The should not be run at more than the continuous stall torque value.
Are you thinking of CNC'ing the knee as Z axis?, this is not considered a good idea due to the inertia of combined knee table and any work piece.
For operations such as peck drilling etc, the inertia is extremely large usually requiring a high gearing ratio.
The torque required to turn the axis is the break-away torque, the torque required is calculated on the desired accel/decel rate.
Which has to be within acceptable motor to load inertia ratio.
There is free sizing software on the Kollmorgen site.