About Muscle Quality

Four Essential Questions Related to Muscle Quality  

1. What is Muscle Quality?
2. Why is Muscle Quality important?
3. How is Muscle Quality assessed?
4. How can Muscle Quality be improved?

1. What is Muscle Quality?

Muscle Quality (MQ) is a measure of a muscle’s strength relative to its size (mass). This will differ between individuals because muscles of the same size in different people do not necessarily have the same amount of strength.

2. Why is Muscle Quality important?

Maximizing a muscle’s strength for its size is obviously beneficial, however the importance of MQ is far greater than simply strength and mass: it has significant health, medical and fitness implications. This was first emphasized more than 20 years ago at the 1996 National Institute on Aging workshop “Sarcopenia and Physical Performance in Old Age”.

“... age-associated changes in muscle quality (MQ), aside from decreased mass, could play important roles in the development of physical functional problems in older adults.” (Dutta, 2000).

In support of this statement, research has since confirmed that MQ  is important in strength, function, power and cardiovascular performance in older adults (Cadore et al., 2012, Watanabe et al., 2013). In addition, links have also been reported between MQ and a range of other exercise and health related issues. This has included sports performance (Hirsh et al. 2016), injury risk (Roelofs et al., 2014), overall health and quality of life (Fragala et al., 2015), a range of metabolic, orthopedic and neurological conditions commonly seen in rehab settings (Addison et al., 2014), and even mortality (Newman et al., 2006).

3. How is Muscle Quality assessed?

A muscle is made up, generally, of two major types of tissue: one that contracts (contractile tissue) and one that does not (non-contractile tissue). MQ is determined by the relative amounts of these tissues in your muscle.

Contractile tissue is made up of specialized fibers that enable the muscle to exert force. Non-contractile tissue consists mainly of connective and fatty tissue. Connective tissue provides a structural framework for the muscle,  and stays relatively constant in volume. Fat deposits inside muscle (IntraMuscular Adipose Tissue - IMAT), can be a source of energy. However, when IMAT accumulates in excess, it increases the non-contractile proportion of the whole muscle and reduces MQ. So, although the muscle may not change in size, its ability to exert force (i.e. its strength and power) will decrease. The greater the proportion of a muscle's contractile to non-contractile tissue, the greater the amount of force it can produce for its size, and the greater its MQ.

Until recently, MQ calculations were based on a maximum strength test of the muscle involved, together with a measure of its muscle mass or cross-sectional area. A ratio of strength to muscle mass was then calculated, and this represented an assessment of MQ.  However, assessing muscle mass in this way is only possible using sophisticated, expensive and relatively inaccessible electronic equipment.

In contrast, MuscleSound has developed a convenient and comfortable method of measuring MQ by directly assessing IMAT estimations.  MuscleSound has automated (with permission) the UltraSound IMAT calculations from (Young et al., 2015). Young concluded that...

"Muscle ultrasound is a practical and reproducible method that can be used as an imaging technique for examination of percent intramuscular fat."

In the ultrasound images, muscle fibers (contractile tissue) show as darker areas, while fat and connective tissue (non-contractile tissue) show as brighter areas. When the image is processed these brighter and dark areas can be quantified and compared.  This technique quantifies total muscle echo intensity (EI → brightness) using gray scale analysis with the assumption that the higher the mean pixel intensity of a muscle region, the lower the muscle quality.

4. How can Muscle Quality be improved?

There are three approaches to improving improving MQ: (i) increase the strength and power of contractile tissue, (ii) reduce the amount of non-contractile tissue or, (iii) do both simultaneously. Any of these can be achieved  through strength training.  There is already substantial evidence that strength training can increase strength and power. More recent research has shown that fatty deposits in muscle can be impacted by exercise

A recent comprehensive review has stated that…

Our data, in addition to the available literature, suggests that fatty infiltration into muscle is a dynamic process that is responsive to exercise, a countermeasure that can prevent or reverse its occurrence. (Marcus et al., 2010)

In addition, there is substantial evidence that such a ‘dynamic process’ may be particularly impacted with strength training exercise (Dutta, 2000; Ivy et al., 2000, Fragala et al., 2015, Tracy et al., 1999)

The value and importance of MuscleSound is that the impact of different training routines/rehab interventions can be conveniently, economically and rapidly tracked  and monitored over time.

References

1. Addison, O. et al. Intermuscular Fat: A Review of the Consequences and Causes Odessa International Journal of Endocrinology 2014 (2014) 1-11.
2. Beattie K. et al., The effect of strength training on performance in endurance athletes. Sports Med. 44 (2014) 845-65.
3. Cadore, EL. Echo intensity is associated with skeletal muscle power and cardiovascular performance in elderly men. Experimental Gerontology 47 (2012) 473–478.
4. Dutta, C. Commentary on “Effects of Strength Training and Detraining on Muscle Quality: Age and Gender Comparisons” Journal of Gerontology 55A (2000) B158–B159.
5. Fragala, MS. Muscle Quality in Aging: a Multi-Dimensional Approach to Muscle Functioning with Applications for Treatment. Sports Med 45 (2015) 641–658.
6. Fukumoto, Y. et al., Age-Related Ultrasound Changes in Muscle Quantity and Quality in Women. Ultrasound in Medicine and Biology 41 (2015) 3013-3017.
7. Hairi, NN. Loss of Muscle Strength, Mass (Sarcopenia), and Quality (Specific Force) and Its Relationship with Functional Limitation and Physical Disability: The Concord Health and Ageing in Men Project. JAGS 58 (2010) 2055–2062.
8. Hirsch, KR. Body Composition and Muscle Characteristics of Division I Track and Field Athletes. Journal of Strength and Conditioning Research 30 (2016) 1231-1238.
9. Ivey, FM. Effects of Strength Training and Detraining on Muscle Quality: Age and Gender Comparisons Journal of Gerontology 55A (2000) B152–B157.
10. Liu, CJ &, Latham, NK. Progressive resistance strength training for improving physical function in older adults. Cochrane Database Syst Rev. 2009 Jul 8 (3).
11. Marcus, RL. Skeletal Muscle Fat Infiltration: Impact of Age, Inactivity, and Exercise. J Nutr Health Aging. 14 (2010) 362–366.
12. Newman, AB. et al. Strength, but not muscle mass, is associated with mortality in the health, aging and body composition study cohort. J Gerontol A Biol Sci Med Sci. 2006 Jan;61(1):72-7.
13. Naclerio, F. et al. Effects of different resistance training volumes on strength and power in team sport athletes. J Strength Cond Res. 27 (2013) 1832-40.
14. Reid, KF & Fielding, RA. Skeletal Muscle Power: A Critical Determinant of Physical Functioning In Older Adults Exerc Sport Sci Rev. 40 (2012) 4–12.
15. Roelofs, EJ. Muscle Size, Quality, and Body Composition: Characteristics of Division I Cross-Country Runners. J Strength Cond Res. 29 (2015) 290–296.
16. Takai, Y. et al., Sit-to-stand Test to Evaluate Knee Extensor Muscle Size and Strength in the Elderly: A Novel Approach J Physiol Anthropol. 28 (2009) 123–128.
17. Tracy, BL Muscle quality. II. Effects of strength training in 65- to 75-yr-old men and women. J. Appl. Physiol. 86 (1999) 195–201.
18. Watanabe, Y. et al., Echo intensity obtained from ultrasonography images reflecting muscle strength in elderly men. Clinical Interventions in Aging 8 (2013) 993–99.
19. Young, H. et al., Measurement of Intramuscular Fat by Muscle Echo Intensity. Muscle Nerve 2015 December; 52(6): 963–971