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For runners who race marathon or ultramarathon distances it is important to optimize fueling. The human body stores carbohydrate as [[Glycogen]] in the muscles and liver, and the depletion of that glycogen can cause fatigue and impaired performance. A common pattern of blood glucose while exercising is for the level to rise during the first part of training as the body [[Warmup| Warms up]], then gradually declines until exhaustion. (The exhaustion can be caused by many different factors besides low blood sugar.) The level at which blood glucose starts to impact performance appears to be somewhat different for different individuals. For me, my performance often (but not always) suffers when my blood glucose drops below 100 mg/dl, and is significantly impaired if it goes below 80 mg/dl. If you know how your blood glucose impacts your performance you can then evaluate how effective your fueling is. =Glucose Tolerance Test=A [https://mayoclinic.org/tests-procedures/glucose-tolerance-test/about/pac-20394296 Glucose Tolerance Test] is typically used to diagnose diabetes, but it can provide some useful insight into both healthy and diabetic runners. I performed a number of tests to compare how my body uses glucose. I started with a standard GTT, in which I took 75g of Dextrose after an overnight fast and checked my blood glucose every 15 minutes for two hours. A GTT often just looks at the blood glucose level at the two-hour mark, but I was interested in the shape of the curve and the area under the curve. I then checked my blood glucose during a fasted long run to see how things go without any fueling. I was surprised my blood glucose was as low as it was given that I felt fine and was happy to carry on running for anther two hours after the test. I only checked blood glucose every 30 minutes as it requires slowing down to a walk to check, which interrupts the run. My third test was to take the 75g at the start of the long run and see how that compares. As you can see, my blood glucose rose at the three-hour mark, but nowhere near as high as when resting, and by the hour mark its back to baseline. This suggests that for me, under these conditions, 75g of dextrose will be consumed within 60 minutes. My next tests will be to take the glucose immediately before a short, hard interval session, then repeat it taking the glucose immediately after a similar interval session. [[File:GTT.jpg|center|thumb|500px|My Glucose Tolerance Test results]]The results above can't be generalized to anyone else, and are provided as an example of how you can use blood glucose testing. =What's involved in testing?==

==Accuracy ==Generally , blood glucose meters are accurate to +/- 20%. Normally glucose meters define their accuracy in terms of the percentage of samples that have a given error. For instance the TRUE2go meter has 55% of samples within 5%, 82% within 10%, 96% within 15% and 99.7% within 20%. What's that mean in practice? A single reading is good enough for clinical use, but for more rigorous use it's worth taking several reading and averaging them. For my TRUE2goinstance, averaging multiple samples improves the accuracy like this:{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"

==Which glucose meter=My Testing Technique=I have three glucose meters've found a lot of variation between samples taken at the same time, which is frustrating. Taking two samples and averaging them helps, each with their own pros and cons. * [http://www.amazon.com/BLOOD-GLUCSE-TRUE-2GO-Size/dp/B001Y7EIG0 TRUE2go] is if they're too far apart, take a tiny meter that actually clips onto the top of the pot that holds the test stripsthird. The test strips only require I suspect it helps to draw a tiny drop of blood, much smaller than many other meterswipe it away and draw another drop for testing. The [http://www.amazon.com/TRUEtest-Test-Strips-100-Count/dp/B002CGT09M TRUEtest Taking the test strips] are also cheaper than some others. The TRUE2go has from a memory much larger drop of readings, but it does not display the time with blood than the minimum required also seems to resultin more repeatable readings. This can make it tricky if you record Obviously, ensuring your finger is clean is critical, as even a number trace amount of samples during a long run, then want to record them latersugar will corrupt the reading. (<jfs id="B001Y7EIG0" noreferbWhich glucose meter?="true"/>)* [http://www.amazon.com/TRUEResult-Blood-Glucose-Starter-Kit/dp/B002CGT08S TRUEresult] is I have tried a slightly larger meter than the TRUE2gonumber of glucose meters, and I got it because it has a better display which includes found the time Contour Next One is one of each sample recordingthe best. It's cheap to buy and reasonably accurate. (<jfs id{{Template:BuyAmazon|AZID="B002CGT08S" noreferbB06Y42FL2R |AZN= Contour Next One }}=Which Lancet?="true"/>)* [http://www.amazon.com/Precision-Blood-Glucose-Monitoring-System/dp/B000N64MZA Precision XTRA] is unusual in that it will [[Measuring Ketones| measure Sticking yourself with a lancet to draw blood ketones]] as well as glucoseisn't a great experience. I only use mine for ketone measurement because read of the Lifescan Onetouch Delica and its "reduced vibration" which they claim reduces the [http://wwwpain.amazon.com/Precision-Xtra-Blood-Glucose-Strips/dp/B0017JKD6Y XTRA glucose strips] are more It's still not pain free, but it seems better than twice the price of other lancet devices I tried, and much better than the TRUEtest strips and require a 50% larger blood sample. The XTRA requires you to insert a calibration strip each time you open a new box of test strips, something free devices that is not required often come with the TRUE systemmeters. However, if you want to only have one meter that does both blood and ketone testing, this is it. (<jfs id{{Template:BuyAmazon|AZID="B000N64MZA" noreferbB0044AI2K2|AZN="true"/>)Lifescan Onetouch Delica }}