Reflex
something that is so simple yet people didn't realise it. By doing things that you know fast, actually conditions your body to it. As you do it WITHOUT thinking much -> you will need your body to react to it faster than you think about it.
Simple exercises like doing turnovers. You may think, how boring. or can't recall what to do about it..but WHAT IF, you do a turnover the minute you touch your partner or the moment your partner comes out of it and its your turn to it?
do you realise the SPEED and FAMILIARITY that is required of you to do it? and the thrill of doing it when done in good sporting spirit with your partner?
The coach had a good point. When your opponent or partner is in that position, you shouldn't be thinking too long on what to do as your will have missed your chance by then. It should just come naturally. Not just for groundwork, it applies for all other techniques (standing and groundwork)
So its doing every single exercise fast once you have the right position or right stance.
even small ones like push ups, situps, sprints. These train your muscles to be fast, so that you can be fast when you need to..
am sure this applies to not just judo but to all other sports.
being AWARE of what you are doing. Do it well, do it with a purpose.