Step 3: Smoothing and pushing the basic forms
Once I have my leg separated, I first go to Mesh > Smooth to give me more points to push about. At this early stage, I am already thinking about where the patella will emerge from and how to define the ridge of the tibia that sits just below the flesh. Once I have pushed the vertices as much as possible, I use the Split Polygon Tool to start defining the edge flow. To access the Split Polygon Tool (hidden from the menu) hold Shift+RMB over the model and go Split > Split Polygon Tool. Beginning with the Sartorius, I make a deep cut from the anterior superior iliac spine towards the inside of the knee and continue to carry it through to the ankle (in reality, the muscle inserts into a tendon on the inside of the knee).
Smoothing the model and beginning to cut into it to define the Sartorius muscle
Step 4: Extruding out the masses
Continuing to bring out the major masses, I select a series of faces and then use Edit Mesh > Extrude to pull them out before working back into the model. I do this for the quadriceps and the patella. I'm not looking to create Mr. Universe here so I'm always softening the muscles back into the geometry but defining one or two edges to highlight the existence of the muscle. You may be thinking: Why add the flow if we won't really be able to see it? The reason for doing so is that if I need to animate the leg and show tension, the topology will be there and will support me to do so. To soften the muscle masses back into the form, I go Mesh > Sculpt Geometry Tool with the Operation set to Relax. By painting over the geometry, you can even out the edges.
Building up the quads and extruding the geometry to create the patella
Step 5: Adding further muscle masses
At this stage, I am still only adding as much detail needed to bring the forms out. Going in too heavily will mean you have lots of points to push and pull and can make things more complicated than they need to be. Work on the major forms and edges first and then you can always up the resolution. I continued to work on the lower leg by extruding out faces to act as the tibialis anterior, which is the muscle at the front of your lower leg that you'll notice in action when you lift your toes up (dorsiflexion). Again, during deformation, indicating that this muscle lives below the surface will add extra believability to your work. Continuing to work round to the back of the lower leg, indicate the calf muscles and notice how one of the heads of the gastrocnemius muscle sits higher than the other. Whist working on the back of the lower leg, you can also bring out the Achilles tendon by bringing the edges tighter together at the back of the ankle.
Continuing to focus on the key muscles that affect the surface