The Respiratory System

What It Does

The respiratory system draws air into the lungs, extracts oxygen, transfers it into the bloodstream, and expels carbon dioxide. At rest you breathe roughly half a litre per breath — your tidal volume — around fifteen times per minute. During maximal exercise breathing frequency rises to forty or more breaths per minute and total air volume can exceed one hundred and fifty litres per minute. The diagram below shows the lungs, trachea and diaphragm at work. Use the buttons to see how the system responds at different intensities.

Why You Gasp After a Hard Set

After a heavy set of squats or deadlifts the body has accumulated carbon dioxide faster than it can be cleared. The gasp at the end of the set is the respiratory system urgently restoring balance. Carbon dioxide — not oxygen depletion — is the primary driver of the urge to breathe. This is why breath-holding during a heavy lift is possible for a short period: the oxygen is still available but the CO₂ is building rapidly. The body clears it the moment the rep ends.

VO2 Max — What It Actually Means

VO2 max is the maximum volume of oxygen the body can consume per minute per kilogram of bodyweight — the gold standard measure of aerobic fitness. It is not fixed. It improves significantly with consistent training, particularly interval work that pushes effort toward and beyond the lactate threshold. Click each fitness level below to see what it means in practical terms.

How Training Improves Respiratory Efficiency

Trained individuals breathe more efficiently than untrained individuals at the same workload. This is not because the lungs grow larger — lung volume changes little with training. It happens because the breathing muscles strengthen, the diaphragm works more effectively, and trained muscles extract oxygen from blood more efficiently, reducing total demand on the respiratory system at any given intensity.

Breathing Technique — Underrated and Overlooked

The Valsalva manoeuvre — a controlled breath-hold with intra-abdominal pressure — is correct technique during maximal and near-maximal lifts. It protects the spine by creating a rigid cylinder of pressure through the trunk, far more effective than trying to breathe throughout the lift. For submaximal work — the majority of training — exhale on the exertion, inhale on the recovery. Never breathe erratically across multiple repetitions. Oxygen debt accumulates quickly and performance drops sharply.

A Coaching Observation

In thirty years of coaching and training, breathing is the thing I see neglected most consistently. Watch someone performing a difficult set and the breathing is chaotic — random, reactive, uncontrolled. The moment you impose a deliberate breathing pattern, the quality of the session improves. Movements feel more controlled. Fatigue comes later. The set feels more purposeful. This is not a minor detail. The breath is the foundation of every repetition.