Field note
Workout effort is how hard a session felt to you, usually on a simple one-to-ten scale, separate from how much heart-rate work the same session actually cost.
Two honest readings of one workout. Effort is how hard it felt. Load is how hard it was. Keeping them side by side is the point.
Ten is everything you had. One is barely trying. It is one of the oldest measures in sport, and one of the most trusted, because the body is a remarkable judge of its own strain. Add up how the legs feel, how the lungs are working, and how loud the head has gotten, and you land on a single honest number.
Borg (1982) set out the psychophysical bases of perceived exertion. That idea has held up across decades of studies as a genuine window into how hard the body is working. Foster and colleagues (2001) turned session ratings into a practical training-load method many coaches still use.
| Band (plain language) | Honest feel |
|---|---|
| Easy | Warm-up pace you could hold all day |
| Moderate | Steady work you could talk through |
| Hard | Work you feel and look forward to ending |
| All out | Efforts you can only hold for minutes |
On Apple Watch, if you rated the workout yourself, that rating should win. Nobody knows how a session felt better than you. If you did not rate it, the watch can estimate from heart rate and the shape of the effort. An estimate is a model, not a feeling. It cannot know you slept poorly, or that heat made an easy pace brutal. You can.
So if the number ever looks wrong, set your own rating and trust that instead. The estimate only exists for cardio efforts the watch understands well, like runs, rides, rows, and hikes. For strength and yoga it usually waits for your own rating.
Scherr and colleagues (2013) found Borg ratings track closely with heart rate and with lactate, the chemical marker of hard work. Haddad and colleagues (2017) reviewed session-RPE as valid and useful, while naming the factors that color it. Music can make a hard effort feel easier. Heat, caffeine, mood, and a bad night can push the number around without the work itself changing. None of that makes the rating wrong. It means one workout's effort is a reading of you on that day.
Effort is the inside view. Heart-rate load is the outside view. Blend them into one number and the gap vanishes. Some days a workout feels far harder than the heart-rate work suggests. A high effort over a modest load often means your body was already taxed by poor sleep, lingering fatigue, or stress.
That disagreement is the interesting part. It pairs with What is training strain? and What is cardio load? for the objective side of the same session, and with How fast should my heart settle after exercise? for how quickly you come back down afterward.
A watch estimate that leans on a single heart-rate average can undercount short, very hard bursts like sprints and intervals. A stop-and-go session may feel like a nine yet read lower, because the average smooths over the spikes.
Effort is best read workout by workout, and best paired with objective load and how you actually feel. One high number is information, not an instruction. The pattern across weeks tells you whether you are training in a place your body can keep absorbing.
What it felt like is not what it cost you. Keep both readings. That is the line worth remembering.
I write these because I build Aera, an iPhone app that reads Apple Health against your own baseline and puts the research and the error bars underneath every number it shows you, including this one. You do not need it to use anything above.