Cardio Load: see how your training spreads across heart rate zones

What Cardio Load shows

The Cardio Load card gives the number of workouts in your chosen window and your top zone, the one where you spent the most training time. Open it for the full picture.

• Zone Distribution: how your workout time divides across the five zones, and how many of your workouts had heart rate data.
• Zone by Workout Type: the zone mix for each activity, so you can see that your rides are mostly steady while your interval sessions spend real time near the top.
• Workout Breakdown: the zone split for each individual session, with a filter by workout type.
• Insights: short, plain readings of your pattern, such as a solid aerobic base, a healthy intensity mix or a polarized training pattern, and gentle flags when high intensity is taking over.
• Zone Terminology: switch between naming styles for the zones, from everyday labels like Fat Burn and Cardio to coaching and scientific terms, each with a description of how that zone feels.

Why your intensity mix matters

Different intensities train different things. Long, easy efforts build the aerobic base that supports almost every sport and everyday stamina. Harder efforts raise your top-end fitness and speed. Many people drift into the middle, where every session feels moderately hard: tiring enough to need recovery, but not hard enough to bring the gains of true high-intensity work.

A common approach in endurance training is to keep most sessions easy and make a smaller share genuinely hard. You do not need to follow any one method, but seeing your real split helps you notice when you have been going too hard too often, or when your training has become so comfortable that it no longer challenges you.

Looking across days rather than at one workout is the point. A single hard session tells you little. Two weeks where nearly all your time sat in the top zones is a pattern worth knowing about, especially if your recovery has been lower than usual.

Choosing the window

Cardio Load covers the last 7, 14, 30 or 60 days, with 14 days as the default. A week shows how your current routine is balanced. A month or two smooths out one-off sessions and shows the shape of a training block, which is more useful when you are preparing for an event or rebuilding after a break. The window ends on the selected day, so you can look back at any earlier stretch too.

What data it needs

Cardio Load uses workouts that include heart rate, from Apple Watch or another device that saves heart rate to Apple Health during the session. Workouts without heart rate still count in your workout total, but cannot be placed in zones, and the screen tells you how many of your workouts had heart rate data.

FitRest is not a medical device. Heart rate zones here are a training guide, so talk to a doctor if you have questions about exercising at higher intensities.