An apparatus, comprising: a processor; a sensor; a memory; and a non-transitory computer-readable medium comprising computer-executable instructions that when executed by the processor are configured to: receive, for each exercise session of two or more exercise sessions, a plurality of periodic sensor data points from the sensor, the plurality of sensor data points each indicating a location of a user during the exercise session, each exercise session having a prescribed duration between a start time and an end time and the user exercising at an intensity above a critical intensity during at least a portion of the prescribed duration, the critical intensity corresponding to a power level between a power level corresponding to a lactate threshold at which lactate starts to accumulate in the bloodstream of the user and a power level corresponding to the maximum rate of oxygen consumption for the user; store the received plurality of periodic sensor data points for each exercise session in the memory; calculate, for each exercise session, a total distance travelled by the user during the exercise session using the stored plurality of periodic sensor data points; determine, for each exercise session, an exercise period summary data point using the calculated total distance travelled by the user during the exercise session and the prescribed duration of the exercise session, each exercise period summary data point expressing the calculated total distance travelled and the prescribed duration as a coordinate point; calculate a regression line through the two or more calculated exercise period summary data points; calculate a critical speed of the user using at least a portion of the calculated regression line by calculating a slope of the regression line; and output the critical speed, whereas the critical speed corresponds to an exercise intensity associated with constant muscle oxygenation percentage. a processor; a sensor; a memory; and a non-transitory computer-readable medium comprising computer-executable instructions that when executed by the processor are configured to: receive, for each exercise session of two or more exercise sessions, a plurality of periodic sensor data points from the sensor, the plurality of sensor data points each indicating a location of a user during the exercise session, each exercise session having a prescribed duration between a start time and an end time and the user exercising at an intensity above a critical intensity during at least a portion of the prescribed duration, the critical intensity corresponding to a power level between a power level corresponding to a lactate threshold at which lactate starts to accumulate in the bloodstream of the user and a power level corresponding to the maximum rate of oxygen consumption for the user; store the received plurality of periodic sensor data points for each exercise session in the memory; calculate, for each exercise session, a total distance travelled by the user during the exercise session using the stored plurality of periodic sensor data points; determine, for each exercise session, an exercise period summary data point using the calculated total distance travelled by the user during the exercise session and the prescribed duration of the exercise session, each exercise period summary data point expressing the calculated total distance travelled and the prescribed duration as a coordinate point; calculate a regression line through the two or more calculated exercise period summary data points; calculate a critical speed of the user using at least a portion of the calculated regression line by calculating a slope of the regression line; and output the critical speed, whereas the critical speed corresponds to an exercise intensity associated with constant muscle oxygenation percentage. receive, for each exercise session of two or more exercise sessions, a plurality of periodic sensor data points from the sensor, the plurality of sensor data points each indicating a location of a user during the exercise session, each exercise session having a prescribed duration between a start time and an end time and the user exercising at an intensity above a critical intensity during at least a portion of the prescribed duration, the critical intensity corresponding to a power level between a power level corresponding to a lactate threshold at which lactate starts to accumulate in the bloodstream of the user and a power level corresponding to the maximum rate of oxygen consumption for the user; store the received plurality of periodic sensor data points for each exercise session in the memory; calculate, for each exercise session, a total distance travelled by the user during the exercise session using the stored plurality of periodic sensor data points; determine, for each exercise session, an exercise period summary data point using the calculated total distance travelled by the user during the exercise session and the prescribed duration of the exercise session, each exercise period summary data point expressing the calculated total distance travelled and the prescribed duration as a coordinate point; calculate a regression line through the two or more calculated exercise period summary data points; calculate a critical speed of the user using at least a portion of the calculated regression line by calculating a slope of the regression line; and output the critical speed, whereas the critical speed corresponds to an exercise intensity associated with constant muscle oxygenation percentage.