9.81 m/sec^2

It seems unfair to me that going down stairs / downhill hurts more than going up stairs / uphill after a difficult workout or race. I mean, gravity is working in our favor on the way down... have to fight it on the way up... so, what's the deal? Turns out, going down a slope requires an eccentric muscle contraction (muscle lengthens), whereas going up requires a concentric muscle contraction (muscle shortens). It is the former that results in lactic acid build-up, and is currently "of interest" because people with degrees higher than mine have noticed an increased rate of muscle soreness and injury. However, just because it hurts more going down stairs doesn't mean that you are actually working harder (this is apparently a relatively common myth... not sure why... guess they haven't had to draw zillions of free body diagrams). #20