What factors can affect heart rate?

The selected answer includes a comprehensive array of factors that can influence heart rate. Age plays a significant role as younger individuals tend to have higher resting heart rates compared to older adults. Fitness level is crucial since regular aerobic exercise typically leads to a lower resting heart rate, reflecting improved cardiovascular efficiency.

Hormonal influences, such as the release of adrenaline during stress, can increase heart rate, illustrating the body's acute response to stimuli. Temperature also affects heart rate, as higher body temperatures can increase heart rate to facilitate heat dissipation. Finally, the autonomic nervous system's role is critical in heart rate regulation; the sympathetic nervous system increases heart rate during physical activity or stress, while the parasympathetic system can decrease it during rest.

Other choices may mention some relevant factors, but they don't provide as complete a picture. For instance, while environmental factors like humidity and altitude can influence heart function, they do not encompass the broad spectrum of factors affecting heart rate as effectively as the selected answer does. Additionally, dietary influences and hydration levels can have indirect effects on heart rate, but they are not as directly impactful or comprehensive compared to the myriad physiological and biological factors outlined in the chosen response.