I guarantee you will injure yourself on this trip. Whether it's one tiny blister (lucky you), a lingering tendonitis or two twisted ankles, there really is no way to avoid pain on a 750km hike. I ended up needing emergency surgery on my Camino.
Get Travel Insurance
I can't stress this enough. You'll be tempted to ignore your injuries, especially when everyone around you has similar problems. Do yourself a favour and get travel insurance and don't think twice about seeing a doctor. I spent CAD$270 for two months of travel insurance. I ended up claiming over €1380 in medical bills.
Some people get none, some people get them non-stop. The right combination of shoes, socks, blister covers and midday breaks will go a long way. Always try to deal with your blisters in the evening, when your walk is over and they can dry overnight.
Swap Out Your Socks
My blisters were caused by humid feet. My shoes weren't ventilated enough, and my sweaty feet would soften and blister more easily. Stopping once a day to put on a fresh pair of socks and air out my shoes was extremely helpful.
It's Coming: Blister Covers
Blister covers come in all different brands, but the one you'll see most often in France and Spain is Compeed. About €7 per pack of six. These work extremely well if you notice and cover the problem area quickly. If you wait for a blister bubble to form, the Compeed won't do much. I found blister covers always came unstuck during the day unless I diligently aired out my feet each break.
It's Here: To Drain Or Not To Drain
A favourite debate topic among pilgrims. My advice: don't drain a stiff blister and never cut off the protective layer of bubbled skin, even after it's drained. The raw skin below is sensitive and easily infected. If you can help it, wait for the stiff bubble to relax slightly (like a sad, old balloon) and then drain it in two spots with a disinfected needle. Do this before bed so it can dry out overnight.
Someone might suggest threading your blister with string to keep the drains open. I tried this but found it painful. Keeping it open also seems like an invitation for infection.
Tendonitis is the second most common injury I heard about on the Camino. Hiking with extra weight over uneven ground for 6-8 hours a day puts a lot of repetitive stress on your legs and feet, no matter how fit you are. The tiny abrasions on your tendons will be debilitating if you don't deal with them early. Check this page for more medical information.
I developed tendonitis (plantar fasciitis and peroneal tendonitis) fairly early on and struggled with it in both feet until Santiago. I saw three doctors during my trip and each told me to stop walking. They were right, but I didn't. Here's a list of avoidable causes and solutions:
1- Your bag is too heavy.
Get your bag fitted in a store before you leave so that it's balanced properly, and don't pack more than 10% of your body weight.
2- Cushion your soles.
Use insoles, even if your shoes are broken in. Consider that each step is a small whack at your tendons.
You should get in a few leg and back stretches every morning and at each break during the day. Stiff muscles will cramp and change your natural gait.
4- Drink more water.
Always true, but especially important for avoiding tendonitis. Don't wait until you feel thirsty. You should be sipping away all day.
5- Reduce inflammation.
I didn't find the prescription anti-inflammatory patches did much to reduce the pain I was in, but ibuprofen in the morning/afternoon and ice packs at night helped a lot.
6- See a doctor, take a break.
They'll tell you to stop walking, and you should. At least for a couple of days. Tendonitis can linger for a long time if you ignore it, and you don't want to bring it home with you.
Your shoes will either be your biggest asset or your biggest liability. If this is your first multi-week (or month!) hike, here's some general advice that applies to everyone:
Buy Shoes Half a Size Bigger
Bare minimum! Hiking all day will make your feet swell and your normal shoes will be uncomfortable. My feet went up an entire size by the end of my Camino! It ended up costing me a lot to replace my shoes on the go.
Break Them In
Especially if you're wearing new hiking boots with stiff ankle support. Try to take them for a couple hikes before you go, not just around town.
Do They Need to be Waterproof?
This depends a lot on when you're going and how sweaty your feet are. I had waterproof boots during Le Puy because of the cold and wet weather, but they kept my feet from drying out and I had more blisters as a result. Ventilated quick-drying shoes are a better choice in my experience.
It's worth the extra weight to have open toed shoes at the end of the day. Air out your feet with sandals you've already broken in.
Don't laugh! Walking pole pilgrims are doing it right. The extra weight is worth the support they give your knees on harsh descents and the attractive new arm muscles you'll walk away with.
I didn't follow my own advice. I bought shoes that were slightly too small and completely waterproof, which led to crushed toes and endless blisters. By my second week both of my big toenails had died. No big deal! But they didn't fall off, and the added friction led to infected blisters trapped underneath.
I ignored the pain in my feet for weeks until, finally, an extremely generous local woman saw how much danger I was in and took me to the hospital. My ignorance and stubbornness led to surgery and a 2 week hiatus from my Camino. Had I ignored the infections any longer and let them spread to my bones, I would have lost my toes.
It was an expensive, time-consuming and painful error... don't make my mistake!