All you need is a SMARTPHONE, downloading the APP and optionally a pulsometer
Decide by the coach or athlete
Its LOW COST will allow you to control periodically during the season, which is critical since frequency zones vary with fitness level.
since it equates to a training session, primarily, of maximum aerobic power which can replace a training session of this kind
Without having to wait for lab results
Enables the determination of functional training zones VERY RELIABLY.