Respiratory Muscle Training Boosts Special Forces Selection Rate by 30% in 6 weeks

During intense, sustained exercise, the inability to meet respiratory demand and exercise-induced dyspnea lead to physiological limitations and exercise cessation. Metabolic demands during high-intensity exercise are associated with extreme ventilation and gas exchange.

In addition, the chemical stability of the blood is compromised during intense exercise, as ventilation is unable to buffer the blood pH, contributing to the build-up of carbon dioxide and lactic acid. Furthermore, when the functional capacity of the respiratory system is reached, the respiratory muscle metaboreflex will compromise arterial oxygenation and limb oxygen flow.[1]

Performance-defeating acquired breathing behaviors, poor respiratory muscle condition, and compromised diaphragm function have a negative impact on physiology, psychology, health, and performance. [2] [3] However, these behaviors can be deconditioned and reversed by specific countermeasures to improve performance, physiological health, and psychological status. [4] [5]

To qualify for selection into the Special Forces Unit, warriors are required to excel in physiologically and psychologically challenging environments. The number of candidates qualified for the Special Forces Unit selection process has declined in recent years, posing a threat to National security, as there are simply not enough qualified candidates to fill the needs of our Armed Forces.

The Special Forces Assessment and Selection (SFAS) course failure rate was four times (4x) in 2017, compared to 2014 (passing rate in 2014: 12%, in 2017: 3%). In addition, SFAS candidates in the Army Physical Fitness Test (APFT) have five times (5x) the failure rates and a 22% increased injury rate since 2014. (FY2014: Medical: 6.4%; APFT: 2.9% FY2017: Medical: 8.2%; APFT: 13.9%).

Hypothesis

Warriors applying for SF recruitment often present with postural changes due to a variety of causes, including trauma, fixed positions, unergonomic gear carry, repetitive motions, suboptimal performance form/mechanics, sleep disruption, medication, and dietary changes. These can compromise the respiratory system and respiratory function, leading to faster rates of fatigue, increased risk of overexertion injuries and illnesses, and higher Selection Course failure rates.

Changing these respiratory behaviors to reverse over-breathing patterns should result in improved physical performance, reduced injuries, and, consequently, higher passing rates on the selection course.

We investigated whether a 6-week intervention study during the SFAS course, incorporating RMT alongside respiratory and behavioral countermeasures, enhances physical performance and improves the selection pass rate.

Study aims

The mission of the 6-week study described here is to help soldiers enhance their breathing strength and performance by applying behavioral learning principles to breathing physiology during physical training in preparation for the Special Forces Assessment and Selection Course.

Study design

All subjects who enrolled in the study underwent a baseline assessment, including pulmonary function testing (spirometry), respiratory muscle strength (maximum inspiratory pressure (MIP), maximum expiratory pressure (MEP)), and exhaled carbon dioxide testing (EtCO2). All subjects also performed a 2-mile run.

For all subjects of group A, their capnic status at the anaerobic threshold was assessed during a loaded squat test.

Group A followed a 6-week intervention including two (2)sessions of RMT per day. Each RMT session consisted of two (2) sets of 10 breaths at an intensity setting corresponding to 70% of maximum effort. To avoid overtraining, subjects were instructed to reduce or skip sessions on days of strenuous exercise.

Furthermore, group A was instructed in a set of 3 types of countermeasures to:

1. Improve ventilation at the point of exercise cessation

2. To increase mindfulness

3. To improve the quantity and quality of sleep.

These countermeasures aimed to equip subjects in Group A to withstand the physiological and psychological challenges presented during the SFAS course and the subsequent selection process.

Subjects in Group B completed the SFAS course alongside those in Group A.

Due to warfighting requirements, the endline assessment was limited to a 2-mile run and to a comparison of the selection pass rate to historical pass rate data.

Results and discussion

In total, 19 soldiers were enrolled in the study and were assigned to either Group A (intervention group) or Group B (control group).

Table 1 shows the demographics and baseline measurements of subjects enrolled in the study. The difference in demographics and baseline measurements between the two groups was assessed using ANOVA (StatPlus) and revealed no significant difference between the groups at baseline, except for respiration rate, which showed a significant difference between group A and group B (highlighted by *).

The observed difference may be attributed to activities before arrival at the assessment station, stress or anxiety about the measurement methods, lower levels of aerobic fitness, or other factors. As the differences in respiration rate were not reflected by other baseline parameters, they were disregarded for outcome analysis.

Table 1: Soldier Demographics

Performance and selection outcome

All subjects performed a 2-mile run at baseline and endline of the study under comparable conditions and without load. Following the 6-week SFAS course, subjects from both groups underwent SF selection.

Table 2 demonstrates the 2-mile run times after the study duration (Endline) were significantly different between the groups (highlighted by *, ANOVA, StatPlus). The average improvement in the intervention group A was 3.55%, while subjects in group B only improved by 0.52% on average. This difference in physical performance at the time of entering the special unit selection may have given warriors in group A a critical advantage, which is reflected in the selection rate. The selection rate in group A was at 30%, while none of the subjects in group B were selected.

Table 2: Comparison of Major Outcomes at Baseline, Endline, and Selection Rate

Figure 1, panel A depicts the significant difference in the average 2-mile run time between the groups (p=0.02, error bars represent standard deviation), while panel B shows the notable difference in average improvement in both groups. However, this difference in the percentage of improvement fails to reach significance, most likely due to the range of variability within the group (standard deviation in group A: 7.59, in group B: 9.62).

FIGURE 1: AVERAGE ENDLINE (POST INTERVENTION) RUN TIMES AND IMPROVEMENT

FIGURE 2: SELECTION RATE COMPARED TO HISTORIC DATA AND TREND

Conclusions

A 6-week intervention program, incorporating strengthening and preventive measures, as well as countermeasures, was introduced into the SFAS course to enhance physiological and psychological performance, resilience, and mindfulness, in preparation for selection into special units.

Respiratory performance training, which involves resistive breathing exercises to strengthen the diaphragm and other respiratory muscles, was introduced along with education on situation-specific adjustments of breathing patterns. This approach aims to optimize respiratory function and prepare the cardiopulmonary system optimally for the extreme demands of the selection process.

The intervention program was compared to the accomplishment of the SFAS course without adjunct intervention. We demonstrate that the intervention program, including performance breathing training, increases the average run time in the 2-mile time trial.

We also show that the breathing training increases the selection rate to 30%, compared to 0% in the control group. Compared to historic selection rates from 2014 and 2017, the achieved selection rate of 30% could reverse a downward trend and increase selection rates for the future (orange trend line). However, the findings from this pilot study require confirmation in larger studies.

We therefore recommend the intervention program as an effective measure to support recruitment to Special Forces and enhance warrior resilience and performance.

References

[1].  Respiratory Muscle Training: Theory and Practice 1st Edition

[2].  Effect of diaphragm fatigue on subsequent exercise tolerance in healthy men and women

[3].  Work of breathing influences muscle sympathetic nerve activity during semi-recumbent cycle exercise

[4].  Recent Advancements in Our Understanding of the Ergogenic Effect of Respiratory Muscle Training in Healthy Humans: A Systematic Review

[5].  Effects of inspiratory muscle training on exercise responses in normoxia and hypoxia