In all seriousness, I'm not sure why exercise is a potentiator of herxheimer reactions. I suppose it's due to several factors; raising the body's core temperature, the greater cellular oxygenation that happens during exercise, as well as immune system stimulation.
What I haven't figured out is how to schedule my treatments around my exercise regimen in order to create this reaction. Okay, so I'm not enjoying writing this right now with flu-like achiness running through my limbs, but I'm excited that my 45-minute yoga session in my backyard out here in the tropics has provoked a visit from ol' Jarisch because it means I've eliminated yet another layer of infection.
Since this has only happened to me on a couple of other occasions, it would seem that exercise rarely perpetuates a herx, but that may not necessarily be true. It may depend upon not only the timing of treatments but also the intensity of exercise, what stage the bugs are at in their lifecycle and the strength of the immune system, among other factors.
Try performing a Lyme disease treatment an hour or two prior to exercise. It just may bring ol' Jarisch a-knockin' at your door!