I have found a lot of content on the patellar reflex, but I cannot find any studies on how fast the reflex is, from onset of stimulus to innervation of muscles. Does anyone know of either a study or at least a ballpark number for how fast that reflex is?
Mamizuka et al. (2007) calculated acceleration data of the patellar reflex.
Their study measured the reflex generated in response to the tapping force applied to the patellar tendon with a customized tendon hammer. They measured using a tri-axial accelerometer placed at the ankle joint.
the time delay (29.6+/-6.0 ms) and the acceleration time (150.8+/-19.5 ms) of the speed response were quite constant for all participants.
Mamizuka, N., Sakane, M., Kaneoka, K., Hori, N. and Ochiai, N., 2007. Kinematic quantitation of the patellar tendon reflex using a tri-axial accelerometer. Journal of Biomechanics, 40(9): 2107-2111