Leg extensions are a simple, single-joint exercise that offer an excellent way for beginners to develop enough strength to move on to more technically demanding exercises. This is one of the best exercises for isolating the quadriceps, a group of four muscles located on the front of the thigh. The quadriceps are powerful knee extensors used in climbing, jumping, running and rising from a seated position.
Rectus Femoris
This is the most superficial muscle of the anterior thigh. It is the longest muscle of the quadriceps group and the only one to cross the hip joint. The rectus femoris originates at the front of the hip bone and attaches to the tibia via the patellar ligament. This muscle not only works to extend the knee but also to flex the thigh at the hip. Leg extensions stretch this muscle, which makes the work on it more intense.
Vastus Lateralis
This muscle is the largest of the group and forms the lateral, or outside, border of the thigh. The vastus lateralis muscle runs from the upper, lateral femur through the patellar ligament to the tibia. This muscle is responsible for extending and stabilizing the knee.
Vastus Medialis
The vastus medialis forms the lower, medial aspect of the thigh. This muscle's upper attachment is to the upper border of the femur. It then joins the other quadriceps muscles in the attachment to the tibia through the patellar ligament. The vastus medialis not only extends the knee but is also responsible for stabilizing the knee cap.
Vastus Intermedius
This muscle lies between the vastus lateralis and the vastus medialis and below the rectus femoris. The vastus intermedius is the smallest muscle of the quadriceps group and is used only to extend the knee. It runs from the upper femur through the patellar tendon to the tibia.
References
- "Anatomy & Physiology, Second Edition"; Elaine N. Marieb; 2005
- "Strength Training Anatomy, Second Edition"; Frederic Delavier; 2006
- ExRx.net: Lever Leg Extension
