Organ Guide

A fist-sized muscle sitting slightly left of center behind your breastbone, beating around 100,000 times a day without being asked. It has four chambers: the right side pushes used blood to your lungs to pick up oxygen, the left side pushes the freshly loaded blood out to everything else. It is the one organ that unmistakably gets stronger when you train — a fitter heart moves more blood per beat, which is why a resting pulse drops as your fitness climbs.

Keep it healthy: steady, unhurried cardio is the main course — the sort of pace where you can still hold a conversation, most days of the week. Add a couple of strength sessions, keep blood pressure and cholesterol in view, and treat a falling resting heart rate as the scoreboard rather than how hard any single session felt.

In qFIT:Zone 2 / Easy Steady-State CardioLower Resting Heart RateBlood Pressure Check🔁 Blood Pressure & Isometric Strength

Exercise trains this directly

The thick-walled, muscular tubes that carry blood away from the heart, from the garden-hose-width aorta down to vessels finer than a hair. They are not passive plumbing: their inner lining releases signals that widen or narrow them minute by minute, which is what sends blood to your legs when you run and to your gut after a meal. Stiff or narrowed arteries are what “high blood pressure” and most heart trouble actually are.

Keep it healthy: the levers are unglamorous and they work — regular cardio, less salt, less smoking, more vegetables, and keeping blood pressure and cholesterol measured rather than guessed. Isometric holds (wall sits, planks) have a surprisingly good track record for blood pressure specifically.

In qFIT:Lower Blood PressureLower CholesterolBeetroot / Dietary Nitrate🔁 Blood Pressure & Isometric Strength

Exercise trains this directly

Not an organ but a tissue — about five liters of it, roughly half cells and half straw-colored plasma. Red cells carry oxygen on iron-rich hemoglobin, white cells fight infection, platelets patch leaks, and the plasma ferries everything else: sugar, hormones, waste, heat. Endurance training measurably increases how much of it you have, which is a large part of why cardio makes hard work feel easier.

Keep it healthy: drink enough that your blood is not thick and sluggish, eat enough iron and B12 (the two shortfalls that quietly flatten your energy), and get periodic bloodwork rather than guessing — a low ferritin is invisible until someone measures it.

In qFIT:Periodic LabworkIronRaise SpO2 Levels (Oxygen Saturation)

Exercise trains this directlyA tissue, not an organ

Two spongy bags filling most of your ribcage, branching into around 300 million air sacs whose walls are one cell thick. Spread flat they would cover half a tennis court. Oxygen crosses into the blood there and carbon dioxide crosses out — that is the whole job. Lung size barely changes with training; what improves dramatically is everything around it, which is why fitter people breathe more easily at the same pace rather than having bigger lungs.

Keep it healthy: not smoking or vaping is worth more than everything else on this card combined. Beyond that: get properly out of breath a couple of times a week, breathe through your nose when you can, and get outside — time in fresh air beats time in a stuffy room for reasons that have nothing to do with exercise.

In qFIT:Raise VO2 Max (Maximal Oxygen Consumption)Quit Smoking or VapingBreathwork🔁 Breathing & Ribcage

Exercise trains this directly

The branching tube system that carries air down: the trachea in your throat, splitting into two bronchi and then into thousands of finer bronchioles. Their lining is carpeted with microscopic hairs that sweep dust, pollen and germs back up to be swallowed — a conveyor belt running all day that smoke paralyzes within minutes. When those tubes tighten and inflame, that is asthma.

Keep it healthy: mostly about what you don't put in them — smoke, vape aerosol, workshop dust without a mask. Warm up gradually in cold air rather than sprinting straight out into it, keep vaccinations current, and when you're properly sick, rest instead of training through it.

In qFIT:Quit Smoking or VapingTrain or Rest When Sick (Neck Check)Vaccinations / Flu Shot🔁 Breathing & Ribcage

Mostly about protecting it

Your nose filters, warms and humidifies every breath before it reaches your lungs, and the sinuses are the air-filled spaces in the bones around it that lighten your skull and add resonance to your voice. The roof of the nose also carries your sense of smell, which is most of what you think of as taste. Nose breathing adds resistance and produces nitric oxide, which helps open the blood vessels in your lungs — mouth breathing skips all of that.

Keep it healthy: breathe through your nose whenever the effort allows, including during easy cardio. Stay hydrated so the lining stays thin rather than sticky, and keep vaccinations current — most sinus misery starts as an ordinary virus.

In qFIT:BreathworkHydration (100+ oz)Vaccinations / Flu Shot🔁 Breathing & Ribcage

Mostly about protecting it

The short cartilage box at the top of your windpipe — the lump you can feel at the front of your throat. Two folds of tissue inside it vibrate to make your voice, and a small flap above them slams shut every time you swallow so food goes down the right tube. It is also what you close against when you brace hard for a heavy lift, which is where the grunt comes from.

Keep it healthy: hydration is the main thing — vocal folds work badly when they're dry. Avoid shouting over noise for long stretches, don't clear your throat repeatedly when it's sore, and treat weeks-long hoarseness as a reason to get it looked at rather than to rest it longer.

In qFIT:Hydration (100+ oz)Green Tea / Herbal TeaQuit Smoking or Vaping🔁 Breathing & Ribcage

Mostly about protecting it

A muscular tube about 25cm long running behind your windpipe from throat to stomach. It doesn't drop food — it squeezes it down in a travelling wave, which is why you can swallow lying down or upside down. A ring of muscle at the bottom stays shut to keep stomach acid where it belongs, and reflux is simply that ring opening when it shouldn't.

Keep it healthy: stop eating two or three hours before bed — that one habit fixes more reflux than any other. Smaller portions, slower eating, and going easy on late alcohol all pull in the same direction. A gentle walk after a meal helps; lying flat straight after one does not.

In qFIT:PENALTY: Ate/Drank Right Before BedMindful / Slow EatingPortion Control🔁 Digestion & Gut Comfort

Mostly about protecting it

A J-shaped muscular bag under your left ribs that holds a meal, churns it, and douses it in acid strong enough to dissolve metal — while a mucus layer stops it dissolving itself. It kills most of what you swallow that shouldn't be alive, starts on protein, and then releases the result into the small intestine slowly, over hours. It also signals hunger and fullness, and those signals run about twenty minutes behind reality.

Keep it healthy: eat slowly enough for the fullness signal to arrive before the plate is empty. Regular meals suit it better than long gaps followed by a huge one, and alcohol is a direct irritant to its lining. If you take anti-inflammatories often, take them with food.

In qFIT:Mindful / Slow EatingBreakfastPENALTY: Drank Alcohol🔁 Digestion & Gut Comfort

Food, drink and sleep do the work

Around six meters of coiled tube where nearly all of your food actually enters you. Its lining is folded, then fringed, then fringed again, so the absorbing surface is enormous for the space it occupies. Protein, fat, carbohydrate, vitamins and minerals all cross here — and B12 crosses at one specific spot near the end, which is why that particular vitamin is the one that goes missing.

Keep it healthy: eat enough protein for it to have something to absorb, spread across the day rather than in one hit. If you eat little or no meat, B12 is worth taking deliberately rather than hoping. Bloating that follows specific foods every single time is information, not a character flaw — worth writing down.

In qFIT:ProteinVitamin B12Multivitamin🔁 Digestion & Gut Comfort

Food, drink and sleep do the work

A small green pouch tucked under the liver that concentrates and stores bile, then squirts it into the intestine when a fatty meal arrives to break the fat into droplets small enough to absorb. You can live perfectly well without it — a great many people do — because the liver simply drips bile in continuously instead. Gallstones form when the stored bile becomes too concentrated.

Keep it healthy: regular meals with some fat in them keep it emptying rather than sitting full. Fiber and a stable body weight both reduce stone risk; crash dieting increases it sharply, which is a real argument for losing weight steadily rather than fast.

In qFIT:Healthy FatFiberPortion Control🔁 Digestion & Gut Comfort

Food, drink and sleep do the work

A flat gland lying behind the stomach doing two unrelated jobs. Most of it makes the enzymes that digest protein, fat and starch, and pipes them into the small intestine. Scattered through it are small islands of cells that instead release insulin and glucagon straight into the blood — the pair that hold your blood sugar in a narrow band all day. Type 2 diabetes is that second job gradually failing under load.

Keep it healthy: muscle is the biggest sink for blood sugar you own, so strength work helps here as much as diet does. A walk after a meal blunts the spike measurably. Keep an eye on the actual number rather than how you feel — HbA1c drifts up for years without symptoms.

In qFIT:Get blood sugar (HbA1c) into a healthy rangeTrack Blood Sugar / GlucosePost-Meal Walk🔁 Weight, Cholesterol & Metabolic Health

Food, drink and sleep do the work

A finger-sized pouch hanging off the start of the large intestine, long written off as a leftover. The current view is kinder: it carries immune tissue and appears to act as a safe house for gut bacteria, reseeding the colon after an illness clears it out. It is on this page mainly because of what happens when it blocks and inflames — appendicitis is one of the few genuine surgical emergencies an otherwise healthy person meets.

Keep it healthy: nothing you do trains it. What matters is recognizing trouble: pain that starts vaguely around the navel and settles into the lower right over some hours, with nausea and a temperature, is a same-day medical problem, not something to sleep on.

In qFIT:Red Flag Check (see a doctor first)Prebiotics/ProbioticsFiber

Mostly about protecting it

A muscular balloon low in your pelvis that stores urine and then squeezes it out on command. The command part depends on your pelvic floor — the sling of muscle underneath — relaxing and contracting in time with it. Leaking when you cough, sneeze, laugh or land from a jump is extremely common, rarely mentioned, and usually improvable; it is a strength problem more often than a plumbing one.

Keep it healthy: train the pelvic floor deliberately — it responds like any other muscle, and it needs to relax as well as squeeze. Don't habitually go “just in case”, which teaches the bladder to signal earlier and earlier, and don't fix leaking by drinking less. The pelvic floor's own card is in the Muscle Guide.

In qFIT:Core: Pelvic FloorCore: Pelvic Floor (stretch)Hydrated (fully)🔁 Pelvic Floor & Core Recovery

Mostly about protecting it

The two ureters are narrow muscular tubes carrying urine down from each kidney to the bladder, squeezing it along rather than relying on gravity. The urethra is the single outflow pipe from the bladder. They rarely get a thought until something goes wrong in them — a kidney stone travelling down a ureter is the origin of one of the worst pains there is, and the urethra is the route infections take upward.

Keep it healthy: dilute urine is the whole strategy. Drink enough that it stays pale, replace fluid and electrolytes properly after heavy sweating, and don't routinely hold on for hours. Recurrent stones or infections deserve a proper investigation rather than another round of hoping.

In qFIT:Hydration (100+ oz)ElectrolytesCore: Pelvic Floor🔁 Pelvic Floor & Core Recovery

Mostly about protecting it

About 1.4kg of tissue that runs everything else on this page, from your heartbeat to your opinion of this sentence. It takes roughly a fifth of your blood supply and a fifth of your oxygen while weighing about 2% of you. It is not fixed hardware: it rewires with use throughout life, and exercise is one of the strongest known triggers for that — aerobic work raises the growth factors that keep neurons healthy, and improves mood on a timescale of one session, not one year.

Keep it healthy: sleep is the non-negotiable one — the brain does its clearing-out overnight and there is no substitute. After that: move most days, keep learning something that is genuinely a bit hard, stay socially connected, manage chronic stress rather than enduring it, and protect your head. Nearly everything good for the heart turns out to be good for the brain.

In qFIT:Sleep 7+ Hours Last NightBrain Training / Cognitive ExercisesManage StressMeditate🔁 Sleep & Wind-Down🔁 Stress & Anxiety Relief

Exercise trains this directly

A bundle of nerve tissue about as thick as your thumb, running from the base of your brain down inside the bony canal of your spine, with pairs of nerves branching out between every vertebra. Everything your brain sends to your body below the neck, and nearly everything your body reports back, travels through it. It also runs plenty of things on its own — reflexes fire from the cord before your brain has heard about them.

Keep it healthy: a strong, mobile back is its armor. Learn to hinge at the hips for heavy or awkward lifts, change position often rather than holding one for hours, and build the muscle around the spine rather than avoiding all load. New weakness, numbness or loss of bladder control is a same-day medical problem, not a training question.

In qFIT:Strengthen back; reduce/eliminate back painGet in habit of keep back straight and not rounding lower backPosture Check🔁 Back Pain/Bulletproofing

Mostly about protecting it

The network running from the spinal cord out to every muscle and patch of skin you own — the longest single one reaches from your lower back to your foot. They carry commands out and sensation back, and they need to glide freely through the tissue around them, which is why a nerve can be irritated by a position rather than by damage. Tingling, numbness and burning are nerve complaints; a dull ache usually isn't.

Keep it healthy: blood sugar is the single biggest factor in long-term nerve health, by a wide margin. Beyond that: keep B12 adequate, avoid parking a limb in a compressed position for hours, and check your feet regularly if sensation there is unreliable — a wound you can't feel is the actual danger.

In qFIT:Track Blood Sugar / GlucoseVitamin B12Daily Foot Check🔁 Sciatica & Deep Buttock Relief

Mostly about protecting it

A pair of fluid-filled spheres that focus light onto a screen of light-sensitive cells at the back and send the result to your brain as electrical signals. The focusing muscles inside them are working constantly, and they hold that focus at one fixed distance for as long as you stare at a screen — which is most of what “eye strain” is. The retina is also the one place a doctor can look directly at your blood vessels, which is why an eye exam catches problems that have nothing to do with vision.

Keep it healthy: look at something far away every twenty minutes or so and let the focusing muscles relax. Get outside in daylight — in children especially, that is the strongest known protection against becoming short-sighted. Sunglasses in bright conditions, safety glasses for anything that throws debris, and an actual eye exam on a schedule rather than only when something seems wrong.

In qFIT:Periodic Eye ExamEye Strengthening ExercisesLimit Screen TimeSun Protection (Sunscreen, Hat, Shade)🔁 Desk Posture Reset

Mostly about protecting it

A butterfly-shaped gland wrapped round the front of your windpipe. It releases the hormone that sets your metabolic rate — how fast every cell in you burns fuel — which is why an underactive one produces cold, tired, heavy, slow, and an overactive one produces the opposite. Behind it sit four grain-sized parathyroid glands doing a completely unrelated job: holding the calcium level in your blood steady, borrowing from your bones when your diet falls short.

Keep it healthy: nothing you do trains it, but a lot of what gets blamed on “a slow metabolism” is actually thyroid and is easily measured — a blood test settles it. Get enough iodine (ordinary iodized salt or fish covers it), enough calcium and vitamin D so the parathyroids aren't raiding your skeleton, and take any prescribed replacement consistently.

In qFIT:Periodic LabworkCalciumVitamin D🔁 Strength & Bone for Aging

Food, drink and sleep do the work

Two small caps sitting on top of your kidneys. The inner part fires adrenaline in seconds — the jolt you feel when a car pulls out in front of you. The outer part releases cortisol on a slower daily rhythm: high in the morning to get you going, tailing off by night. Cortisol is not a villain; it also mobilizes fuel for training. The problem is when the rhythm flattens because the stress never lets up.

Keep it healthy: the useful lever is the rhythm, not the gland. Daylight early, darkness late, sleep at consistent times, and something in the week that reliably drops you out of alert mode — slow breathing, a walk, meditation. Note that hard training is itself a stressor: if life is already relentless, more intensity is the wrong prescription and a rest day is the right one.

In qFIT:Manage StressSleep 7+ Hours Last NightPENALTY: Lots of Salt🔁 Stress & Anxiety Relief

Food, drink and sleep do the work

A pea-sized gland hanging beneath your brain in a small pocket of bone, taking orders from the hypothalamus just above it and passing them on to almost every other gland on this page. It tells the thyroid how much hormone to make, the adrenals when to release cortisol, and the kidneys how much water to keep. It also releases growth hormone — mostly in pulses during deep sleep and after hard resistance training, which is the honest version of what supplement adverts promise.

Keep it healthy: you reach it through sleep and training, not directly. Deep sleep early in the night is when most of its growth-hormone release happens, so a consistent bedtime does more than any supplement; heavy compound lifting is the other reliable trigger.

In qFIT:Consistent Sleep ScheduleSleep 7+ Hours Last NightAt Least 2 Strength Exercises🔁 Sleep & Wind-Down

Food, drink and sleep do the work

A gland the size of a grain of rice, deep in the middle of your brain, with essentially one job: release melatonin when it gets dark. That is the signal that tells the rest of you night has arrived and it is time to wind down. It takes its cue from light hitting your eyes, which is the whole reason a bright screen at 11pm delays sleep and why morning daylight sets the clock for the following night.

Keep it healthy: light discipline, and it's cheap. Get outside within an hour of waking — even a cloudy morning is far brighter than any room. Dim things down in the last hour before bed and keep screens out of it. Melatonin as a supplement is a timing cue rather than a sedative, and works best in small doses well before bed.

In qFIT:Get Some Sun First Thing in the MorningNo Screens Before BedMelatonin🔁 Sleep & Wind-Down

Food, drink and sleep do the work

A soft gland behind your breastbone that trains T-cells — the immune cells that recognize infected cells and, crucially, learn not to attack you. It is largest in childhood and shrinks steadily from your teens onward, gradually replaced by fat. That slow fade is one of the real reasons infections hit harder with age, and it happens to everyone.

Keep it healthy: you can't regrow it, but you can support what it produces. Enough protein, enough zinc and vitamin D, and enough sleep — T-cell function measurably drops after even one badly short night. Chronic stress suppresses the same system, which is why people get sick after a hard month rather than during it.

In qFIT:ZincVitamin DSleep 7+ Hours Last Night🔁 Everyday Immune Support

Food, drink and sleep do the work

A fist-sized organ under your left ribs that filters blood the way lymph nodes filter lymph. It strips out worn-out red cells and recycles their iron, holds a reserve of white cells and platelets, and is the body's specialist at clearing certain bacteria from the bloodstream. People without one (removed after injury, usually) need specific vaccinations for exactly that reason.

Keep it healthy: not much to train here. Keep iron and bloodwork in range so it isn't clearing red cells faster than you replace them, and keep vaccinations current. If you've had glandular fever recently, take the advice about avoiding contact sport seriously — an enlarged spleen is genuinely fragile.

In qFIT:Vaccinations / Flu ShotIronPeriodic Labwork🔁 Everyday Immune Support

Food, drink and sleep do the work

The soft tissue inside your larger bones, and one of the busiest places in the body — it makes roughly two million red blood cells every second, plus your white cells and platelets, all from a small population of stem cells. It is tissue rather than an organ, but it does an organ's job. Endurance training pushes it to produce more; iron or B12 shortfalls stop it, which is what most anemia actually is.

Keep it healthy: give it the raw materials — iron, B12, folate and enough protein — and check them with bloodwork rather than symptoms, because “tired” has a hundred causes and this is one of the few you can measure and fix outright.

In qFIT:IronVitamin B12Periodic Labwork🔁 Everyday Immune Support

Food, drink and sleep do the workA tissue, not an organ

Patches of immune tissue at the back of the throat and behind the nose, positioned where air and food both arrive — they sample what comes in and start the response. They are most active in childhood and shrink with age. When they're enlarged they crowd the airway, which is why they're a common cause of heavy snoring and disturbed sleep, particularly in children.

Keep it healthy: nothing to train. What's worth acting on is sleep quality: loud snoring with pauses in breathing, or waking unrefreshed after a full night, is worth screening for rather than living with — untreated sleep apnea drives blood pressure, heart rhythm problems and daytime exhaustion.

In qFIT:Sleep Apnea Screening / CPAP UseVaccinations / Flu ShotTrain or Rest When Sick (Neck Check)🔁 Everyday Immune Support

Mostly about protecting it

Both are made of keratin, and both are technically dead by the time you see them — growth happens only at the root. That makes them a slow-motion record of the last few months: a period of illness, crash dieting or serious stress often shows up as a ridge across a nail or a wave of hair shedding weeks later, long after the event. Nails grow about a millimeter a week, so the record runs roughly six months deep.

Keep it healthy: there is no shortcut — they get built from spare protein, iron and zinc, so they suffer first when intake is thin. If nails are brittle or hair is thinning noticeably, look at whether you're actually eating enough overall before buying a supplement. Keep nails trimmed and dry; check the ones on your feet if you can't feel them well.

In qFIT:ProteinIronTake Care of Skin, Teeth, Nails, etc.

Food, drink and sleep do the workSkin appendages, not organs

Not dry scaffolding — living tissue with its own blood supply, constantly being dismantled and rebuilt, so the skeleton you have now is not the one you had a decade ago. It stores your calcium reserve, houses the marrow, and remodels itself in response to load: bone laid down exactly where force goes through it. Peak density arrives around your late twenties and slowly declines after, faster if nothing is asking anything of it.

Keep it healthy: load it. Impact and resistance both work — jumping, hopping, running, and lifting things that are actually heavy for you; swimming and cycling, for all their virtues, do very little here. Calcium and vitamin D are the raw materials. If you're past midlife or have a family history of fractures, a density scan turns guesswork into a number.

In qFIT:Impact / Bone-Loading ExerciseBone Density Scan (DEXA)CalciumVitamin D🔁 Strength & Bone for Aging

Exercise trains this directly

Wherever two bones meet, the ends are capped with cartilage — a smooth, slippery, shock-absorbing surface with no blood supply of its own. It is fed instead by the fluid inside the joint, and that fluid only circulates when the joint moves. Movement is literally how cartilage eats, which is why joints stiffen when you sit still and loosen after a few minutes of walking. Cartilage is not a brake pad that simply wears out on a mileage schedule.

Keep it healthy: move them through their full range regularly, and build the muscle around them — strong muscle is what spares a joint load, and it is the best-evidenced treatment for arthritic knees and hips there is. Progress load gradually rather than in jumps, and keep body weight in a sensible range for the big weight-bearing joints. “Rest it completely” is usually the wrong answer.

In qFIT:Stretch or Do Mobility 3+ DaysImprove Hip MobilityGlucosamine / Chondroitin🔁 Whole-Body Stiffness Reset

Exercise trains this directlyConnective tissue, not an organ

Not an organ but an entire system — and, at roughly 40% of your body weight, the largest tissue you own. Beyond moving you, muscle is where most of the sugar in your blood goes, a reserve of protein your body raids when ill, and the strongest single predictor of staying independent in old age. It also loses ground quietly from your thirties onward unless something asks it to stay.

Keep it healthy: resistance work at least twice a week and enough protein to build with. The full story — every muscle qFIT tracks, what it does and what trains it — is on the Muscle Guide, which is this page's sibling.

In qFIT:Exercise Each Muscle Group At Least OnceProtein🔁 Gym (total body workout)

Exercise trains this directlyA whole system — see the Muscle Guide