Running Respiratory Muscle Training (IMT): The Science of Boosting V̇O2max by 2–3% in 3 Months

Why Respiratory Muscles Are the Hidden Bottleneck in Running

Most runners spend 95% of their time training their legs, but respiratory muscles (diaphragm + intercostal muscles) fatigue in the latter stages of a marathon—this is the so-called respiratory metaboreflex: when respiratory muscles are oxygen-deprived, they “steal” blood flow from the leg muscles, accelerating leg fatigue.

A 2023 Sports Medicine meta-analysis found that 8 weeks of inspiratory muscle training (IMT) can:

• Improve V̇O2max by 2~3%
• Improve time to exhaustion by 12~16%
• Reduce breathing frequency at the same intensity by 7~12%
• Improve 5K and 10K time-trial performance by 1.5~3%

Translated into real-world terms: a runner with a 90-minute half marathon could potentially run 87~88 minutes after IMT.

The Physiological Basis of IMT

The primary inspiratory muscles are the diaphragm and the external intercostals. Like all skeletal muscles, both can gain strength and endurance through resistance training.

IMT devices provide adjustable resistance valves: you must overcome resistance while inhaling, similar to a squat against a barbell. Common resistance is expressed as a percentage of maximal inspiratory pressure (MIP):

• 50% MIP: endurance training range
• 75% MIP: strength training range
• 90% MIP: maximal strength

8-Week IMT Training Protocol

The following protocol is based on combined recommendations from POWERbreathe and other studies:

Weeks 1~2: Adaptation Phase (50% MIP)

• Once daily, 30 inhalations per session
• One round in the morning and one in the evening
• Focus: find a setting that is “comfortable but with resistance”

Weeks 3~4: Building Phase (60~65% MIP)

• Once daily, 30 inhalations per session
• Begin to notice a “slight warmth in the inspiratory muscles”
• Combine with diaphragmatic breathing techniques

Weeks 5~6: Strengthening Phase (70~75% MIP)

• Once daily, 30 inhalations per session
• Completing 30 reps should now feel noticeably effortful
• Begin integrating into your running warm-up

Weeks 7~8: Peak Phase (75~80% MIP)

• Once daily, 30 inhalations per session
• Use 30 reps after training as a “respiratory muscle cool-down”
• Begin testing real-world performance effects

Comparison of Two Mainstream IMT Devices

POWERbreathe Medic Plus / Plus

Features: traditional adjustable resistance valve device

• Resistance range: 9~78 cmH2O (10 levels)
• Price: approximately NT$2,000~4,500
• Pros: simple and durable, no app required, backed by extensive research
• Cons: trains inspiration only, no data logging

Airofit Active / Pro

Features: smart device connecting to an app via Bluetooth

• Resistance range: can train both inspiration and expiration
• Price: approximately NT$5,000~8,000
• Pros: app-guided workouts, data tracking, MIP measurement
• Cons: depends on the app, battery life requires attention

Recommendation: choose the POWERbreathe Medic Plus if on a budget; choose the Airofit Pro if you want advanced data and structured workouts.

Integration with Running Training

Warm-Up Application

5 minutes of IMT before a run (50% MIP, 30 reps) can:

• Raise diaphragm temperature
• Activate respiratory muscle neural pathways
• Make breathing deeper from the start of your running form

After High-Intensity Training

Doing 30 reps at 60% MIP after interval training helps:

• Accelerate lactate metabolism
• Activate the parasympathetic nervous system (lower heart rate)
• Prevent cumulative respiratory muscle fatigue

Race Day

Do a full IMT session (75% MIP, 30 reps) 30 minutes before a marathon start to warm up the respiratory muscles without causing fatigue.

Common Misconceptions

Misconception 1: “Running already trains my respiratory muscles”

Wrong. Regular running only requires 40~60% of maximal inspiratory muscle force, which cannot reach the strength training threshold. The 75% MIP training provided by IMT cannot be replicated through running.

Misconception 2: “I can just blow up balloons instead”

Partially correct. Blowing balloons primarily trains the expiratory muscles, which differs from the inspiratory muscles targeted by IMT. The feeling of “not being able to get air in” in the latter stages of a marathon mainly comes from inspiratory muscle fatigue.

Misconception 3: “More IMT every day is better”

Wrong. Research shows that 30 reps daily, 5~6 times per week yields the best results. Overtraining instead keeps respiratory muscles in a state of sustained fatigue, harming running performance.

Methods for Testing Effectiveness

You can self-test even without laboratory equipment:

Test 1: Maximum Inhalations in 30 Seconds

• Time yourself for 30 seconds
• Inhale as deeply and quickly as possible
• Compare the increase in reps before and after training

Test 2: Breath-Hold Time

• Hold your breath after a normal inhalation
• Usually extends by 10~30% after training

Test 3: Running Breathing Frequency

• Count breaths over 30 seconds at the same pace
• Usually drops by 1~3 breaths after training (deeper and slower)

Who Should Use It

• ✅ Half-marathon and longer runners (greatest benefit)
• ✅ 5K runners over 25 minutes (respiratory muscle bottleneck is evident)
• ✅ Over-breathing runners (shallow and rapid breathing)
• ✅ Asthma patients (under medical supervision)
• ❌ Sprinters under 5K (limited benefit)
• ❌ During acute respiratory infections
• ❌ Uncontrolled severe hypertension

Conclusion

IMT is one of the few supplementary running training methods with strong evidence, low cost, and high ROI. The 8-week protocol requires only 5~10 minutes per day, yet can yield a 2~3% improvement in V̇O2max—for a 90-minute half-marathoner, that is a 2~3 minute improvement.

Rather than spending money on new running shoes, spending NT$3,000 on a POWERbreathe first may be the highest-value investment for improvement.

Combined with respiratory rhythm training (2-1-2 or 3-2 breathing patterns), scientific respiratory muscle training can become the invisible booster for your running progress.

Related Reading

• Can Respiratory Muscle Training Devices (IMT) Really Improve Cycling Performance? POWERbreathe vs. Airofit Field Test
• Respiratory Muscle Training for Cycling: Research on the Effects of Inspiratory Muscle Training (IMT) on Endurance Performance
• Benefits of Respiratory Muscle Training (IMT) on Endurance Performance: A Systematic Review of Randomized Controlled Trials
• Respiratory Muscle Training: The Scientific Benefits of Inspiratory Muscle Training (IMT) for Cycling Performance