Final answer:
The nervous system has the highest adaptation rate to new training stimuli, rapidly initiating physiological changes via the sympathetic division of the autonomic nervous system.
Step-by-step explanation:
The system of the body that has the greatest adaptation rate when exposed to a new training stimulus is the nervous system. The nervous system quickly produces a response based on the stimuli perceived by sensory structures, which can include the activation of muscular and skeletal systems, adjustments in the circulatory system, and changes in glandular secretions. When exposed to a threat or exercise, the sympathetic division of the autonomic nervous system orchestrates the physiological changes such as increased heart rate and sweating to support the body's fight-or-flight response.