ALMI: The Muscle Number We Track

Body fat percentage gets most of the attention. The number I pay closest attention to on a DEXA report is ALMI, because it tells us how much working muscle you carry and how that compares with people like you.

What ALMI is

ALMI stands for appendicular lean mass index. "Appendicular" means the arms and legs. The calculation is simple:

ALMI = lean mass in the arms and legs (kg) ÷ height in meters squared

We use the arms and legs because lean mass there is mostly skeletal muscle. Lean mass in the trunk also includes organs, which do not tell us much about strength or mobility. Dividing by height squared lets us compare people of different sizes fairly, since a taller person naturally carries more muscle.

As an example, a hypothetical man who is 5 foot 10 inches (1.78 meters) with 25 kg of lean mass in his arms and legs has an ALMI of about 7.9 kg/m².

What the percentiles mean

An ALMI value on its own is hard to read, so we compare it to age and sex percentiles. The 50th percentile is the middle: half of people your age and sex have more, half have less. The 25th percentile means three out of four have more.

There are also widely used cutoffs for low muscle. An ALMI below about 7.0 kg/m² in men or 5.5 kg/m² in women is considered low and is one part of the definition of sarcopenia.

One thing to keep in mind is that average is a moving target. Muscle declines with age in most people, so the average 70 year old already carries less muscle than is ideal. Sitting at the 50th percentile for your age is not the same as being in a good place. For that reason we generally aim higher than average, especially in the 40s and 50s, when there is still time to build a reserve before the decline speeds up.

Why it matters

Low ALMI predicts frailty, falls and loss of independence later in life. It also tracks with how well the body handles blood sugar, since muscle is where most glucose is stored.

The useful part is that ALMI responds to what you do. Strength training and adequate protein are the two main levers, and a repeat DEXA about every 6 months shows whether your ALMI is holding, rising or falling. A hypothetical 52 year old woman at the 30th percentile could see measurable movement over a year of consistent lifting.

That's the kind of thing we measure.

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This article is educational and is not medical advice.