The good news is that you don’t need to spend a lot of time improving your general fitness, and it probably won’t make a huge amount of difference if you do. So long as you don’t overdo things at first you should get fit on the tour. The bad news is that you can pick up some quite serious injuries if you don’t prepare yourself and your bike properly.
The most important physical preparation you can do before touring is to ensure your bike is perfectly adjusted to fit you properly. Small adjustments can make a big difference over long distances. If your seat is just a little too high you could damage your ankles, too low and you could damage your knees. Try and do some long rides on the bike you will tour with to identify any causes of discomfort, which will become much more marked on a long tour. You will also learn your own abilities and limitations. Being incredibly fit is less important than learning to cycle at a rate you can safely sustain.
The most common causes of cycling pain and discomfort are the contact points: seat, handlebars and pedals.
The main physical discomfort you are most likely to get by cycling long distances is a sore bum. Being fit won’t make much difference to this, although if you can cycle faster you won’t need to sit on the saddle for as long! A good saddle is essential for touring, and padded cycle shorts are also highly recommended. A suspension seat-post will also help, though they aren’t always reliable. Fatter tyres at lower pressure will be more comfortable than thinner, higher pressure ones, but slower. If you use a leather saddle make sure it is well worn in beforehand. Take a chamois cream for saddle sores – you will almost certainly need it. It may be worth taking a gel saddle-cover; many cyclists think they make saddle pains worse but you may be glad of it if your bum is really sore.
You can avoid sore wrists by cycling with your arms slightly bent so that shocks are absorbed by the muscles rather than the wrists. This takes a lot of strength so takes some time to build up. Try cycling like this for short distances at first and build up to longer ones. Press-ups and other upper body exercises will help, though not as much as cycling. A pair of padded gloves will also help to protect your wrists. Use thick handlebar tape, even two layers, or decent grips. If your bike has flat handlebars a pair of bar ends will make a huge difference to bike comfort over long distances. On long climbs your shoulders and back can get very sore. Cycling out of the seat can help relieve the tension.
The height of your handlebars is very important. If they are either too high or too low you can get a sore back. They should be roughly the same height as the top of the saddle.
Cleated cycling shoes are the most comfortable for cycling long distances. Any shoes you use should have fairly stiff soles. Walking boots can make surprisingly good cycling footwear as they have stiff soles and keep your feet in a fixed position. Toe straps can make your feet go numb so make sure they aren’t too tight.
Working on pedalling technique is less important for touring cyclists than racing ones. However, over long distances it can make a difference. If you use cleated shoes or toe-straps, concentrate on the upstroke to maximise your pedalling efficiency. You could even try cycling one-legged for short distances and then switch legs. Try to minimise ankle movements – pedalling power should come from the legs – or you could damage your Achilles tendon.
Don’t worry too much about diet. In fact, if you’re going on a long tour you might be as well to bulk up a bit, as you will probably lose a lot of weight on the road. On the other hand, if doing a short but long tour (which due to time constraints is what most people tend to tackle) you’ll probably want to be as lean as possible. A few extra kilos can make a big difference on the hills.
When touring you should try and eat and drink regularly as you will burn a lot of calories and sweat heavily. You should also replace the salt lost from sweating in order to avoid cramps.
It’s a good idea to do some stretching and warming up before a long cycle. The Achilles tendon, in particular, is prone to damage while cycling so leg stretches are a good idea. Your back, shoulders and neck will also benefit from stretching exercises.
Remember, on a long cycle tour you are going to suffer a certain amount of discomfort and pain. There is no real way to avoid it, other than doing very low mileage per day, and would it really be fun otherwise?