Excellent discussion as we all prepare for paddling season. Reading between the lines I keep seeing the importance of making the most use of that mass of gray between our ears. In my younger days and in racing shape for triathlons I portaged Grumman canoes while carrying  full packs. I do not know when I actually herniated the disc but do know it took five years to recover. Now, like KF my limit is 70 pounds and that is up for consideration. At 6feet one I am really topheavy when portaging. For the bushwhacking days, IMO caution and patience are the utmost virtues. I refuse to suck it up and push on to the end. Fatigue will win over the best body type and then accidents follow. If we really know our bodies and all their weaknesses we can plan accordingly.