The patello-femoral joint reaction force has a different pattern and
different values during level walking than the tibio-femoral joint
reaction force.
Morrison (1967) obtained in his experiments a mean peak value of
3.4 body weight for the tibio-femoral joint reaction force during level
walking.
We calculated as the highest value for the PFJR force 35 kg or 0.5
body weight. The patello-femoral joint reaction force is not only
dependent upon the quadriceps muscle force, but also upon the angle
of knee flexion (Figure 3). Since the angles of flexion are kept quite
low during the activity, the PFJR force is always smaller than the
QF muscle force.
The opposite is true for an activity during which the knee is flexed
to larger angles, such as deep knee bends.
Here, the larger angles of flexion yield a higher value for the vector
sum of the QF force and the patellar tendon force, which the PFJR
force must equilibrate. The maximum value calculated for the PFJR
force during this activity was 650 kg. The subject's body weight was
85 kg and this joint reaction force represents a force which is 7.6
times body weight.