleration loads, the forces required to slow down the arm after release. If an athlete maintains high arm speed with a significantly heavier implement, the eccentric demands during the deceleration phase would be substantially greater, even if the measured valgus torque during acceleration remains unchanged. The fact that experienced pitchers naturally slowed their pelvis rotation with heavier balls may be the self-regulation mechanism that prevents this eccentric overload from becoming problematic.

But here's the critical context that often gets overlooked in discussions about weighted ball research, the study doesn't specify whether the implements used were plyoballs, the soft sand-filled training tools that compress on impact, or hard leather weighted baseballs that maintain the rigid feel of a regulation ball. This distinction matters enormously. The material properties of the implement affect grip, release characteristics, impact forces on the hand and forearm, and potentially the stress distribution through the elbow and shoulder. A 7-ounce plyoball and a 7-ounce hard leather baseball might weigh the same, but they don't behave the same in the hand, and they're not typically used the same way in training programs. The lack of specification in most weighted ball research makes it difficult to compare studies, apply findings appropriately, or understand whether the safety profile observed in one context transfers to another.

What the Study Found

The researchers had each pitcher throw baseballs of five different weights, 85 grams (roughly 3 ounces), 142 grams (5 ounces, which is regulation), 156 grams (5.5 ounces), 170 grams (6 ounces), and 198 grams (7 ounces). Ball weight had a massive effect on pitch velocity, with an effect size of eta-squared equals 0.944, meaning that ball weight explained 94 percent of the variance in how fast the ball came out of the hand. The 85-gram underload produced the highest velocities, and velocity declined linearly as the balls got heavier. This is exactly what you'd expect based on physics, lighter objects accelerate faster when the same force is applied, and the athletes weren't able to generate enough additional force with the heavier implements to compensate for the added mass.

What's more interesting is what happened to the body's movement patterns. Pelvis rotation velocity, shoulder internal rotation velocity, and elbow extension velocity all increased significantly with the lighter balls. The athletes were rotating faster and extending their elbow more rapidly when throwing underload implements compared to when they were throwing overload. This makes intuitive sense, if you're trying to maximize velocity with a light ball, your body ramps up the speed of every segment in the kinetic chain to take advantage of the reduced inertia. Conversely, when the ball gets heavier, the system slows down. Pelvis rotation velocity decreased as ball weight increased, which the researchers noted could reflect either a subconscious bracing strategy to protect the arm or a deliberate attempt to preserve timing and sequencing in the kinetic chain.

Maximum elbow flexion and anterior trunk tilt at ball release changed slightly with ball weight, but the differences were small, three degrees or less on average. This suggests that while segment velocities were changing substantially, the overall positions and postural configurations the athletes were getting into remained relatively consistent. They weren't dramatically altering their mechanics to accommodate different weights, they were modulating speed and timing within a stable movement framework.

The most important finding, and the one that contradicts a lot of the fear surrounding weighted ball training, is that shoulder and elbow joint kinetics did not differ significantly across ball weights. Elbow varus torque, the primary load that stresses the UCL, was statistically the same whether the athlete was throwing a 3-ounce ball or a 7-ounce ball. Shoulder internal rotation moment, the primary driver of stress on the rotator cuff and labrum, also remained unchanged. This tells us that these experienced throwers were able to regulate their mechanics in a way that kept joint loading relatively constant even as the implement weight varied by more than twofold.

But again, we don't know what type of weighted balls were used. If these were plyoballs, the soft compressible nature of the implement might have influenced how the athletes gripped and released the ball, potentially affecting the forces transmitted through the forearm and elbow. If these were hard leather balls, the rigid contact surface and different weight distribution within the ball could create different stress patterns despite similar overall mass. The study simply doesn't tell us, and that limits how confidently we can generalize these findings to all weighted ball training contexts.

Why This Information Is Important

To be honest, this reminds me of every conversation I've had where someone asks whether weighted balls are safe or dangerous, as if there's a single answer that applies universally. The better question is how to use them as a training tool effectively. This study shows that experienced throwers can manipulate implement weight across a wide range to create different training stimuli, underload for overspeed training, overload for strength-speed development, without acutely spiking the measurable kinetics during the acceleration phase. That's valuable information for program design. It tells us the tool has utility when applied appropriately.

But we need to be precise about what "no increase in joint kinetics" actually means. The study measured elbow varus torque and shoulder internal rotation moment, both of which occur primarily during the acceleration phase when the athlete is generating force to propel the ball forward. What the study did not measure, and this is critical, is the eccentric loading during the deceleration phase. After ball release, the arm must decelerate rapidly, and the heavier the implement, the greater the eccentric demand placed on the muscles, tendons, and ligaments responsible for controlling that deceleration. If an athlete maintains high arm speed with a 7-ounce ball, the rotator cuff, posterior shoulder musculature, and elbow stabilizers have to absorb significantly more energy to slow the arm down compared to a regulation 5-ounce ball, even if the valgus torque during acceleration was the same.

This is where the observation about pelvis rotation velocity becomes crucial. The fact that experienced pitchers naturally slowed their pelvis with heavier balls likely isn't just about timing or coordination, it's a protective mechanism that reduces downstream segment velocities and, by extension, the eccentric deceleration demands after release. If coaches or athletes try to override this natural modulation by cueing maximum pelvis speed with heavy overload implements, they might be maintaining concentric phase kinetics at safe levels while dramatically increasing eccentric loads that the tissues aren't prepared to handle. This distinction matters enormously for how you program weighted ball training and what cues you give athletes during execution.

The observation that pelvis rotation velocity decreased with heavier balls is particularly important. If you think about the kinetic chain as a series of linked segments transferring energy from the ground up through the body and into the ball, the pelvis is one of the early drivers in that sequence. When pelvis rotation slows down with heavier implements, it likely means the athlete is either bracing to handle the load or adjusting their timing to maintain coordination. This could be a protective adaptation. If the pelvis were to rotate at normal speeds with a much heavier ball, the downstream segments, the trunk, the shoulder, the elbow, might experience higher velocities and potentially higher forces. By slowing the pelvis, the athlete may be preventing a situation where the arm has to accelerate an overload implement at speeds it's not prepared to handle.

But here's the double-edged sword. If you're a coach who sees this data and decides to cue athletes to maintain or increase pelvis rotation velocity while throwing heavy balls, thinking that will transfer more energy and improve training stimulus, you might actually be creating a problem. Athletes who don't have the strength, coordination, or experience to manage that increased rotational demand could end up disrupting their timing, over-relying on distal segments to generate force, and ultimately increasing stress at the shoulder or elbow. Research on professional versus high school pitchers makes this point clearly. Professional pitchers generate more velocity with less relative elbow torque by using greater trunk and pelvis rotation throughout their delivery. High school pitchers, who haven't yet developed that level of coordination, rely more heavily on the arm itself to create velocity, which ties their elbow stress much more directly to how hard they throw. The professionals have learned to distribute force efficiently across the entire kinetic chain. The high schoolers are still figuring that out, and if you load them with heavy implements before they've mastered sequencing, you're not building efficiency, you're reinforcing inefficiency under load.

The distinction between plyoballs and hard leather weighted balls becomes critical when we think about application. Plyoballs are soft, they compress in the hand, and that compressibility changes the grip and release mechanics compared to a regulation baseball. Some coaches use plyoballs specifically because of this constraint, the soft ball forces the athlete to adjust their grip pressure and release timing, which can be valuable for certain types of motor learning. Plyoballs are also frequently used in more varied contexts, constraint-based drills, positional variations, intent-based throws from different arm slots or body positions. Hard leather weighted balls, on the other hand, feel much more like a regulation baseball. The grip is similar, the release is similar, and they're often used in more structured max-intent throwing programs designed to overload or underload velocity. The fact that most studies don't specify which type of implement was used makes it very difficult to know whether their findings apply to both contexts.

A study of seven youth pitchers, average age 15.7 years, found that throwing overweight baseballs significantly increased shoulder distraction force by 20 percent compared to regulation balls. Distraction force is the load that tries to pull the humeral head out of the glenoid socket, and it's resisted primarily by the rotator cuff, the biceps tendon, and the labrum. A 20 percent increase in that force is substantial, especially in young athletes whose tissues are still developing. But again, the study doesn't tell us what type of ball was used. If it was a hard leather 7-ounce ball, that's one scenario. If it was a plyoball, that's potentially a different scenario. The lack of specification makes it impossible to compare this finding directly to the study showing no increase in joint kinetics in experienced throwers. Are we seeing a difference due to athlete experience level, ball type, or both? We don't know.

Research on the effects of ball weight and size offers another piece of the puzzle. A study that examined slightly heavier and larger baseballs, not dramatically different from regulation, found that elbow varus torque decreased by about 4 percent when using these modified balls. But velocity also dropped significantly, from 85.1 miles per hour with a standard ball to 81.3 miles per hour with the heavier, larger ball. If the goal of training is to enhance velocity, a tool that reduces both velocity and elbow stress might not be achieving what you're hoping for. On the other hand, if the goal is rehabilitation or building volume in a lower-stress context, a slightly modified ball might have value. But again, we're left guessing about whether these were custom leather balls or some other type of implement, and that guessing undermines our ability to apply the findings with confidence.

The importance of sequencing and coordination shows up repeatedly in research on throwing mechanics. A study examining the role of the drive leg and stride leg in pitching found that the drive leg primarily contributes linear power transfer while the stride leg contributes rotational power transfer. Both legs work together to fuel velocity, and disruptions in how they coordinate affect energy flow up the chain. Similarly, research on abdominal oblique strength in adolescent pitchers found strong correlations between core strength and both pelvis and trunk rotation velocity. Stronger obliques weren't just stabilizing the athletes, they were enabling them to rotate faster, which is a key component of generating velocity. If you're working with an athlete who has good mobility but weak core strength, their ability to actually use weighted balls effectively is compromised. The implement might be safe in isolation, but if the athlete can't generate and control rotational force, the training stimulus either won't transfer to performance or will force compensations that increase risk elsewhere.

Research on muscular fatigue adds another layer of context. A study of adolescent pitchers found that after just 35 pitches, athletes showed measurable declines in hip strength and rotational coordination. Torso rotation angle decreased, hip-to-shoulder separation dropped, and the timing of maximum shoulder internal rotation velocity shifted, suggesting altered sequencing. If sequencing starts to degrade after 35 pitches in young athletes throwing regulation balls, what happens when you add the challenge of varied implement weights? Athletes who are fatigued may not be able to maintain the motor control needed to regulate joint loading across different ball weights, and that's when acute injury risk could increase. The fact that the main study examined experienced throwers in a single session, presumably when they were fresh, means we don't know how fatigue interacts with weighted ball training over the course of a longer workout or competitive season.

A prospective study of 128 high school baseball players found that nearly 70 percent had a prior elbow injury history, and that history was one of the strongest predictors of future injury. Throwing mechanics, including metrics like elbow torque and arm slot, didn't predict who would get hurt. What this tells us is that individual factors, tissue history, prior injury, structural variations, matter more than global mechanics in determining injury risk. An athlete with a history of elbow problems might not tolerate weighted ball training the same way a healthy athlete does, even if their mechanics look similar on paper. This reinforces the idea that programming decisions need to account for individual context, not just population-level research findings.

How Can This Information Be Applied

Weighted balls are a valuable training tool when used appropriately. The research shows that experienced throwers can manipulate implement weight to create specific training adaptations, using underload balls to train overspeed mechanics and neural drive, using overload balls to build strength-speed qualities and expose the system to varied stimuli, all without necessarily increasing the measured kinetics during the acceleration phase. This opens up programming possibilities that weren't available with regulation balls alone. The key is understanding how to apply the tool based on athlete readiness, training phase, and the specific adaptation you're targeting.

That said, implementation requires precision. If you're a coach or athlete considering weighted ball training, recognize first that the research showing no increase in acceleration phase kinetics was conducted in experienced throwers. These were collegiate and professional athletes with well-developed motor patterns and, presumably, prior exposure to varied training stimuli. The finding that concentric forces stayed constant doesn't guarantee that eccentric deceleration loads stayed constant, and in fact, basic physics tells us they didn't. A heavier ball moving at similar arm speed requires more force to decelerate. The athletes in this study likely managed that by naturally reducing pelvis rotation velocity with heavier implements, which cascaded into lower arm speeds and more manageable eccentric demands. If you're working with high school athletes, especially younger or less experienced throwers, you cannot assume they'll self-regulate as effectively.

Second, be aware of the type of implement you're using and match it to your training goals. Plyoballs and hard leather weighted balls are not interchangeable. Plyoballs, because of their compressibility, create a different sensory and mechanical experience. They can be useful for constraint-based learning, positional variation work, or lower-intensity throwing where the goal is to explore movement variability rather than maximize velocity. Hard leather weighted balls feel more like regulation baseballs and are better suited for structured velocity development programs where you want the athlete to throw with intent and experience realistic release mechanics. The lack of specification in research makes it hard to know which findings apply to which tool, so err on the side of caution and don't assume that because one study shows safety with "weighted balls," all types of weighted balls are equally safe in all contexts.

Third, pay close attention to sequencing and full-body mechanics, not just arm speed or velocity outcomes. The fact that pelvis rotation velocity decreased with heavier balls in the main study suggests that the athletes were modulating their movement to manage both timing and eccentric demands. If you're cueing athletes to override that natural modulation, to maintain high pelvis speeds or force maximal intent with overload implements, you might be creating a situation where acceleration phase kinetics look safe but deceleration phase demands become excessive. Remember, the study measured valgus torque and shoulder IR moment during ball acceleration, not the eccentric forces required to decelerate the arm after release. A heavy ball moving at high speed creates substantially greater eccentric loads on the rotator cuff and posterior shoulder than the same speed with a lighter ball. Athletes who naturally slow their pelvis with heavy implements are probably protecting themselves from eccentric overload. Respect that self-regulation rather than trying to coach through it.

This is especially important in younger or less coordinated athletes who may not have the kinesthetic awareness to recognize when their sequencing is breaking down or when eccentric demands are exceeding their tissue capacity. Use video analysis, velocity tracking, or even just careful observation to monitor whether mechanics stay consistent across different ball weights. If you see timing shifts, postural changes, or compensatory patterns emerging, that's a sign the athlete isn't ready for that particular implement weight, training volume, or intent level.

Fourth, consider the athlete's strength and coordination baseline before introducing weighted balls. Research on oblique strength and its relationship to pelvis and trunk rotation tells us that core strength is a prerequisite for generating rotational power safely. If an athlete has limited core strength, adding weighted implements might force them to compensate by over-relying on the arm or disrupting their timing. Similarly, research showing that professional pitchers use more trunk and pelvis rotation to minimize elbow torque tells us that efficiency matters more than isolated range of motion or strength. An athlete who can't coordinate their lower body, trunk, and arm effectively with a regulation ball isn't going to magically develop that coordination by throwing heavier balls. Fix the sequencing first, then add load.

Fifth, monitor for fatigue and adjust volume accordingly. The study showing that hip strength and coordination degrade after 35 pitches in adolescent athletes is a reminder that fatigue affects sequencing, and sequencing affects joint loading. If you're incorporating weighted balls into a throwing session, consider where they fit in the fatigue curve. Early in a session, when athletes are fresh, they're more likely to maintain good mechanics across varied implement weights. Late in a session, when fatigue has set in, the motor control needed to regulate joint loading may be compromised. This doesn't mean you can't use weighted balls when fatigued, it means you need to be more conservative with volume, intensity, or implement selection during those periods.

Sixth, recognize that individual variability is enormous. Research on long-toss programs shows that while ball velocity increases consistently with distance, elbow torque shows high individual variability in how it responds. Some athletes' torque plateaus after 120 feet, others continue to increase. The same principle applies to weighted balls. Some athletes will tolerate heavy overload implements with no issues, others will show signs of increased stress or altered mechanics even with moderate overload. Use objective measures, velocity, video, wearable sensors if available, to track how each athlete responds rather than assuming that if one athlete handles a 7-ounce ball safely, all athletes will.

Seventh, don't mistake acute findings for chronic safety. The main study examined what happened during a single session. It didn't track whether repeated exposure to weighted ball training over weeks or months produces cumulative tissue stress, adaptation, or increased injury risk. A study that followed a team through a six-week training block found that both control and intervention groups lost 4 to 8 miles per hour of velocity and 40 Newton meters of elbow varus torque over that period, suggesting that something about the overall training program was problematic. The point is that even when acute studies show safety, chronic implementation can go wrong if volume, intensity, and recovery aren't managed appropriately. Periodize your weighted ball training, include rest and deload phases, and monitor athletes longitudinally rather than assuming that because they handled one session well, they can handle unlimited exposure.

Finally, work with athletes to develop their own kinesthetic awareness around what feels safe versus what feels risky. Experienced throwers in the main study were likely self-regulating, slowing their pelvis rotation with heavier balls to maintain control and protect their arm. That self-regulation is a learned skill, and younger athletes may not have it yet. Teach athletes to recognize the difference between productive discomfort, the fatigue and challenge that comes with training, and warning signs that something is off, pain, mechanical breakdown, loss of command. Encourage them to communicate when a particular implement weight or drill doesn't feel right, and adjust accordingly. Weighted ball training should be a tool for development, not a source of fear or a test of toughness.

Conclusion

Weighted baseballs are a valuable training tool that allows coaches and athletes to manipulate implement weight to create specific training stimuli. The finding that they don't acutely increase measured joint kinetics during the acceleration phase in experienced throwers provides important evidence that the tool can be applied safely when used appropriately. The study examined collegiate and professional pitchers who had well-developed motor patterns and, likely, prior experience with varied training stimuli. These athletes were able to modulate their mechanics, specifically slowing pelvis rotation velocity with heavier balls, to maintain relatively constant acceleration phase loading across a wide range of implement weights.

But precision matters in how we interpret and apply these findings. "No increase in joint kinetics" refers specifically to the forces measured during the acceleration phase, elbow varus torque and shoulder internal rotation moment. It does not account for eccentric deceleration loads, which increase substantially when arm speed remains high with heavier implements. The natural reduction in pelvis rotation velocity that experienced throwers demonstrated with heavy balls is likely a protective mechanism that cascades into lower arm speeds and more manageable eccentric demands during deceleration. Coaches who try to override this self-regulation by cueing maximum intent or maintaining high segment speeds with overload implements may be keeping concentric forces safe while dramatically increasing eccentric stress that tissues aren't prepared to handle.

The lack of specification about whether the study used plyoballs or hard leather weighted balls is a significant limitation, not just in this study but across most weighted ball research. The material properties of the implement matter. Plyoballs compress in the hand and are often used in constraint-based or exploratory movement contexts. Hard leather weighted balls feel like regulation baseballs and are typically used in structured velocity development programs. These are different tools with different applications, and research findings from one may not transfer cleanly to the other. Until studies start specifying what type of weighted ball they're using, we're left making educated guesses about how to apply the findings.

The distinction between skilled and less skilled throwers shows up repeatedly in research on throwing mechanics. Professionals use greater trunk and pelvis rotation to generate velocity with less relative elbow torque. High school athletes rely more on the arm and show a tighter coupling between velocity and elbow stress. Youth athletes show increased shoulder distraction force with heavier balls, suggesting they can't regulate joint loading as effectively as experienced throwers. Fatigue degrades sequencing, even in healthy athletes, which raises questions about how weighted ball training interacts with accumulated workload over a session or season. Individual variability is enormous, and prior injury history predicts future injury better than mechanics alone.

All of this points to the same conclusion. Weighted ball training is a tool with real utility for velocity development and motor learning when applied correctly. For experienced throwers with good sequencing, appropriate strength, and the kinesthetic awareness to self-regulate, weighted balls can create training adaptations that aren't possible with regulation implements alone. The ability to manipulate ball weight allows for targeted overload and underload protocols that develop different qualities across the force-velocity curve. But the tool's effectiveness and safety depend entirely on understanding what you're actually stressing when you use it, recognizing that acceleration phase kinetics are only part of the picture and that eccentric deceleration demands matter just as much, matching implement selection and intent to athlete readiness, and respecting the self-regulation mechanisms that experienced athletes demonstrate naturally.

For younger, less coordinated, or previously injured athletes, the programming considerations change. The lack of specification about implement type, plyoballs versus hard leather weighted balls, in most research makes direct application challenging. The distinction between skilled throwers who can distribute stress efficiently and novice throwers who rely more heavily on distal segments means that blanket recommendations don't work. There's no one-size-fits-all protocol, and pretending there is does a disservice to the athletes we're trying to develop. Use the tool intentionally, monitor the response individually, and build the physical and technical foundations that allow athletes to self-regulate effectively across varied training stimuli.

References

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