Here's some tips! In the world of exercise physiology, there is something called the SAID principle. SAID is the acronym for Specific Adaptations to Imposed Demands. In a nutshell the body will adapt to the stressors to which is it is exposed.
You mentioned that your legs were tired. We called that localized fatigue in exercise phys world. What you can do to get you legs strong in an endurance kind of way is to engage in resistance training for endurance outcomes.
What do I mean?????
Light weights high reps. It teaches the muscular system to use aerobic glycolysis more effectively and your legs won't tire out so quickly.
I hope this is helpful to you.