Short answer: The second law of thermodynamics means that concentrations of specific chemicals or positive or negative charges will always "want" to disperse and randomly mix in their environment, making concentrations of ions such as sodium or potassium a form of potential energy. While the pump normally uses energy from ATP to invest into creating those concentrations, if ATP levels are low and sodium and potassium are already highly concentrated on opposite sides of the cell membrane, their potential energy can be released by mixing across the membrane, and can be used to synthesize ATP. Watch the video or listen to the podcast with the links below. You can obtain a full transcript of the episode by signing up for the Masterpass at https://chrismasterjohnphd.com/q&a Please consider supporting my work by making a purchase using these links at one of my affiliates: https://chrismasterjohnphd.com/foursigmatic, https://chrismasterjohnphd.com/paleovalley, https://chrismasterjohnphd.com/seekinghealth, https://chrismasterjohnphd.com/ancestralsupplements, https://chrismasterjohnphd.com/magicspoon, https://chrismasterjohnphd.com/lmnt  Plenty more at https://chrismasterjohnphd.com/support! If you would like to be part of the next live Ask Me Anything About Nutrition, sign up for the CMJ Masterpass, which includes access to these live Zoom sessions, premium features on all my content, and hundreds of dollars of exclusive discounts. You can sign up with a 10% lifetime discount here: https://chrismasterjohnphd.com/q&a DISCLAIMER: I have a PhD in Nutritional Sciences and my expertise is in performing and evaluating nutritional research. I am not a medical doctor and nothing herein is medical advice.