Hi there, this is Coach Andy W. and the following is an email response that I sent back to a confused/frustrated rider. He was having some issues concerning the height of his handlebars and was also the victim of some bad bike-advice from arguably the most common source of bad bike-advice: a riding buddy!
And that takes us back to bar position: bars too far forward (too low--away from you) means giving up the bend in your arms (range of motion) and your weight will end up tossed (bucked) forward onto your hands (if your arms are already straight, and your front wheel has to drop a foot, your core is going to have to go forward with the bike and your weight will be thrown onto your hands). Bad news. Bars too high and your arms will be all cramped up/bunched up in your chest and you won't be able to manipulate the bike effectively, thus you'll start to lean back to get your arms in a better position and then you'll be too far off the back, giving up the balanced, stable, and neutral position (this is why you shouldn’t lean back on descents, but instead stay neutral by continuing to keep your weight over the bottom bracket). Also, muscles function best (strength, reaction time, balance) when the muscle belly is half contracted. This is another reason why the half push-up, half squat is most effective athletic position for the human body.
Many riders also believe that if the bars are set-up to descend well, then they are too high for effective climbing. Not true. Proper climbing depends, again, on core position, not bar height or where a rider’s hands are located.