WHAT IS OVERLOAD AND UNDERLOAD TRAINING
By increasing and decreasing weight loads during training, muscles will increase response and strength. At its most basic form, fitness can be examined as a prime example of overload training and underload training. For pitchers, long toss is the earliest form of such, as longer distances act as the "overload Training". Weighted baseballs and their throwing programs utilize this type of training, but be wary of what they do NOT tell you (as described below).
To increase or decrease load, one can utilize weights, resistance, elevation, or decline. Additionally speed and tempo can be utilized to maximize training results under this type of training.
HOW WEIGHTED BASEBALLS WORK
Weighted baseball "experts" utilize maximum overload training and underload training through baseballs that weigh between 3 - 10oz. A regulation baseball weighs 5oz, and the idea is that by uploading and underloading the throwing shoulder, muscle response, support, and arm speed will adapt - effectively increasing velocity. Basically, the weighted baseballs retrain motor patterns and shoulder strength so that arm speed increases. However, there are two issues that not addressed (and ignored), which are support and fulcrum leverage.
FULCRUM LEVERAGE AND SUPPORT
Fulcrum levers are joints utilized to move body parts. In throwing terms, shoulders and elbows. These levers work hand-in-hand with support from the lower half and abs. For example, curl 20lbs. Now do it on one foot in a release point position (for pitchers). Now do it on a slope.
What you will find is that 20lbs on flat ground with proper support can be easily curled. Fatigue is minimal. However, once support is minimized by (1) taking out one leg, (2) applying pressure upon the abs to keep the upper body erect during release point position, and (3) slope of mound - 20lbs is very difficult to curl.
Here in lies the issue, as support changes considerably - based upon body positioning, work plane, and weight. Even though the dumbells weigh 20lbs, they weight much more under the conditions listed above.
Another issue to consider is that since a shoulder and elbow are fulcrum levers, they are the weakest "link" in the chain of support. The most amount of pressure and stress is placed upon the fulcrum joint - as per physics THEORUMS. Hence, injury risk is great and exposure towards such can be greater.
Lastly, the further away the load is placed from support, the more it increases the kinetic weight of such load - causing even more stress on the fulcrum joints. This requires a major increase in strength or compensations occur in support SUBCONSCIOUSLY - resulting in breakdowns and potential injury.
WHY WEIGHTED BASEBALLS ARE DANGEROUS
By taking into account physics and their THEORUMS (not theories), we can understand why weighted baseballs come with major health risk factors. Young pitchers are still learning to throw properly, their bodies are underdeveloped and cannot support the strain that weighted baseballs place upon fulcrum joints, strength levels, and support.
Additionally, weighted baseball throwing programs clump athletes and we all know that every pitcher moves differently and is at a different growth rate.
Although the ideal of over and under load training has proven to be successful, the "loads" are placed far from the body (into the throwing hand) and fulcrum joints are stressed considerably.
Weighted baseball experts continually state their findings are backed by science and research. The issue is that their research comes from the DeRenne and Coop projects from the late 80's, did not consider individual pitching experience or strength levels, and were completely flawed when it pertained to normal pitching conditions.
Another thing to consider is that injury can never be tracked scientifically and weighted baseball experts continually cite a proven track record of health. This is misleading and at times - completely false.
Track injury rates in your area. If you see a pattern or correlation between injuries and weighted baseballs, you can come to a better judgment call as to whether weighted baseballs will not place stress upon your throwing arm.
At CPU, pitchers utilize over and under load training by keep the "load" close to the body's support to ensure fulcrum levers are not stressed. This type of positioning has a stellar health bill that has produced over 85 NCAA and professional baseball pitchers.