You may have noticed, when looking at your dual X-ray absorptiometry (DXA) report, a value called the appendicular skeletal muscle index (ASMI) or relative skeletal muscle index (RSMI). Basically, the ASMI or RSMI is the sum of the lean muscle mass of the upper and lower extremities (lean muscle mass of arms [kg] + lean muscle mass of legs [kg]) adjusted for height (meters) squared (m2). The ASMI value has been used to assess sarcopenia in populations such as the elderly (Baumgartner et al., 1998; Kim et al., 2014; Pongchaiyakul et al., 2013) or cancer patients (Dieli-Conwright et al., 2018). 

Baumgartner et al. (1998) reported an ASMI value of 7.7+0.7 kg/m2 in elderly men (73.6+0.5.8 years) and 5.9+0.6 kg/m2 in elderly women (73.7+6.1 years). Compare these values to young adult males (8.6+1.1 kg/m2) or young adult females (7.3+0.9 kg/m2) (Gallagher et al., 1997). I thought it would be interesting to look at ASMI values in some college athletes. Using the data (Table 1) from a paper we published on college football players (Bosch et al. 2019); you can see that, regardless of position, the ASMI value was greater than the value reported by Gallagher et al (1997) in male adults and considerably larger than the value Baumgartner et al. (1998) reported in elderly male adults. Just looking at the male college football players there are significant position differences in ASMI with both offensive and defensive linemen having significantly higher ASMI values than all other positions. Wide receivers displayed significantly smaller ASMI values than both offensive and defensive linemen, tight ends, linebackers, running backs, and defensive backs. The larger ASMI values in linemen are not surprising given the height and as well as the amount of lean muscle mass these individuals typically carry.  

Football athletes offer the largest contrast in size among the athletes that play that game. However, if we examine athletes from sports that have little differences in size or body composition among the different positions, such as baseball players we see a little different outcome. Table 2 compares ASMI values in collegiate male baseball players by position from a study we recently published (Czeck et al., 2019). Similar to male collegiate football players the male collegiate baseball players had a higher ASMI value than that reported by Gallagher et al. (1997) in young adult males.  Like collegiate football players, there were significant differences between positions with catchers having higher ASMI values than pitchers and infielders, but not different than outfielders.  

We can also compare female collegiate athletes by calculating ASMI values in a group of female collegiate softball players that we examined (Czeck et al., 2019).  These female collegiate softball players had higher ASMI values than both elderly women Baumgartner et al. (1998) reported as well as the young adult females’ ASMI values Gallagher et al. (1997) reported. Interestingly, unlike male collegiate baseball and football players, there was no difference in ASMI values by position in these female collegiate softball players.

I guess the main question is: Should coaches, trainers, and athletes be concerned with the ASMI value? To be honest there may be some value to it, but coaches should probably be more concerned with symmetry between the left and right sides of the body. In addition, ratios that examine total upper to lean legs ratio (TULLR) or lean upper to lean legs mass ratio (LULLR) may be of more value than ASMI in evaluating athletes. Finally, the ASMI value has importance when studying older adults or trying to assess sarcopenia.

Baumgartner RN, Koehler KM, Gallagher D, Romero L, Heymsfield SB, Ross RR, Garry PJ, Lindeman RD. Epidemiology of sarcopenia among the elderly in New Mexico.  Am J Epidemiol 1998;147:755-763.

Bosch TA, Carbuhn A, Stanforth PR, Oliver JM, Keller KA, Dengel DR. Body composition and bone mineral density of division 1 collegiate football players: a consortium of college athlete research study. J Strength Cond Res 2019;33(5):1339-1346. 

Czeck MA, Raymond-Pope CJ, Stanforth PR, Carbuhn A, Bosch TA, Bach CW, Oliver JM, Dengel DR. Total and regional body composition of NCAA division I collegiate female softball athletes. Int J Sports Med 2019;40:645-649.

Dieli-Conwright CM, Courneya KS, Demark-Wahnefried W, Sami N, Lee K, Buchanan TA, Spicer DV, Tripathy D, Bernstein L, Mortimer JE. Effects of aerobic and resistance exercise on metabolic syndrome, sarcopenic obesity and circulating biomarkers in overweight or obese survivors of breast cancer: a randomized controlled trial. J Clin Oncol 2018;36:875-883.

Gaqllagher D, Visser M, DeMeersman RE, Sepulveda D, Baumgartner RN, Pierson RN, Harris T, Heymsfield SB. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J Appl Physiol 1997;83(1):229-239.
Kim, Y.-P.; Joh, J.-Y.; Kim, S.; Hwang, H.-S.; Shin, I.-S. The application of different appendicular skeletal muscle cutoff points and research definitions associated with health-related quality of life in Korean older people: Data from KNHANES 2008–2011. BMC Geriatr 2014;14:1–12.

Pongchaiyakul, C.; Limpawattana, P.; Kotruchin, P.; Rajatanavin, R. Prevalence of sarcopenia and associated factors among Thai population. J Bone Miner Metab 2013;31:346–350.

About the Author
Donald Dengel, Ph.D., is a Professor in the School of Kinesiology at the University of Minnesota and is a co-founder of Dexalytics. He serves as the Director of the Laboratory of Integrative Human Physiology, which provides clinical vascular, metabolic, exercise and body composition testing for researchers across the University of Minnesota.

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