Mountain bike bars (and by extension -'Hybrid' bars) have a 'sweep' (the backward angle of the grip section)of 6 degrees or less which encourages the use of the 'attack position' - a riding position which is characterised by an elbows out riding style. It allows for flex in the arms to absorb bumps and woops in the trail and is useful when there's a requirement to move around the bike - shifting the body's CofG forwards for uphills and off the back of the saddle for steep downs. Whether 'flat' or riser, what a mountain bike bar finds difficult to deliver is comfort. For comfort you require a bar with a much greater backsweep of the type which some - particularly Euro style - city bikes come equipped with. But a high back-sweep bar doesn't allow for much position shifting, 'body English' as the Amercans call it, and they limit how far you can turn the bars before they clash with your knees. Flat bars cannot be comfy if used with straight arms (and a too long cockpit can also cause wrist probs in a rider forced to adopt straight arms just to reach the bars). And often, even fresh from the shop, bikes come set up with the bar's sweep poorly aligned, forcing the wrists into an even less natural angle. The sweep should line up with the forearms. Watch out too for brake levers which are too high, they should be angled somwhere close to 45 degrees from horizontal. You want close to a straight line through the sweep, the wrist and the lower arm.
More and more mountain bikers, particularly the long distance off-road touring chaps are using bars with a lot more sweep.
I might start a campaign against bars with inadequate sweep.
