Other quotes:
“The second exercise used is Closed Kinetic Chain Exercise (CKCE). CKCE are performed where the foot is fixed and cannot move. The foot remains in constant contact with the surface, usually the ground or the base of a machine (8). These exercises are typically weight bearing exercises, where an athlete or patient uses their own body weight and/ or external weight. When external weight is added, it is usually rested across the back of the shoulders or the front of the chest. Examples of these exercises would be the Squat (both front and back)…CKCE concentrates on a co-contraction of the quadriceps, hamstrings, hip flexors, soleus, and gastrocnemius muscles (9). In addition, this is a multi-joint movement, which focuses on the knee, hip, and ankle. CKCE are labeled as being “sport specific movements” (11).”
“Closed Chain: An exercise or movement in which the end segment of the exercised limb is fixed, or the end is supporting the weight. Most compound exercises are closed chain movements.”
“CLOSED KINETIC CHAIN EXERCISES are those in which the force
applied is not great enough to overcome the resistance. Examples would be the
push-up and squat exercises. To clarify for the novice list reader, even
though the load applied during the squat is on the body, the force generated
is applied to the ground, not the bar. To move the bar, the lifter must apply
a force against the earth great enough to overcome the resistance created by
the load on the bar. (Paul Chek)”
Hopkins et al. (An Electromyographic Comparison of 4 Closed Chain Exercises, J Athl Train. 1999 Oct?Dec; 34(4): 353?357.) studied 4 closed chain movements including “quarter squats”.
The originator of the closed chain/open chain concept, Dr. Steindler, defined it this way:
"A closed kinetic chain, on the other hand, is one in which the terminal joint meets with some considerable external resistance which prohibits or restrains it free motion. Eventually, the external resistance may be overcome and the peripheral portion of the joint may move against this resistance, for instance, in pushing a cart or lifting a load; or the external resistance is absolute, in which case the proximal part moves against the peripheral, as for instance, in chinning oneself on a horizontal bar; or the limitations of the muscular effort may assert itself both peripherally and proximally and may be unsurmountable, in which case no visible motion is produced. Only in the latter instance is the kinetic chain strictly and absolutely closed.
However in common use we apply the term to all situations in which the peripheral joint of the chain meets with overwhelming external resistance."
Do a review of literature about using closed chain movements for knee rehanb and in a VAST majority of cases, the squat is categorized as a closed chain exercise.