Whats the physiological basis for the notion that cross-training with swimming and running improves overall endurance performance, and are there any studies that actually quantify the specific benefits of this combination versus other forms of cross-training, considering the vastly different movement patterns, muscle groups, and energy systems engaged in each activity, and shouldnt we be looking at the specific demands of our sport and tailoring our cross-training accordingly, rather than blindly following the conventional wisdom that swimming and running are the ultimate cross-training combination, especially when you consider that cycling, for example, requires a very different type of endurance and muscle engagement compared to running and swimming, and arent we just assuming that the benefits of swimming and running will automatically translate to other sports without any concrete evidence to support this assumption.