NTRVL: Norwegian 4x4 Trainer

YOUR NUMBER, EVEN WITHOUT A SENSOR The number this app is built around — how far your pulse drops in the minute after a hard interval — does not need a heart-rate monitor. It needs a finger and twenty seconds. Athletes measured it that way long before watches existed. So if you train by feel, the interval no longer ends in nothing. When it does end, NTRVL walks you through it: find your pulse, tap along with it for twenty seconds, catch your breath, then tap again one minute later. The difference between the two is your heart rate recovery, and it appears on screen. It is counted by hand, so the app says so, and says roughly how close it is. If your tapping wanders, it tells you and offers another go rather than handing you a number that means nothing. During the interval itself you now see where those four minutes are heading. That was the part that was missing: something to push towards. None of this appears if you already have an Apple Watch or AirPods Pro 3 measuring for you. You have the number already.