What factor does NOT affect resting heart rate?

Genetic traits do not have a direct influence on resting heart rate in the same way that the other factors do. While genetics can determine certain physiological characteristics, resting heart rate is primarily influenced by immediate and external factors such as body position, age, and dietary/hydration status.

Body position affects heart rate because lying down can lead to a lower heart rate compared to standing, as gravity has less impact on venous return to the heart. Age is associated with changes in heart rate, where resting heart rates tend to decrease in well-conditioned individuals and increase with age in sedentary populations. Dietary and hydration status can also play a role; for example, dehydration might lead to an increased heart rate.

In contrast, while genetic traits can influence baseline heart functions and cardiovascular health, they do not fluctuate substantially in response to daily activities or environmental changes, making them less relevant in the context of resting heart rate variations.