When my sister, Alison, and I hiked the Tour du Mont Blanc (TMB) this summer, one of our primary goals was simple: Stay upright and protect your focus. That may sound like a modest ambition, but on a steep mountain trail covered with loose rocks, roots, boulders, and uneven footing, it requires considerable effort – particularly for two hikers over 60.

Going uphill was physically demanding. Going downhill was trickier. A rock that looked stable could move under your boot. A root could catch you...