CO2 Tolerance and Strength Training: What Breathing Practice Can Do

CO2 tolerance is a useful description of how strongly rising carbon dioxide stimulates the urge to breathe. It is not a magic strength quality, and a longer breath hold is not automatically better conditioning.

For lifting, the practical issue is simpler: you need to create enough trunk pressure for the task, keep the bar path controlled, and recover between sets without becoming dizzy or panicked. Respiratory-muscle training may improve respiratory measures in athletes, but that evidence should not be turned into a promise of heavier squats or faster hypertrophy.

What the evidence is about

Respiratory-muscle training usually means structured work against an inspiratory or expiratory resistance, or controlled ventilation protocols. That is different from casually holding your breath after a set.

A 2025 systematic review and meta-analysis of respiratory-muscle training in athletes found improvements in measures such as maximal inspiratory pressure, but rated the overall evidence low to very low and included many endurance athletes rather than strength trainees (Xavier et al.). An earlier review found improved respiratory-muscle endurance after training, again without establishing a specific benefit for barbell strength (Illi et al.).

So the defensible conclusion is narrow: structured respiratory training can change respiratory measures in some athletes. There is not a validated “10 minutes a day” breath-hold protocol that reliably improves lifting performance.

CO2 is not the enemy

Carbon dioxide is a normal product of metabolism and one of the signals that helps regulate breathing. During a hard set, ventilation, blood flow, muscle fatigue, and the Valsalva maneuver all interact. Feeling breathless does not tell you that you have a low CO2 tolerance, and it is not a reason to override dizziness or pain.

Do not hyperventilate before a heavy lift to “clear CO2.” Rapid over-breathing can reduce carbon dioxide in the blood and make lightheadedness or tingling more likely. It can also make the next breath-hold feel easier while increasing risk.

Breathing for a heavy repetition

For a heavy squat, deadlift, or press, many experienced lifters use a brief breath and brace through the demanding part of the repetition. A brace is a coordinated trunk contraction, not simply pushing the stomach out or holding air indefinitely.

Use a conservative sequence:

1. Set your stance and position before taking the breath.
2. Inhale enough to expand the lower ribs and abdomen without forcing a maximal gulp.
3. Brace around the torso and start the repetition.
4. Release or reset when the demanding portion is complete.
5. For repeated reps, take another controlled breath rather than trying to hold one breath for the whole set.

The right timing depends on the lift, load, skill, and set length. A coach can help you find a repeatable pattern.

Why caution matters

The Valsalva maneuver changes cardiovascular pressure. A study of novice lifters found that breath-holding produced the highest blood-pressure responses among the tested breathing conditions (Sawai et al.). A newer controlled study in healthy, resistance-untrained adults also found greater acute mean arterial-pressure increases when a Valsalva was combined with resistance exercise (Perry et al.).

That does not mean every healthy lifter must avoid a brief brace. It does mean that “safe for everyone,” “protects the spine,” and “hold longer to get stronger” are not evidence-based instructions. People with cardiovascular disease, uncontrolled hypertension, glaucoma, pregnancy-related concerns, a recent operation, fainting episodes, or other relevant conditions should ask a qualified clinician before deliberately using maximal breath-holding.

Never practise prolonged breath holds in water, while driving, alone in a risky environment, or immediately after a hard set. Stop if you become lightheaded, develop visual changes, chest pain, unusual shortness of breath, or lose coordination.

Lower-risk ways to practise breathing

If your aim is better control rather than a breath-hold record:

• use quiet nasal or relaxed breathing during warm-ups when it does not impair the task;
• take a few slow breaths between sets and wait until you can speak normally before starting the next set;
• practise diaphragmatic or rib-cage expansion without forcing end-range inhalation;
• if you want respiratory-muscle training, use a validated device and follow its instructions or a respiratory professional’s plan;
• log whether a breathing change improves comfort or technique, not just how long you can hold your breath.

Do not use a breathing drill to mask wheezing, exercise intolerance, faintness, or unexplained breathlessness. Those symptoms deserve assessment.

The bottom line

Respiratory training can improve some breathing measures, but the evidence does not establish a direct muscle-building or strength benefit from DIY CO2 tolerance drills. For lifting, learn a calm, task-appropriate breath-and-brace pattern, keep breath holds brief, and treat symptoms as a reason to stop—not as a sign that the exercise is working.

Related reading

• Bracing and Intra-Abdominal Pressure in Strength Training
• Breathing Techniques for Heavy Lifts
• Blood Pressure and Resistance Training

Applying this article

For your next training block, change one breathing cue at a time. Use a load you can control, record the lift quality and symptoms, and stop the experiment if you become dizzy or unusually breathless. Do not treat a longer breath hold as a performance target.

Limits of the evidence

Most respiratory-training trials involve endurance athletes, devices, or rehabilitation-style protocols rather than heavy resistance training. They report physiological or sport-specific outcomes, not a universal increase in 1RM or hypertrophy.

Sources

• Respiratory muscle training in athletes: systematic review and meta-analysis. Reports respiratory outcomes but rates the evidence low to very low.
• Respiratory muscle endurance after training. Meta-analysis of respiratory-muscle endurance, not a barbell-strength trial.
• Breathing techniques and blood pressure during resistance exercise. Older controlled study showing a larger blood-pressure response with Valsalva.
• Resistance exercise with combined Valsalva manoeuvre. Recent acute study in healthy, resistance-untrained adults.