What is the role of reactive oxygen species (ROS) in exercise adaptation?

• A. ROS are always damaging and harmful.
• B. ROS act as signaling molecules at moderate levels to promote adaptation.
• C. ROS have no impact on exercise adaptation.
• D. ROS only arise during rest.

Answer: (B)

During exercise, cells generate more reactive oxygen species as metabolism ramps up. At moderate levels, these ROS serve as signaling molecules that trigger adaptive responses. They help turn on pathways that boost the body's antioxidant defenses, increase mitochondrial biogenesis, and improve metabolic efficiency. This hormetic effect means a controlled, temporary rise in ROS helps muscles become tougher and better at handling future stress.

The signaling role of ROS hinges on balance. If ROS stay within a moderate range, they promote adaptation; if they rise too high, they can cause damage. This is why regular training improves endurance and metabolic health—the body learns to respond to these ROS signals with stronger antioxidant systems and more mitochondria. The other views miss this nuance: ROS aren’t always damaging, they clearly influence adaptation, and they arise during exercise, not only at rest.