Almost every breath you take is powered by one muscle, a thin dome that separates your chest from your belly. Breathing in is mostly the diaphragm pulling down like a plunger, while breathing out is usually the lungs simply springing back.1Pulmonary Physiology for Pre-Clinical Students. How the Diaphragm Works: From Anatomy to Breathing The same muscle that works on autopilot day and night can also be steered on purpose, which is why it shows up in everything from singing to calming exercises.
Where the Diaphragm Sits and What It Is Made Of
The muscle’s outer edge anchors all around the bottom of the ribcage. At the front it attaches to the tip of the breastbone.2Kenhub. Diaphragm Along the sides it attaches to the inner surfaces of the lower ribs, roughly ribs 7 to 12.3Kenhub. Diaphragm At the back, two thick strands anchor it to the upper lumbar spine, around the first three lower-back vertebrae.4TeachMeAnatomy. The Diaphragm – Actions – Innervation – TeachMeAnatomy From these edges the muscle fibres run up and inward to meet in a flat central tendon at the top of the dome.5Wikipedia. Thoracic diaphragm The heart’s protective sac sits on and is fused to that tendon, so the heart rests right on the diaphragm.6TeachMeAnatomy. The Diaphragm – Actions – Innervation – TeachMeAnatomy
The top of the dome reaches up about to the level of your lower nipples, higher than most people assume. You can feel the lower rim by pressing just under the edge of your ribs.
The dome really has two halves, a left and a right, each shaped like its own arch and each moving on its own. That is why one side can be weak while the other works normally. The right half normally sits a little higher because the liver pushes up from beneath it. The heart rests on the central part, so the middle sits slightly lower than the two humps on either side.
It is skeletal muscle, the same type as in your arms and legs, which is why you can also control it. Unlike arm muscles, though, it works every few seconds for a lifetime. The tendon in the middle does not contract; the pull comes from the muscular rim around it.
Several structures have to pass between chest and belly, so the diaphragm has three main openings: one for the aorta, one for the oesophagus (food pipe), and one for the large vein returning blood from the lower body.7Kenhub. Diaphragm Fibres from the right strand loop around the food-pipe opening and act like a valve that helps keep stomach contents from rising.8TeachMeAnatomy. The Diaphragm – Actions – Innervation – TeachMeAnatomy
How a Breath Moves In and Out
When the diaphragm contracts, the dome flattens and moves down toward the belly.9Pulmonary Physiology for Pre-Clinical Students. How the Diaphragm Works: From Anatomy to Breathing The chest cavity gets bigger.10SEER Training Modules. Mechanics of Ventilation Pressure inside the lungs drops below the air pressure outside, so air flows in through the nose and mouth to even out the difference.11Pulmonary Physiology for Pre-Clinical Students. How the Diaphragm Works: From Anatomy to Breathing The lungs themselves do no sucking. The lungs are passive bags, and the work is done by the walls around them.
The ribcage helps. As the dome flattens, the lower ribs are lifted and pushed slightly outward, so the chest widens as well as deepening. Muscles between the ribs also help raise them, mostly in deeper breathing. In quiet breathing the diaphragm does most of the work, and the rib and neck muscles join in more when you breathe hard.
Your belly moves for a related reason. As the dome pushes down, it presses the stomach and intestines down and forward. That outward belly movement is the sign of “belly breathing” and shows the diaphragm is doing the work. Shallow chest breathing leans more on the neck and upper-chest muscles.
Ordinary breathing out is passive and uses no extra muscle energy.12Lumen Learning. How the Diaphragm Works: From Anatomy to Breathing As the diaphragm and rib muscles relax, the stretchy lung tissue and chest wall recoil to their resting position.13OpenLearn. Blood and the respiratory system The chest shrinks, pressure in the lungs rises above the outside air, and air leaves.14Lumen Learning. How the Diaphragm Works: From Anatomy to Breathing
That changes when you blow hard, cough or exercise. Then the muscles between the ribs and the abdominal muscles actively squeeze air out.15OpenLearn. Blood and the respiratory system
What Tells the Diaphragm to Contract
Groups of nerve cells in the lowest part of the brainstem generate the breathing rhythm.16PubMed Central. The respiratory control mechanisms in the brainstem and spinal cord: integrative views of the neuroanatomy and neurophysiology Their signals travel down through the spinal cord to the nerves that drive the diaphragm.17PubMed Central. The respiratory control mechanisms in the brainstem and spinal cord: integrative views of the neuroanatomy and neurophysiology The diaphragm’s own nerve, the phrenic nerve, comes from spinal nerves high in the neck, at levels C3 to C5.18Wikipedia. Thoracic diaphragm So a spinal injury high in the neck can stop the diaphragm, while one lower down usually doesn’t. When the signal is lost, the diaphragm goes slack and a person may need a machine to breathe.
Chemistry fine-tunes the pace. Breathing is adjusted by feedback about carbon dioxide and oxygen in the blood.19PubMed. CO2, brainstem chemoreceptors and breathing Sensors in the neck arteries detect oxygen and strongly boost breathing if it falls.20PubMed. CO2, brainstem chemoreceptors and breathing Carbon dioxide is sensed both there and by sensors in the brainstem.21PubMed. CO2, brainstem chemoreceptors and breathing
That is why the urge to breathe after holding your breath is mainly about carbon dioxide, not a lack of oxygen. It builds up as you hold, and the brainstem eventually forces the diaphragm to restart. In normal circumstances you can’t hold your breath until you pass out.
The shared neck nerves also explain why diaphragm problems can cause shoulder pain. The diaphragm’s nerve comes from the same neck nerves that serve the shoulder area, so irritation of the central diaphragm can be felt as pain at the tip of the shoulder. The outer rim sends sensation through rib nerves instead.22Wikipedia. Thoracic diaphragm
Jobs Beyond Breathing, Core, Reflux and Hiccups
When you move your arms or legs, the diaphragm and a deep belly muscle stay switched on together.23PubMed. Changes in intra-abdominal pressure during postural and respiratory activation of the human diaphragm Pressure inside the belly rises in step with the force of the movement, stiffening the trunk.24PubMed. Changes in intra-abdominal pressure during postural and respiratory activation of the human diaphragm The diaphragm keeps breathing at the same time by changing the shape of this pressurised belly rather than releasing it.25PubMed. Changes in intra-abdominal pressure during postural and respiratory activation of the human diaphragm
You feel this when you lift a heavy bag: you instinctively take a breath and tighten. The same pressure helps when you push during a bowel movement or childbirth. Lifters are taught to breathe and brace rather than hold the breath loosely for this reason.
The diaphragm also forms part of the reflux barrier. In a hiatus hernia, part of the stomach slips up through the diaphragm’s food-pipe opening. People with a hiatus hernia get more acid reflux, especially when straining or breathing in deeply.26PubMed. Excess gastroesophageal reflux in patients with hiatus hernia is caused by mechanisms other than transient LES relaxations The opening around the food pipe is looser in this condition, so the diaphragm’s valve-like grip is less effective.
A hiccup is a reflex involving the phrenic and vagus nerves.27PubMed Central. Hiccups: a common problem with some unusual causes and cures. The diaphragm and rib muscles jerk suddenly, then the vocal cords snap shut, making the “hic” sound.28PubMed Central. Hiccups: a common problem with some unusual causes and cures.
Common tricks such as holding your breath or sipping water may work by interrupting the reflex rhythm. Most bouts stop on their own within minutes. Hiccups lasting over 48 hours deserve a doctor’s visit.
Does Slow Belly Breathing Really Calm You
Slow diaphragmatic breathing increases activity of the “rest and digest” side of the nervous system, which shows up in heart rate patterns.29PubMed Central. Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity Heart rate variability, a marker of that calming activity, rises during slow breathing and stays higher afterwards.30PubMed. Effects of voluntary slow breathing on heart rate and heart rate variability: A systematic review and a meta-analysis A single 5-minute session of deep, slow breathing lowered anxiety in both younger and older adults.31PubMed Central. Benefits from one session of deep and slow breathing on vagal tone and anxiety in young and older adults It is a free, low-risk tool with few side effects. Not every study agrees, though, so effects vary from person to person.32PubMed Central. Breath of Life: The Respiratory Vagal Stimulation Model of Contemplative Activity
To try it, lie or sit with one hand on your chest and one on your belly. Breathe in through the nose so the belly hand rises more than the chest hand. Breathe out slowly, a little longer than the in-breath. Aim for roughly five to six breaths a minute for a few minutes. Heart rate tends to speed up slightly on the in-breath and slow on the out-breath, so lengthening the out-breath leans into that pattern.
It can help before a stressful meeting, at bedtime or during a tense moment. Calm may come within minutes, but it is not a treatment for anxiety disorders on its own. If you feel dizzy, you are breathing too fast or too deep, so slow down.
When the Diaphragm Weakens or Stops Working
Weakness of one half often causes no symptoms unless there is also obesity or heart or lung disease.33PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat? When it does cause symptoms, they include breathlessness on exertion and breathlessness when lying flat.34PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat?
Failure of both halves commonly causes trouble lying down and, in severe cases, breathlessness at rest.35PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat? People then lean on neck and shoulder muscles, so raising the arms or lifting can be hard.36PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat? Poor sleep with daytime sleepiness can be a sign.37PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat?
Lying flat is hard because the belly contents press up against the diaphragm, which makes its job harder. A strong diaphragm copes, but a weak one struggles. Sitting up lets gravity pull the belly contents away, which is why people with a weak diaphragm sleep propped up. Needing several pillows to breathe at night, breathlessness that is worse lying flat or in water up to the chest, or new shortness of breath after chest or neck surgery are all worth a doctor’s visit.
Several things can weaken the muscle. Injury to the diaphragm’s nerve inside the chest, for example during surgery, can paralyse it.38PubMed. Phrenic Nerve Reconstruction with Short-Term Diaphragm Pacing Corrects Diaphragm Paralysis Due to Intrathoracic Nerve Injury Very hard endurance exercise, above about 85% of maximum effort, can fatigue the diaphragm in healthy people.39PubMed Central. Exercise-induced diaphragmatic fatigue in healthy humans On a breathing machine, the diaphragm starts wasting within 18 to 24 hours.40PubMed. Ventilator-induced diaphragm dysfunction: cause and effect Fibres can shrink by more than half after 18 to 69 hours of total rest.41PubMed. Rapid disuse atrophy of diaphragm fibers in mechanically ventilated humans
With age, diaphragm strength falls by around 30%.42PubMed Central. Ageing of the Diaphragm Muscle Weaker coughing in older adults can make clearing the airways harder.43PubMed. Diaphragm muscle structure in the elderly: Findings from an autopsy study
Doctors usually use breathing tests plus moving images by ultrasound or X-ray video, often while you sniff.44PubMed Central. Quantitative analysis of diaphragm motion during fluoroscopic sniff test to assist in diagnosis of hemidiaphragm paralysis A lung function test often shows lower than normal breathing volume.45PubMed Central. Diaphragm dysfunction: how to diagnose and how to treat? Surgery can tighten a floppy diaphragm so it stops pressing on the lung.46PubMed Central. A porcine model of postoperative hemi-diaphragmatic paresis to evaluate a unilateral diaphragmatic pacemaker When both sides fail, nerve repair or a diaphragm pacemaker can restore movement in some people.47PubMed Central. Treatment for bilateral diaphragmatic dysfunction using phrenic nerve reconstruction and diaphragm pacemakers