u/ArtInevitable3556

i ride once a week at a riding school and have done so for about 2 years so have been being put on stronger horses for quite a while. not an issue since none of them are dangerous or frequent in any of their quirks. however, one of my most regular horses has suddenly woken up with a bolting issue these past 2 rides. i have since been told it is because he dislikes the outdoor arena and cantering behind another horse / being left behind even slightly, both of which we've been doing. i wouldnt mind if it wasnt constant. i think these past 2 rides, i've been bolted with at least 6 times. i am only 4'11 and he is a fit unit of a 15.2hh cob that rides like a 16.2hh, so its hard to keep my nerve when he gallops off with me. i have had to do a one rein stop already so i do know how to handle the bolting at basic level, is there even anything more i can do about it apart from sit deep, control my breathing and prepare for the bolt? since he is not my horse, i cant even do extra work with him around it. any tips would be appreciated, thank you!!

i dont know if im just really unfit but five minutes into a moderate to brisk walk on my treadmill and my lower back is sore beyond belief. its really frustrating because nothing else is hurting, just my lower back. is it my posture? my striding? what am i doing wrong? its very early into the fitness journey so maybe im just unfit?