Final answer:
It is true that excessive unaccustomed exercise can stress the immune system, as chronic stress impairs immune function and increases disease susceptibility. The field of psychoneuroimmunology is exploring the complex links between stress and immune system health.
Step-by-step explanation:
The statement that unaccustomed high volume, high-intensity exercise training that far exceeds recommended guidelines may stress the immune system is TRUE. Extensive research has shown that various stressors, including chronic stress and excessive exercise, can impair the immune system, leading to weakened immune responses. While most short-term stress does not significantly impair the immune system, and can even enhance innate immune responses, chronic stress has been found to suppress both innate and adaptive immune responses, which may increase susceptibility to illnesses.
Moreover, the emerging field of psychoneuroimmunology highlights the intricate connections between the nervous, endocrine, and immune systems, and how stress affects their interactions. This, combined with studies showing that individuals under high stress may be more susceptible to infections like the common cold, indicates that keeping stress levels, including those from exercise, within recommended limits is crucial for maintaining a robust immune system.