by jdeks » Fri 25 May, 2018 5:41 pm
I might be able to add a bit of sports science to help explain this a bit.
Not to be a wet blanket but the perceived 'fitness' gain after an increase in a single exercise's load is indeed largely psychological, although the body does trigger some short term hormonal and metabolic responses to the physical stress to facilitate recovery. This is what you're likely feeling now, which in turn encourages and motivates you, resulting in more effort in exertion, thus feeling 'fitter'.
This is also why it feels like your 'fitness' drops off after a period of rest. No physical gain was actually made over a single trip - it's just your stress response winding down (because it's not needed if you're not stressing anything) . Veeeeery common with beginner weightlifters - you feel like you're superman about after a week in, stack on the plates, then suddenly your progress flat-lines.
Actual physiological changes take weeks of stress and recovery cycles normally. If you've been doing 18 months worth of hikes you would have undoubtedly already made some fitness gains this way, but it sounds like your Mt Barney trip was a bit more strenuous and sustained than your average load volume. Hence, the stress response was triggered anew.
This is where the concept of progressive overload becomes critical. If you walk 20km, 3 times a week, for 18 months, your body will adapt to become very good at being as efficient as possible at walking 20km three times a week, and no more. Truth be told, you were probably as fit as you were going to get doing that after 3 months. What you need to do is steadily increase that exercise volume over time, to keep triggering that stress response, and keep the body continually adapting to cope with greater loads - aka getting fitter.
The trick is not pushing too hard, too fast. Thats where both chronic and acute injury becomes a risk. Especially if you're a big fella doing a lot of walking, you need to keep in mine the knee support structures take longer to recover and grow than, say, your cardio does.
Try mixing it up a bit. Walk a few weeks and try to drop 5% of time or add 5% of distance each week. When you can't improve any further, rest for a week to reset that stress response and heal a bit, then go back and hit the trails with a mountain bike and try the same thing. Each rest cycle 'resets' that stress response surge and allows you to keep pushing the goalposts higher and make progress .