Joint Actions
All full ROM squats effectively train both hip flexion and knee extension.
Primary movers
- Quadriceps
- Gluteals
Synergists
- Hamstrings
- Adductors
- Spinal erectors
- Abdominals
Image source: http://www.freefitnessguru.com/Anatomy/images/Power%20Squat%20front%20combined.jpg
Quadriceps
The quadriceps consist of a 2-joint muscle (rectus femoris) and 3 single-joint muscles (vastus medialis, vastus intermedius and vastus lateralis). The vastus muscle all originate on the femur and insert down on the tuberosity of the tibia (via the patella).
All of the quadriceps muscles are responsible for knee extension movements, but only the rectus femoris crosses the hip and originates from the iliac crest, allowing it to contribute to hip flexion as well.
