If you want the best breathing trainer for all-around athletic development, our choice is the Isocapnic BWB series. That recommendation is based on a specific goal: training inhalation and exhalation through large respiratory volumes, demanding breathing rates and sustained work, rather than measuring only how much pressure you can generate during a short set of resisted breaths.
Commercial disclosure: Isocapnic manufactures the BWB products discussed in this guide. This is not an independent review and we are not pretending otherwise. The comparison uses published research, publicly available manufacturer information and clearly stated selection criteria. Where another device is a better fit, we say so.
Best breathing trainer comparison
At-a-glance buying comparison. Detailed explanations and source links follow the table. Expand-A-Lung and the discontinued SpiroTiger / Idiag P100 systems are discussed separately below.
| Attribute | Isocapnic BWB | POWERbreathe | Airofit | O2 Trainer | The Breather |
|---|---|---|---|---|---|
| Best for | All-around athletic training | Inspiratory strength | Smart resistance and data | Simple inspiratory work | Accessible dual resistance |
| Primary method | High-volume isocapnic training | Pressure or tapered resistance | Connected resistance | Fixed-orifice resistance | Adjustable resistance |
| Inhalation | Yes | Yes | Yes | Yes | Yes |
| Exhalation | Yes | Separate product | Yes | No | Yes |
| CO₂ management | Calibrated rebreathing circuit | No dedicated circuit | No dedicated circuit | No dedicated circuit | No dedicated circuit |
| Guidance and feedback | Guided app programs | Available on select models | Extensive connected feedback | Training guide | Training guide and app support |
| Availability | Current | Current | Current | Current | Current |
| Attribute | BWB | POWERbreathe |
|---|---|---|
| Best for | All-around training | Inspiratory strength |
| Method | High-volume isocapnic | Pressure or tapered resistance |
| Inhalation | Yes | Yes |
| Exhalation | Yes | Separate product |
| CO₂ control | Calibrated circuit | No dedicated circuit |
| Feedback | Guided app | Select models |
Our recommendation
For an athlete seeking the best breathing trainer for complete, stand-alone respiratory conditioning, we recommend Isocapnic BWB. Its calibrated rebreathing circuit recaptures a controlled portion of exhaled air while continuously admitting fresh air. This allows sustained, high-volume training of both inhalation and exhalation while helping maintain CO₂ and support normal oxygen saturation during standard training.
Another trainer may be a better fit for a narrower goal. POWERbreathe is an excellent option for targeted inspiratory strength. Airofit combines inspiratory and expiratory resistance with useful testing and app feedback. O2 Trainer, The Breather and Expand-A-Lung offer simpler and less expensive ways to add respiratory resistance. SpiroTiger and its successor, the Idiag P100, are no longer in production, but remain important historical method-level comparisons because they also used isocapnic hyperpnea.
How we chose the best breathing trainers
After more than two decades of testing and coaching athletes, I do not judge a respiratory trainer by how uncomfortable one breath feels. I look at the training problem it solves and the progression it makes possible.
We compared each system across seven practical criteria:
- Direction of training: inhalation, exhalation or both.
- Primary overload: pressure, airflow resistance, sustained ventilation or a combination.
- Training duration: whether the device supports short strength sets, sustained respiratory work or both.
- Volume and frequency: whether the athlete can progressively train large breaths at demanding breathing rates.
- CO₂ management: whether the system limits the excessive CO₂ loss that normally ends vigorous voluntary hyperventilation.
- Feedback and progression: app guidance, measurement and the ability to progress training.
- Practical fit: portability, complexity, availability and the athlete most likely to benefit.
Our use of “best all-around breathing trainer” therefore has a defined meaning. It does not mean one device is universally superior for every person, sport or clinical objective.
What should a complete respiratory trainer actually train?
Your lungs are not skeletal muscles, but the work of breathing is performed by the diaphragm, intercostals, abdominal muscles and accessory respiratory muscles. During hard exercise, those muscles do much more than produce one forceful contraction. They repeatedly generate force while moving large volumes of air, often for a long time.
Athletic respiratory performance therefore includes:
- Strength: the pressure your respiratory muscles can generate.
- Endurance: how long they can continue working before fatigue becomes limiting.
- Usable volume: how much of your available breathing range you can access and control.
- Frequency: how rapidly you can repeat effective breathing cycles.
- Coordination: how respiratory rate, depth and muscular effort work together.
A 2025 narrative review described pressure-threshold and tapered-resistance methods as primarily strength-oriented, while voluntary isocapnic hyperpnea was more closely associated with respiratory endurance and high-volume ventilation. The review also noted that common resistance protocols may use 30 inspiratory efforts twice daily, while isocapnic programs may involve 20 to 40 minutes of vigorous ventilation. Read the review.
Why resistance alone is an incomplete comparison
Resistance is useful. It lets an athlete overload the respiratory muscles and is particularly effective when inspiratory pressure is the quality that needs attention. The mistake is treating resistance as the only meaningful training variable.
We would not evaluate every cycling workout only by how hard the pedals are to push. Duration, cadence, range, total work and the intended adaptation also matter. The same thinking should be applied to respiratory training.
Why CO₂ changes respiratory training
If you breathe deeply and rapidly while sitting still, you can expel carbon dioxide faster than your metabolism produces it. As CO₂ falls, cerebral blood vessels constrict and cerebral blood flow decreases. Tingling, lightheadedness and discomfort can appear before the respiratory muscles receive the sustained training stimulus you intended.
Voluntary isocapnic hyperpnea was developed to solve that problem. A rebreathing circuit helps maintain CO₂ while ventilation increases, allowing the breathing muscles to perform vigorous work for longer. This is the physiological principle behind the BWB. For a deeper explanation, read Isocapnic Hyperpnea vs Resistance Breathing Trainers.
The BWB is not resistance-free. Airflow through the circuit creates inspiratory and expiratory loading that becomes more demanding as ventilation rises. The training stimulus is the combination of inhalation, exhalation, respiratory rate, tidal volume, duration and coordination.
1. Isocapnic BWB: best all-around breathing trainer
Best for: Athletes who want to make respiratory training its own complete training modality.
The BWB is built around sustained respiratory overload. It trains inhalation and exhalation through progressively larger volumes, higher breathing frequencies and longer sessions. The Isocapnic app provides guided sessions and programs for warm-up, volume, endurance, strength and power, coordination, recovery and advanced applications.
Within the currently accessible consumer products in our primary comparison, BWB is the only respiratory system that combines sustained, high-volume training of both inhalation and exhalation with a mechanically calibrated rebreathing circuit designed to maintain CO₂ while supporting normal oxygen saturation.
Our verdict: Best overall respiratory trainer for an athlete seeking one system to develop respiratory strength, endurance, usable volume, frequency and control together.
2. POWERbreathe: best for targeted inspiratory strength
Best for: Athletes whose primary goal is maximal inspiratory pressure and focused inhalation strength.
POWERbreathe is one of the best-established names in respiratory muscle training. Its traditional devices require the athlete to generate enough inspiratory pressure to open a valve. More advanced electronic models adjust resistance through inspiration and provide measurements and feedback.
Most POWERbreathe IMT products primarily load inhalation. The company also offers a separate expiratory trainer. If an assessment shows that inspiratory strength is the main deficit, POWERbreathe may be the more specific choice. It is not designed around sustained, CO₂-managed high-volume ventilation.
Our verdict: Excellent for focused inspiratory strength. Less complete as a single-device system for sustained full-cycle respiratory conditioning. Visit POWERbreathe.
3. Airofit: best smart resistance trainer
Best for: Athletes who prioritize connected testing, guidance and training data.
Airofit trains both inspiratory and expiratory function. Its connected systems can assess accessible lung volume and breathing pressures, guide sessions and track progress. That makes it compelling for athletes who value measurement and a polished digital experience.
The meaningful difference between Airofit and BWB is not simply session length. Airofit is fundamentally a resistance-based system. BWB is designed to turn sustained high-volume ventilation into the primary training stimulus while managing CO₂.
Our verdict: Best resistance-based option for athletes who prioritize testing, app feedback and connected data. Review Airofit’s current systems.
4. O2 Trainer: best simple inspiratory trainer
Best for: Athletes who want a portable and inexpensive way to train inhalation against progressive resistance.
O2 Trainer uses interchangeable apertures to change inspiratory resistance. It is small, requires no battery and uses a short protocol. That simplicity can make consistent use easier.
The device primarily targets inhalation, with exhalation left unrestricted. It does not provide a dedicated CO₂-management circuit or the measurement features of Airofit. It is therefore a focused inspiratory trainer rather than a full-cycle high-volume conditioning system.
Our verdict: Strong value for athletes who want straightforward inspiratory resistance with minimal setup. Visit O2 Trainer.
5. The Breather: best accessible dual-resistance trainer
Best for: Users who want simple inspiratory and expiratory resistance in one device.
The Breather independently adjusts resistance for inhalation and exhalation. The current standard device offers six inspiratory settings and five expiratory settings. It is straightforward and trains both sides of the respiratory cycle.
Its primary overload comes from restricted airflow rather than sustained, CO₂-managed ventilation. That may be entirely appropriate for someone seeking an accessible dual-resistance device.
Our verdict: Good value for simple inspiratory and expiratory resistance. Visit The Breather.
6. Expand-A-Lung: best no-frills dual-resistance trainer
Best for: Users who want a small, simple and adjustable resistance device.
Expand-A-Lung adds adjustable resistance during inhalation and exhalation. The manufacturer currently recommends sets of 10 to 15 breaths. Its advantages are portability, simplicity and a low barrier to entry.
The trade-off is a narrower training platform. It does not include dedicated CO₂ management, measurement or the same depth of guided progression found in BWB or Airofit.
Our verdict: A practical choice for uncomplicated respiratory resistance. Visit Expand-A-Lung.
7. Idiag P100 and SpiroTiger: the discontinued method-level comparison
Current status: SpiroTiger and the Idiag P100 are no longer in production and are not current buying options.
Idiag P100 grew out of the SpiroTiger system and is important to acknowledge because it also used the isocapnic hyperpnea principle. Its manual describes electronic measurement of airflow, pressure and end-tidal CO₂, along with endurance and respiratory strength modes.
We have included it so this comparison does not create the false impression that BWB invented the scientific method or that no other isocapnic system has ever existed. The important commercial distinction is that these electronic systems are discontinued, while BWB is currently available as a simpler, mechanically calibrated consumer training system.
Our verdict: A sophisticated historical and method-level comparator, but no longer a purchase option. Read the archived Idiag P100 manual.
What does the research actually establish?
Respiratory muscle training has a meaningful research base, but it does not prove that one device is universally superior. Different methods create different adaptations, and study quality, population and protocol all matter.
- A 2025 systematic review and meta-analysis of 25 studies involving 522 athletes reported improvements in respiratory muscle measures and some pulmonary-function and performance outcomes. The authors rated much of the evidence as low or very low quality. Read the systematic review.
- A 2023 study compared voluntary isocapnic hyperpnea using SpiroTiger with inspiratory threshold loading using POWERbreathe. Both groups showed respiratory adaptations. The threshold-loading group showed a larger VO₂peak improvement in that study. This is method-level evidence and was not a trial of BWB. Read the head-to-head study.
- A 2026 randomized crossover pilot trial from the Institute of Sport in Warsaw used ISO-BWB-S devices and the Isocapnic app during a five-minute VIH intervention in simulated altitude. This is direct BWB research, but it studied an acute hypoxic application rather than long-term athletic training or superiority over consumer competitors. Read the Warsaw study.
No published head-to-head trial has established BWB as superior to every device in this article for every outcome. Our recommendation is a criteria-based coaching judgment about the breadth of training available from one system. Explore the complete Isocapnic research and evidence library.
Which BWB should you choose?
BWB-Sport
The best starting point for most athletes. It is compact, portable, mechanically simple and easy to use for warm-ups and stand-alone daily respiratory training. Use a nose clip if you leak air through your nose.
BWB-Mask
The better choice for hands-free use, nasal or oral breathing, longer sessions and practitioner-guided advanced protocols. It removes the need to hold a mouthpiece throughout the session.
If you are not sure whether respiratory training is right for you or which system fits your goals, complete the respiratory performance assessment for a personalized starting point.
Frequently asked questions
What is the best breathing trainer for athletes?
For all-around stand-alone respiratory conditioning, we recommend the Isocapnic BWB series because it trains inhalation and exhalation during sustained high-volume ventilation while using a calibrated rebreathing circuit to help maintain CO₂. Athletes focused specifically on inspiratory pressure may prefer POWERbreathe. Athletes prioritizing connected measurement may prefer Airofit.
Is BWB better than Airofit?
It depends on your goal. Airofit has an advantage in integrated testing, connected measurements and live digital feedback. BWB is our preferred option when sustained high-volume ventilation and full-cycle respiratory conditioning are the priorities.
Is BWB better than POWERbreathe?
For all-around respiratory development, we choose BWB. For isolated inspiratory strength and pressure generation, POWERbreathe may be the more specific tool.
Do breathing trainers increase lung capacity?
A breathing trainer does not simply enlarge healthy adult lung tissue. Training can improve respiratory muscle function and may change how effectively you access and use your available respiratory volumes. Track usable volume, respiratory pressures, ventilation, breathing endurance and sport performance rather than relying on one loosely defined idea of “lung capacity.”
How long should respiratory muscle training last?
Duration depends on the method and goal. Resistance protocols may prescribe a fixed number of breaths. Isocapnic sessions can involve sustained ventilation for several minutes or longer. Follow a progressive program rather than assuming every respiratory trainer should use the same dose.
Are breathing trainers worth it?
They can be worthwhile when the device and protocol match a real training need. Respiratory training should be treated like other supplemental conditioning: assessed, progressed and integrated with sport training, not sold as a shortcut that replaces it.
The takeaway
When I assess an athlete, I am rarely interested in one impressive breath. I want to know whether the respiratory system can repeatedly generate the volume, speed and control the sport demands without becoming the ceiling on performance.
POWERbreathe is an excellent inspiratory strength tool. Airofit is the strongest connected resistance platform in this comparison. O2 Trainer, The Breather and Expand-A-Lung make resistance training accessible. The discontinued SpiroTiger and Idiag P100 remain important historical isocapnic reference systems, but they are not current buying alternatives.
For the athlete who wants one portable system to train inhalation, exhalation, usable volume, respiratory rate, endurance and control together, Isocapnic BWB is our choice for the best all-around breathing trainer.
This article is intended for athletic and general wellness education. BWB products are not medical devices for diagnosis or treatment. People with respiratory, cardiovascular or other health conditions should consult their clinician before beginning respiratory training. Follow the app, manual and safety guidance. Stop if you feel dizzy, lightheaded or unwell. Individual results vary.
AUTHORSHIP AND TRANSPARENCY
About this article
Written by
Coach Luke Way is the founder and CEO of Isocapnic and has coached endurance athletes for 20 years. He specializes in elite triathlon, mountain biking, CrossFit, and physiology-led athlete assessment.
Scientifically reviewed by
Dr. Andrew Sellars is a Canadian physician, anesthesiologist, performance physiologist, entrepreneur, and coach with a Master's degree in Athletic Coaching. He co-founded VO2 Master and is Co-Founder, Chief Science Officer, and Physiology Advisor at Isocapnic Technologies Inc., where his work focuses on biomarker-guided training and respiratory performance.
Review completed: August 21, 2026
