In reply to Trangia:
> I wonder if a similar scenario could affect ice climbers?
Where's Dorothy Grace Elder when you need her?...
From my experience, a fair number of 'sedentaries' have patterns of movement where they hinge ( flex and extend) from the low back, with the lower limbs contributing the minimum of effort.
In terms of snow shovelling, this would tend to result in them staying flexed in the trunk, with any straightening up still keeping them flexed at the trunk, just less so.
The diaphragm doesn't work too well like this, so you'd tend to recruit your shoulder girdles to help with the increased effort of breathing - this is a very energy demanding form of breathing and also the volume of breath would be smaller because the abdominal contents are squishing the bottom of your lungs in this situation. Not only that, but the shoulder girdle muscles would already be doing shovelling work.
By contrast, unless you're having an epic, in climbing you'll be spending a lot more time with a relatively vertically aligned trunk, and the lower limbs contributing massively to working against the forces of gravity.