A sophisticated app aimed at group testing and advanced individual testing. Please take some time to examine it (see https://youtu.be/yFrDFCJUfyE). Do a few "dry" runs before going live with it.

Yo-Yo Intermittent Pro is an enhanced version of the free Yo-Yo Intermittent Test app available at https://play.google.com/store/apps/details?id=rudy.android.yoyo.

Both help conduct the Yo-Yo Intermittent test (Recovery Level 1, 2 and Endurance Level 1, 2) as defined by Jens Bangsbo of Copenhagen University

In addition to what the free version has to offer, Pro provides the following:
Multiple Users, large group. See https://goo.gl/D13dmC
--- Maintain lists of names - save/reload them
--- Edit, delete, save, reload results
--- Graphical analyses -- various
--- Switch between "Enclosure" and "Name" mode
--- Import names ...sdCard, Cloud [Gdrive]

- Estimates vo2Max (Recovery Level 1, minimum 1000m)
- View progress ... multiple graph options
- Training options - skip levels, loop a level
- Sort Results. Name, Distance or Date
- Export results, via email
--- Paste-Special directly to GoogleSheet
--- Or load into other spreadsheets

Work out, stay fit, rock on!

[Reference: Fitness Training in Football, a scientific approach - by Jens Bangsbo (December 1994)]

Caution: Audio. There are tens of thousands of Android phone variants. Invariably, the odd one has issues. Validate audio (incl. Bluetooth) using the free version.