An AI fitness coach that runs your strength workout on Apple Watch

If you searched for an AI coach on Apple Watch, you probably met Workout Buddy first. It is Apple's spoken companion in the Workout app: it cheers you on, calls out milestones and reads a summary when you finish, and it supports Traditional Strength Training. Lenjo covers the part before and between those moments: what to lift today, how heavy, and when to start the next set.

With your permission, the coach reads sleep, heart rate variability and resting heart rate from Apple Health next to the workouts you have saved in Lenjo. A short night or an HRV dip below your usual range can mean fewer hard sets or a lighter top set; a good week can mean adding load. The plan card shows exercises, sets, reps, weight and rest, and you can edit any of it before you start.

You can also just tell it what is going on, for example “I only have 40 minutes” or “my shoulder is cranky on overhead work”, and it rewrites the session and says what changed.

How a plan should change after a short night or a missed target is covered in our guide to an adaptive workout plan.

Start the workout on iPhone and send it to the watch. There you open an exercise, start a set, and see the target, weight and live heart rate. When you finish, turn the Digital Crown to the reps you actually did and tap to finish the set. Lenjo does not count reps for you; the plan fills them in and you confirm. Timed holds count down and finish on their own.

You can change weight or reps for any set, add a set, or take sets out of order on the watch. Finished sets sync back to the iPhone workout, and you have 8 seconds to undo a set you finished by mistake.

A rest timer counts down the same time whether the last set was easy or brutal. Lenjo watches how your heart rate comes down after each set and combines it with elapsed rest, how hard the last set was and your own history. These are real screens from one rest period on lat pulldown.

Ready is a combined call, so a planned rest timer running out does not flip it on its own while live heart rate is available. Heavy lifts keep a minimum rest even if heart rate settles quickly. Without live heart rate, the planned rest time is used instead. Either way you decide when to lift: the button lets you start early or keep resting.

The research behind heart-rate-guided rest, and why heavy lifts keep a minimum rest, is in Apple Watch next-set readiness.

For typical rest ranges by goal before any watch is involved, see how long to rest between sets.

On iPhone, the saved workout shows heart rate for every set on one timeline, with the active part of each set marked and the rest in between. Sets started and finished on the watch are labelled as measured; sets logged only on the phone are labelled as estimated.

Ask the coach for a review and it reads weight, reps, RPE and those set summaries together, then suggests what to do next time for each exercise: add weight, hold, reduce, or swap the exercise. With your permission, finished workouts are also saved to Apple Health.

• →iPhone with iOS 17 or later, and an Apple Watch with watchOS 10 or later paired to it, with Lenjo installed on the watch.
• →Apple Health permission for heart rate, sleep and HRV. Missing samples are shown as missing; they are never treated as good recovery.
• →Lenjo Pro for watch workouts. Without it, you can still plan, run and log workouts on iPhone for free.

Recovery cues are training guidance, not medical monitoring. Heart rate says nothing about how tired the working muscle is, so treat the cue as one more check next to your breathing, setup and confidence. Stop and get help for chest pain, dizziness or unusual shortness of breath.