An apparatus (102, 104, 106, 108) for processing exercise-related measurement data comprising a processor (706, 726) configured to cause the apparatus to: acquire a plurality of heart rate variability values and a plurality of exertion parameter values measured during an exercise, wherein the heart rate variability values represent a measure of variation in heart beat intervals and correlate with the exertion parameter values through a human physiological mechanism, and wherein the exertion parameter values characterize the physical exertion of the exercise; construct a mathematical correspondence from the plurality of measured heart rate variability values and associated exertion parameter values, the mathematical correspondence describing correlation between the heart rate variability values and the exertion parameter values and describing the user's physiological state during the exercise; and characterised in that the processor (706, 726) is further configured to cause the apparatus to: determine a training effect of the exercise for each of a plurality of exertion level zones by deriving from the mathematical correspondence a factor characterizing the training effect at that exertion level zone in the current physiological state of the user as follows: a) when the mathematical correspondence indicates that the user is tired or exhausted, a higher weight is assigned to lower exertion level zones than to higher exertion level zones to provide a better training effect on the lower exertion level zones than on the higher exertion level zones; and b) when the mathematical correspondence indicates that the user is well rested, an equal weighting is assigned to all exertion level zones. acquire a plurality of heart rate variability values and a plurality of exertion parameter values measured during an exercise, wherein the heart rate variability values represent a measure of variation in heart beat intervals and correlate with the exertion parameter values through a human physiological mechanism, and wherein the exertion parameter values characterize the physical exertion of the exercise; construct a mathematical correspondence from the plurality of measured heart rate variability values and associated exertion parameter values, the mathematical correspondence describing correlation between the heart rate variability values and the exertion parameter values and describing the user's physiological state during the exercise; and characterised in that the processor (706, 726) is further configured to cause the apparatus to: determine a training effect of the exercise for each of a plurality of exertion level zones by deriving from the mathematical correspondence a factor characterizing the training effect at that exertion level zone in the current physiological state of the user as follows: a) when the mathematical correspondence indicates that the user is tired or exhausted, a higher weight is assigned to lower exertion level zones than to higher exertion level zones to provide a better training effect on the lower exertion level zones than on the higher exertion level zones; and b) when the mathematical correspondence indicates that the user is well rested, an equal weighting is assigned to all exertion level zones. determine a training effect of the exercise for each of a plurality of exertion level zones by deriving from the mathematical correspondence a factor characterizing the training effect at that exertion level zone in the current physiological state of the user as follows: a) when the mathematical correspondence indicates that the user is tired or exhausted, a higher weight is assigned to lower exertion level zones than to higher exertion level zones to provide a better training effect on the lower exertion level zones than on the higher exertion level zones; and b) when the mathematical correspondence indicates that the user is well rested, an equal weighting is assigned to all exertion level zones. a) when the mathematical correspondence indicates that the user is tired or exhausted, a higher weight is assigned to lower exertion level zones than to higher exertion level zones to provide a better training effect on the lower exertion level zones than on the higher exertion level zones; and b) when the mathematical correspondence indicates that the user is well rested, an equal weighting is assigned to all exertion level zones.