How many days per week should I run to optimize my physical fitness while also considering the importance of recovery? Is there a specific number that balances the benefits of cardiovascular endurance and muscular strength without leading to overtraining or fatigue? Furthermore, should my running frequency vary based on my individual goals, such as whether I am training for a marathon, seeking general health improvements, or aiming to lose weight? Are there particular factors, such as my current fitness level, age, and previous running experience, that I should factor in when deciding the ideal frequency? Moreover, do I need to incorporate cross-training or strength sessions into my weekly regimen, and if so, how does this impact the number of days I should dedicate to running? Ultimately, what strategies can I employ to listen to my body, ensuring that I neither overexert myself nor become complacent in my training routine?