Which in turn means, I think, that your legs are probably more stressed than you think they are, and probably need more recovery between hard workouts than you think they do.
When we're training fairly hard, we're walking a thin line between peak fitness and injury/breakdown. So, often we're closer to going over that line than we think. So...be careful. Give yourself recovery days and recovery weeks, even if you don't think you need them (get a massage to help you realize you do need them).
Fri: X-trng (wts, abs, arc trainer 10 mins, bike 20 mins)
Sat: 10k easy in 56:36 (30:07, 26:29)