Beg to differ. Hips rotated back is the way to go. Straighter back brings in you butt and lower back muscles much more into play, increasing your power.
The whole idea is to arch you back and bend in the lower middle of your back.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1