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The Dirt with Jeff Browning


Athletes are known to push themselves. Aerobic Deficiency Syndrome (ADS) is particularly common in those who push themselves in uphill running.  

ADS occurs when the proportion of training is off between high-intensity training and aerobic base training. It’s important to balance high-intensity (zone 3 and above) with low (zone 1) and medium (zone 2) intensity training. Finding that balance between our bodies and our aerobics can lead to better conditioning, improved strength, and even longevity.  

But don’t just take it from us—hear from Altra Elite Athlete, Ultrarunner, and coach, Jeff Browning. 

He’s seen it, researched it, and discovered ways to overcome the syndrome. In part 6 of his monthly series, The Dirt, he shares what he’s learned. 

Ready to dig up some dirt, kick up some dust, and sift through the soil? Let’s get started! 






Emily had been fighting running injuries and issues for years. When she called me for help, it was a last-ditch effort to get her running back on track or trade the sport in for something more sustainable. Fortunately, with a little heart rate data over a week or two of workouts, the culprit reared its ugly head—Aerobic Deficiency Syndrome (ADS). Emily’s aerobic heart rate zone (zone 1 and 2) was under-trained. Like many runners, she’d been spending too much time in the metabolic gray zone (zone 3) by simply running slightly too hard in her everyday runs. With Aerobic Deficiency Syndrome, the aerobic capacity represents a small window of heart rate range. The answer: Spend 8-12 weeks strictly at or below MAF (Maximum Aerobic Function) heart rate in order to expand aerobic capacity (zone 1 and zone 2 heart rate). I’m happy to say, Emily is still healthily running three years later.


Jeff Browning running in Moab, Utah


A Single Solution 

Dr. Phil Maffetone coined the phrase “Aerobic Deficiency Syndrome” to explain the common issue he witnessed in endurance athletes—an overtrained anaerobic system (heart rate zones 3-5) and an under-trained aerobic system (See Figure 1). His solution: Maximum Aerobic Function (MAF) heart rate, also known as Aerobic Threshold (AeT). The ADS issue has a single solution: a high volume of low to moderate intensity training—staying below MAF. A runner must approach this phase with patience, consistency and diligence. Unlike anaerobic training (intervals, HIIT, etc.), aerobic adaptations are slow to accumulate. However, the pay-off is huge. 


A chart describing the correlation between heart rate and blood lactose concentration



Building Your Base 

Building your aerobic base is the first and foremost step every endurance athlete should take, especially when coming off injury or time off from training. Just like the old college mentality of cramming before a test, the same applies to building aerobic capacity; it simply doesn’t work. The top goal of every endurance runner should be to build and maximize aerobic capacity. That can only be done by training 80-90% (and at first 100%) of your weekly run volume at or below MAF. As your aerobic capacity improves, your Aerobic Threshold (AeT) will shift to represent a higher percentage of your overall heart rate zones (See Figure 2) vs. Aerobic Deficiency Syndrome (See Figure 1). 



Chart showing the correlation between heart rate and blood lactose concentration



MAF Math 

So, how do you find out what your MAF heart rate is? The most accurate way is to take a Respiratory Quotient (RQ) test (available at many fitness and wellness centers). RQ is determined by calculating your Respiratory Exchange Ratio (RER) and is a gauge of which fuel (carbohydrate or fat) you are metabolizing to supply your body with energy. The Cross Over Point (COP) is the point at which your metabolism shifts from primarily burning fat as your fuel to burning carbohydrate. Just below your COP is your MAF heart rate. Keeping your effort below your COP will stimulate deeper fat burning for energy. And, as this fat utilization improves, your Cross Over Point will shift to a greater heart rate zone at which you can race and train. 

What if you can’t obtain an RQ test? This is where Maffetone’s MAF Formula comes in. To obtain your MAF heart rate, calculate 180 minus your age. Don’t go over that number when building your aerobic base. Keep in mind, this is an estimate and Dr. Maffetone details definite nuances based on running history, injuries (past and recent), and age.



MAF 180 Formula* 

  • 180 - Age = MAF Heart Rate
  • Simply use the original MAF equation if you’ve been training regularly (at least 4x per week) for up to two years without any of the problems mentioned below.
  • Subtract 10 if recovering from a major illness (heart disease, operation or hospital stay), rehab, regular medication, or experiencing burnout.
  • Subtract 5 if you’re injured, if you have regressed or aren’t improving in training or competition, if you get more than two colds, flu or infections in a single year, if you have seasonal allergies or asthma, are overweight, in stage 1 or 2 of overtraining, if you aren’t consistent, just beginning, or are just getting back into regular training (at least 4x per week).
  • Add 5 if you’ve been training for more than two years without experiencing the aforementioned problems, have improved in MAF tests, have improved in competition, and are not currently injured.  

Exceptions to the Rule 

  • If you are over the age of 65, you may need to add 10 if you’ve been training for more than two years without experiencing the aforementioned problems, have improved in MAF tests, have improved in competition, and are not currently injured. 
  • If you are 16 or younger use a MAF heart rate of 165 instead.  




The positive feedback I get from athletes who embrace this approach is encouraging. Most talk about how energized they feel. With the MAF training approach, you’ll encourage your body to burn more body fat for fuel, bump up your energy and brain function, and decrease your injury risk — all while building greater endurance and fitness. If you couple this with strength and mobility work, you have a solid road to running longevity.  




About the Author

Jeff Browning is a veteran ultrarunner and ultra-endurance coach. As a masters athlete, he has embraced both mobility and strength consistently in his training to slow down aging and to prepare his body for the rigors of up to five 100-milers per season—some just weeks apart. You can learn more about him, his adventures, and his coaching at GoBroncoBilly.com or on Instagram: @GoBroncoBilly