Muscle Fuel Symmetry - MFS


  • Assesses the symmetry (balance) of MuscleSound scores between contralateral (dominant and nondominant) muscles of the upper or lower body
  • Reported as a percent lower than the muscle with higher fuel values,
    • No side difference would result in a 0% lower value.
    • The maximum side difference would result in one side’s displaying -100% lower.


  • Asymmetric differences in strength and power output levels between dominant and nondominant limbs have been reported in professional athletes.
  • Such differences have been linked to increased injury risk and performance deficits.
  • To date, these differences have been assessed and reported in Isokinetic, biomechanical, strength, power or field test measures.
  • The Fuel status of a muscle contributes significantly to the strength and force of its contraction.
  • MFS can act as a surrogate for these traditional measures, and used as an easily obtained early warning of potential injury risk for coaches and/or nutritionists  .


  • An additional and highly convenient tool that can provide early indications of potential injury risk.
  • By utilizing the MFS assessment, potential strength/power deficits may be quickly screened, and a much earlier determination can be made as to the need for further testing.
  • Can be applied to rehab as well as performance and training situations. NOTE: Inadequate rehabilitation and premature return to play after injury have been suggested risk factors for recurrence of injury.
  • Can be used to develop and monitor training routines designed to reduce observed deficits.
  • Can be used to identify and report trends in improvements over time.

The Calculation

  • From our database, calculate the biggest contralateral difference in MuscleSound scores between pairs of muscles from the same ultrasound model. NOTE: Different ultrasound models produce different scores for the same muscle.
  • The largest contralateral difference in our database is represented as a 100% difference in symmetry.
  • Calculate the difference between the two individual values for each muscle pair in this session.
  • Compare this difference value to the maximum difference found in the database.
  • Calculate the symmetry score for the lower scoring side as a percentage of the higher scoring side.
    • No side difference would result in perfect symmetry or 0% difference.
    • The maximum difference would result in one side being 100% lower than the other.


Assume the raw image value for each side of a particular muscle  is 47.58 (For the left side muscle)  and 46.11 (for the right side muscle).

  • Find the difference between Left and Right sides
  • Difference = 47.58 - 46.11 = 1.47
  • The largest difference between sides for this muscle with this ultrasound device is 8.64
  • Percent difference = (1.47 / 8.64) x 100 = 17%
  • This would be presented as the Right is 17% lower than the Left

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