Low Cardio Fitness Event

A Low Cardio Fitness Event records a notification that estimated VO2 max has remained in Apple's Low fitness classification. It is a category event, not a new oxygen-consumption measurement. Its value is 1 (lowFitness). Apple's HealthKit documentation distinguishes the notification from the estimates that underlie it.

There is no single VO2-max cutoff for every user. Classification depends on personal characteristics, including age and sex. The event can carry the triggering estimate and the threshold used for that classification in metadata. A numeric event code of 1 is not a VO2 max of 1 mL/kg/min.

The Low label is a fitness classification, not a diagnosis of cardiovascular disease. A database without event metadata cannot reconstruct the exact threshold used. Review VO2 Max for estimate units, recording selection and interpretation.

Users must enable the feature. Apple describes notifications for consistently low estimates over time, with repeat notifications approximately every four months. That reminder cadence does not mean VO2 max is measured every four months, or that every Low estimate creates an event. See Apple's event documentation.

The current database window, October 2025–September 2026, contained no low-cardio-fitness events. No triggering values, event thresholds, notification gaps or event-context comparisons were available. VO2-max estimates elsewhere in the database do not establish notification eligibility, settings or whether a reminder should have been sent.

Apple Watch estimates cardio fitness using eligible outdoor walks, runs and hikes. Indoor workouts do not contribute to the estimate in the same way. Apple lists age, sex, weight, height and heart-rate-affecting medications among the inputs. See Apple's cardio-fitness guide.

The notification is a summary of the estimate history, rather than a moment-by-moment response to a workout. A notification timestamp near a workout does not prove that particular workout triggered it. The notification time should not be treated as the measurement time for the estimate.

Inspect the actual VO2 Max trend, source changes, workout eligibility and health-profile inputs before interpreting a change. Walking Heart Rate Average and Resting Heart Rate describe related but different measurements; neither substitutes for an oxygen-consumption estimate.

A change in fitness, a change in measurement conditions and a change in the estimation method can all affect a trend. The watch estimate is not the same as a laboratory exercise test. Discuss persistent concerns, exercise limitations or relevant medication effects with a clinician rather than treating the notification as a prescription for a particular training intensity.