I've been training Muay Thai for a bit and just recently joined a gym that teaches more boxing styled striking. In addition to learning a new stance, relaxing my shoulders, etc. I'm being taught to keep my fist vertical and turn it horizontal upon impact (when throwing the jab). The principle being that you'll be more relaxed and punch faster with a vertical fist and you only want to stiffen your arm (by turning your fist horizontal) on the moment of impact. What I'm having trouble with is integrating this into my punching. How exactly should I be training? Should I just throw a vertical fist when shadowboxing? What about focus mitts and heavy bags? How long does it take to begin doing this naturally? Currently I find it really awkward to rotate my fist after extending my arm and it slows down everything I'm doing so then sometimes I'll just throw a vertical fist and sometimes I'll just throw a horizontal fist because it's just most comfortable. If I spar I would definitely go back to what's most comfortable. Also is this technique done with only the jab or should the fist be turned with the cross as well? Thanks.