TRNR's gel balls GEL BALLS are a set of 3 balls that are ideal for grip strength training. It is effective for muscle training and as a handgrip ball to train grip strength. There are three types of strength: 10 kg, 20 kg, and 30 kg, and a wide range of strengths can be used to improve grip strength. Since it can be used on a daily basis as a health device, it is also useful for relieving stress. It's lightweight and portable, so you can train anywhere. It is an item that supports a healthy body!