Efficiency seems like a bad target, I'd rather aim for minimum damage. Food is cheap, we've got fridges and don't need to store much of our own energy as fat,

Efficiency seems like a bad target, I'd rather aim for minimum damage. Food is cheap, we've got fridges and don't need to store much of our own energy as fat, and many of us no longer do enough physical labor to experience significant fatigue. Plus, athletic performance is no longer a matter of everyday practicality. The biggest concerns, as I see it, become whatever mechanism causes health issues from being sedentary, and damage to joints by wear and tear.