What is the impact of protective equipment on the breathing and performance of tactical operators? This is the question we set out to answer with this one-of-a-kind experiment.

In this article, I will walk you through the thought process in designing and implementing this pilot study.

The main goals were the following:

• Observe the differences in metabolic and respiratory responses during a resting metabolic rate (RMR) test, with and without protective equipment
• Observe the differences in metabolic and respiratory responses during a standardized step test, with and without protective equipment
• Observe the impact of protective equipment on respiratory muscle fatigue

So let’s get into it!

How it all started

A couple of years back, a tactical operator got in touch with me regarding his training and preparation for the specific demands of his upcoming missions. We had great success including low-intensity training (zone 2) into his routine and giving him a broader conditioning base to work from with dedicated run and bike training.

Recently we spoke again about the impact of protective equipment on performance and respiratory parameters. More specifically, we wanted to find out how much respiratory muscle fatigue might be incurred after an intense effort while wearing his full protective gear (around 22kg of equipment including a bullet-proof vest, a tactical belt, leg protection & a protective helmet).

This is what we set out to investigate.

A working hypothesis: protective equipment induces respiratory muscle fatigue

We know from prior research that compression of the ribcage through external forces (water, protective equipment, backpack) increases respiratory muscle fatigue. The inverse is also true: if the movement of ventilation can be assisted, respiratory muscle fatigue decreases and blood flow to locomotor limbs/muscles increases.

Indeed, the respiratory muscles sit higher than locomotor muscles on the hierarchy of blood flow distribution. This means that any fatigue incurred by respiratory muscles will negatively impact locomotor limb blood flow and thus, limit performance.

On that basis, could we measure the drop in respiratory performance (capacity, function) following an intense effort wearing protective gear? This would strengthen the idea that protective equipment induces respiratory muscle fatigue and directly impacts physical performance (and potentially cognitive performance as well).

Following this, can a respiratory training intervention decrease the drop in respiratory performance following an intense effort wearing protective gear?

We will try to answer this second question over the next few months. For now, let’s focus on the first part of the experiment: Assessing the impact of full protective equipment on respiratory and metabolic parameters at rest and during exercise.

Study design

Coming from a non-academic background, I didn’t have any prior experience setting up a study like this one. I did my best using my critical thinking skills and basic knowledge in science methodology. That being said, I’ve already found some significant flaws in this study design that I will address later in this article.

I’m open to constructive feedback so be sure to leave a comment below when and where you see opportunities for improvement.

In order to have a baseline to work from, we decided to spread the tests over 2 days.

We would use Day 1 to do the testing without equipment (”control setting”). The second day would be dedicated to testing with the protective equipment and quantifying potential respiratory muscle fatigue.

Day 1: Measuring respiratory and metabolic parameters without protective equipment

Day 1 was structured in the following way:

• Resting Metabolic Rate test (measuring VO2, ventilation and heart rate)
• Spirometry test (measuring lung capacity and expiratory power)
• Respiratory function test (measuring inspiratory muscle performance)
• Walking step test (measuring HR, lactate, ventilation, VO2, muscle oximetry, RPE, pace and incline)
• 10’ break
• Spirometry test (measuring lung capacity and expiratory power)
• Respiratory function test (measuring inspiratory muscle performance)

Day 2: Measuring respiratory and metabolic parameters with protective equipment

Day 2 consisted of the same elements as day 1 but we also did the 2 respiratory tests (capacity & function) before and after adding/removing the equipment.

The day went as follows:

• Spirometry test w/o equipment (measuring lung capacity and expiratory power)
• Respiratory function test w/o equipment(measuring inspiratory muscle performance)
• Put on the equipment (21.9kg of additional weight)
• Resting Metabolic Rate test with equipment (measuring VO2, ventilation and heart rate)
• Spirometry test with equipment (measuring lung capacity and expiratory power)
• Respiratory function test with equipment (measuring inspiratory muscle performance)
• Walking step test with equipment (measuring HR, lactate, ventilation, VO2, muscle oximetry, RPE, pace and incline)
• 10’ break
• Spirometry test with equipment (measuring lung capacity and expiratory power)
• Respiratory function test with equipment (measuring inspiratory muscle performance)
• Take off the equipment
• Spirometry test w/o equipment (measuring lung capacity and expiratory power)
• Respiratory function test w/o equipment (measuring inspiratory muscle performance)

Walking Step Test protocol:

After consulting with my colleague David Lipman, we settled on the following protocol:

• 4’ constant speed stages with 1’ passive rest between each stage
• First 4 stages: Progression in 1 km/h increments from 3 to 6 km/h walking on a flat treadmill (0% incline), straight into
• Last 7 stages: Progression in 3% incline increments from 3 to 21% at constant walking speed (4km/h)

Let’s look at each step one at a time and the data we collected.

Day 1: Physiological testing without protective equipment

Subject Characteristics

The subject of the study is a 31 year old male. He weighs 97.4kg and measures 190cm. He is an active tactical operator is very good physical condition. To maintain good ecological validity, we decided to have him wear his usual work clothes for this first day of testing.

Resting Metabolic Rate test

This test was done using the VO2 Master Pro unit. We did a 5’ settling-in time + a 5’ measuring time.

The results were as follows:

Average VO2 [mL/min]: 368

Average VO2 [ml/kg/min]: 3.8

Average Heart Rate [bpm]: 73

Average Respiratory Frequency [bpm]: 12.2

Average Tidal Volume [L]: 0.95

Average Minute Ventilation [L/min]: 10.5

Spirometry Test 1 (pre step test)

The spirometry was conducted using a MIR Spirobank Smart unit with disposable turbines. 2 attempts were done each time to validate the measurement.

The results were as follows:

FVC or Lung Capacity [L]: 6.53

FEV or Expiratory Power [L/s]: 4.76

FVC/FEV Ratio [%]: 72.89

Respiratory Function Test (pre step test)

This test was setup using an arbitrary resistance setting (2 full turns of the resistance wheel, or “level 2”) on the PowerBreathe Blue Version. I asked the subject to signal when he felt that inhaling became difficult and to stop when his respiratory mechanics changed significantly.

From a seated position, he was instructed to fully exhale (empty his lungs) and then to take a full inhale against the resistance of the device while maintaining as much volume as possible (avoid shortening the inhale). He did this test at around 12-15 breaths per minute.

He signaled the first signs of fatigue at rep 13 and stopped after rep 20. He said he felt like he couldn’t use his diaphragm fully at the end of the inhale and also felt a blockage in his throat on the last rep. We used this as the criteria for all other respiratory function tests over the 2 testing days.

Walking Step Test without protective equipment

As I outlined above, we used a “hybrid” protocol to test both flat and inclined walking in the same session.

Heart Rate and RPE measurements

The heart rate was measured continuously using a Polar H10 chest strap linked to the VO2 Master Manager App on an iPad. Heart rate was then averaged over the last minute of each 4’ stage. Heart rate recovery was measured as the difference between the max HR at the end of the preceding stage and the minimum heart rate during the 60″ recovery period.

RPE (rating of perceived exertion) was assessed at the end of each stage on 3 different levels:

• Muscle pain/difficulty (1-10)
• Respiratory difficulty (1-10)
• Global fatigue (1-10)

Using multiple scales helps magnify relative differences in sensations in the body during physical activity. you can read more about it in this study on RPE.

Ventilatory & VO2 measurements

Ventilatory and VO2 measurements were done using the VO2 Master Pro unit. Respiratory Frequency, Tidal Volume, Minute Ventilation and VO2 were measured continuously and were each averaged over the last minute of each 4’ stage.

Lactate measurements

Lactate was measured at the end of each stage (earlobe sampling) using a Lactate Scout 4 device.

Smo2 measurements

Muscle Oximetry was measured using multiple Moxy Monitor sensors. The placements or the sensors we used were as follows:

Moxy 1: Left Rectus Femoris

Moxy 2: Left Calf

Moxy 3: Left Forearm (non-involved muscle)

Spirometry Test 2 (post step test)

The second spirometry test was conducted exactly 10 minutes after the end of the last stage on the walking step test.

The results were as follows:

FVC or Lung Capacity [L]: 6.38

FEV or Expiratory Power [L/s]: 4.89

FVC/FEV Ratio [%]: 76.65

Respiratory Function Test 2 (post step test)

On this second respiratory function test, the same setup and resistance were used.

The subject signalled difficulty at rep 16 and completed 27 repetitions in total. He noted that he experienced the same sensations (reduced diaphragmatic contraction at the end of the inhale + blockage in the throat) on his last rep as he did during the first test.

Day 1 comments

Before even looking at day 2 measurements and comparing them with day 1, a couple of elements already stand out from this first day of testing:

• The subject felt better on the second round of respiratory tests (spirometry and function), after the step test was completed. He also performed significantly better on the second function test compared to the first one (max reps on the PowerBreathe increased from 20 to 27 , a 26% improvement in performance). We hypothesize that this is the consequence of the respiratory muscles being well warmed up after the step test. Takeaway: A respiratory warm up before conducting the first function test is likely necessary to truly compare pre and post values in this kind of setting.
• In addition to this, a metronome could be used to fix the breathing frequency, normalizing this parameter.
• Given the associated RPE, HR, Ventilation, VO2 and SmO2 values, the lactate sample on stage 9 (4 km/h + 15% incline) is likely a measurement error.

Now, let’s dive into our second day of testing.

Day 2: Physiological testing with protective equipment

As indicated earlier, we conducted a round of respiratory tests (capacity + function) before the subject put on his protective equipment.

Spirometry Test 3 (pre equipment, pre step test)

The results were as follows:

FVC or Lung Capacity [L]: 6.60

FEV or Expiratory Power [L/s]: 4.89

FVC/FEV Ratio [%]: 74.09

Respiratory Function Test 3 (pre equipment, pre step test)

The subject signalled difficulty at rep 17 and completed 25 repetitions in total. He said that he felt more familiar with the test and had a better “feeling” in general.

Resting Metabolic Rate test (with protective equipment)

The RMR test was done after the subject put on his protective equipment (tactical belt, bulletproof vest, leg protection and helmet).

Before putting on this protective gear, his weight (including clothes and boots) was 102.4kg. After wearing the protective equipment, his total weight was 124.3kg (or 21.9kg of equipment).

The results were as follows:

Average VO2 [mL/min]: 352

Average VO2 [ml/kg/min]: 3.6

Average Heart Rate [bpm]: 75

Average Respiratory Frequency [bpm]: 13.9

Average Tidal Volume [L]: 0.75

Average Minute Ventilation [L/min]: 9.75

Spirometry Test 4 (with equipment, pre step test)

The results were as follows:

FVC or Lung Capacity [L]: 5.71

FEV or Expiratory Power [L/s]: 4.42

FVC/FEV Ratio [%]: 77.41

Respiratory Function Test 4 (with equipment, pre step test)

The subject signalled difficulty at rep 19 and completed 30 repetitions in total. He said that he couldn’t breathe in as deeply as before because of the equipment, which could explain the few extra repetitions he was able to complete (less range of motion ⇒ less metabolic work done by the respiratory muscles?).

This could also be associated with his respiratory muscles being “warmed up” after the first round of respiratory tests without the protective equipment.

Walking Step Test with protective equipment

Without surprise, the step test with the equipment was significantly harder than the test done without on the first day.

Heart Rate and RPE measurements

The same approach was used to measure and average the heart rate data as was done on day 1.

Ventilatory & VO2 measurements

GRAPH VENTILATION with

GRAPH VO2 with

Lactate measurements

Smo2 measurements

To prevent the leg protections from turning off the Moxy Monitor, a cardboard ring was added above the power button.

Spirometry Test 5 (with equipment, post step test)

The 10’ break was respected (after the end of the last stage) before conducting the next spirometry test.

The results were as follows:

FVC or Lung Capacity [L]: 5.09

FEV or Expiratory Power [L/s]: 4.37

FVC/FEV Ratio [%]: 85.85

Respiratory Function Test 5 (with equipment, post step test)

The subject signalled difficulty at rep 19 and completed 28 repetitions in total. He mentioned the same feeling as he did in test 4: the equipment was restricting his ability to inhale fully on each breath.

After this test, the subject removed his protective hear and conducted one more round of respiratory tests.

Spirometry Test 6 (without equipment, post step test)

The results were as follows:

FVC or Lung Capacity [L]: 5.16

FEV or Expiratory Power [L/s]: 4.6

FVC/FEV Ratio [%]: 89.15

Respiratory Function Test 6 (without equipment, post step test)

The subject signalled difficulty at rep 13 and completed 19 repetitions in total. This time, he said that he could feel significant fatigue around his diaphragm, which limited his performance on the test.

Comparing Test Results

Below I’ll go over the comparisons between the two tests (equipped and unequipped) to quantify the added metabolic, mechanic and perceptual load of the protective equipment. Finally, we will compare the respiratory data collected on day 2 to determine if the protective equipment and the step test resulted in any respiratory muscle fatigue.

Comparing RMR Test results

Here’s the data comparing the results of the resting metabolic rate tests conducted with and without protective equipment. We can see a slight increase in respiratory frequency and an slight decrease in tidal volume with the protective equipment.

RMR COMPARISON

Comparing the Step Test results

It’s important to note that the two step tests were not technically performed at the same metabolic intensity, given the added load and thoracic restriction on day 2 because of the protective equipment. Future tests might be required to differentiate between the fatigue incurred by the protective equipment alone VS the intensity of the test itself.

Comparing ventilatory results

Respiratory frequency difference ranged from 8 to 31% between the two step tests. The difference was bigger after stage 6 (4km/h + 9% incline), highlighting the added metabolic load that the protective gear imposed on the inclined walking portion of the test.

Stage	3	4	5	6	4+3%	4+6%	4+9%	4+12%	4+15%	4+18%	4+21%
RF w/o	10	13	13	16	17	16	17	17	18	18	23
RF EQ	13	14	16	18	19	19	24	24	23	24	33
Difference	23.07%	8.34%	18.65%	13.04%	11.42%	14.35%	28.67%	28.13%	23.10%	25.67%	30.89%

Tidal volume (the volume of air moved with each breath) varied only slightly between stages, although there was significantly different at 3 and 5 km/h (likely due to voluntary manipulation of breathing by the participant at these intensities).

Stage	3	4	5	6	4+3%	4+6%	4+9%	4+12%	4+15%	4+18%	4+21%
Tidal Volume w/o	2.8	2.3	1.6	2.5	2.2	2.8	2.9	3.2	3.6	3.9	3.7
Tidal Volume EQ	2.0	2.5	2.8	2.9	2.5	3.1	2.9	3.3	3.7	4.2	3.7
Difference	-36.68%	9.65%	41.94%	12.72%	11.74%	8.93%	-1.61%	3.76%	3.16%	6.75%	0.22%

Minute ventilation (the volume of air moved each minute) significantly increased in the test with protective equipment compared to the step test on day 1.

Stage	3	4	5	6	4+3%	4+6%	4+9%	4+12%	4+15%	4+18%	4+21%
VE w/o	28	29	26	40	36	41	48	54	64	71	84
VE EQ	22	35	39	52	44	54	67	78	87	101	123
Difference	-30.20%	17.50%	33.71%	23.61%	18.29%	23.99%	28.86%	31.11%	26.31%	29.64%	31.87%

Comparing Oxygen Consumption Results

VO2 is the volume of oxygen that your body consumes during a physical activity.

Unsurprisingly, oxygen consumption was higher when wearing protective equipment. The added weight and thoracic restriction means more work needs to occur to move the body in space. While the second day testing was intense, the participant would have needed to push his effort to the maximum in order to reach his VO2max.

Comparing Blood Lactate Results

Lactate is a byproduct of glycolysis, the energy pathway that the body uses to break down sugars and recycle ATP. Blood lactate concentration is a way to quantify metabolic load. At low intensity, BLa usually remains stable (or drops) while the intensity increases. The drop in blood lactate is usually associated with an increase rate of fat oxidation.

At medium intensity (also called the heavy intensity domain), blood lactate levels increase but remain stable over time. At high intensity, lactate levels increase rapidly because the metabolic steady-state has been exceeded.

In this instance, we can see that from a metabolic standpoint, the inclined waking (above 12% incline) with the equipment was significantly more stressful than without the PE.

Comparing Muscle Oximetry Results

The Moxy Monitor measures the balance of oxygen delivery and utilisation inside the muscle’s capillary bed. To learn more about SmO2 trend analysis, you can refer to my presentation from the 2022 Moxy Summit event:

SmO2 often responds in the opposite was that lactate does. At low intensity, oxygen delivery exceeds utilisation, so the trend goes up. At medium intensity, oxygen delivery matches consumption, so the trend flattens. At high intensity, utilisation of oxygen exceeds delivery (since oxygen delivery is maximised beyond the second lactate threshold). This results in a negative trend.

These reactions are clearly observable in all 3 sensor placements. We can also observe the higher systemic load imposed by the PE by looking at the SmO2 reactions of the forearm (non-involved muscle).

Comparing RPE Results

Rating of Perceived Exertion is a subjective measure of effort difficulty. Contrary to popular belief, it is highly reliable, valide, and is sometimes even more precise than heart rate when estimating maximum capacity.

In the context of this test, general, respiratory and muscular RPE were all higher while wearing protective equipment.

Comparing Lung Capacity Results

It is interesting to note that no significant differences in baseline lung capacity (Forced Vital Capacity or FVC) were observed between the two days (6.5L on test 1 VS 6.6L on test 3). Neither did lung capacity change after the first day’s step test (6.5L pre VS 6.4L post step test).

However, significant changes in lung capacity were observed on day 2.

FVC dropped from 6.6L to 5.7L (-15%) between tests 3 and 4, showing the influence of the protective gear on lung capacity.

After the step test on day 2, FVC was down to 5.1L (with equipment and without equipment), which is a 12% drop compared to test 4 result.

In conclusion, we can say that lung capacity was restricted by the addition of protected gear (6.6L VS 5.7L) and that FVC was further limited by the fatigue incurred by the step test with protective equipment (5.1L post step test). The lack of change between the measurements post EQ and post w/o from day 2 (5.1L in both instances) might highlight the inspiratory fatigue that resulted from the step test with equipment.

Comparing Expiratory Power Results

No significant difference was observed in FEV (Forced Expiratory Volume in 1 second) on day 1 (4.8L pre VS 4.9L post step test).

On day 2, an 11% drop in FEV was observed after the protective equipment was added (4.9L w/o VS 4.4L EQ, pre step test).

No further drop was observed post step test (4.4L EQ post). FEV even increase slightly (+4%) after the protective gear was removed (4.6L in test 6).

The difference in change (pre and post step test) between lung capacity (-29%) and expiratory power (-11%) might be attributable to the fact that the expiratory muscle were not strained during the effort, unlike the inspiratory muscles.

Comparing Respiratory Function Test Results

On day 1, maximum reps on the respiratory function test increase by 26% (20 reps on test 1 VS 27 reps on test 2) after the step test. We hypothesise that this is due to the step test serving as a “respiratory warm up”, highlighting the necessity for proper respiratory warm ups before conducting any respiratory function tests.

On day 2, maximum reps increased once the protective gear was added (25 VS 30 reps on tests 3 and 4 respectively). This is likely due to the fact that protective gear restricts inspiratory range of movement, which means that each breath was shallower, finishing farther away from maximum inspiratory pressure being equal to the resistance applied. It might also show the warming up effect of the first respiratory function test conducted that day without equipment.

After the step test, maximum reps decrease slightly (28 reps post VS 30 reps pre). But surprisingly, a significant drop in maximum reps was observed once the protective equipment was removed (19 reps max). This strengthens the hypothesis that physical effort wearing protective gear induced significant inspiratory muscle fatigue.

Overall Step Test Conclusions

The test conducted with protective equipment elicits a higher metabolic, metabolic and perceptual load compared to the test without PE.

Overall Respiratory Conclusions

These results seem to indicate that in this specific setting, a sub-maximal step test performed while wearing protective equipment induces inspiratory muscle fatigue, measured by both spirometry and function tests. Expiratory power is only slightly affected. We can also note that a full respiratory warm up is recommended before conducting a respiratory function test.

Tactical Operators, Protective Equipment & Respiratory Muscle Fatigue

The goal of this first trial was to determine if respiratory muscle fatigue could be quantified following physical exertion wearing tactical protective equipment. Despite the limitations of the N=1 case, the results seem to indicate that it can. But those conclusions need to be taken with a grain of salt. Indeed, current research on the topic seems to point in different directions (thanks Tomek for the references).

I look forward to conducting a few months of respiratory training with this individual to see if we can attenuate the fatigue response following the equipped step test next time around.

A big thank you to Kenzen Physio Center in Nyon for welcoming us with the project.

In the meantime, I also look forward to reading your comments, suggestions, and potential corrections below!