The Kaiō-Ken is a special technique created by Kaiō-Sama. The technique amplifies your Chi to boost all of your status parameters hugely. More multipliers can be added by the user but it is highly discouraged as it boots tremendous strain on your heart and body, putting you in tremendous pain and needless danger of death. It is designed to be used as a last resort and not for prolonged periods of time.
Son Goku however pushed his body to it's limit while fighting Vegeta, pushing past x2 to x3 and even further, leaving him to be hospitalized indefinetely. However through rigorous training, Son Goku was able to effortlessly sustain a x20 Kaiō-Ken, something Kaiō-Sama never even thought was possible. Son Goku stopped using this technique after his Super Saiyan ability was awakened and the technique is never seen again in Dragon Ball Z. It is possible and likely that Piccolo, Tenshinhan, Chouzu and Yamcha all know this technique as well, as they all trained under Kaiō-Sama in the afterlife.