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


  1. Brughelli, M, Cronin, J, Mendiguchia, J, Kinsella, D, and Nosaka, K. Contralateral leg deficits in kinetic and kinematic variables during running in Australian rules football players with previous hamstring injuries. J Strength Cond Res 24(9): 2539–2544, 2010 
  2. Keeley, DW, Plummer, HA, and Oliver, GD. Predicting asymmetrical lower extremity strength deficits in college aged men and women using common horizontal and vertical power field tests: A possible screening mechanism. J Strength Cond Res 25(6): 1632–1637, 2011 
  3. Croisier, J-L., Ganteaume, S., Binet, J., Genty, M., and Ferret, J-M. Strength Imbalances and Prevention of Hamstring Injury in Professional Soccer Players. The American Journal of Sports Medicine 36(8):1469-1475, 2008
  4. Hamilton, RT, Shultz, SJ, Schmidt, RJ, and Perrin, DH. Triple-hop distance as a valid predictor of lower limb strength and power. J Athl Train 43: 144–151, 2008. 

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