Question: When I started cycling in the late ’70s, coaches were of the view that building an aerobic base was very important – and specific. Training outside of the aerobic zone interfered with aerobic development and should be avoided at all costs. Does this compartmentalized view still hold up, given the increased knowledge we have of sports science? It seems to have fallen away in the general fitness arena, with HIIT being the latest craze in gyms, boot camps, etc. Given that we now know that all three energy systems work more or less concurrently, depending on effort, is it necessary to “build an aerobic base” from a fitness development point of view – or will the aerobic system “take care of itself” over time with any reasonable program? —Colin McFerran
Coach Hughes Replies: Colin, you’re exactly right about how training was prescribed back then. I also started cycling in the ’70s and used the Italian Olympic Cycling Training Manual, which said I should ride at least 1,000 km on my fixed gear to build my base before doing any harder riding. If I didn’t have a fixie, then I should ride at least 1,000 km in the small chain ring.
Also, that manual specified that I should avoid the “dead zone,” which lay between an aerobic workout and an anaerobic workout.
Energy Metabolism and Muscle Fiber Types
You are also correct that all three energy systems work more or less concurrently, depending on effort. The three energy systems are:
1. Oxidative aerobic system (low power / long duration), which is composed of two different sub-systems:
- Fat metabolism uses beta oxidation.
- Glycogen metabolism uses a different metabolic system.
Each subsystem takes place in a different part of the muscle cell and uses different enzymes.
2. Glycolytic anaerobic system, which metabolizes glycogen (moderate power / short duration of about two minutes)
3. ATP-CP, which metabolizes glycogen (high power / short duration up to 10 seconds)
Likewise, your legs have three different types of muscle fibers:
1. Slow-twitch (low power, great endurance)
2. Fast-twitch IIa (moderate power and endurance)
3. Fast-twitch IIb (high power and shorter endurance)
Your body recruits the energy systems and muscle fiber types progressively. When you are riding at an easy aerobic pace, you are using your slow-twitch muscle fibers, and most of your energy comes from the beta oxidation of fat, with the rest of the energy coming from oxidative aerobic metabolism of glycogen.
As you ride somewhat harder, you continue to metabolize fat and burn increasing amounts of glycogen.
Riding still harder, the proportion of energy coming from glycogen (in addition to energy from fat) increases even more, and your body recruits your fast-twitch IIa muscle fibers, in addition to your slow-twitch fibers.
If you push the pace even more, your body recruits your fast-twitch IIb fibers. You’re riding fully anaerobically, and the glycolytic anaerobic system also provides energy, in addition to the aerobic metabolism.
Finally, when you are riding extremely hard – like sprinting – your ATP-PC system provides the final boost of energy.
HIIT and Hard Intervals Recruit All Energy Systems
Colin, you are also correct that when you are doing High Intensity Training (HIT) or other hard intervals, all of your energy systems are in operation.
However, each energy system and fiber type responds to different kinds of training.
As I often emphasize, effective training results from:
- Overload and recovery.
- Progressive overload.
When you do very hard, short HIT-type workouts, you need more recovery between the workouts, which means that within a week you get less total stimulus to your slow-twitch and fast-twitch IIa muscles.
When you aren’t going flat out, just hammering hills, you need less recovery between workouts than between HIT-type workouts. However, you still need more recovery between workouts than between endurance rides, and you don’t get as much weekly overload of your slow-twitch fibers as you would during a longer endurance ride.
Building a Base
The cumulative stimulus in workouts is what produces the overload so that a muscle fiber type and energy system improve. The rule of specificity applies: to improve a specific fiber type and energy system you need to do the right kind of workout.
The importance of building a base is still correct.
Base endurance riding increases the overall fitness of your muscles, ligaments and tendons, making them fit enough to support harder training without injury. Base training produces the following physiological adaptations:
- Boosts the endurance of the cycling muscles by increasing the number of mitochondria. The mitochondria are subcellular structures in the muscles where aerobic energy is produced.
- Boosts the respiratory system, providing more oxygen to the blood supply.
- Increases the efficiency of the heart so it can pump more blood to the muscles. Endurance training improves the stroke volume, the amount of blood pumped per heartbeat.
- Increases the capacity of the liver and muscles to store carbohydrates. Your body can store approximately 1800 calories’ worth of carbohydrate as glycogen. You can exhaust your glycogen stores during several hours of hard riding. Through endurance training, you can increase your ability to store glycogen by 20 to 50%!
- Furthers the neuromuscular efficiency of pedaling. Power is a function both of the strength of the muscles and the coordination of the firing pattern of the nerves to activate the right muscle fibers at the right time so you go forward with less wasted energy. (This is like dialing in the timing of a car engine.) Early season endurance training is also a great time to work on pedaling with a rounder stroke and being able to spin smoothly at a higher cadence.
- Boosts the capacity to burn fat during long rides. Through endurance training, your fuel mix on endurance rides shifts to more fat and less glycogen, sparing precious glycogen stores. Note that this doesn’t automatically result in weight loss; that is a function of calories in and calories out.
- Tunes the thermoregulatory system by increasing the blood flow to the skin. Your skin is your largest organ, and the ability to dissipate heat will pay off later in the season.
Winter’s coming (or has already arrived, depending on where you live), and it’s tempting to just hammer on the trainer instead of suffering in the cold. However, even in cold weather you need to do base endurance exercise. In my next several columns, I’ll discuss how to ride your bike in cold weather, the benefits of cross-training, and the effective use of the trainer.
For more information see my eArticles:
Productive Off-Season Training This 27-page eArticle provides two 12-week programs. Each program is in four-week blocks so you can adapt either to your schedule:
- Program for Health and Fitness Riders trains riders for 15- to 25-mile (25- to 40-kilometer) weekend rides by the end of the program.
- Program for Recreational Riders trains riders for 20- to 45-mile (30- to 70-km) weekend rides by the end of the program, with optional longer rides to prepare for 40- to 90-mile (60- to 145-km) rides in the Base phase.
Off-Season Conditioning Past 50 This 26-page eArticle includes:
- Review of the physiological effects of aging.
- Training modalities to combat these.
- 12-week off-season training program with a range of options.
Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.
Peter K says
Thanks for explaining this, I’ve been wondering the same thing for a while now. It makes sense that if your HIIT training requires more rest, then you have less time to dedicate to training the slow-twitch fibers. If I had 20 hours to train each week but did a HIIT session every other day (maybe 5 total), since I have to recover I probably don’t ride at all in my “remaining” 15 possible hours.
But what if you only have a limited amount of time in the first place? If I only have 5-6 hours a week for training, does HIIT make more sense than base training? (Obviously with 6 hours of training per week it’s not about racing, it’s about maintaining pace on long group rides)