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VIII. ABOUT RESULTS
BMI =
( )
total body weight
height
2
kg
m
2
FFMI =
( )
fat-free mass
height
2
kg
m
2
SMI =
skeletal muscle mass
height
2
( )
kg
m
2
The Fat-free Mass Index (FFMI) and Skeletal Muscle Index (SMI) is an equivalent concept to
BMI, but using fat-free mass and skeletal muscle mass rather than total weight mass. This makes
it possible to determine body type, and the source of weight.
Fat-free Mass is the weight of the body after fat mass has been subtracted, and includes Skeletal
Muscle Mass. An increase in SMM (muscle gains) will cause an increase in FFM. However, the
opposite isn't necessarily true - an increase in FFM is not necessarily due to muscle. One major
reason for this is because a significant portion of FFM is water.
Combining the Fat-free Mass Index and Skeletal Muscle Index makes it possible for fitness
professionals to evaluate whether increases in FFM are due to muscle increase, or other factors
such as body water increase.
Cut-off points for risk of sarcopenia:
Various literature is available regarding the definition of cut-off points, but no universal standards
exist. Cut-off points can vary based on age and ethnicity. As a guideline though, the following
cut-off points can be considered for reference as indicators of lower than normal fat-free mass
and skeletal muscle mass:
FFMI: <16.7kg/m
2
(men) and <14.6kg/m
2
(women)
16
SMI: < 8.5kg/m
2
(men) and < 5.75kg/m
2
(women)
17.
Fat-free Mass Index and Skeletal Muscle Index
16. Schutz Y, Kyle UU, Pichard C. Fat-free mass index and fat mass index percentiles in caucasians aged 18-98 y. Int J
Obes Relat Metab Disord J Int Assoc Study Obes. 2002;26(7):953–960
17. Janssen I, Baumgartner R, Ross R, Rosenberg IH, Roubenoff R. Skeletal Muscle Cutpoints Associated with Elevated
Physical Disability Risk in Older Men and Women, Am J Epidemiol, 2004;159:413-41
