Why pedal with knee slightly bent?

A smooth pedaling stroke has always been the way to go. Smooth power application
is one of the keys to developing good power AND not wasting energy. If you fully extend your leg this somewhat interrupts that smooth stroke because your leg tends to sort of "lock out" at full extension and then it has to "unlock" to continue. Kind of like how you walk or run in that the knees never fully lock out. This locking would interfere with smooth movement and you would be walking kind of "jerky"(for lack of a better word).
Also there isn't a lot of power available, if any, in that last little bit of "lock out" or full extension.

Dennis Noward

Richard36 wrote:

When pedalling with a bent knee the leg are the muscles being properly stretched? If not is there any benefit if doing a long ride of doing the last 10 miles or so with the leg straight so that the leg muscles are properly stretched?

No.

Be aware that riding with a saddle that is too high can cause problems in and around the back of the knee. This has happened to myself as well as many others and can take a while to recover from, just warning you as it can happen.

BTW. For most people the muscles are not being stretched very much when cycling anyway.

There have been multiple studies done into optimum power vs. leg extension and the number is something like 89-91%. It's a common preconception that maximum extension is better - witness the number of people of TT / Tri bikes with hyper-extension in the belief that it is more aero - moving hips is a dead give-away. As well as posterior knee ligament problems, it also causes increased perineal numbness as you are pulling yourself onto the saddle, which people then alleviate with silly saddle angles....

bobtbuilder wrote:

Be aware that riding with a saddle that is too high can cause problems in and around the back of the knee.

+1 for this. Your saddle only needs to be slightly too high and it can cause nasty calf problems.

Calf problems not the only problem that a too high seat can cause. Hamstrings can also be overstretched by this. This is probable worse than muscle strain. By extending the hamstring too much can cause minor tears. Streching the hamstring should be done in a fairly static way to avoid this.

I'm not a physio or anything like that. But I spent a lot of time on the physios bench working on this with my hamstring (Tendonitis in mine) .... lots of static stretching....and dropped the height of my track bike seat by almost 1/2 inch... cured it...