Let's start here, and maybe this is going to show some bias, but what is magical about the weight of a baseball (5oz)? Hear me out, you’re going to the beach for a hike and your 12 y/o child picks up a rock, do you have a scale in your back pocket to weigh the rock to ensure it’s safe to throw before he launches it into the water or at the tree down the way?
Look, it's no secret that weighted balls (plyo balls) have grown a ton in popularity in recent years and become increasingly polarizing as they get blamed for the rise in injuries we see from the youth level to the pro level. But is that deservedly so?
Mike Reinold ran a study that showed that weight balls carried an injury risk in athletes between the ages of 13-18, as two were hurt during the study and two in the following season. The participants in the weighted ball program started at a higher velocity than the control group and increased velocity 2.2 mph. Reinold has also produced a study showing increased external rotation following a weighted ball routine, an increase in external rotation or lay back does contribute to increased velocity but also potential stress to the medial elbow. There are many other studies showing the efficacy of weighted ball programs to increase pitching velocity as seen in the photo below taken from Driveline's website.
While velocity improves with lighter loads (3.5oz ball v 5oz ball) in both skeletally mature and immature athletes, which theoretically should accompany increased torque (stress) of the elbow, that increased stress only occurs in skeletally mature athletes. A study by Okoroaha et al saw stress to the medial elbow decrease with weights lighter than a baseball even with an increase in velocity and arm speed. This begs the question, should we be using more under load baseballs in youth athlete programs or should the baseballs they play/ practice with be decreased. Would we see fewer injuries to adolescent athletes?
The correlation between increased velocity and injury risk has been made clear through numerous studies and especially when you throw harder than kids in your age/ developmental bracket. But what's your alternative, to be bad at baseball?
Even though velocity is increased with lighter loads, this study has changed how I progress my rehab throwing plans for these younger athletes coming back from Little League Elbow or Little League Shoulder. While a mature high school athlete may start their throwing plan with an overweight ball due to decreased relative torque at the elbow, a youth athlete's plan may start with underweight baseballs as we slowly build the capacity of the elbow to tolerate the stress of throwing.
In my opinion weighted balls are a tool and like anything, and something we can use to manipulate stress/torque. Ultimately it’s just the weight of the ball and it's more important how we manage volume and intensity of throws per week/month/season/year. It also appears the risk may not be worth the reward for kids to throw a lot of over weight plyo balls with high intent, but why not utilize more under weight baseballs? Why not teach kids to improve their arm speed without adding increased torque to the elbow? We may not need these kids to be on these comprehensive velocity programs but again, the weight of the ball is not the sole cause of injury. Injuries are complex, its one piece of the amount of stress applied at the elbow.
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