Methods and apparatuses for an oxygen consumption monitoring system are disclosed herein. In one embodiment, an oxygen consumption monitoring system is disclosed. The oxygen consumption monitoring system may comprise a probe, wherein the probe comprises a light source and a photodetector; and a main unit, wherein the main unit comprises a microcontroller and wireless transmitter. The probe may be hermetically sealed and may be capable of being implanted onto tissue. The photodetector may be capable of collecting reflectance data from the light emitted by the light source. The reflectance data may be capable of being sorted into arterial and venous blood oxygen consumption data for the tissue onto which the probe was placed or implanted. The data from the probe may be further sorted and processed to produce perfusion, heart rate, energy expenditure, caloric burn, blood pressure, hemoglobin concentration changes, and tissue oxidative stress.