Muscle Size for Physical Therapy and Sports Medicine


Muscle Size is considered here as the thickness of a muscle 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?

Skeletal muscle has 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.

While it is typically only thought of in a rather narrow fitness and sports related context, in reality the skeletal muscle system has a deeper more foundational contribution to aspects of life that underpin these, more noticeable, aspects of physical performance4. It also 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 our “MuscleHealth” – defined as “The capacity of a muscle to store, generate and replenish energy”, something that is relevant to all rehab and healing processes.

Why is Muscle Size Important in PT and Sports Medicine?

Physical Therapists and Sports Medicine practitioners predominantly use treatment oriented modalities in their practice. The ability to track and monitor the impact of such treatments in a timely manner is one of the keys to a successful rehab program. Assessing Muscle Size is a potential part of this process.

Muscle Size is one component of MuscleHealth and has been reported as an important contributor to health and wellbeing 4. Age-related loss of muscle size (Sarcopenia) has been described as the single most frequent cause of late-life disability5. In sports-related situations Muscle Size has been linked to greater endurance, delayed fatigue and increased bone integrity in female collegiate runners6, increased muscle strength7, and enhanced speed and power8;

The ability to easily assess and monitor changes in Muscle Size therefore can provide practitioners with valuable supplementary, and actionable information on the impact of prescriptive treatments. For example, monitoring Muscle Size can be used to assess...

  • Prevention/reversal of injury related muscle atrophy
  • Return of muscle size symmetry to contralateral limbs, post injury
  • The age-related rate of muscle mass loss (Sarcopenia)
  • Assessment of potential game-related injury risk

Although some of these outcomes can be assessed by other methodologies, these tend to be either time consuming, (e.g. 1RM tests) highly subjective (MMT) or require expensive and/or relatively inaccessible equipment such as MRI, DEXA or BIA.

MuscleSound, in contrast, is a rapid, convenient and comfortable method of determining Muscle Size that fits well with a busy clinic schedule. Results can be downloaded within seconds to a tablet or laptop for later analysis or historical context. The ability to access real-time information from inside the muscle, enables a more comprehensive, detailed evaluation of patient status.

  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 musclethickness 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. Wolfe, R., The under appreciated role of muscle in health and disease. Am J ClinNutr 84: 475–82, 2006.
  5. Cruz-Jentoft, AJ, et al., Sarcopenia: European consensus on definition and diagnosis. Age and Aging, 39: 412–423, 2010.
  6. 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.
  7. 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
  8. Delecluse, C. Influence of Strength Training on Sprint Running Performance Current Findings and Implications for Training. Sports Med. 24: 147-156, 1997.

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