Just Sweat is a mode that allows players to use a workout regime while dancing. This mode started to appear in Just Dance 2, and it has appeared in many games since.
Just Sweat first appeared in Just Dance 2 in two formats. One format allowed for thee player to workout to any song without a log to track it down, while the other one came with a log, telling the player to reach certain goals in order to get a stellar workout. Both formats included a second bar that appeared while they were playing, tracking down the number of "Sweat Points" they've earned while dancing. This concept was used in Just Dance 3 and in multiple spin offs of the series. (Summer Party/Extra Songs, Wii, Wii 2, Best: Of, and Greatest Hits)
In Just Dance 4, the mode was drastically revamped. Instead of there being a bar, there were now five different workouts programs the player could choose, with one of them needing to be unlocked through the Wheel of Gifts prior to using it. Each program came in three time incriments: 10 minutes, 25 minutes, and 40 minutes, and the layout of the workout consisted of first a Warmup, then a song, then a routine from the workout, and then another song. The program would alternate between workout routine and song until a Cool Down routine was reached, and after that was completed, the workout program was finished.
Throughout the program, there would be two trackers that would coordinate with how intense the player was moving. One was represented as a bar, which also tracked the number of kCal the player was burning, and the other as a line that would curve according to the intensity of the player. When the end of one performance was done, the line's ending position would determine the level of the next routine. (Either an Intense performance or a Cool performance would ensue) Each performance also included markers that were used as a guide of where the player should be during the workout. At the end, all of these markers would be added up to determine how successful the player was during the workout. A chart was also shown to visualize how the player progressed throughout the workout.
The idea of separate workout plans was dropped in Just Dance 2014, and it reverted it back with a standard bar. Along with playing freely, there was also the ability to make a custom playlist while working out. Using the same time incriments from Just Dance 4, a player could make a playlist of 10 minutes, 25 minutes, or 40 minutes. Each one allowed a certain number of songs in the playlist. (10 allowed 3, 25 allowed 6, and 40 allowed 10) Each type of playlist would be saved when the player finished selecting, and it would remain that way until the player changed the playlist, if the player desired to. This has remained the current concept for future games in the main series and in some spin offs, although the name of the mode was renamed from Just Sweat to Playlist (2015) and then to Sweat & Playlists. (2016 and 2017) Starting in Just Dance 2016, the player also has the ability to create a playlist of up to 25 songs and name it, but this feature is only available in eighth generation consoles.