I find this guy is very good for technical advice and drills for fitness too: https://www.instagram.com/mattgoddardfitness/?hl=en Any others? YouTube as well.
There's a few instagram accounts I follow which are great For S&C and fitness.. There's this guy called 'Boxing Science' on insta - S&C stuff mainly. Not that instructional, but gives a good insight into the sports science element of training. He has a few good boxers training with him - got links with the Ingle gym but also has Callum Beadrow, Anthony Fowler (eww) and a few others. Linked to that is this account called 'Red Zone Running' which is a really good account for HIIT training if you're looking for that. On the boxing side.. Tony Jeffries has set himself up as a sort of celebrity boxing coach in the US. Some of his instructional videos and drills are quite good though. Does boxing fitness work with the likes of Robbie Williams. @Mustafahsboxingtraining is a really good account for the technical side - he's got loads of nice videos with tips on boxing technique.
