### Description

From measurement of the arm muscle area, it is possible to approximate the total body muscle mass. The mid-arm circumference is adjusted for the tricep skin fold thickness to adjust for subcutaneous fat. Further corrections are needed to adjust for the presence of bone and for the assumption of a circular mid-arm muscle compartment.

Technique:

(1) The mid-arm circumference is measured in centimeters midway between the olecranon process and the acromium.

(2) The triceps skin fold is measured in millimeters with calipers at the same level as the mid-arm circumference, on the posterior of the arm, over the long head of the triceps brachii.

uncorrected arm muscle area in cm^2 =

= ((((midarm circumference in cm) - (π * (triceps skin fold thickness in cm))) ^2) / (4 * π))

corrected arm muscle area in cm^2 for men =

= ((((midarm circumference in cm) - (π * (triceps skin fold thickness in cm))) ^2) / (4 * π)) - 10

corrected arm muscle area in cm^2 for women =

= ((((midarm circumference in cm) - (π * (triceps skin fold thickness in cm))) ^2) / (4 * π)) - 6.5

Notations:

• The triceps skin fold thickness is typically measured in millimeters. It is converted to centimeters for these equations.

Interpretation:

• The average error for arm muscle area by the equations is 7-8%.

• The minimum range for arm muscle area compatible with survival is 9-11 cm^2, with values < 9 cm^2 associated with death.

Limitations:

• The precision in performing skin-fold thickness measurements varies with the measurer, the site assayed, and the size of the subcutaneous fat mass.

• Edema and nonuniform fat distribution may result in misleading results.

• Skin-fold thickness is relatively insensitive to acute changes in nutritional status.

• The equations were developed for patients 20-70 years of age and may not apply to children, as the subtracted factor may be too large.

Upper Arm Muscle Area in square millimeters in Normal Whites (Frisancho)

Men

Women

Age

5th%

50th%

95th%

5th%

50th%

95th%

1-1.9

956

1278

1720

885

1221

1621

2-2.9

973

1345

1787

973

1269

1727

3-3.9

1095

1484

1853

1014

1396

1846

4-4.9

1207

1579

2008

1058

1475

1958

5-5.9

1298

1720

2285

1238

1598

2159

6-6.9

1360

1815

2493

1354

1683

2323

7-7.9

1497

2027

2886

1330

1815

2469

8-8.9

1550

2089

2788

1513

2034

2996

9-9.9

1811

2288

3257

1723

2227

3112

10-10.9

1930

2575

3882

1740

2296

3093

11-11.9

2016

2670

4226

1784

2612

3953

12-12.9

2216

3022

4640

2092

2904

3847

13-13.9

2363

3553

4794

2269

3130

4568

14-14.9

2830

3963

5530

2418

3220

4850

15-15.9

3138

4481

5900

2426

3248

4756

16-16.9

3625

4951

6980

2308

3248

4946

17-17.9

3998

5286

7736

2442

3336

5251

18-18.9

4070

5552

8355

2398

3243

4767

19-24.9

4508

5913

8200

2538

3406

4940

25-34.9

4694

6214

8436

2661

3573

5541

35-44.9

4844

6490

8488

2750

3783

5877

45-54.9

4546

6297

8458

2784

3858

5964

55-64.9

4422

6144

8419

2784

4045

6247

65-74.9

3973

5716

7453

2737

4019

6214