A stamina monitoring device for estimating a stamina level of a user, comprising: a sensor module configured to sense a physiological signal from the user; a user interface configured to receive a biological information of the user and to output the estimated stamina level; a storage module configured to store the biological information and at least one mathematical model; characterized by: a processing module configured to use the at least one mathematical model to perform a process comprising steps of: estimating an anaerobic energy level and an aerobic energy level in real time based on the physiological signal and the biological information, wherein estimating the anaerobic energy level and the aerobic energy level in real time comprises: estimating the anaerobic energy level based on anaerobic estimation settings, wherein the anaerobic estimation settings are adjusted based on the estimated anaerobic energy level when the actual physical condition of the user is underestimated; and estimating the aerobic energy level based on an aerobic estimation settings, wherein the aerobic estimation settings are adjusted based on the estimated aerobic energy level when the actual physical condition of the user is underestimated; and estimating the stamina level based on the anaerobic energy level and the aerobic energy level. a sensor module configured to sense a physiological signal from the user; a user interface configured to receive a biological information of the user and to output the estimated stamina level; a storage module configured to store the biological information and at least one mathematical model; characterized by: a processing module configured to use the at least one mathematical model to perform a process comprising steps of: estimating an anaerobic energy level and an aerobic energy level in real time based on the physiological signal and the biological information, wherein estimating the anaerobic energy level and the aerobic energy level in real time comprises: estimating the anaerobic energy level based on anaerobic estimation settings, wherein the anaerobic estimation settings are adjusted based on the estimated anaerobic energy level when the actual physical condition of the user is underestimated; and estimating the aerobic energy level based on an aerobic estimation settings, wherein the aerobic estimation settings are adjusted based on the estimated aerobic energy level when the actual physical condition of the user is underestimated; and estimating the stamina level based on the anaerobic energy level and the aerobic energy level. a processing module configured to use the at least one mathematical model to perform a process comprising steps of: estimating an anaerobic energy level and an aerobic energy level in real time based on the physiological signal and the biological information, wherein estimating the anaerobic energy level and the aerobic energy level in real time comprises: estimating the anaerobic energy level based on anaerobic estimation settings, wherein the anaerobic estimation settings are adjusted based on the estimated anaerobic energy level when the actual physical condition of the user is underestimated; and estimating the aerobic energy level based on an aerobic estimation settings, wherein the aerobic estimation settings are adjusted based on the estimated aerobic energy level when the actual physical condition of the user is underestimated; and estimating the stamina level based on the anaerobic energy level and the aerobic energy level. estimating an anaerobic energy level and an aerobic energy level in real time based on the physiological signal and the biological information, wherein estimating the anaerobic energy level and the aerobic energy level in real time comprises: estimating the anaerobic energy level based on anaerobic estimation settings, wherein the anaerobic estimation settings are adjusted based on the estimated anaerobic energy level when the actual physical condition of the user is underestimated; and estimating the aerobic energy level based on an aerobic estimation settings, wherein the aerobic estimation settings are adjusted based on the estimated aerobic energy level when the actual physical condition of the user is underestimated; and estimating the anaerobic energy level based on anaerobic estimation settings, wherein the anaerobic estimation settings are adjusted based on the estimated anaerobic energy level when the actual physical condition of the user is underestimated; and estimating the aerobic energy level based on an aerobic estimation settings, wherein the aerobic estimation settings are adjusted based on the estimated aerobic energy level when the actual physical condition of the user is underestimated; and estimating the stamina level based on the anaerobic energy level and the aerobic energy level.