A method of monitoring a body tissue, comprising the steps of: determining, with reference to a position of an m-th light emitting unit among a plurality of light emitting units configured to generate optical signals toward the body tissue to be monitored, a position of an n-th light reception unit among a plurality of light reception units configured to detect the optical signals from the body tissue, and a distance between the m-th light emitting unit and the n-th light reception unit, an area and a depth of the body tissue which corresponds to a pair of the m-th light emitting unit and the n-th light reception unit; measuring hemodynamics of the body tissue at the area and the depth corresponding to the pair of the m-th light emitting unit and the n-th light reception unit based on the optical signal generated by the m-th light emitting unit and detected by the n-th light reception unit; wherein the method further comprises the step of estimating an exercise quantity of a subject to be measured based on information on a posture or motion of a body portion associated with the body tissue; estimating an activity of the body tissue on an area basis and a depth basis based on the hemodynamics at at least one of the area and the depth of the body tissue; evaluating an exercise efficiency of the body tissue with reference to information on the measured hemodynamics and the information on the estimated exercise quantity, wherein the body tissue is a muscle, and wherein in the evaluation step, an amount of oxygen consumption per unit exercise quantity is calculated, and it is determined that as the calculated amount increases, the exercise efficiency of the muscle is decreased. determining, with reference to a position of an m-th light emitting unit among a plurality of light emitting units configured to generate optical signals toward the body tissue to be monitored, a position of an n-th light reception unit among a plurality of light reception units configured to detect the optical signals from the body tissue, and a distance between the m-th light emitting unit and the n-th light reception unit, an area and a depth of the body tissue which corresponds to a pair of the m-th light emitting unit and the n-th light reception unit; measuring hemodynamics of the body tissue at the area and the depth corresponding to the pair of the m-th light emitting unit and the n-th light reception unit based on the optical signal generated by the m-th light emitting unit and detected by the n-th light reception unit; wherein the method further comprises the step of estimating an exercise quantity of a subject to be measured based on information on a posture or motion of a body portion associated with the body tissue; estimating an activity of the body tissue on an area basis and a depth basis based on the hemodynamics at at least one of the area and the depth of the body tissue; evaluating an exercise efficiency of the body tissue with reference to information on the measured hemodynamics and the information on the estimated exercise quantity, wherein the body tissue is a muscle, and wherein in the evaluation step, an amount of oxygen consumption per unit exercise quantity is calculated, and it is determined that as the calculated amount increases, the exercise efficiency of the muscle is decreased. <EOS>