What happens to resting heart rate in relation to illness?

Resting heart rate typically becomes noticeably higher in response to illness. This increase occurs because the body is working harder to fight off infections or other health issues. When the body encounters pathogens, the immune system activates, leading to inflammatory responses and changes in hormonal levels, such as an increase in adrenaline. These physiological changes can raise heart rate as the body requires more oxygen and nutrients to support immune function and repair processes.

Moreover, fevers commonly associated with illness can also elevate heart rate due to the increased metabolic demands. This physiological reaction demonstrates the body's natural defense mechanisms in action. Recognizing this pattern is essential for fitness professionals, as it highlights the need for adaptive training and recovery protocols for clients who may be ill or recovering from sickness.