Can military service and its physical demands accelerate progression of pes planus (flatfoot) in young adults?

Can Military Service Accelerate Pes Planus Progression?

Yes, military service and its physical demands can accelerate progression of pes planus in young adults, primarily through high-volume weight-bearing activities, heavy load carriage, and the inability to modulate training intensity when symptomatic.

Evidence for Progression Risk

Training Volume as Primary Driver

Military basic training creates a uniquely high-risk environment where total training mileage is the most important determinant of musculoskeletal injury, with documented thresholds above which additional training increases injury without improving fitness 1, 2. Unlike civilian exercisers who can adjust their activity when experiencing foot pain, military trainees must complete standardized training regardless of personal fitness level or developing symptoms 1, 2.

• 60-80% of military basic training injuries are overuse injuries, with 80-90% affecting the lower extremities, including foot conditions 2
• Cumulative injury rates during basic training range from 42-67% in 8-week Army programs 2
• The combination of non-modifiable training demands, heavy load carriage, and prolonged equipment wear creates conditions that can worsen pre-existing pes planus 2

Biomechanical Stress Mechanisms

Repetitive carrying of heavy objects creates mechanical loading on the lower extremities and spine, leading to cumulative trauma disorders and degenerative changes 3. This mechanical stress is particularly relevant for individuals with pes planus, as the flattened arch provides less shock absorption and distributes forces abnormally across the foot structure 3.

Documented Structural Changes

Interestingly, one recent study showed that after 8 weeks of intensive military training, foot structure actually changed to a higher arch while foot function demonstrated less over-pronation 4. However, this finding should be interpreted cautiously:

• The study measured only 8 weeks of training in healthy cadets 4
• These adaptive changes may represent compensatory mechanisms rather than true improvement
• The study did not specifically track individuals with pre-existing pes planus 4

Clinical Outcomes in Symptomatic Cases

The most compelling evidence comes from surgical outcomes data: service members with symptomatic pes planus requiring reconstructive surgery face a 96% chance of failure to return to their preinjury level of function 5. Specifically:

• Only 4% (2 of 50 patients) returned to full duty without restrictions 5
• 56% remained on active duty with permanent duty restrictions 5
• 40% underwent Medical Evaluation Board for separation from the military 5

These outcomes demonstrate that once pes planus becomes symptomatic enough to require surgical intervention in the military context, the condition has progressed to a functionally limiting degree 5.

Risk Factors That Amplify Progression

Low Baseline Fitness

Lower baseline aerobic fitness dramatically increases injury risk, with the slowest runners having 3.2 times the odds of injury compared to the fastest 2. Individuals with pes planus who enter military service with poor conditioning face compounded risk 1.

Smoking

Female smokers entering Army training were 25% more likely to be injured (77% vs 62% for nonsmokers), and male smokers had 1.9-2.3 times higher injury rates 1. This modifiable risk factor can accelerate overuse injuries in those with pes planus 1.

Previous Injury History

Overuse injuries occurred twice as frequently in trainees with a previous history of ankle sprain, and the relative risk for injury in someone with a prior injury in the preceding year was 1.8-2.4 for women 1.

Common Pitfalls to Avoid

Do not assume asymptomatic flexible pes planus will remain asymptomatic under military training demands. The inability to self-pace and the mandatory high training volumes create conditions fundamentally different from civilian exercise 1, 2.

Do not rely on orthotics alone as prevention. While one small trial showed recruits who wore orthotics most or all of the time had no training injuries, only half of those assigned orthotics actually wore them consistently 6. The protective effect requires compliance and may not prevent progression in all cases 6.

Do not dismiss early foot pain as "normal training soreness." Plantar fasciitis is specifically identified as one of the common overuse conditions in military basic training 7, and early intervention may prevent progression to chronic symptomatic pes planus requiring surgical reconstruction 5.

Practical Clinical Algorithm

For individuals with known pes planus considering military service:

1. Assess baseline fitness level - those in the lowest fitness quartile have 1.5-2.4 times greater injury risk 1
2. Mandate smoking cessation before entry if applicable 1
3. Consider prophylactic orthotic fitting with emphasis on compliance education 6
4. Establish baseline foot structure measurements (arch height index) to monitor for progression 4
5. Counsel on realistic expectations - if symptoms develop requiring surgery, there is a 96% chance of not returning to full unrestricted duty 5

The evidence clearly demonstrates that military service creates conditions that can accelerate pes planus progression through unavoidable high-volume weight-bearing activities, though the degree of progression varies based on modifiable risk factors and individual biomechanics 1, 2, 5.