Break each into two primary movement phases such as a lifting phase and lowering phase. For each phase, determine the knee and hip joint movements occurring (i. e Hip Flx, Knee Ext), and then list the knee joint muscles primarily responsible for causing/controlling those movements. Beside each muscle in each movement indicate the type of contraction as follows:

a. I-isometric;
b. C-concentric;
c. E-eccentric.

is seen below

Explanation:

a) Isometric contraction is any contraction of muscles where little or no movement occurs. During this phase muscle tension is present but the muscles do not change length.

The muscles involved here is the abdominal muscle (Transversus abdominis, multifidus, internal oblique, pelvic floor which is a deep abdominal muscles, close to the spine and the rectus abdominis. Another muscle involved is the erector spinae muscles which is along the back and the spine. This muscles produce an isometric counter-tension to stabilize the pelvis and the trunk of the body.

b) Concentric contraction is when the muscle length decreases to perform a movement. This would be the rising phase in squat.

During the Concentric phase enough force is generated for your muscles to work against opposing forces and produce movement.

The the knee and hip joint movements occurring during this phase includes:

*Hip extension

*Knee extension

*Ankle plantarflexion

The muscles involved are;

• Gluteus maximus and the hamstrings (i.e., the long head of the biceps femoris, the semitendinosus, and the semimembranosus). The extensor head of the adductor magnus. They work with the hip during extension.

• Quadriceps femoris muscle group (rectus femoris, vastus lateralis, vastus medius, and vastus intermedius) act on the knee.

• Gastrocnemius, soleus, and plantaris muscles act during ankle plantarflexion.

c) Eccentric motion is when a muscle is lengthened during contraction. The eccentric movement happens during the downward phase of the squat motion as you slowly lower your body, when we squat.

The the knee and hip joint movements occurring during this phase includes:

*Hip flexion

*Knee flexion

*Ankle dorsiflexion

The muscles involved are;

• Gluteus maximus ( the largest but muscle) and hamstring muscles (Biceps femoris, semitendinosus, semimembranosus) works from the hip.

• The quadriceps (Rectus femoris, vastus lateralis, vastus medialis oblique, vastus intermedius) works eccentrically at the knee.

• The calf muscles, ankle flexors and posterior tibialis work eccentrically at the ankle.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.