Training at the Top Rank Gym in Las Vegas Yamanaka has been working alongside Ryota Murata's trainer Ismael Salas. Salas, from Cuba, will be perfectly aware of the talent and potency of Yamanaka's left hand, dubbed the "Left of God", though has noticed some flaws in the champion. These have included Yamanaka's somewhat poor right hook which has been a focus of Salas's training and something he has been working on in particular.
Although we don't expect Yamanaka to become a right hook specialist the training does appear to be working with the Japanese fighter making a number of tweaks to the way he throws the hook. It's fair to say that if Yamanaka can continue to just improve various parts of his game then it's going to be hard to see fighters beating him.
Although no opponent has been officially announced for Yamanaka's next bout, expected in April, we'd be very surprised if it wasn't someone he was going to be able to use that right hook against. This may well add to the strong rumour that it will be Stephane Jamoye that Yamanaka fights next, with Jamoye being the fun to watch aggressive fighter that will act as a straight forward target for an intelligent right hook.