Mountain Climbing and Physical Injury

Going downhill is always going to be high impact on the joints. Less energy is expended, joints hurt more!

Downhills are a killer... Uphill may be a cardio/pulmonary test, but it's the downhill that you'll feel for the next few days afterwards.

i know i would rather go downhill

On a bike!

Down hill is easier in kW terms, however downhill is more "DANGEROUS" if you are behind schedule and the wife is waiting

Going uphill, if the wife is waiting, can be equally as dangerous. NEVER EVER keep a wife waiting.

saw a show on discovery 2 guys going down a hill on a unicycle one of them did pretty well

In general, some of the answers given are correct. Generally, uphill requires more energy to do work (increasing potential energy). Downhill releases potential energy, converting it to kinetic energy, however the human machine must absorb more shock with every footstep to stop motion instantanteously. Going uphill we use gravity to slow our foot motion and shock is reduced.

On the other hand, a sure-footed, experienced, well-conditioned climber, who is not afraid to take chances, can sometimes "bound" down a slope, springing on the balls of his foot and recoiling the energy back from stretched muscles and tendons. This causes less shock to the heels and ankle joint, but may cause a repetetive strain injury to the tendons or ligaments in the toes and arches. The experienced "bounder" probably knows his/her own limits and will not push beyond them. Taking larger steps also means fewer impacts.

Actually, this is more common on lesser slopes than the 45-60 degree (or do you mean percent grade?) slope you mentioned. On very high slopes, you can even rope off and easily bound down-hill, experienced or not, while "on rapell". This takes very little energy, puts almost no shock on the body (the rope takes the shock)can be extremely safe, and does no damage, except to your pride if you manage to flip yourself upside down(I have seen this happen to newbies!).

You've put it much better than I should have, but the really easy way down a 45 to 60 degree slope is scree running, which is excluded from this question and is best done by males in late teens/early twenties. One minor additional point is that it depends whether you have better knees than ankles or vice versa: when I was in my early forties I found it much easier to walk up steep slopes than down them even though I expended more energy in the process.