Which of the following best represents an objective assessment?

An objective assessment is one that is quantifiable and can be measured reliably, typically using specific tools or methods. Heart rate fits this definition perfectly because it is a physiological measure that can be accurately recorded using a variety of devices, such as a heart rate monitor. This data provides clear, numerical insights into an individual's cardiovascular response to exercise or stress, making it an objective metric that can be compared across different individuals or situations.

On the other hand, the other options, while important in their own right, are not considered objective assessments. The PAR-Q (Physical Activity Readiness Questionnaire) is more subjective, as it relies on self-reported answers regarding physical readiness and health status. Energy level is also subjective, as it can vary widely from one person to another based on individual feelings and perceptions at any given time. Medical history, while critical for understanding a client's background and potential risks, is primarily qualitative and dependent on individual reporting of past experiences and conditions.