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Dr. Andy Galpin: How to Build Physical Endurance & Lose Fat | Huberman Lab Guest Series

This is episode 3 of a 6-part special series on fitness, exercise and performance with Andy Galpin, PhD, professor of kinesiology at California State University, Fullerton.

Andrew HubermanhostAndy Galpinguest

Feb 1, 20233h 48mWatch on YouTube ↗

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Framing Endurance: Beyond ‘Cardio’ and Into Fatigue & Fuel
Huberman and Galpin set the stage by redefining endurance as the ability to repeatedly perform at a given quality—across daily life and sport—rather than just doing long, slow cardio. Galpin positions endurance as a core pillar alongside strength and aesthetics, driven by two factors: fuel availability and fatigue management.
- •People exercise to: feel better, look a certain way, and perform well for a long time.
- •Endurance has many forms: daily energy, muscular endurance (stairs), high-output bursts, mid-distance efforts, posture-sustain, and long outings.
- •Two fundamental constraints: (1) fatigue signals (acid, CO₂, etc.), and (2) energy input (phosphocreatine, glycogen, fat).
- •Efficiency and mechanics—especially breathing and posture—are the fastest levers to improve endurance.
- •Nasal breathing tends to auto-correct breathing mechanics for lower-intensity and some moderate-intensity efforts.
Exercise Snacks and High-Intensity Micro-Bouts
Galpin describes ‘exercise snacks’—very short, intense efforts like 20-second stair sprints—as a potent way to improve VO₂ max, cognition, and glucose control without full workouts. Mode of exercise is secondary to intensity and feasibility in real life.
- •Office-worker study: 3×20-second all-out stair sprints per day, 3 days/week for 6 weeks improved VO₂ max and cognition.
- •Similar micro-bouts after high-glycemic meals improved postprandial glucose and insulin responses.
- •Mode is flexible: stairs, burpees, jumping jacks, hallway sprints; intensity and safety are the priorities.
- •Protocol design in studies reflects practicality, not sacred numbers; core idea is to spike heart rate multiple times per day.
- •These micro-bouts can be integrated between meetings or calls with no shower/warmup requirement.
What Is Endurance? Systematic Breakdown of Capacities
Galpin decomposes ‘endurance’ into specific, trainable capacities—from energy across the day to muscular endurance, anaerobic capacity, aerobic capacity, posture endurance, and long-distance work. Each has distinct failure points and therefore distinct training implications.
- •Muscular endurance: repeat small efforts in a local muscle (stairs, push-ups) without burning out.
- •Anaerobic capacity: max work for ~20–80 seconds (sprinting hills, surfing paddles).
- •Maximal aerobic capacity: hard efforts for ~5–15 minutes (1-mile run pace).
- •Postural/sustained position endurance: sitting/standing or holding positions without collapse.
- •Long-duration endurance: maintaining output and feeling okay after long events (hikes, theme-park days).
- •Training should be targeted to the exact endurance limitation you care about.
Carbon, CO₂, and the Biochemistry of Fat Loss
Galpin walks through how body fat is chemically lost: carbons from carbs and fats are broken, energy forms ATP, and carbons are exhaled as CO₂. This ‘carbon economy’ reframes fat loss as managing carbon in versus carbon out, not micromanaging macronutrient ratios.
- •Carbohydrates and fats are chains of carbon; metabolism is the controlled breaking of carbon bonds to make ATP.
- •Free carbons must be bound to oxygen to form CO₂ and exhaled, otherwise they’re toxic.
- •Plants run the cycle in reverse via photosynthesis, inhaling CO₂ and exhaling O₂, creating a carbon loop.
- •Body stores: glucose in blood, glycogen in liver and muscle, fats as triglycerides (glycerol backbone plus fatty acid chains).
- •Fat loss = either ingesting less carbon or exhaling more carbon over time; diet composition is secondary to this balance.
Hyperventilation, Exhaling More, and Why You Can’t Cheat Physiology
They explore the tempting but flawed idea of losing fat simply by exhaling more CO₂ via deliberate hyperventilation. While technically you do lose more carbon, physiological safeguards (panic, hypocapnia) and energy demand realities make exercise the only sustainable way to increase carbon out.
- •You absolutely lose fat by exhaling CO₂; theoretically you could hyperventilate to do it faster.
- •But hyperventilation quickly drives up adrenaline, causes tingling and panic, and is unsustainable.
- •The body self-corrects: post-hyperventilation, breathing slows, negating net carbon out gains.
- •The only viable way to maintain higher CO₂ exhalation is to increase true energy demand (exercise).
- •It doesn’t matter if a session uses carbs or fats; total oxygen in and CO₂ out drive fat loss over time.
Heart, Cardiac Output, and Why Resting HR Drops with Training
Galpin breaks down cardiac output (heart rate × stroke volume) and shows how endurance training increases stroke volume, which allows resting heart rate to drop while maintaining the same cardiac output. He cautions against chasing higher max heart rate; instead, aim for efficiency.
- •Cardiac output must match energetic demand; body auto-adjusts HR and stroke volume to keep it appropriate.
- •Endurance training strengthens the heart, increasing stroke volume so resting HR can drop while maintaining output.
- •Resting HR under ~60 bpm is a practical sign of decent cardiovascular fitness for healthy people.
- •Max heart rate doesn’t increase with fitness and is not a meaningful performance marker to chase.
- •At submax intensity, trained and untrained people may show similar cardiac output, but trained people achieve it with lower HR and higher stroke volume (greater efficiency).
Metabolic Flexibility and Misunderstood ‘Fat Burning’
The discussion turns to respiratory exchange ratio (RER), fasted training, and the crossover from fat to carb dominance with intensity. Galpin shows why maximizing fat oxidation during exercise is not the same as maximizing fat loss, and why ‘fat-adapted’ is often misused.
- •RER/RQ track O₂ in vs CO₂ out; values rise with intensity and can exceed 1.0 at very high effort.
- •At rest and low intensity, a higher percentage of fuel comes from fat, but total energy expenditure is low.
- •As intensity increases, carbs dominate fuel use; at very high intensity you can hit ~100% carb, 0% fat use.
- •Even highly ‘fat-adapted’ individuals rarely exceed ~70% of fuel from fat during exercise.
- •Fasted training is not required for fat loss; glycogen stores are still ample and total energy and adherence matter more.
- •Metabolic flexibility means using the right fuel at the right time (carbs for fast, fat for slow), not maximizing fat use everywhere.
Carbs, Glycogen, and How You Lose Fat While Burning Carbs
Galpin explains how a carb-focused workout can still drive body-fat loss: by depleting glycogen and forcing later dietary carbs into storage while shifting everyday fuel use toward fat. He clarifies that you’re not turning fat into muscle or vice versa, but redistributing energy sources.
- •During high-intensity training, you mainly burn muscle and liver glycogen and blood glucose.
- •Afterward, if you’re in a hypocaloric state, dietary carbs preferentially replenish glycogen, and fat (dietary+stored) becomes favored fuel.
- •You do not permanently deplete liver/muscle glycogen; the body defends these stores and taps fat reserves instead.
- •You cannot convert fat to muscle or muscle to fat; they are distinct tissues with different functions.
- •Key to fat loss: sustained negative carbon balance, not whether the workout itself was ‘fat-burning’ or ‘carb-burning’.
Protein as Fuel, FFMI, and Muscle’s Modest Calorie Burn
They cover why protein is a poor primary fuel, the limited contribution of protein to exercise energy, and the overestimation of how many calories muscle burns at rest. Galpin still advocates for adequate muscle mass due to its many indirect benefits for fat loss and health.
- •Protein is best used for structure, not fuel; typically ~5–10% of exercise energy comes from protein.
- •Using protein as fuel is like burning metal for heat: technically possible, but wasteful and inefficient.
- •Older estimates of ~50 kcal/day per pound of muscle are likely exaggerated; newer estimates ~6–10 kcal/day/lb.
- •Even if muscle’s resting calorie burn is modest, over months/years it still adds up.
- •More importantly, insufficient muscle makes fat loss and metabolic health harder; build and maintain a baseline of lean mass.
How to Improve Carb and Fat Utilization (Real Metabolic Flexibility)
Galpin moves from theory to practical tests for metabolic flexibility and ways to improve both carb and fat utilization. He emphasizes meal composition, pre-exercise fueling choices, and training intensity as levers to bias and train specific fuel pathways.
- •Signs of poor fat use: crashing on fasted runs, poor performance when unfed, slow HR recovery.
- •Signs of poor carb use: extreme sleepiness or ‘crash’ after ~50 g carb, needing caffeine just to tolerate carbs.
- •Improve fat use: some fasted or low-carb sessions at lower intensities; possibly pre-session fat intake (performance tradeoff).
- •Improve carb use: pre-exercise carb feeding, regular high-intensity work that forces glycolytic reliance.
- •Stabilizing blood glucose via protein/fiber-combined meals and overall caloric control supports better energy use.
- •Extremes like chronic very-low-carb diets trade glycolytic performance for fat reliance; acceptable only if performance demands are low or specific.
Deep Dive: Glycolysis, Lactate, and the Krebs Cycle
Galpin walks through carbohydrate metabolism step-by-step: from glucose splitting in the cytoplasm (anaerobic glycolysis) to pyruvate/lactate handling, to acetyl-CoA entering the Krebs cycle in mitochondria, and finally the electron transport chain. He links this biochemistry directly to endurance and fatigue.
- •Anaerobic metabolism (no oxygen) occurs in the cytoplasm: phosphocreatine first, then anaerobic glycolysis.
- •Glucose (C₆H₁₂O₆) splits into two 3-carbon pyruvates, creating small amounts of ATP.
- •When ATP is hydrolyzed, hydrogen ions accumulate; to buffer acidity, hydrogen binds to pyruvate to form lactate.
- •Lactate can be transported to the heart, other muscles, or liver (Cori cycle) to be converted back into pyruvate or glucose.
- •With sufficient oxygen, pyruvate converts to acetyl-CoA, enters the Krebs cycle, and yields large amounts of ATP via the electron transport chain.
- •End-product of full carb oxidation: ATP, water, and CO₂, same as fat.
Fat Oxidation, Carnitine, and Why Fat Is Never the Limiting Fuel
They contrast fat metabolism with carbohydrate metabolism. Fat oxidation is slower, requires mitochondrial entry (often via carnitine), and is virtually unlimited in capacity, making it ideal for long-duration, lower-intensity work but inadequate alone for high-intensity performance.
- •Most fat energy comes from systemic adipose, not local intramuscular triglycerides.
- •Fatty acids must enter mitochondria, often via carnitine shuttles (long-chain FAs), then undergo beta-oxidation (two carbons cut at a time to form acetyl-CoA).
- •Short- and medium-chain triglycerides can enter mitochondria more freely and be quickly oxidized.
- •Fat stores in a lean 170-pound person can fuel 30+ days of basic metabolism; you never ‘run out’ of fat in normal exercise.
- •Fat oxidation is purely aerobic and too slow for peak power demands; carbs are required for high-intensity efforts.
- •Endurance training should build both robust carb and fat systems; one provides flexibility, the other near-unlimited capacity.
Training Muscular Endurance: Local Capillaries and Acid Buffering
The focus shifts to ‘muscular endurance’—the ability of a local muscle group to repeatedly contract (e.g., push-ups, wall sits). Galpin explains the capillary and buffering adaptations involved and offers simple programming guidelines.
- •Muscular endurance is local: planks, wall sits, push-ups, dead hangs; mostly 5–50 reps or long holds.
- •Limiter is local acid buildup and waste clearance, not systemic fuel availability.
- •Training increases capillarization around fibers and improves local waste removal and buffering.
- •Practical programming: 2–3 sessions/week per muscle group; 2–4 sets near (not always at) failure in the target rep/time range.
- •Exercise choice is highly specific: train the exact movement patterns you want to improve.
- •Use progression by adding a rep or a few seconds per week, or by accumulating more sub-failure volume over time.
Building Anaerobic Capacity: Short, Brutal Intervals
Galpin outlines how to build high-intensity anaerobic capacity for 20–90 second maximal efforts. He emphasizes safety, exercise selection, and how much volume is enough to trigger adaptation without overdoing it.
- •Anaerobic capacity = total work you can do for ~20–90 seconds at near-max effort.
- •Limiters: acid buildup, oxygen delivery, waste clearance, and sometimes glycogen if repeated many times.
- •Best exercises: total-body, low-eccentric, low-skill movements like assault bike, rower, hill sprints, sled work, swimming.
- •Example dose: 20s all-out, 40s–60s easy (2–3:1 rest:work), repeated 6–8 times; or 30s on/30s off ×4–8; or 60s all-out ×3–4 with 1–3 minutes rest.
- •Aim for ~5–6 total minutes/week of true all-out work across 1–3 sessions.
- •Quality matters: you must be near maximum effort, which demands adequate rest between sprints.
Maximal Aerobic Output: 5–15-Minute Hard Efforts
They define maximal aerobic output as sustained hard efforts of 5–15 minutes (e.g., best 10-minute run). Galpin describes how to use these time trials to drive VO₂ max adaptations and how to blend them with shorter intervals and longer, easier work.
- •Maximal aerobic output: near-max effort for 5–15 minutes; classic example is a 1-mile best effort.
- •Primary constraints: oxygen transport/delivery, cardiac output, respiratory muscle endurance, and waste clearance.
- •Simple protocol: once a week, go as far as possible in 10 minutes (run/row/bike) and track distance over time.
- •Alternatively: repeat 800 m or similar intervals with generous rest to accustom the body to high but sustainable output.
- •This type of work is potent for VO₂ max and can be kept to ~1 session/week for non-specialists.
- •Support it with 1–2 sessions/week of moderate-intensity cardio (harder than conversational, easier than all-out).
Long-Duration Endurance and Practical Cardio Structures
They cover classic long-duration endurance (30+ minutes) such as hikes, runs, or bike rides, highlighting tissue tolerance, posture, and respiratory muscle fatigue as key limiters. Galpin suggests creative multi-modal circuits as alternatives to monotonous steady-state work.
- •Long-duration endurance typically 30–120+ minutes at moderate intensities.
- •Limiters: tissue tolerance (joints, feet), posture breakdown, intercostal/diaphragmatic fatigue—not fuel, unless very long.
- •Typical prescription: 30–60 minutes once per week is highly beneficial for most people; up to 90+ minutes as goals dictate.
- •Can be conventional (run, bike, swim, weighted hike) or mixed circuits (farmer carries, planks, light squats, jump rope) with no long rests.
- •Long steady work builds capillarization, mitochondrial function, movement skill, and adds meaningful calorie burn with relatively low stress.
- •Can be slotted after strength/power sessions or on separate days; also useful as active recovery if intensity is low and nasal breathing is used.
Breathing Gears, CO₂ Tolerance, and Downregulation
The conversation returns to breathing mechanics, with Brian Mackenzie’s ‘gear’ model as a simple way to self-regulate intensity. Galpin explains how to use nasal vs mouth breathing in training and recovery, and why downregulating after hard intervals is non-negotiable.
- •Gear 1: slow nasal in/out; Gear 2: faster nasal-only; Gear 3: mixed nose–mouth; Gear 4: mouth–mouth for max efforts.
- •Use nasal-only breathing for low and much moderate-intensity work to avoid unnecessary over-breathing and keep RER lower.
- •High-intensity intervals will inevitably require mouth breathing; that’s appropriate when going truly maximal.
- •CO₂ tolerance training helps you feel and respond to rising CO₂ without panic, improving both endurance and emotional control.
- •After sprints, recover until you can return to nasal-only breathing (plus 30s) before starting the next round.
- •Use 3–5 minutes of nasal-only, slow breathing post-workout to bring the nervous system down before returning to work or life.
Putting It Together: A Minimal Yet Comprehensive Endurance Week
Galpin synthesizes the episode into a practical weekly structure that touches all four endurance types and dovetails with strength/hypertrophy training. He emphasizes you don’t need large volumes to get meaningful health, performance, and fat-loss benefits.
- •Core endurance week for a generalist might include: – ~5–6 minutes total of all-out intervals (20–60 seconds each) across 1–3 sessions. – ~10 minutes/week of maximal aerobic work (e.g., best 10-minute run/row) once per week. – 30–60+ minutes/week of steady/moderate cardio (walk, hike, light run, or mixed circuit). – 2–3 short muscular endurance ‘finishers’ (planks, wall sits, push-ups) tied to existing sessions.
- •These can be paired with 2–4 strength/hypertrophy sessions without excessive time burden.
- •Long steady efforts build tissue tolerance and skill; intervals build high-end capacity and buffering; moderate work fills in cardiac and capillary development.
- •Fat loss is driven by the aggregate of this activity plus diet-regulated carbon intake, not any single magic protocol.
- •With this mix, you build energy, aesthetics, and long-term health while retaining flexibility to adjust modalities to preference.

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