A method including measuring time periods in which a reflex point of a subject is struck and a reflex response is observed. A method including determining a resting metabolic rate of a subject by applying the Kail-Waters equation. An apparatus including a striking instrument capable of delivering a kinetic energy to a reflex point of a subject; and a measurement instrument capable of being coupled to a subject and measuring a reflex response. A machine-readable storage medium containing executable program instructions which when executed cause a digital processing system to perform a method including determining time periods in which a reflex point is struck and a reflex response is observed. A machine-readable storage medium containing executable program instructions which when executed cause a digital processing system to perform a method including determining a resting metabolic rate of a subject by applying the Kail-Waters equation.