Muscles do a wonderful job of supporting all of the bones in the body. Each muscle has been intricately designed for a purpose. Some muscles work primarily to move the body and others work to position and support. It is the complex coordination of hundreds of muscles that allows a range of activities from walking to running, sitting to standing, squatting to jumping, and pushing to pulling.
Every muscle does one thing well, pull bones and tendons that attach to bone. Due to muscle structure and physiology, muscles can only pull to varying amounts. Since muscles cannot push bones, many muscles have a counterpart which pulls in the opposite direction.
One of the determining factors of a muscle’s function is where it originates and where it inserts. If you know where a muscle starts and ends, you will be able to determine how it pulls. Some muscles are simple and attach two adjacent bones and cross one joint. Certain muscles will cross two joints of the body, attaching bones that are not right next to each other.
Muscles that cross two joints can easily become stiff and lead to decreased flexibility. If left unchecked, decreases in flexibility can lead to problems with overall function. Since walking is a universal task, I will identify common muscles of the legs that cross two joints along with stretches to maintain their flexibility.

Gastrocnemius

This muscle is located on the back side of the lower leg attaching the heel bone (calcaneus) and the thigh bone (femur) together by crossing both the ankle and the knee.  This muscle has the important function of pulling the heel off the ground when walking, running, and jumping. It is also used to press the gas pedal of a vehicle. Decreased flexibility in the gastrocnemius can cause problems walking, especially walking down stairs.
calcaneous
To stretch the gastrocnemius: stand one-two feet away from the wall, keep the heel along the ground and lean in towards the wall, being sure to keep the knee straight. This stretch should be felt on the back side of the lower leg.

Rectus Femoris Muscle (a muscle of the quadriceps)

This muscle is located on the front side of the thigh attaching the shin bone (tibia) and the pelvis together by crossing both the hip and the knee.  This muscle has the important functions of pulling the leg forward and straightening the knee when walking, running, and kicking. Decreased flexibility in the rectus femoris can cause knee pain, especially when running.
Rectus-femoris-3D
To stretch the rectus femoris: Lay on your stomach, bend knee, and grab ankle with hand helping the knee bend farther. The stretch should be felt on the front side of the hip and thigh.
 

Hamstring Muscles (three separate muscles)

These muscles are located on the back side of the thigh attaching the pelvis and the shin bones (tibia and fibula) together by crossing both the hip and the knee.  These muscles have the important functions of pulling the leg backwards and bending the knee. Decreased flexibility in the hamstring muscles can cause problems with low back pain and bending down to touch the toes.
Hamstrings
To stretch the hamstrings: Sit with your legs straight in front of you and reach towards your toes. The stretch should be felt on the back side of the thigh. Note: the hamstring does not go down into the toes, therefore, if you feel the stretch in the toes you are likely putting a stretch on the nerve rather than the hamstrings.
 

Psoas Muscle

The psoas muscle is located on the front side of the hip attaching the low back (lumbar spine) and the thigh bone (femur) together by crossing both the hip and the joints of the spine.  This muscle has the important function of pulling the leg forward. Decreased flexibility in this muscle can cause problems with low back pain and standing up straight. Extended periods of sitting can lead to the tightening of this muscle.
Psoas-major
The psoas stretch: Stand near a counter and place one leg behind the other, keep the back leg and spine straight, and lean forward towards the front foot.  Stretch should be felt on the front of the hip.
 
If you have a tendency toward tight muscles and stiffness, you may benefit greatly from the stretches listed above, along with strengthening. For people without flexibility issues, the focus should lean toward strengthening these muscles to improve the stability and function of the joints.
I would like to encourage you to keep your body active and limber with a good combination of strengthening, aerobic, and flexibility exercises. 150 minutes of aerobic exercise a week along with 2 days of strengthening is recommended as the minimum amount of exercise for health benefits. If those numbers seem daunting, start with 5-10 minutes a day and gradually increase as the body adapts to the positive stressor of exercise. If you want guidance for any stretches or starting an exercise program, call for a free 15-minute phone consult.
 
 
4 Major Lower Body Muscles Impact on Flexibility and Function
 

4 Major Lower Body Muscles’ Impact on Flexibility and Function

 
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References:
Netter, F. H., & Colacino, S. (1997). Atlas of human anatomy. East Hanover, N.J: Novartis.