Javier Martin said:
It's good to walk with your backpack, to let your back to know about this extra weight.
Javier makes a point that I would like to expand on. General fitness for most urban dwellers doing ordinary things focuses on (1) aerobic capacity, (2) flexibility, (3) strength, and (4) endurance. These are the "Big Four" aspects of fitness.
However, each of these factors focuses on "subsystems" of the body, such as heart/lungs, muscles, tendons and joints. That's fine for normal, everyday life and typical sports as practiced by the average person - not elite athletes. Moreover, the "big four" deal only with the body - not the mind.
For unusual activities, such as sustained walking over weeks (eg the Camino), high-altitude trekking (eg Nepal, Andes), we need to adress a 5th fitness factor. I have called this factor "work hardening" in posts here last year, but a better word might be "contitioning".
Conditioning involves doing training activities as close as possible to the actual activity being prepared for (eg the
Camino Frances). Conditioning trains the body and mind as one holistic entity, in conditions of terrain, weather and mental state similar to the actual event.
While gym workouts are useful for everyday fitness, they are done indoors, in comfortable weather, when one feels like it. In other words, gym conditions don't mimic the mental conditions one might face on a long distance walk, on which one might become tired, injured or simply de-motivated. The same comments apply to swimming and cycling, neither of which are remotely relevant to walking the Camino.
During the Camino, one will be carrying a pack in good and bad weather, so train with a pack and try to go out in bad weather as well as on nice days. In bad weather, when tired or hungry the bodily sub-systems and the mind adapt to those stressors in a connected way.
It's difficult to explain the concept properly in a short posting here, but I hope these remarks provide a glimmer of insight into why it is so important to train by doing the actual activity. Of course, that's exactly how the pilgrims of yester-year did it: they trained by doing the actual pilgrimage itself, taking rests and longer term stops as required. That's a valid way of proceeding, but most of us today are driven by fixed vacation and flight schedules, so we don't have time to "waste" (if I can put it so inadequately).
Anyway, I would be happy to expand on the topic if readers desire it.
Regards
Bob M