Muscle Fiber Activation & Aerobic Base Building
“Physiology of base training There are two basic energy systems you use when training; anaerobic and aerobic. Unfortunately, you can not build both your aerobic and anaerobic systems at the same time very well. The idea behind base training is to train your aerobic energy system specifically and solely. Why is this important? The more work you perform aerobically, or in the presence of oxygen, the more efficient you are. Prolonged aerobic training produces muscular adaptations that improves oxygen transport to the muscles, reduces the rate of lactate formation, improves the rate of lactate removal, and increases energy production and utilization. These adaptations occur slowly over time.” – Matt Russ, Aerobic Base Training – Going Slower to Get Faster, www.trifuel.com
“Building a good aerobic base means training only aerobically. During the base period, no anaerobic workouts (including racing) should be incorporated. Anaerobic activity will jeopardize the efficient development of your aerobic base, so every workout is aerobic. That includes your long run on Sunday, your hilly runs in the park, and any other workouts where you’re heavily influenced by other athletes or the terrain…Anaerobic training can decrease the number of aerobic muscle fibers, sometimes significantly. This can happen in just a few short weeks of higher heart rate training.” – Dr. Phil Maffetone, Want Speed? Slow Down, www.rrca.org
“…the best way to cause improvements in slow-twitch fibers was to run long and slow at 70% VO2peak (adaptation began from as low as 50% VO2peak pace). Faster was not better.” – Hadd, citing the research studies of Dudley & Hickson
“A strong aerobic base is essential if you want to remain injury free or run that fast race you are aiming for. Aerobic training involves running at 60-75% of your maximum heart rate. This translates to a pace that is 1½ to 2 minutes per mile slower than 10K race pace.” – Kirk West, Building an Aerobic Base, www.rrca.org
Claims about base building:
- You cannot build both your aerobic and anaerobic system at the same time.
- Anaerobic training jeopardizes the development of aerobic base
- Anaerobic training can decrease the number of aerobic muscle fibers.
- Slow-twitch fibers are best trained at 70% of VO2peak
- Aerobic training is running at 60 – 75% of max Heart rate
The above comments and claims about aerobic base building are normal. If you run a google search of aerobic base building and read many of the cited articles you will find that the above claims are repeated often. Are the claims true? Does anaerobic training jeopardize aerobic base? Do aerobic adaptations occur best from low intensity training? It doesn’t matter if you believe base building to be an effective training method or not; the issue is if the physiological claims being made about aerobic base building are accurate. Let’s have a look at the research and see if it supports the oft-repeated claims made by base building proponents.
In his internet-famous article on base building, Hadd cited studies by Hickson and, especially, Dudley in support of his claim that slow twitch fibers were best trained via easy paced running at 70% of VO2peak. However, a review of Dudley’s research shows this is not the case at all.(1)
Dudley examined changes in slow twitch, fast twitch oxidative, and fast twitch glycolytic fibers by training rats at intensities ranging from 62% – 116% VO2peak.(2) Dudley found that both slow twitch and fast twitch oxidative fibers showed significant adaptations even at the lowest training intensity of 62% VO2peak. Both fibers continued to adapt as training intensity increased, with adaptations peaking at about 94% VO2peak. In fact, at intensities of 94% or less, the mitochondrial adaptations in fast twitch oxidative were actually higher than those in slow twitch fibers.
Fast twitch glycolytic fibers began adapting at between 73% and 83% VO2peak and continued to adapt all the way to 116% VO2peak.
Not only does Dudley’s research not support the claim that running at 70% VO2peak is the best way to cause aerobic adaptations in slow twitch fibers, it showed that:
a) easy paced running caused significant adaptations in fast twitch fibers,
b) adaptations from easy paced running was greater in fast twitch oxidative fibers than in slow twitch fibers,
c) intensities between about 80% VO2peak – 100% VO2peak caused the greatest adaptations in both slow twitch and fast twitch oxidative fibers
d) adaptations in fast twitch glycolytic fibers began occurring between 73%-83% VO2peak
In short, this research shows that both slow twitch and fast twitch oxidative are active and producing force at paces of about 60% VO2peak – 100% VO2peak. Fast twitch glycolytic fibers become active at between 73%-83% VO2peak. At paces beyond about 100% VO2peak, the activation of slow twitch fibers seems to drop off, replaced by increasingly active fast twitch glycolytic fibers.
Muscles and Marathon Training
Is there a human study supporting the findings of Dudley’s animal study? Yes, there is. A study was conducted on muscle adaptations from marathon training in novice runners.(2) The training program these novice runners followed was a 4 days-per-week, 18 week program of running at an intensity of 60%-75% heart rate reserve (an easy to moderate training intensity).(3)
Researchers measured changes before and after training in many physiological factors, including changes in different muscle fibers types. They discovered major changes in the strength and power of both slow twitch and fast twitch oxidative muscle fibers as a result of the training. Since adaptations only occur in muscle fibers that are active during exercise this study confirms the findings of Dudley, showing that both slow and fast twitch fibers are active during easy to moderate intensity run training.
Let’s examine the results of these studies in relation to some of the claims noted above about base building.
Claim: Aerobic training is running at 60 – 75% of max heart rate.
Truth: Aerobic adaptations occur in both slow twitch & fast twitch oxidative fibers at intensities up to 116% VO2peak, with maximum adaptations occurring around 94% VO2peak. Adaptations in fast twitch glycolytic fibers begin to occur at around 73% VO2peak.
Claim: You cannot build both your aerobic and anaerobic system at the same time.
Truth: Slow twitch and fast twitch oxidative fibers are active and adapt during both easy and fast paced training. Fast twitch glycolytic fibers begin adapting at about 73% VO2peak.
Claim: Anaerobic training jeopardizes the development of the aerobic base.
Truth: Slow twitch fibers adapt to training up to an intensity level of 116% VO2peak, with peak adaptations occurring around 94% VO2peak.
Claim: Slow-twitch fibers are best trained at 70% of VO2peak.
Truth: Slow twitch fibers adapt during both easy and fast paced training. Maximum aerobic adaptation in slow twitch fibers occurred at around 93% VO2peak.
Standard base building training theory proposes that easy paced running is the best method for developing the aerobic system and that slow twitch muscle fibers are best trained at an intensity of about 70% VO2max. Research contradicts this belief by showing that aerobic adaptations in slow twitch fibers occur at intensities ranging from 63% – 116% VO2peak, with maximum aerobic adaptations occurring at around 94% VO2peak. Research also shows that fast twitch oxidative fibers are very active during easy paced running and that fast twitch glycolytic fibers become active at about 73% VO2peak. In short, easy paced training involves the use of both slow twitch and fast twitch oxidative fibers. Moderate intensity and higher training involves the use of all three major types of muscle fibers.
- An Analysis of Hadd’s Approach to Distance Training, Part 2, http://www.powerrunning.com/Training/An%20Analysis%20of%20Hadd’s%20Approach%20to%20Distance%20Training%20part%202.htm
- Dudley G., Abraham W., Terjung R., Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle J. Appl. Phsiol 1982, 53(4), 844-850
- Trappe S, Harber M, Creer A, Gallagher P, Slivka D, Minchev K, Whitsett D., Single muscle fiber adaptations with marathon training, J Appl Physiol, 2006, 101: 721-727.
- Dolgener FA, Kolkhorst FW, Whitsett DA., Long slow distance training in novice marathoners, Res Q Exerc Sport, 1995, 65:339-346.