Final answer:
Among the described clients experiencing disrupted sleep patterns, the client most at risk for obstructive sleep apnea (OSA) is a 49-year-old man who is an avid cross-country runner (Option C).
Step-by-step explanation:
The 49-year-old man who is an avid cross-country runner is most at risk for obstructive sleep apnea due to age and gender, which are significant risk factors for the condition.
Risk factors for obstructive sleep apnea include being overweight, having a higher neck circumference, males being more prone than females, and older age.
Although being an avid runner is generally positive for health, the age and gender of this individual place him at a higher risk compared to the other clients mentioned, who do not have these specific risk factors.
Treatment options for sleep apnea often include the use of a continuous positive airway pressure (CPAP) machine during sleep to keep the airway open, along with lifestyle modifications such as weight loss and avoiding alcohol and sleep-apnea-promoting drugs.
Hence, the correct answer is Option C.