Heart Rate Training (HRT) – Part 9

Part 1 of this series.

Does participation in strenuous physical exercise provide a shield against metabolic disorders? (Strenuous in this instance being defined as exercise at a heart rate above the MAF number).

The reason I ask is that one of the founders of Crossfit, Greg Glassman, says that Crossfit has the cure for metabolic syndrome (Chronic Disease: “We Have the Answer”). But what does the scientific data say about strenuous athletics and metabolic disorders?

Is blood sugar dysregulation primarily the result of lack of strenuous activity? Can diabetes be reverse by strenuous exercise?

Here’s a really interesting 2016 study on Blood Sugar levels in athletes (Felicity Thomas, BE(Hons), Chris G. Pretty, PhD, Thomas Desaive, PhD, and J. Geoffrey Chase, PhD. Blood Glucose Levels of Subelite Athletes During 6 Days of Free Living. J Diabetes Sci Technol. 2016 Oct; 10(6): 1335–1343). The study notes the mechanistic view that:

Physical training is known to improve insulin sensitivity, both immediately postexercise (up to 2 hrs) and through multiple adaptations in glucose transport and metabolism.

Therefore, it could be expected high BG would not be frequently seen in athletes and low BG would be of greater concern due to increased energy expenditure.

However, the data did not support that mechanistic view. As the study noted:

However, this hypothesis does not appear to be the case in the data we have collected.

Wow! Data that doesn’t match the theory? For this study they looked at…

Ten fit, healthy subelite athletes (resting HR <60 bpm) were recruited…

There wasn’t much in the study to indicate the normal intensity level of the activities except:

All subjects regularly trained > 6 hours per week in a range of endurance based sports, predominantly running and cycling.

However, the study did a fasted exercise – ramp test on day 2 – where the participants did 60 minutes of warmup and 30 minutes of exercise to exhaustion.

The researchers measured the subject’s blood sugars using continuous glucose monitors (and other parameters) and data was recorded for six days. They expected the athletes to be in good metabolic health but instead they found that:

4/10 athletes studied spent more than 70% of the total monitoring time above 6.0 mmol/L even with [sic: when] the 2-hour period after meals is excluded.

Fasting BG was also in the ADA defined prediabetes range for 3/10 athletes.

The conclusion of the study was:

Contrary to expectations high BG appears to be more of a concern for athletes then [sic: than] low BG even in those with the highest energy expenditure and consuming below the recommended carbohydrate intake.

This study warrants further investigation on the recommended diets and the BG of athletes to better determine the causes and impact of this hyperglycemia on overall athlete health.

Here is the most interesting paragraph:

However in contrast, strenuous exercise is known to increase circulating concentrations of catecholamines, such as adrenalin and noradrenaline, to near pathological levels, resulting in hyperglycemia and hyperinsulinemia post–intense exercise.

I wonder if all of this has a cause in the intensity of the activity? That seems to be an implicit part of the study which sought to look at:

asks what impact their increased insulin sensitivity, heightened energy expenditure and increased exposure to stress hormones have on their BG levels.

My n=1

I recently did my own measurements in relationship to strenuous activity (Ketones and Blood Sugar Responses to Exercise). This experiment showed my blood sugar rise from 92 to 129 and my ketones fall from 1.0 to 0.3 with 45 minutes of strenuous activity. That’s the highest blood sugar I have recorded in a long time. But that’s also the first time I measured my blood sugar in response to strenuous activity. I assume it always does the same thing.

I took my blood sugar after MAF heart rate activity and it didn’t rise much. In my view, a number of factors work against a diabetic Low Carb athlete:

  1. Strenuous exercise raises the RER out of the fat burning zone into the carbohydrate burning zone.
  2. In response to the high demand, the body mobilizes additional glucose from the body’s glycogen stores.
  3. Glycogen stores are seriously limited in a Low Carb athlete but still present.
  4. The ketogenic state creates a state of glycogen/glucose sparing in the muscles which resists taking up glucose.
  5. If the body didn’t resist taking up glucose the person would have no glucose since dietary sources are limited and it is metabolically costly to make glucose from other substrates (Fat and Protein).
  6. Diabetics have an attenuated first phase insulin response from their pancreas to glucose in the blood stream so they are unable to respond properly to the additional glucose that comes with strenuous exercise.

The only solution to these issues is either:

  1. Abandon Low Carb diets or increase carbs around exercise
  2. Suffer lower performance when performing strenuous activities
  3. Perform physical activities which are not glycogen dependent

This is where MAF fits the bill perfectly.

This is also where Crossfit fails miserably.


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