The exact mechanism on how weighted baseballs increase velocity is unknown. However, Soviet-science research on over/underweight implements provides a great hypothesis: With underweight training the arm will move at higher speeds with less muscle force generated. Overload training causes the arm to move at a slower speed but with greater muscle force. Over- and under-weighted-ball training can be seen as a form of “speed-strength” or “power” training for the arm. Power training by definition conditions the neuromuscular system to develop the greatest amount of force in the least amount of time.

Effect of Baseball Weighted Implement Training: a Brief Review

Authors: DeRenne, Coop; Szymanski, David 2009

This is the study to start with if you are interested in learning about weighted baseballs and weighted-bat training. Between reading the review and looking up the references, we found a solid research base in the support of weighted-implement training in baseball. This is a great complement to the decades of research in support of weighted-implement training in Track and Field.

  • This paper looked at 11 weighted-baseball studies and suggests that weighted-ball training not only increases velocity but also may be used for injury prevention.
  • It also looked into the use of weighted bats and their use in warm-ups and improving swing velocity.

Effects of Throwing Overweight and Underweight Baseballs on Throwing Velocity and Accuracy

Authors: Escamillia, RF; Speer, KP; Flesig, GS; Barrentine, SW; Andrews, JR 2000

This study reviewed a number of weighted-ball studies and how different training protocols affected velocity and accuracy.

  • Four out of five studies found that training or warming-up with an overweight baseball produced an increase in the velocity of the baseball.
  • Warming-up with heavier baseballs was not found to increase velocity for that training day.
  • More research is needed on the effects of warm-up with baseballs of different weights.
  • No study found that accuracy was improved by using heavier baseballs in training.
  • Ten of the eleven studies showed an increase in velocity using both over- and underweight balls.
  • No injuries were reported, but more research should be done on arm stress with baseballs, specifically ones of varying weight.
  • More research should be done on the kinetic and kinematic difference between throwing a baseball versus and over- and underweight balls.

This paper does an excellent job of breaking down the variety of training protocols that have been experimented with using weighted baseballs. The relationship between accuracy and weighted baseballs is something we are currently investigating with different training protocols. Expand for Vocab

Effects of Under- and Overweighted implement training on pitching velocity

Authors: DeRenne, Coop; Buxton, Barton P; Hetzler, Ronald K; Ho, Kwok W 1994

This study took 45 high schoolers and 180 university pitchers and randomly assigned them to two experimental groups and one control group. Group 1 pitched with a heavy, light and standard baseball 3 days a week for 10 weeks. Group two pitched with a heavy and standard baseball for the first 5 weeks, and then a light and standard baseball for the final 5 weeks. Group 3 served as the control group and pitched with a standard baseball for 10 weeks.

The training program consisted of increasingly longer bullpens. The weighted-ball sequence did not vary, and the pitch totals for the weighted baseballs in sequence were a 2:1 ratio (non-standard to standard weight). The subjects were also not allowed to participate in any other weight-training program during the study.

Statistically significant velocity improvements were seen between the weighted-ball groups and the control group. However, there were no significant difference between the two weighted-ball groups. This suggests that both a combined or blocked approach to programming may be effective in increasing velocity, which means athletes could potentially choose the programming they wish. Expand for Vocab

Comparison of Kinematics Between Overarm Throwing with 20% Underweight, Regular, and 20% Overweight Balls

Authors: Van den Tillaar, Roland; Ettema, Gertjan 2011

This study examined different joint movements during a throw in experienced female handball players. Maximal angles, angles at ball release, and maximal angular velocities of the joint and their timings were analyzed during the throw.

Both maximal internal-rotation velocity of the shoulder and maximal elbow-extension velocity significantly changed when throwing the weighted balls. The timing of the maximal elbow-extension velocity changed significantly as well as the timing of the maximal external-rotation angle of the shoulder. Maximal external rotation of the shoulder occurred closer to ball release when throwing the light ball when specifically compared to the other balls.

Previous studies by van den Tillaar and Ettema (2004, 2007) showed that the internal rotation of the shoulder and elbow extension were the main contributors for the maximal ball-velocity at release.

This supports the notion that weighted baseballs improve velocity by training internal rotation and elbow extension. Motor-learning research shows training small variations of a movement results in faster learning rather than repeating the same skill.

Effect of Different Training Programs on the Velocity of Overarm Throwing: A Brief Review

Authors: van den Tillaar, Roland 2004

This is a large review of how different training studies affect velocity. The studies were divided into 4 categories for review:

(a)  specific resistance training with an overload of velocity.

(b) specific resistance training with an overload of force.

(c) specific resistance training with a combination of overload of force and velocity.

(d) general resistance training according to the overload of force.

If you are looking to read further on results of using weighted balls in controlled settings, this study is a great resource. This review looks critically at how these studies were run with control groups, group sizes, training age, number of throws, etc.

The data presented indicates that training with underweight balls alone or in combination with overweight training enhances velocity. Training studies with overweight balls gave conflicting results.

A Force-Velocity Relationship and Coordination Patterns in Overarm Throwing

Authors: van Den Tillaar, Roland; Ettema, Gertjan 2004

This study examined the force-velocity relationship with handball players using ball weights varying from 0.2 to 0.8 kg. An examination of the data found a significant, negative relationship between force and maximal-ball velocity, as well as between ball weight and maximal-ball velocity. This means that the heavier the ball weight, the lower velocities that were seen. It was also seen that the heavier the ball weight, the more time it took before release. Angular velocities of the arm joints also decreased with the increasing ball weight.

It was also found that there were no changes in the relative timing of the different joints, suggesting that the overall coordination pattern of throwing is independent of ball weight.

Internal rotation of the shoulder (63%) and elbow extension (32%) were found to be the main contributors to total ball velocity at release. Maximal internal-rotation of the shoulder occurred at ball release and maximal extension of the elbow occurred on average 0.01 seconds before ball release. Elbow extension preceded the onset of the internal shoulder rotation. These joints most likely obtain these high speeds by making use of slower movements in other joints in a kinetic chain of movement.

Effects of Overload Training on Velocity and Accuracy of Throwing

Authors: DE, Brose; DL, Hanson 1967

This study randomly placed 21 baseball pitchers into three equal-sized groups. One group threw weighted balls; another used a pulley device to resist the mechanics of throwing. Once assigned to their groups, each pitcher trained three days a week for six weeks.

For both the pre and post test, each pitcher threw at maximal ability for 20 throws at a target located 35 feet away.

A general conditioning program was offered to improve the athletes’ motor fitness before the experiment started. The participants had three days of throwing for six weeks.

A warm-up was provided with a regulation baseball; five repetitions were thrown with their respective overload at moderate speed, followed by 20 reps at max. Following the overload, 20 maximal throws with regulation baseballs were made at a target 35 feet away. The wall-pulley group had a resistance tension of 10 lbs, whereas the control group followed the same procedure, but threw regulation baseballs instead of overload ones.

Both groups saw significant in-group increases in throwing velocity as a result of the training, with no significant change in accuracy. However, there was no significant difference indicated between training groups and the control group. Because there was not a significant difference between groups, the researchers concluded that overload methods do not significantly alter throwing velocity or accuracy. They also noted that the athletes were verbally told to emphasize throwing velocity, but the athletes also knew that their accuracy was being tracked. This suggests that they might have reduced their throwing speed in an attempt to gain accuracy.

Overload: Effect on Throwing Velocity and Accuracy

Authors: D, Litwhiler, L, Hamm 1973

Selected from the varsity and junior-varsity teams at Michigan state, 5 pitchers were assessed as needing gains in throwing velocity. The entire program was 12-weeks long, from fall through winter. The weight of the baseballs used increased every two weeks. For the first two-week period, a 7-oz ball was used; for the second, a 9-oz ball was used. One ounce was added to the overload after that, which means that during the last two-week period, a 12-oz ball was used.

Every player threw 3 times a week. They were allowed to warm-up on an individual basis with regulation baseballs. They then performed 15 throws with the weighted ball, 20 with the regulation ball, 10 with same weighted ball, and 10 with the regular ball. This resulted in 25 weighted-ball throws and 30 regulation throws. All throws were from the mound, and the athletes were instructed to alternate each weighted-ball throw between sub-max and max execution.

Throwing velocity was measured using Dekan Performance Analyzer, and the mean throwing velocity increased from 112.3 feet per second to 128.7 feet per second. Although the increases in testing velocity were constant throughout the study, the final test was conducted after a 24-day quarter break.

Throwing accuracy also increased, but it was not statistically significant. The researchers also mention possible bonus of increased conditioning and decreased drudgery of training.

Increasing Throwing Velocity

Authors: C, DeRenne; R, Tracy; P Dunn-Rankin 1985

Ten high-school pitchers took part in this study, all between ages of 16 and 18. They were split into two groups of five, with half in a group of overload exercises only and the other half in what was considered variable speed training (VST).

The entire program lasted 10 weeks, with each pitcher performing exercises three times a week. The pitchers were instructed to not do any other weight-training exercises during this time period. The underload and overload baseballs in this study only changed in weight by one-quarter of an ounce, from 4-6 ounces.

The overload group began each day by warming up for 15 minutes with a heavy ball, playing catch, and long tossing (to 150 feet) for a 15-minute period. After, they would throw at half to three-quarter speed to a catcher for 10-15 minutes. Once a week during an additional bullpen, each pitcher would throw hard for 20-25 minutes, with the first 10-15 minutes throwing the heavy ball and the remaining 10 throwing a regulation baseball. The pitchers used one heavy ball for two weeks and then moved on to the next heaviest baseball.

The VST group warmed up with a regulation baseball,played catch for 5-10 minutes, and long tossed, up to 150 feet, with the specific underload ball for 5-10 minutes. The pitchers then threw a 15-minute bullpen at half to three-quarter speed. Similar to the above group, once pea week the pitchers threw a hard underload bullpen for 10-15 minutes followed by hard throwing of 1-10 mins with a regulation baseball. The weight of the ball changed every two weeks.

The researchers found that both the overload and underload groups made significant gains in velocity. The average gains were almost twice as great in the underload treatment than the overload group (3 mph – 1.5 mph).

The Effects of a Baseball Throwing Velocity Improvement Program on Shoulder Range of Motion (Thesis)

Authors: Corey Rodrigo 2014

This study had 32 individuals complete either a control (20 athletes) or weighted-ball (12) throwing program. The program lasted 10 weeks. In total, the weighted-ball group threw 4 times a week, twice under the supervision of a training complex and twice under their own supervision.

After the 10-week training period, the only significant difference between the groups was that the weighted-ball group showed a significant decrease in dominant-arm total arc of motion (16.4 +/- 11 degrees). There was no other significant difference.

The researchers mentioned several limitations, including a wide range of ages in both groups: between 8 and 17 years old. The programming was done individually, but the researchers did not have a role in how athletes were programmed. There were also athletes that dropped out of the study, but they were not required to state why they dropped out of the training. Alternative workouts may have also been conducted, either lifting or other baseball work, which may have affected the results. The findings also have low statistical power, in part because of the small sample size.

Effect of a 6-Week Weighted Baseball Throwing Program on Pitch Velocity, Pitching Arm Biomechanics, Passive Range of Motion, and Injury Rates

Authors: M, Reinold; L, Macrina; G, Flesig; K, Aune; J, Andrews 2018

This is another long-term weighted-ball study looking at different programming. This study had 38 athletes randomly assigned to either a control throwing program or one that did the control and weighted-ball program.

The subjects in the weighted-ball group used balls weighting 2-, 4-, 5-, 16-,and 32-ounces, and they performed Half-Kneeling Throws, Rocker Throws, and Run and Guns.

The researchers found pitch velocity had a statistically significant increase: 4.3% of external rotation in the weighted ball group. The overall injury rate was 24% in the weighted ball group (4/17, as two members were removed for non-throwing injuries).

The velocities of both groups were low for high-school athletes (69.1 ->69.8 / 66.9 ->69.1), and although the programming started off lighter compared to the final week, it still consisted of three high-intent days a week. It’s also unknown what the control programming was, as the weighted ball group did both.

It’s unknown how the results would change under a different set of athletes or how the results would change with minor adjustments of programming on a per-athlete basis.

There is a longer write up on this study that you can find here.