The large spikey massage ball can be used to release tight,-uncomfortable muscles and can help to release toxins and improve circulation. Best used as a pair (sold separately) to work through trigger points or for dual muscle massage. You can use them with one in each hand,-under each foot or to provide balance when placed either side of the spine,-or under the buttocks. The larger size provides less intense pressure,-if you are looking for a harder pressure we also have a smaller version available in a 7cm size. Product details: Dimensions - 9cm diameter Colour Blue Material -Phthalate Free PVC