Apple Workout Swim 100 m Medley Distance Issue

7100 meters in 1:44:39 at an average pace of 1:28, including over 1,000 meters of butterfly and 1,000 meters of breaststroke? Impressive. Very Impressive. And also very impossible for all but the strongest, near Olympic-level swimmers. The Apple Workout app, and the Apple Watch workout session system fail to correctly measure individual medley swim distances for 100 meter individual medley segments in a 50 meter pool, or 50 meter individual medley segments in a 25 yard pool.

7,100 meters in 1:45:39 is an impossibly impressive 1:28 100-meter pace with several thousand meters of breaststroke, backstroke and butterfly

The Apple workout data system assumes that swimmers only change strokes at the completion of a lap of the pool. But in a 100 m IM in a 50 meter pool, you change strokes both mid-lap and at the end of the lap. In a 25 yard pool swimming a 50 yard IM, you switch strokes every 12.5 yards.

This particular workout included 30 50-meter IMs in a 50-meter pool, requiring swimmers to change strokes every 12.5 meters. The total distance for the workout including warm up and cool down was only 3,600 meters in reality - far less than the 7,100 meters reported by Apple.

The Swim+ app corrects for this issue by validating the time for each reported lap based on the user’s selected cruise pace. Typically, a swimmer’s sprint pace is 50% faster than a swimmer’s cruise pace. So, for a swimmer with a 1:40 100-meter cruise pace, if the Apple workout data system reports a 50-meter freestyle lap time less than 33 seconds, that indicates a time that is almost impossibly fast, and suggests that the swimmer has changed stroke style mid-lap. Swim+ will add a corrected length lap event for each partial lap that it detects. Swim+ uses a similar approach scaled for each stroke style to estimate partial butterfly, backstroke, and breaststroke laps.