Hip Flexors: Measuring Length, Strength, and Interpreting Results

How do you measure hip flexors?

Measuring hip flexors primarily involves assessing their length and flexibility through specific orthopedic tests, and less commonly, their strength to identify imbalances, potential restrictions, or weaknesses that could impact posture and movement.

Understanding Hip Flexor Function and Importance

The hip flexors are a group of muscles located at the front of the hip, responsible for bringing the knee towards the chest (hip flexion). Key muscles in this group include the iliopsoas (comprising the iliacus and psoas major), rectus femoris (one of the quadriceps muscles), sartorius, and tensor fasciae latae. These muscles are critical for:

• Locomotion: Walking, running, jumping, and climbing.
• Posture: Maintaining an upright stance and contributing to pelvic position.
• Sport-Specific Movements: Kicking, sprinting, and dynamic balance.

Measuring hip flexor status is crucial because imbalances—whether tightness (shortening) or weakness—can lead to a cascade of issues, including:

• Low back pain due to excessive anterior pelvic tilt.
• Compensatory movement patterns during exercise.
• Reduced athletic performance.
• Increased risk of injury to the lower back, hips, or knees.

Assessing Hip Flexor Length and Flexibility

The most common and clinically relevant way to "measure" hip flexors is by assessing their length, which indicates flexibility. This is typically done through specific orthopedic tests.

Thomas Test

The Thomas Test is a highly regarded assessment for hip flexor tightness, particularly of the iliopsoas and rectus femoris.

• Procedure:
  1. The individual lies supine (on their back) at the edge of an examination table, with their hips positioned so that the sacrum is supported but the thighs can extend freely off the edge.
  2. The individual fully flexes one hip, bringing the knee towards the chest, and holds it firmly with both hands to flatten the lumbar spine against the table.
  3. The examiner observes the opposite, extended leg.
• Interpretation:
  • Normal: The back of the thigh of the extended leg remains in contact with the table, and the knee of the extended leg can flex to approximately 80 degrees or more.
  • Iliopsoas Tightness: The extended leg lifts off the table, indicating an inability to achieve full hip extension due to tightness in the iliopsoas.
  • Rectus Femoris Tightness: The extended leg remains on the table, but the knee extends (straightens) past 80 degrees, indicating tightness in the rectus femoris. The knee will not be able to achieve 80 degrees of flexion.
  • Combined Tightness: Both the thigh lifts off the table and the knee extends.

Ely's Test (for Rectus Femoris)

Ely's Test specifically assesses rectus femoris tightness.

• Procedure:
  1. The individual lies prone (on their stomach) on an examination table.
  2. The examiner passively flexes one of the individual's knees, bringing the heel towards the buttocks.
• Interpretation:
  • Normal: The heel can reach the buttocks without the hip on the same side lifting off the table or the pelvis rotating.
  • Positive (Rectus Femoris Tightness): As the knee is flexed, the hip on the same side spontaneously flexes, causing the buttocks to lift off the table, or the pelvis rotates anteriorly. This indicates the rectus femoris is too short to allow full knee flexion without pulling the hip into flexion.

Goniometry for Objective Measurement

While the above tests are qualitative, a goniometer can be used to objectively measure the available hip extension range of motion during the Thomas Test.

• Procedure: With the individual in the Thomas Test position, align the goniometer's fulcrum with the greater trochanter, the stationary arm along the midline of the trunk, and the moving arm along the lateral midline of the femur. Measure the angle of hip extension (how far below horizontal the thigh rests).
• Interpretation: A lack of full extension (thigh resting above horizontal) quantifies the degree of hip flexor restriction.

Assessing Hip Flexor Strength

Measuring hip flexor strength helps identify weakness or imbalances between sides.

Manual Muscle Testing (MMT)

MMT is a common clinical method to grade muscle strength against gravity and resistance.

• Procedure:
  1. The individual is seated with knees bent at 90 degrees, or supine depending on the specific muscle being tested.
  2. For hip flexion, the individual is asked to lift their knee towards their chest.
  3. The examiner applies resistance against the distal thigh/lower leg while the individual attempts to hold the position.
• Interpretation (Grading Scale 0-5):
  • Grade 5 (Normal): Full range of motion against gravity and maximal resistance.
  • Grade 4 (Good): Full range of motion against gravity and moderate resistance.
  • Grade 3 (Fair): Full range of motion against gravity, no resistance.
  • Grade 2 (Poor): Full range of motion with gravity eliminated.
  • Grade 1 (Trace): Visible or palpable muscle contraction, no movement.
  • Grade 0 (Zero): No contraction.

Isometric Dynamometry

Handheld dynamometers provide a more objective and quantifiable measure of peak isometric hip flexor strength.

• Procedure: The individual performs a maximal voluntary isometric contraction (MVIC) against the dynamometer, which is held by the examiner. Several repetitions are typically averaged.
• Interpretation: Provides a numerical value (e.g., in Newtons or pounds) for strength, allowing for precise tracking of progress and comparison between limbs or against normative data.

Interpreting Measurement Results

Understanding the results of these measurements is key to developing an effective intervention strategy.

• Tight Hip Flexors: Indicated by a positive Thomas Test or Ely's Test, or limited hip extension range of motion. This often correlates with anterior pelvic tilt, compensatory lumbar extension, and can contribute to low back pain or hamstring strain.
• Weak Hip Flexors: Indicated by low MMT grades or dynamometer readings. This can manifest as difficulty with activities requiring strong hip flexion (e.g., high knee lifts, sprinting), or contribute to a shuffling gait.
• Asymmetry: Significant differences between the left and right sides in either flexibility or strength can indicate an imbalance that may require targeted intervention.

Best Practices and Considerations

When measuring hip flexors, adhere to these guidelines for accuracy and safety:

• Consistent Positioning: Ensure the individual is consistently positioned for each test to ensure reliable results.
• Stabilization: Proper stabilization of the pelvis and trunk is crucial to prevent compensatory movements that can skew results.
• Clear Instructions: Provide clear, concise instructions to the individual being tested.
• Holistic Assessment: Remember that hip flexor status is just one piece of the puzzle. A comprehensive assessment should include evaluation of core stability, gluteal strength, and overall movement patterns.
• Professional Guidance: While some tests can be performed by knowledgeable fitness enthusiasts, interpretation and prescription of exercises are best guided by a qualified personal trainer, physical therapist, or exercise physiologist. If pain or significant limitation is present, a healthcare professional should be consulted.

By systematically assessing hip flexor length and strength, fitness professionals and individuals can gain valuable insights into musculoskeletal health, guiding targeted interventions to improve posture, performance, and reduce injury risk.