A variety of physiologic, metabolic, and pathologic states influence the duration of the ankle reflex response as measured by simple photoelectric devices. Youth and hyperthyroidism are associated with shorter measurements. Aging, diabetes mellitus, hypothyroidism, and the puerperium are associated with prolongations of the measurements. The clinical usefulness and application of ankle reflex measurement will be limited if such measurements are regarded as exclusively related to thyroid function.
Reinfrank RF, Kaufman RP, Wetstone HJ, Glennon JA. Observations of the Achilles Reflex Test. JAMA. 1967;199(1):1-4. doi:10.1001/jama.1967.03120010045007