SHAKE Wight Arm & Chest Muscle Up Muscle Training Equipment I purchased this new about 5 years ago, but I no longer use it, so I'm selling it. The structure is such that when you hold it in your hands and shake it up and down, the upper and lower weights are揺れる by a spring, making it heavier than the actual weight of the body. The weight changes depending on how vigorously you shake it up and down. Your arms get quite tired after only a few dozen shakes, but if you keep at it, your muscles will get stronger. I work at a desk, so I kept it around my desk and used it during breaks, so I was able to keep using it quite consistently. There are no noticeable stains, and I think the condition is good. Condition: Good Dimensions: W36 x H12 x D12 cm Weight: 2.2kg Color: Yellow Made in Taiwan Training Goods Muscle Strengthening Muscle Building