J-Bands from Jaeger Sports are a must-have item for all youth baseball and softball players. All of the coaches my kids have had over the last few years recommend them, and they are crucial for any player who is pitching. Many kids start to have problems with their elbows and shoulders because they are weak and underdeveloped, and J-Bands help to strengthen them and also increase stamina.
J-Bands are surgical tubing straps with wrist cuffs for band resistance training, that create resistance at a level that anyone can use. It is recommended that players warm up with these before every practice and game to increase arm, shoulder, and elbow strength. This is something that players can easily carry in their ball bags and they will actually use them. All they need is a fence or a place to hook them to and they are ready to go. They are highly recommended by pitching coaches and they get great reviews on Amazon.
The reason these work so well is that they allow shoulder and arm rotation with resistance, resulting in strengthening of shoulders, arms, and elbows. And, as opposed to using weights which could be too heavy, anyone using them can go at their own stretching pace. If you start your kids early with these, they will develop the habit of using them every time they practice or play.
I have included a video below from Alan Jaeger, the creator of J-Bands, which shows some of the exercises he recommends doing with them.