Flat Feet (Pes Planus): Understanding the Condition and Its Impact

Introduction

Flat foot, also known as pes planus, describes a foot shape where the inner arch (the curved part inside your foot) is lower than usual or touches the ground completely when standing.
Some people are born with flat feet, while others develop them gradually over time due to muscle weakness, ligament strain, or wear and tear.

In most cases, flat feet are flexible, the arch appears when you lift your foot, but flattens when you stand. In others, it may be rigid, where the arch remains flat even when not weight-bearing.
In adults, a gradual loss of the arch is often called Adult Acquired Flatfoot Deformity (AAFD), which can result from weakening of the posterior tibial tendon. This key structure supports the arch.

Why the Foot Arch Matters

Your foot arch works like a spring, absorbing shock, helping with balance, and propelling you forward when you walk or run.
When the arch collapses, it changes how forces travel through your foot and leg. Over time, this can affect the ankles, knees, hips, and even your lower back.

What Causes Flat Feet?

Common factors include:

• Genetics: Some people naturally have lower arches.
• Muscle or tendon weakness: Especially of the posterior tibial tendon, which supports the arch.
• Injury or overuse: Repeated strain on the ligaments and tendons of the foot.
• Tight calf muscles: Limited ankle flexibility can increase downward pressure on the arch.
• Excess body weight: Higher loads increase stress on the arch structures.
• Age or degenerative changes: Soft tissues lose elasticity over time, allowing the arch to drop.

How Flat Feet Affect Movement

Having flat feet isn’t always painful, many people live comfortably without issues. However, when symptoms appear, they often include:

• Pain or tiredness in the arch, heel, or inner ankle
• Swelling or tenderness along the inside of the foot
• Foot fatigue after long periods of standing or walking
• Knee, hip, or back discomfort from altered posture or movement patterns

Biomechanical research shows that flat feet can:

• Increase inward rolling (pronation) of the foot and heel
• Shift pressure toward the inner side of the foot during walking
• Cause the leg to rotate inward, affecting knee alignment
• Lead to earlier fatigue in the muscles that stabilise the arch

A 2024 study of young adults found that people with flexible flat feet performed worse on balance and agility tests than those with normal arches, showing how the condition can subtly influence function and stability.

How Flat Feet Can Contribute to Other Musculoskeletal Problems

Flat feet don’t just affect the foot, they can change how the entire lower limb and spine move and absorb load.
Because the body works as a kinetic chain, even a small change in foot alignment can create ripple effects further up.

Here are some common secondary problems linked to flat feet:

1. Heel and Ankle Pain

• Plantar fasciitis: Flattening of the arch overstretches the plantar fascia, causing heel pain.
• Posterior tibial tendon dysfunction: The tendon supporting the arch works overtime and can become painful or degenerate.
• Achilles tendinopathy: Overpronation alters ankle alignment and increases strain on the Achilles tendon.

2. Knee Problems

• Excessive pronation of the foot causes the tibia (shin bone) to rotate inward. This can lead to:
  • Patellofemoral pain syndrome (runner’s knee)
  • Medial knee strain due to poor alignment and load imbalance
  • Early degenerative changes in individuals with longstanding flatfoot and poor lower limb mechanics

3. Hip and Pelvic Issues

• When the leg rotates inward due to foot collapse, the hip follows, placing strain on hip stabilisers.
• This may cause:
  • Gluteal weakness or overuse
  • Hip bursitis or groin discomfort
  • Pelvic asymmetry influences walking and balance

4. Lower Back Pain

• A flattening arch alters posture throughout the chain, sometimes increasing lumbar rotation or tilt.
• Over time, this compensation may contribute to non-specific low back pain or lumbar muscle fatigue, especially in those who stand for long hours.

5. Overuse Injuries in Sports

• Athletes with flat feet may be more prone to:
  • Shin splints (medial tibial stress syndrome)
  • IT band irritation
  • Hamstring or calf tightness from repetitive compensation
• Poor shock absorption from a collapsed arch can also increase stress across joints during running or jumping.
  

In short, Flat feet can act as a hidden driver for multiple musculoskeletal conditions. Addressing the underlying foot mechanics is often the key to resolving recurring or unexplained pain elsewhere in the body.

Does Flat Foot Affect Daily Life?

Flat feet can influence comfort and performance in everyday tasks:

• Walking and commuting: You may feel early fatigue or arch aching after long walks.
• Standing for long hours: Common in jobs like retail, teaching, or healthcare, leading to foot pain by the end of the day.
• Stairs and uneven ground: The foot works harder to stabilise, which can sometimes cause strain or discomfort.
• Exercise and sport: Activities like running, football, or jumping can increase stress on the feet and legs, raising injury risk.

These impacts vary, some individuals adapt well, while others notice progressive symptoms over time.

What the Research Says

Recent studies continue to explore the relationship between foot posture, pain, and function:

• Prevalence: Flexible flatfoot is seen in around 30–40% of children aged 6, reducing to about 10–12% by early teens. In adults, flatfoot is often linked to age-related tendon changes and higher BMI.
• Pain and quality of life: A study in J Orthop Surg Res (2025) found that individuals with flat feet reported higher pain scores and lower physical activity levels than those with normal arches.
• Biomechanics: Studies confirm greater medial pressure and heel eversion in flatfooted individuals, which can affect balance and muscle control.
• Supportive insoles: Evidence suggests that arch-support insoles can reduce pressure on the inner heel by about 7% of body weight and improve walking mechanics, though they work best when combined with strengthening exercises and professional guidance.

When to Seek Help

You should consider an assessment if you experience:

• Persistent pain in your arch, heel, or ankle
• Difficulty standing or walking for extended periods
• Noticeable flattening or asymmetry between feet
• Changes in your foot posture over time

An in-depth assessment by a physiotherapist can identify whether your flat feet are flexible or structural, and whether your symptoms stem from muscular imbalance, joint stiffness, or tendon dysfunction.

How Nottingham Physio Can Help

At Nottingham Physio, we take a biomechanical and evidence-based approach to managing flat feet.
Our physiotherapists assess how your feet move during standing, walking, and functional tasks, using this information to:

• Identify contributing factors (e.g. tightness, weakness, alignment)
• Guide you through a personalised rehabilitation plan
• Advice on footwear and load management
• Help you restore comfort and function safely
  

Whether your flat feet are causing pain, affecting your sport, or just making daily life uncomfortable, our team can help you understand your foot mechanics and build long-term strength and stability.

Final Takeaway

Flat feet are standard and often manageable, but when the arch collapses enough to cause pain or fatigue, it’s worth seeking professional advice.
Addressing flatfoot early can prevent secondary problems in the ankle, knee, hip, or back and help maintain comfort during your daily activities.

If you have flat feet or are experiencing related symptoms, book an assessment with me at Nottingham Physio today. Our clinicians will help you understand your condition and design a rehabilitation plan tailored to your goals.

References

• Kardm SM et al. J Orthop Surg Res, 2025: Prevalence and functional impact of flexible flatfoot in school-aged children.
• Lin et al. BMC Musculoskeletal Disorders: Kinematic differences between children with and without flat feet.
• BMC Musculoskeletal Disorders, 2023: Systematic review: Orthoses and patient outcomes in flexible flatfoot.
• J Orthop Surg Res, 2024: Plantar pressure distribution and BMI in adolescents with flatfoot.