Can i use a martingale with a english hackamore bit?
A running martingale should never be used with any leverage bit or hackamore. Leveraged hackamores include both bosals with heel knots and mechanical hacks with shanks. You can combine a standing martingale (which is independent of the reins and is attached with its own noseband) with a leveraged hackamore, and that is the only way to correctly do this. If you want to use a running martingale or German martingale, etc. that acts on the reins, you should only use it with a plain, non-leveraged snaffle bit. I am not sure if one can be used with a bitless bridle like the Dr. Cook effectively, but that might be an option.