What are the biomechanics of a barbell bench press?

[Hønter]

Since I train powerlifting I have started to get interested in the mechanical analysis of the different exercises. But the bench press I haven't been able to figure out. When I am considering a dumbbell bench press the mechanics seems simple, but when I consider a barbell bench press it becomes difficult. When the hand is fixed to the barbell, I can't figure out what happens at the elbow. So can someone please help me figure this out. If you could use the figure or make your one figure and explain the forces and torques involved i would appreciate it.

 

[zhermes]

I'm not exactly sure what you're asking, the elbow (B) moves up and towards the center (i.e. moves towards the line connection A and C).

When you start from horizontal: the lever-arm is just A-B, which is being torqued. That becomes transferred via B-C to lift the bar. This is probably a good approximation throughout the motion, but technically I think it gets a little more complicated as your start to raise your elbows.

Does any of that help with your question?

 

[Hønter]

This is probably a good approximation throughout the motion, but technically I think it gets a little more complicated as your start to raise your elbows.

That is exactly when I don't understand things. If you consider the situation with dumbbells, the torque at the shoulder is the force from the bar (F) times the horisontal distance between A and C. The same for the torque at the elbow which is the F times the horisontal distance between B and C. But when the hand is fixed to the barbell things get changed.