A trainer is teaching a client about the body's reaction to stressors placed on it...

The NASM CPT7 Study Guide describes the General Adaptation Syndrome (GAS) as the body’s three-stage response to stressors such as exercise:

Alarm reaction – The initial response to a new stressor, where the body experiences delayed onset muscle soreness (DOMS), neural activation changes, and temporary performance reduction.

Resistance development – The body adapts to the stimulus, improving performance and efficiency.

Exhaustion – Overtraining or excessive stress without adequate recovery leads to performance decline and potential injury.

The alarm reaction stage is the immediate physiological response after introducing a new or intense activity, involving increased neural recruitment and tissue stress. Therefore, the correct answer is C. Alarm reaction.