First of all, if you're a shepherd who does his/her own shearing, I recommend the book Shearing Day, although I'm going to disagree in a bit on the diet recommendations within it. The tips on how to prepare the shears and how to hold the sheep were very helpful.
The biggest health related note about shearing, is that this is an endurance exercise. Champion shearers can finish a sheep in a couple minutes, and they maintain that pace for eight hours. A sheep can weigh up to 300 lbs, and although most of the time the majority of their weight is on the floor, you have to move that weight around in a precise manner through six positions to keep the sheep calm enough to remain passive while you get to every inch of it's body. (And that's after you've managed to catch a sheep and move it to the shearing floor.) That is a lot of work.
I'm no Champion shearer. I'm not even sure I've really understood position 1 yet, and I couldn't tell you how to transition to position 2. Last night we spent some time in position 1, got some belly wool clipped and hoof trimming done. By this time I was exhausted and called it a night. But the sheep was also exhausted, and decided not to try very hard to get up. I took advantage of her passive nature and sat down beside her to clean off her head and shoulder in a completely inefficient pattern. Eventually I decided I was really really done, and rolled the sheep onto her feet to help her up.
Afterward, I was sore. There is lots of bending over from the waist going on during shearing, and the legs knew it. I was severely handicapped at bending over, climbing stairs, or even rising from a chair. I could walk or stand fairly comfortably. I went to bed and fell asleep with my glasses on and book out while the lovely heated mattress pad soothed my tired body.
In the fibromyalgia days, overdoing it to the point of muscle exhaustion would have been followed by a night of cramps, a half day of walking with crutches while I stretched out those cramps, and a week or two of recovery through drugged sleep. Now? I'm a little sore, but I'm recovered enough to consider doing it again tonight.
Here's a couple of my girls before and after shearing:
A bit about diet. Yes, I was starving when I came in. I had exceeded my aerobic capacity while shearing. The diet recommendations in the book reflect standard recommendations for other endurance sports, eating a high complex carbohydrate diet every two hours, with lots of water to lubricate that carbohydrate digestion. I see no reason why I can't train my body otherwise, like a ketogenic endurance runner would. I think on future shearing sessions I'm going to bring my heart rate monitor and see if I can set a slower pace that my metabolism can better keep up with. If I can't keep my heart rate down, then perhaps I should shorten the sessions.