Foot Flexibility: Measuring Techniques, Importance, and Interpretation

How do you measure foot flexibility?

Assessing foot flexibility involves a combination of clinical measurements and functional tests that evaluate the range of motion at the ankle, subtalar, midfoot, and toe joints, providing crucial insights into biomechanical function and potential imbalances.

Understanding Foot Flexibility and Its Importance

Foot flexibility refers to the range of motion available at the various joints within the foot and ankle complex. This intricate structure, comprising 26 bones, 33 joints, and over 100 muscles, tendons, and ligaments, is designed for both stability and adaptability. Adequate foot flexibility is paramount for:

• Efficient Gait and Movement: Allowing the foot to adapt to uneven surfaces, absorb shock during impact, and act as a rigid lever for propulsion.
• Injury Prevention: Both excessive stiffness (hypomobility) and excessive laxity (hypermobility) can predispose individuals to common lower extremity injuries such as plantar fasciitis, Achilles tendinopathy, ankle sprains, shin splints, and even knee or hip pain.
• Optimized Performance: Critical for athletes in sports requiring dynamic movements, jumping, and rapid changes in direction.
• Footwear Selection: Understanding foot mechanics can guide choices in supportive or flexible footwear.

Key Components of Foot Flexibility Assessment

When measuring foot flexibility, we typically focus on the range of motion at several key areas:

• Ankle Dorsiflexion: The ability to bring the top of the foot towards the shin. This is crucial for squatting, walking, and running.
• Ankle Plantarflexion: The ability to point the toes downwards.
• Subtalar Joint Motion (Inversion/Eversion): The side-to-side rocking motion of the heel, allowing the foot to adapt to uneven ground and absorb rotational forces. Inversion is turning the sole inward; eversion is turning it outward.
• Midfoot Flexibility: The ability of the arch to flatten and recoil, essential for shock absorption and propulsion.
• Toe Extension (Especially Great Toe): The ability to bend the toes upwards at the metatarsophalangeal (MTP) joints, vital for the push-off phase of gait.

Clinical and Practical Assessment Methods

Several methods, ranging from precise clinical measurements to functional field tests, can be used to assess foot flexibility.

1. Goniometric Measurement

Goniometry is the gold standard for measuring joint angles with high precision. A goniometer is a protractor-like device used to quantify the range of motion at specific joints.

• Ankle Dorsiflexion (Non-Weight Bearing):
  • Procedure: The individual lies supine or sits with the knee extended or flexed (as gastrocnemius and soleus muscles affect dorsiflexion differently). The fulcrum of the goniometer is placed at the lateral malleolus, the stationary arm aligned with the lateral fibula, and the moving arm aligned with the fifth metatarsal. The individual then actively dorsiflexes their foot.
  • Normal Range: Approximately 15-20 degrees with the knee extended, and 20-25 degrees with the knee flexed.
• Ankle Plantarflexion (Non-Weight Bearing):
  • Procedure: Similar setup to dorsiflexion, but the foot is pointed downwards.
  • Normal Range: Approximately 40-50 degrees.
• Great Toe MTP Extension:
  • Procedure: The individual sits with the foot flat or relaxed. The fulcrum is placed over the dorsal aspect of the first MTP joint, the stationary arm along the first metatarsal, and the moving arm along the proximal phalanx of the great toe. The great toe is then extended upwards.
  • Normal Range: Approximately 60-70 degrees.

2. Weight-Bearing Lunge Test (Ankle Dorsiflexion)

This is a highly functional and commonly used field test that assesses weight-bearing ankle dorsiflexion, which is crucial for activities like squatting and running.

• Procedure:
  1. Stand facing a wall, placing the toes of the foot being measured on the ground, with the heel flat.
  2. Place the foot at a measured distance from the wall (e.g., 10-12 cm).
  3. Keeping the heel on the ground, lunge forward, aiming to touch the knee to the wall without lifting the heel.
  4. If the knee touches the wall easily, move the foot further back incrementally until the maximum distance from the wall is found where the knee can still touch the wall without the heel lifting.
  5. Measure the distance from the great toe to the wall.
• Interpretation: A distance of less than 10-12 cm (approx. 3.9-4.7 inches) often indicates restricted ankle dorsiflexion, which can be a risk factor for various injuries.

3. Navicular Drop Test (Midfoot Flexibility/Arch Collapse)

This test assesses the dynamic change in the height of the navicular bone (a bone on the top of the midfoot) from a neutral subtalar joint position to a relaxed standing position, indicating the degree of pronation or arch flexibility.

• Procedure:
  1. Mark the most prominent part of the navicular bone on the medial side of the foot while the individual is seated with the foot non-weight-bearing and in a neutral subtalar joint position. Measure the height of this mark from the floor.
  2. Ask the individual to stand naturally, distributing weight evenly on both feet.
  3. Re-measure the height of the navicular mark from the floor.
• Interpretation: The difference between the two measurements is the navicular drop. A drop of 6-10 mm is generally considered normal. A drop greater than 10 mm often suggests excessive pronation or hypermobility of the midfoot, while a drop less than 6 mm may indicate a rigid or high arch.

4. Visual Assessment and Palpation

While subjective, a skilled practitioner can gain valuable insights through observation and touch.

• Observation of Gait: Watching how the foot moves during walking and running can reveal compensatory patterns due to limited flexibility (e.g., early heel lift, excessive pronation).
• Foot Posture: Observing the arch height in standing (static assessment) can give clues about underlying flexibility.
• Palpation: Gently feeling the soft tissues around the ankle and foot for tenderness, tightness, or restricted movement can indicate areas of hypomobility.

Interpreting Your Results

The interpretation of foot flexibility measurements should always be done in context with an individual's activity level, injury history, and overall biomechanics.

• Hypomobility (Restricted Flexibility):
  • Implications: Can lead to increased stress on surrounding joints and tissues, compensatory movements (e.g., excessive pronation, knee valgus), and increased risk of injuries like Achilles tendinopathy, plantar fasciitis, shin splints, and patellofemoral pain.
  • Example: Limited ankle dorsiflexion often results in the heel lifting prematurely during a squat, or the foot excessively pronating to compensate.
• Hypermobility (Excessive Flexibility/Laxity):
  • Implications: While sometimes advantageous in certain movements, excessive flexibility without adequate stability can lead to instability, overuse injuries due to insufficient support, and increased susceptibility to sprains (e.g., recurrent ankle sprains).
  • Example: An excessive navicular drop might indicate a hypermobile flat foot, which may struggle with efficient propulsion.

Factors Influencing Foot Flexibility

Several factors can influence an individual's foot flexibility:

• Genetics: Some individuals are naturally more flexible or stiff.
• Age: Flexibility generally decreases with age due to changes in connective tissues.
• Activity Level and Type: Regular stretching and varied movements can maintain or improve flexibility, while prolonged inactivity or repetitive movements can lead to stiffness.
• Injury History: Previous sprains, fractures, or surgeries can lead to scar tissue formation and reduced range of motion.
• Footwear: Ill-fitting or overly restrictive footwear can impede natural foot movement and contribute to stiffness.
• Muscle Imbalances: Tightness in calf muscles (gastrocnemius and soleus) is a common cause of limited ankle dorsiflexion.

When to Seek Professional Guidance

While self-assessment can provide initial insights, for a comprehensive and accurate evaluation of foot flexibility and its implications for your health and performance, it is highly recommended to consult with a qualified healthcare professional. This includes:

• Physical Therapists/Physiotherapists: Experts in movement assessment and rehabilitation.
• Podiatrists: Specialists in foot and ankle health.
• Certified Athletic Trainers: Focus on injury prevention and performance.

These professionals can perform detailed assessments, interpret results in the context of your specific needs, and provide tailored advice, exercises, or interventions to address any identified flexibility issues.

Conclusion

Measuring foot flexibility is a fundamental step in understanding an individual's lower limb biomechanics. By utilizing both precise goniometric measurements and functional tests like the weight-bearing lunge and navicular drop tests, we can identify areas of hypomobility or hypermobility. This knowledge is critical for preventing injuries, optimizing athletic performance, and ensuring the long-term health and function of the foot and ankle complex. Regular assessment and targeted interventions can help maintain optimal foot flexibility, supporting efficient movement and overall well-being.