Originally Posted by
LoriRose
On my commutes I will go hard when I get a series of green lights. It's short enough that I don't feel the need to pace myself too much. On my long rides I will go hard only during the second half for a few kms, then ride easy for a bit, and then do it again - cuz it's fun and I always seem to get a tailwind coming home!
You don't want to do that.
Not being pedantic about terms you have three systems:
1. aerobic which works indefinitely and runs off your nearly inexhaustible fat stores (9000Calories a kilogram where male athletes are about 6-13% fat and females 14-20%)
2. anaerobic where you have a limited amount of energy you can spend fast or slow which runs off carbohydrates where you have about 100 Calories in your blood, 400 in your liver, and 1600 spread across your muscles with no way to get it back into your blood so different muscles can use them.
3. neuro-muscular which runs out in tens of seconds.
When you "go hard" even briefly, your body starts to draw more from your anaerobic system and continues to do so after you back off so you don't train your aerobic fitness and are slower on long rides.
When you do that frequently you're too fatigued to "go hard" to stress your anaerobic system enough to force training adaptations which make you faster, increase endurance at high speeds, and shorten recovery time.
Lots of endurance athletes (cyclists, cross-country skiers, rowers, swimmers) use polarized training with 20% of sessions above their anaerobic threshold and the rest below their aerobic threshold avoiding the area between them which trains neither system.
Riding five days a week, one hard interval session is enough where the sweet spot is as hard as you can ride for 7-10 minutes.
You also want rest weeks, where one out of four is traditional. That allows adaptation to occur and prevents over-training which is relative - you can over-train on just an hour a day.