Originally Posted by Reno Bay
I think the thing is it's not just one session and you don't do it ever again. That wouldn't do anything...
Doesn't matter. First, you don't build strength by muscle twitches. You need to contract the muscle, and do it over a range of motion. The exercise physiology text I have says, IIRC, that muscle strength is only improved +/- 15 degrees of the position the limb is in. So if you do a bicep curl to 15 deg, then you have had some effect on the muscle when moving between 0 & 30 deg. And that is a muscle under load, not twitching.
Second, twitching a muscle 20 times would do less than using under a load one time. With humans, twitching a muscle for 20-30 minutes straight can help an invalid - assuming repeated sessions over weeks and months. But there is a reason that most athletes don't bother to hook themselves up to electrodes and have their muscles twitch while watching TV - it doesn't work. Not if your goal is getting stronger.
It may or may not feel good to a horse. It won't build strength or muscle.