GOOD FOR NOTHING. Nada. Zip. Zilch. Ixnay. Waste of time.

But 15% grades ARE good for loading your muscles up with that lactic acid we all love. Go for it. Fast twitch? WRONG. Steep hills will WHACK YOUR LEG SPEED. Forget about it.

Look you rocket scientists, if you want to do HILL INTERVALS, find a hill with a nice, rational 3-8% grade, 10% tops, maybe with a couple of SHORT steeper sections. The ideal hill interval terrain has a 5-9% grade and is 1-3 miles long. Then you can nail your HR in the LT zone for 5-15 mins or so and work on increasing your power/tempo on a long upgrade, in the saddle, out of the saddle, mix it up.