Running/triathlon coaches and aerobic instructors see heart rate training differently which it is a battle for the athlete. Spin/aerobic instructors say if your recovery is fast for intervals then your cardio is good. Also, they believe you can do a couple interval workouts a week. Majority of spin instructors don’t even own or bike outside. Now running/triathlon coaches see this is a problem with their athletes because it creates confusion from their side. Running/triathlon coaches use Zones (1-5) for the heart rate training by using the heart rate monitors and RPE (rate of perceived exertion). Depending on what events you are training for that can determine what heart zones you will be most of your training. Half marathon/marathon and half Ironman/full Ironman, you will be training mostly in Zone 1 (easy/recovery) and Zone 2 (endurance). 10K and Olympic training will Zone 1, Zone 2 and some workouts Zone 3 (lactate threshold). 5K and Sprint triathlons are Zone 1, Zone 2 and some workouts Zone 4/5 (above lactate threshold). Now you ask, how are these heart rate zones determine, most common test is FTP test on the bike or lactate threshold test on the treadmill. I have a client that has been struggling to keep her running and biking in Zones 1-2 because most of her training before was done in spin classes. Today, she had a break through with a 70 min ride mostly in Zone 2. At the end of the ride, she felt she could keep on going and felt good. Took her a couple months to understand this, now she gets why Zone 1 and 2 are so important for triathlon training. She sticks to the plan, she will see improvements in a couple months. Be safe and healthy!