Intense work outs and Keto, at least initially is bad news. Your body at higher intensities uses carbs as Fatty acids aren't fast enough to provide the ATP needed. If you are doing high intensity on Keto, You are using lactic acid, glycogen liver produces for fuel. You need to slowly ramp up the intensity as your body gets adjusted to using Fatty acids as fuel at high intensities. Look up RER/RQ (respiratory quotient) to learn about the fuel body utilizes at different intensities. it took me 6 months for my body to use fat as fuel at 90% Vo2 Max instead of glycogen. You either eat complex carbs before work out and continue doing it or don't eat carbs and slowly increase the intensity.