I tried this today and was able to actually go at a slightly faster pace for longer and didn't feel incredibly burned out and feel like I could have ran longer! Great tips! Thank you!
Huh, you don't say! All the other suggestions are familiar to me and I try to follow them but today I tried to run with this new-to-me "slightly clenched fist" and my average hr was 9 BPM lower than couple of days ago... All the external factors were same: same distance, same pace, same temperature, so it must be this technique or some other factors (my stress, nutrition, sleep). Let's see how it goes next time. Thanks for your instruction videos.