Which muscles for walking?

Last year when I went to the PARCC meeting in London there was an interesting table taped to the wall which describes which muscles are used in walking. I took a photo of this, which you can see below.

I took this so that I could double check that my stretches were picking up all the walking muscles, and of course to understand a bit more about the process.

Seven muscle groups are mentioned, and I'm summarising those as follows:

• The iliopsoas are muscles to flex your hips - these are used between when you heel lifts off the ground until the leg is mid-swing.
• The gluteus maximus are muscles to extend your hips - they are only used when and just after your heel strikes the ground.
• The gluteus medius muscles are used to keep your pelvis stable whilst you transfer your weight from one leg to the other.
• The hamstrings muscles are used to bend your knee and flex your hip. They are in use whenever one set of toes are off the ground.
• The quadriceps muscles are also used to bend your knee. They are in use whenever toes are being lifted off the ground or when the heel strikes the ground.
• The pretibial muscles are used to move the lower leg forward and are in use while the leg is swinging. 
• The calf muscles are used to flex your foot are are used when the leg is being swung forward.

I found this page also quite useful: http://www.oandplibrary.org/alp/chap13-01.asp

The summary is that although I hadn't heard of some of these muscle names before I think I've got all the various walking muscles covered in my stretches. I have been interested in seeing how much the muscles are used in the walking cycle - with most of these in use for 50% of the time. The question which this doesn't help me understand is if these are the muscles for the leg in motion, which muscles are being used for the leg which remains on the ground?

The other knowledge gain is the difference between eccentric and concentric activation of the muscles. Concentric activation is the 'traditional' shortening of the muscle to do its job. Eccentric activation of muscles is activating the muscle whilst it is extending. http://muscle.ucsd.edu/musintro/contractions.shtml