Does lactate cause muscle soreness?

No. Lactate regenerates NAD+ so glycolysis can keep running when oxygen is short, and the lactate itself is turned back into glucose by the liver or burned by the heart and slow-twitch fibres. The soreness that arrives a day or two later comes from microscopic damage to muscle fibres and the inflammation that follows, not from lactate.

Can fat be converted into glucose?

Generally no. The step turning pyruvate into acetyl-CoA is irreversible, so there is no path back from fatty acids to glucose. The exceptions are the glycerol backbone released from triglyceride and the tail end of odd-chain fatty acids, which do enter gluconeogenesis.

How does nutritional ketosis differ from ketoacidosis?

Fasting or low-carb eating typically puts blood ketones at 0.5-3 mmol/L, with residual insulin acting as a brake. Diabetic ketoacidosis is that brake failing almost entirely, reaching 15-25 mmol/L and acidifying the blood - a medical emergency. They differ by an order of magnitude.

Do I have to load creatine?

No. Splitting 20 g a day over six days saturates stores quickly, but 3-5 g daily reaches the same level in three to four weeks. Speed is loading's only advantage, and stomach upset is more common with it. About 2 g is lost daily as creatinine, so the maintenance dose simply replaces that.

Is creatine bad for the kidneys?

No kidney damage has been demonstrated in healthy people. The rise in blood creatinine seen with supplementation reflects more creatine metabolite, not failing kidneys. If you have existing kidney disease, talk to a healthcare professional before taking it.

Why is three minutes recommended between sets?

Creatine phosphate recovers about half in 30 seconds and most of it within three minutes. A set aimed at maximal strength needs the phosphagen system recharged to lift the same load again, so 3-5 minutes is recommended. Cutting rest under a minute leaves the next set starting depleted, raising metabolic stress - which is a valid hypertrophy stimulus.

Endocrine Wiki

Follow the three routes that make ATP, and the one route that spends it to build muscle - step by step.

Glucose Oxidation

Fully burning one glucose molecule yields 30-32 ATP - the body's preferred route.

Duration

Tens of seconds to ~90 minutes (until glycogen runs out)

Energy yield

30-32 ATP per glucose

Mainly used

Moderate-to-hard exercise, post-meal, the brain at rest

Pathway schematic

The main route runs left to right. A dashed drop marks a branch, and where the background band changes is where a membrane is crossed. Green text under a node is what that step yields.

Step by step

Energy yield

Skeletal muscle & brain (glycerol-phosphate shuttle)30ATP

Liver & heart (malate-aspartate shuttle)32ATP

Without oxygen (lactate fermentation)2ATP

Going deeper

30 or 32 - the shuttle decides

NADH made in glycolysis sits in the cytosol and cannot cross the inner mitochondrial membrane. Liver and heart use the malate-aspartate shuttle and keep it as NADH for 32 ATP; skeletal muscle and brain use the glycerol-phosphate shuttle, handing it over as FADH2 and losing 2 ATP for a total of 30.

Why the old 36-38 ATP figure changed

Many of us learned 3 ATP per NADH and 2 per FADH2. Once it became clear that the protons needed per ATP are not a whole-number ratio, the accepted values became 2.5 and 1.5. The reactions did not change - the conversion factor got more precise.

Hitting the wall is glycogen running out

Muscle holds roughly 400-500 g of glycogen and the liver 80-100 g. The wall marathoners meet around the 30 km mark is that store emptying and fuel handing over to fat oxidation - which burns more slowly, making the same pace far harder to hold.

The four routes compared

The first three are catabolic routes that make ATP; the last one is the anabolic route that spends it. They do not take turns - all of them run constantly, only the balance shifts.

Group	Pathway	Duration	Energy balance	Mainly used
Energy Metabolism (Catabolism)	Phosphagen System (ATP-PCr)	0 to 10 seconds	1 ATP per reaction, immediately	Sprints, 1-3 rep max lifts, jumps and throws
Energy Metabolism (Catabolism)	Glucose Oxidation	Tens of seconds to ~90 minutes (until glycogen runs out)	30-32 ATP per glucose	Moderate-to-hard exercise, post-meal, the brain at rest
Energy Metabolism (Catabolism)	Fatty Acid Oxidation & Ketones	Hours to weeks - as long as stored fat lasts	106 ATP per palmitate	Fasting, long low-intensity exercise, low-carb diets
Protein Metabolism (Anabolism)	Muscle Protein Synthesis	Stays elevated for 24-48 hours after the stimulus	4 ATP spent per peptide bond	After resistance training, after a protein-containing meal

This material is educational, intended to explain physiology. If you have a medical condition or are considering supplements, talk to a healthcare professional.

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Related Keywords & Hashtags

#Bioenergetics#EnergyMetabolism#MetabolicPathway#ATP#ATPProduction#Glycolysis#KrebsCycle#TCACycle#CitricAcidCycle#ElectronTransportChain#OxidativePhosphorylation#Mitochondria#Pyruvate#Lactate#LactateThreshold#BetaOxidation#FattyAcidOxidation#KetoneBodies#Ketosis#BetaHydroxybutyrate#Acetoacetate#Carnitine#Creatine#CreatinePhosphate#CreatineLoading#CreatineMonohydrate#PhosphagenSystem#ATPPCr#AnaerobicExercise#AerobicExercise#Glycogen#Gluconeogenesis#Metabolism#Catabolism#Anabolism#ProteinMetabolism#MuscleProteinSynthesis#MuscleGrowth#Hypertrophy#mTOR#Leucine#ProteinIntake#AminoAcids#ExercisePhysiology#Biochemistry

A Complete Guide to Energy Metabolism: How Glucose, Fat and Creatine Become ATP

The body makes ATP along three routes, choosing between them by intensity and duration. In explosive efforts such as a sprint, creatine phosphate hands its phosphate straight to ADP to rebuild ATP (the phosphagen system). As moderate-to-hard work continues, glucose is burned completely through glycolysis, the TCA cycle and the electron transport chain for 30-32 ATP per molecule. When carbohydrate runs low or fasting continues, stored fat is broken down by beta-oxidation and the liver converts the product into ketone bodies the brain can use. This wiki walks each route step by step, showing where in the cell the reaction happens and how many electron carriers and ATP each step produces. Yields follow current biochemistry conventions: 2.5 ATP per NADH and 1.5 per FADH2.

Step-by-step pathway diagrams

Follow each route step by step, seeing whether the reaction runs in the cytosol, mitochondrial matrix, inner membrane or liver, along with the ATP, NADH and FADH2 each step yields.

Yields on current conventions

Real figures - 30-32 per glucose, 106 per palmitate, 21.5 per beta-hydroxybutyrate - separated by shuttle type and tissue.

Evidence on creatine

Loading versus maintenance dosing, how much stores rise, the share of non-responders, and the myths worth clearing up.

Last Reviewed: 2026-09-29

Frequently Asked Questions (FAQ)

Older textbooks converted NADH at 3 ATP and FADH2 at 2. Once it became clear the protons needed per ATP are not a whole-number ratio, the accepted values became 2.5 and 1.5. The reactions did not change; the conversion factor got more precise. On top of that, which shuttle carries cytosolic NADH decides the total: 30 in skeletal muscle and brain, 32 in liver and heart.

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