Muscle Size for Fitness and Sports Performance


Muscle Size is considered here as the thickness of a muscle (“Muscle Thickness”) as measured by ultrasound at predetermined muscle locations. Research has shown that Muscle Thickness can be considered a surrogate for Muscle Mass/Volume, particularly in the lower limbs 1-3.

Currently we are able to assess muscle size of the thigh, both the Rectus Femoris (RF) and the Vastus Lateralis (VL). Future assessments may include other muscles of the lower limbs, the Hamstrings (HL), the Calf/Gastrocnemius (GS), and upper limbs, such as the Biceps (BB).

Why is Muscle Size Important?

While it is typically only thought of in a physical, movement-oriented context, in reality the skeletal muscle system is fundamental to life 4, having a little known - but powerful - impact on a range of health issues. It is a unique and extensive body tissue that on average makes up approximately 40% of body mass, depending on gender, age and physical fitness. It contributes to crucial health related functions including breathing, protein metabolism, digestion, blood circulation, immune system status, blood glucose regulation, and overall quality of life. The size of our muscles, therefore, is an important component of the health of our muscles (Our “MuscleHealth”) at any level of fitness and mobility.

Why is Muscle Size Important in Fitness and Sports Performance?

Muscles clearly underpin physical performance in Fitness and Sports where it is their output that is the primary focus, i.e. the ability to demonstrate strength, generate force, and maintain endurance. For example one of the most comprehensive definitions of “Physical Fitness” comes from the Centers for Disease Control (CDC) 5

“...the ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and respond to emergencies.”

“Daily tasks” in this definition can range from walking to marathon running to powerlifting. All of these abilities, to varying degrees, depend on muscle size. In daily living, our muscles gradually lose size and mass over time. As much as 10% of muscle mass is lost per decade between 30 and 70 years of age and up to 15% per decade thereafter 6, 7. This represents a loss of around .5lb of muscle per year, or up to 20lbs of muscle at 70. For an average female weighing 120 lbs, with 100lb of lean mass, this would represent one fifth of her total muscle mass! Importantly, this gradual loss of muscle (known as Sarcopenia) also results in a gradual loss of “...the ability to carry out daily tasks with vigor and alertness…” . In other words a reduction in fitness.

For more “workout oriented” aspects of Fitness and Sports, an increase in Muscle Size (hypertrophy) has long been accepted as one of the prime determinants of “success” for a weight lifting/resistance training program8. In addition, muscle size has been associated with a range of performance related benefits, including greater muscle strength 9, which in turn has been linked with enhanced speed and power10; faster 6K times and increased bone integrity in female collegiate runners together with potential improvements in performance and injury prevention11. The balance (symmetry) of muscle size in contralateral limbs is also important in fitness and sports. Differences in strength and power levels between contralateral muscles of the body have been associated with increased injury risk and performance deficits12. Assessing contralateral Muscle Size Symmetry can provide an early - and easily acquired - injury risk “heads up” for coaches and trainers compared to more traditional, and time consuming, assessments.

While the benefits of maintaining and/or improving muscle size is clear, the ability to easily monitor changes in muscle size is the key to achieving any fitness or sports oriented goals. It will also enable appropriate muscle building intervention programs to be implemented in a more timely fashion.

Assessing muscle mass has, until now, required expensive, complex and relatively inaccessible equipment such as MRI, DEXA or BIA. MuscleSound, in contrast, is a rapid, convenient and comfortable method of determining muscle size. Results can be downloaded within seconds to a tablet or laptop for later analysis or historical context.

In summary, Muscle Size is important in Fitness and Sports Performance...

Because it enables the monitoring of:

  1. Current (baseline) measures of muscle size
  2. The age-related rate of muscle loss
  3. The impact of exercise/strengthening interventions on muscle gain
  4. The symmetry of muscle size in contralateral limbs
  5. An early warning for potential game-related injury risk

  1. Abe, T., et al. Morphological and functional relationships with ultrasound measured muscle thickness of the lower extremity: a brief review. Ultrasound 23: 166–173, 2015
  2. Abe, T., et al. Ultrasound assessment of hamstring muscle size using posterior thigh muscle thickness Clin Physiol Funct Imaging 36: 206–210, 2016
  3. Ogawa, M., et al. Ultrasound Assessment of Adductor Muscle Size Using Muscle Thickness of the Thigh. Journal of Sport Rehabilitation 21: 244-248, 2012
  4. Robert R Wolfe, R., The underappreciated role of muscle in health and disease. Am J Clin Nutr 84: 475–82, 1006
  5. Centers for Disease Control:
  6. Roth SM, et al. Strength training for the prevention and treatment of sarcopenia. J Nutr Health Aging 4: 143-55, 2000
  7. Malafarina V, et al., Sarcopenia in the elderly: Diagnosis, physiopathology and treatment. Maturitas 71: 109–114, 2012.
  8. Kraemer, WJ., et al., American College of Sports Medicine Position Stand on Progression Models in Resistance Training for Healthy Adults. Med. Sci. Sports Exerc.34: 2, 364 –380, 2002.
  9. Hirsch, KR et al., Body Composition and Muscle Characteristics of Division I Track and Field Athletes. Journal of Strength and Conditioning Research, 30: 1231–1238, 2016.
  10. Delecluse, C. Influence of Strength Training on Sprint Running Performance Current Findings and Implications for Training. Sports Med. 24: 147-156, 1997.
  11. Roelofs, EJ. et al., Muscle Size, Quality, and Body Composition: Characteristics of Division I Cross-Country Runners Journal of Strength and Conditioning Research. 29(2)/290–296, 2015.
  12. 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 

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