In my opinion the most frustrating part of training for endurance sports is having to rebuild my base. An athlete needs to rebuild their base after they finish a workout routine that is based on periodization, or after taking some time off from training.
Since I took off nearly 4 months from training my base fitness is horrible. When I jog my heart rate shoots up into zone 3 very quickly. Then I have to stop and walk to get my heart rate back into the base building zone, or zone 2. Running slowly, even jogging with frequent bouts of walking is a frustrating but is a necessary aspect of becoming a fast runner.
One of the things that has helped me to run in the proper heart rate to build fitness is programing my Garmin Forerunner 305 to beep anytime my heart rate rises above zone 2. Here's how:
Go to the main menu, highlight training, push enter (bottom right button)
Highlight training options, press enter.
Highlight alerts, press enter.
highlight HR alerts, press enter.
Highlight Max HR Alert, press enter.
Highlight which zone you want to avoid exceeding, press enter.
Now you can run knowing your training in the proper zone without having to look at your heart rate monitor every few seconds.