What specific physiological adaptations and health benefits can be expected from training for a triathlon, as opposed to focusing on a single sport like cycling, and are these benefits solely due to the varied nature of triathlon training or are there other factors at play? For example, how does the repeated transition from swimming to biking to running impact cardiovascular health, muscular endurance, and mental toughness compared to the repetitive motion of cycling alone? Are there any studies or data that compare the injury rates and overall health outcomes of triathletes to cyclists, and if so, what do they suggest about the relative merits of each type of training? Furthermore, do the nutritional and recovery demands of triathlon training have a significant impact on overall health and performance, and if so, how do these demands compare to those of single-sport training regimes?