Q: What muscles are emphasized when I bench press with my hands close together instead of far apart?

A: Close-grip bench press emphasizes tricep muscles. The regular wide grip bench press emphasizes chest with some support from triceps and shoulders. As the grip gets narrower, and especially once it's shoulder width or less, triceps are emphasized more and more with some support from chest and shoulders. To really hit the triceps, try keeping your elbows close to your body while doing this exercise, as opposed to letting them flare out to the sides which is normal during bench press.

Close-grip bench press is an excellent tricep exercise, probably one of my favorites along with skullcrushers. Always have a spotter if you go to failure on this exercise (or on the regular bench press). Also note that if you can lift same or more weight using close-grip as using regular/wide grip, it's a sign that your chest is relatively weak compared to your triceps -- it's probably a good idea to do more of regular bench presses at that point.