The dietary supplement intervention consists of oral administration of Cordyceps sinensis extract. Participants in the experimental group (Fartlek-Cordyceps) are required to ingest a daily dosage of 500 mg Cordyceps sinensis per capsule. The dosing protocol is strictly timed to maximize absorption and recovery: one capsule is taken every night before bed, and on training days, an additional capsule is administered exactly 1 hour prior to the Fartlek session. This supplementation runs concurrently with the physical training period. To maintain the double-blind design, capsules are identical to the placebo in appearance and taste. This targeted timing aims to protect muscle fibers from acute training stress during exercise and accelerate cellular repair overnight, ultimately acting to suppress inflammatory responses, mitigate oxidative damage, and support bone metabolism markers under high physiological loads.

Participants assigned to this comparator arm undergo a structured Fartlek training program while receiving a placebo intervention to maintain the trial's double-blind design. The physical training protocol consists of continuous running sessions with alternating intensity bursts, identical in frequency, duration, and workload to the experimental group. For the supplementation control, participants are required to orally ingest a daily placebo capsule that is visually identical to the active treatment, matched exactly for size, shape, color, and taste. The dosing schedule mimics the experimental protocol: one capsule is taken every night before bed, and on training days, one capsule is administered 1 hour prior to the Fartlek session. This arm serves to isolate the physiological adaptations of the physical training alone and controls for the placebo effect on muscle damage, inflammation, oxidative stress, bone metabolism, and VO2max.