In my opinion, fartlek training will make you faster. If you use it as part of your 20% hard running. Fartlek runs are a training method that combines endurance and speed training by varying your pace throughout the workout. The term “fartlek” means “speed play” in Swedish. I have been using them in my training since I was a kid. Unlike interval workouts where you have complete stops or walking recoveries at fixed intervals, fartlek challenges your body to adapt to different speeds without break