1. An apparatus comprising: a processor; and a memory storing instructions that, when executed by the processor, cause the apparatus at least to perform operations comprising: processing input specifying a plurality of athletic activities; processing input specifying a heart rate threshold for a particular one of the activities; generating an electronic training script including the heart rate threshold for the particular activity and defining a sequence in which to perform the plurality of activities; measuring a physiological characteristic of a user during the plurality of athletic activities; and prompting the user to perform a next activity in the sequence based on a measurement of the physiological characteristic indicating completion of a previous activity in the sequence.