I have been trying to tease out the limits of low carb performance. Here is a key paper (Metabolism. 1983 Aug;32(8):769-76. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL). Buried within the paper is:
In agreement with this were a three-fold drop in glucose oxidation (from 15.1 to 5.1 mg/kg/min, P less than 0.05) and a four-fold reduction in muscle glycogen use (0.61 to 0.13 mmol/kg/min, P less than 0.01).
This seems buried because of the units used. Another site (September 13, 2017. Why Am I Getting Low Ketone Readings on a Ketogenic Diet? By Mark Sisson) translates these units as:
During the high-carb arm, the group began the workout with 150 grams of glycogen and ended it with 50 grams. While eating ketogenic, the group began the workout with 75 grams and also ended it with 50 grams.
The time of this test was approx 150 minutes.