Effort is a personal observation. It can add context to weight and repetitions, but a larger number is not automatically a better workout. The useful entry is the one that honestly describes this session.
Make one honest note
The CDC intensity guide describes perceived effort as a subjective way to judge relative aerobic intensity. It also uses speech as a practical cue. This does not make effort an objective test or a diagnosis.
Use simple cues
Notice breathing, how easily you can speak, and how challenging the working muscles feel. These cues may disagree, especially when you compare lifting with walking or cycling. Choose the description that best matches the session as a whole.
Record while the feeling is fresh
Make the entry soon after the set or session. Use the same meaning each time you log. Do not raise the rating because you think the app expects a hard answer, and do not lower it to make the record look easy.
Compare like sessions
Compare the same exercise, similar duration, or the same planned session. Add one short note when sleep, heat, illness, equipment, or an unfamiliar movement changed the experience. For the other useful fields, read the workout tracking guide.
Review effort with the other facts
The current Fitonomy gym page says the logger records weight, repetitions, and effort. Read those together. The same load can feel different on another day, but one difficult entry does not prove that the plan must change. Review the broader weekly plan before deciding.
Know when a rating is not enough
An effort note cannot explain chest pain, faintness, severe shortness of breath, sudden weakness, or another concerning symptom. Stop and seek appropriate help. Follow individual clinical limits and advice about conditions or medicines.