The analysis required Heart Rate (HR) data against speed, total Calorie consumption and amount of fat/carbohydrate matabolized. I've been hunting such data and in particular was looking for local ultra athlete to give it relevance to Scottish ultra scene, and last week Caroline McKay posted "Quest to become a metabolically efficient fat burning machine!" entry on here blog. Very kindly Caroline passed on the Metabolic Testing Report for her January session at Napier Uni's. This report provided HR, speed, calorie and Respiratory Exchange Ratio (RER) values that allowed me to compute the fat/carb values, and as there is only a 6 data points provided I've had to fill in the gaps by fitting a mathematical functions to various elements of the data.
For reference I also mapped the data provided by the published MFO article normalizing to match Caroline's HR and total calorie usage so I could do a representative comparison.
The maths behind this analysis is something I've put together this weekend so isn't in any published article or book, and while I could attempt to explain it all I'll not attempt it in this blog entry, it's really not something I'd expect 99% of reader to ever want to get their heads around, ask me if you want to know more. As I'm not trying to write an academic paper rather dwell on the details I'll just cut to the chase and show you the base graphs of the various key parameters, so you'll know where the final analysis is drawn from.
First up we have the relationship between HR and speed that Caroline's fitness test found - I've fitted the original test data to the straight line as this matched really well and allows me to extrapolate them to lower ultra-marathon relevant paces.
Next I turned to fitting a curve to the total calorie and fat usage for Caroline's report, and did the same for the MFO data whilst recalibrating the values to match Caroline's HR range and total calorie consumption. The key was making the comparison of the data representative. In the HR to Calorie/Fat chart below red data is Caroline's data, and yellow is the MFO reference, while blue is the total Calorie usage rate (Calories per hour).
While the graph above is staggering, what does this mean in practice when running an ultra? Like many in the Scottish Ultra scene the next big race for us is the 53.1 mile Highland Fling that runs along the southern half of the West Highland Way. Using an estimate of 5,772ft of ascent for the route that John Kynaston kindly provided, and some of my own mathematical models for cost of elevation/descent on running efficiency I estimated a 9% time and energy cost for all those hills. Then using the HR to speed and HR to energy usage graphs above I then extrapolated how many Calories of Carbohydrates would be required for different finishing times:
There is no way Caroline will be able to sustain her maximum HR for the whole route, but I thought it would be useful to see the effect on carbohydrate needs on the extremes both at maximum speed and at slow enough to just squeeze in before the 15 hour cut off. Several amazing things drop out of this graph:
- Normally trained runner requires at minimum 3000 calories of carbs to complete the race, this means consuming at least 1000 calories of carbs as well as burning all their 2000 Calories of stored glycogen.
- If Caroline was happy to do a slow trot she could get by with just burning 500 calories of carbs.
- Caroline's 2011 PB of 10:34 would now require less than 1000 calories of carbs.
- While a normally trained runner would require nearly 3500 calories of carbs for the same PB pace.
- A course record of 7 hours would require just under 4000 calories of carbs for a fat burner like Caroline, this would entail eating about 285 calories of carbs per hour to make up the extra 2000 calories required over glycogen stores.
- While a normally training runner to run a course record would require over 6000 calories, and a staggering 571 Caloris/hour
- I believe these figures suggest that for a 7 hour course record we'll need athletes that are even more fat adapted than Caroline, as well as having the extraordinary speed over distance that we've always expected.
- Assumed the fat/carb consumption doesn't change through out the race, I couldn't factor this in without any concrete data so rather than guess I've just left this as an assumption. The assumption will mean that the above figures are likely an over estimate of actual carb requirements.
- The hills and rough terrain may well be cost more than 9%, so this might push up/pull down the data a bit.
- Weather effects fat/carb consumption, again this is large unknown so not possible to factor in so for the analysis I'm assuming that the temperature is the same as for Caroline's test.
- Consumption of fluids and nutrition will have an effect on fat/carb consumption, again as I can't quantify this I've assumed it's net effect is zero.
- Pacing is consistent through the race - I'm planning to specifically look at this issue in a follow up article (although as spoiler I can say from a carb sparing perspective the most efficient split is an even split - negative and positive splits will required more carbs overall.)
- Food Mix -> Fuel Mix : The low carb, high fat diet that Caroline has been following this year clearly is very effective at supporting high fat utilization across all running paces and especially at ultra race paces.
- Typical trained runners with high carb western diets metabolize carbs over fats, even at slow paces and will require large amounts of carbohydrates to finish the Fling, consuming at least 100 calories of carbs per hour will be required.
- For capable fat burners like Caroline it should not be necessary to consume large amounts of carbohydrates.
- Reducing the amount of carbohydrates consumed reduces the risk of stomach problems
- Consuming carbs at too fast a rate is likely to induce a insulin response which switches off fat metabolism, so if you don't need them desperately then limiting consumption is likely to be lower risk
- Might the new wave of engineered starches like SuperStarch help avoid the insulin response? Is anyone selling them in the UK yet?
Poscript: Just adding a small note: since writing this blog entry Caroline has run the Highland Fling 53 ultramarathon, setting a new personal best of 9:36 for the race, which an hour faster than her previous best. Caroline in her blog entry, A Fling with Friends, reports that she felt strong throughout the race despite eating less than in previous years. This performance provides good evidence that she has achieved her goal of becoming efficient at metabolising fats and as consequence has achieved a very impressive improvement to her ultramarathon race performance.