Perceived effort during the same workout can change because perception is an integration of body signals, brain regulation, and context. Objective measures such as heart rate or power may be identical, but the felt effort depends on physiology, environment, psychology, and culture. Subjective scales therefore reflect more than raw workload.
Physiological and environmental drivers
Physiological state alters the internal signals that feed perception. Andrew M. Jones at the University of Exeter has shown that metabolic markers and cardiovascular responses influence how hard an effort feels, so variations in glycogen, hydration, illness, or recent sleep change perceived intensity even when external work is unchanged. Tim Noakes at the University of Cape Town proposed that the brain regulates exercise to protect the body, meaning small changes in core temperature, inflammation, or muscle fatigue can trigger higher perceived strain to limit risk. Environmental stressors such as heat, humidity, and altitude raise cardiovascular and thermal strain and therefore inflate perceived exertion compared with cool, comfortable conditions.
Psychological, social, and cultural influences
Psychology and context reshape the interpretation of bodily signals. Samuele Marcora at the University of Kent developed a psychobiological perspective showing that motivation, attention, and expectation determine willingness to tolerate discomfort; the same physical workload will feel easier when motivation is high or distraction is present. Social factors and cultural norms also matter: athletes from cultures that valorize stoicism may report lower exertion, while environments that emphasize safety or self-monitoring can make identical effort feel harder. Momentary mood, anxiety, and perceived consequence of stopping alter reported effort as much as physiology does.
Consequences of this variability include misjudged training loads, inconsistent pacing in competition, and potential safety risks when perceived effort underestimates true physiological strain. For practitioners, combining subjective RPE with objective measures reduces error and respects individual experience. Recognizing cultural and personal differences prevents overreliance on a single metric and supports tailored coaching and public-health guidance. Understanding perceived exertion as a dynamic, context-sensitive signal explains why identical workouts rarely feel identical across days, places, and people.