Final answer:
The athlete biological passport is a personalized, electronic record that monitors an athlete's biological variables over time to detect possible doping, rather than only measuring fitness metrics once.
Step-by-step explanation:
The athlete biological passport is a personalized, electronic record in which an athlete's biological values are measured and monitored over time. Contrary to a one-time fitness profile or instantaneous measurements after a competition, the passport focuses on tracking changes in selected biological variables that indirectly reveal effects of doping rather than detecting the doping substance itself. By comparing an athlete's current values with their established baseline, the passport can highlight fluctuations that may suggest the use of performance-enhancing drugs.
It is known that relative fitness is a critical concept, emphasizing an individual's ability to survive and reproduce in comparison to others within a population. Sports scientists apply a similar comparative approach when analyzing athletes, which contributes to the integrity of the sport by aiming to ensure fair competition. Hence, option (c) 'a series of biological variables that is measured repeatedly over time for a given athlete' correctly describes the athlete biological passport.