Moving forward will put more stress on your knees, as you use more of your quads in a forward position. However, it's something to which most people are able to adapt. As for going with a shorter stem, that's only one part of the equation. Moving your saddle forward allows you to be lower in front with the same hip angle. If you choose a shorter stem, and keep your 6cm-back saddle position, you would need to raise your front end to keep your hip angle the same.

I do not mean to argue, withthe other post, but.. Why do you think it changes the use/strain on your various muscle groups?

I often hear that moving forward (or back) puts more (or less) strain on your quads (or hamstrings, glutes, etc...).

It seems to me that, other than a change in relation to gravity, that moving forward, as long as the saddle to bb distance is kept the same and the angle of the hips to the upper body is kept the same, that the strain on your muscles groups should not change. Obviously, bike handling will change, but I can not figure out why the use of muscle groups should change.

If you move forward and open up your hip angle or move forward and closed your hip angle then I can see why aspects of muscle use will change.

David K

If you do a web search on 'seat tube angle muscle' or some other variant, you'll find a ton of articles (some good, some questionable) that describe seat tube angle's effect on muscle use. Here's a rather good one:

"The position of the knee over the pedal axle should be regarded as the starting point from which minor adjustments can be made. A saddle positioned too far forward will decrease the knee angle at TDC; increased quadriceps activity will thus be required to extend the knee, raising the risk of patellofemoral injuries. Conversely, a saddle positioned too far backward reduces the effective working of the hip extensor (hamstrings and gluteus maximus) and knee flexor (gastrocnemius) muscles."

- http://www.pponline.co.uk/encyc/cycling-biomechanics.html

Steeper seat tube angles are also used by many triathletes becaue it puts more force requirement on teh quadriceps and leaves the hamstrings and glutes (primary running muscles) less fatigued.

From personal experimentation, I found that I can produce a little more power in the aero position with a more slack seat tube angle (75 degrees - but this is relative because I have fairly short femurs) but I can run much, much faster off the bike (2-3 minutes for a 10k), with only a slightly lower peak wattage output on the bike (~10 watts), at a steeper seat tube angle (78/79 degrees). I probably gain the equivalent of 10 watts on the bike just by being more aero.

I read your post and realize I know way too little about what I am doing.

Very impressive.