Everybody has varying levels of fitness and different ideas on how you should prepare for an event like this. Most people agree that if you have little or no fitness you should start slowly and build up over a period of time, doing more miles each time until you can manage the daily amount of miles you want to achieve. I am lucky in that I already have a decent level of fitness. During the spring and early summer months I clock up about 100 / 150 miles a week over three or four days. Not a huge amount I know, but regular and enough for what I expect to achieve.
Another aspect is that this ride will be more challenging than a normal road bike ride. Although some of the towpath will be pretty easy to manage, I know that a lot of it will be muddy with long grass and exposed hills with headwinds and steady climbs. My mountain bike weighs 19kg, my kit weighs 10kg, my water bottles about 2kg and I weigh 75kg. A total of over 100kg to pull over the Pennines in what will probably be wet or windy conditions.
There's only one way to prepare for this and that's to try and train in similar conditions. Luckily, the summer hasn't been that hot and sunny yet! As of the end of June I've started back at the gym in order to build up my core muscles and stamina under the watchful eye of my new personal trainer! Hopefully, he can manage my fitness in a way that won't cause any aggravation to my knee.