Measuring abdominal muscle weakness in patients with low back pain and matched controls: a comparison of 3 devices

To compare 3 hand held devices used to measure isometric abdominal muscle strength: the adapted sphygmomanometer, the vigorometer and the Penny & Giles myometer.

Subjects were men, aged 22 to 43 years. Fifteen had a history of low back pain and 18 age matched controls had no low back pain. The test position was a half sit-up at 45 degrees, knees at 90 degrees, feet secured. The single observer applied pressure with one of the devices downwards, just below the sternal notch, while the patient maintained that position. Order of methods was random, controlled by a series of 3 x 3 Latin squares. The vigorometer and myometer were calibrated to mm Hg. Even numbered subjects were tested twice; odd numbered subjects had their measurements timed.

One subject was unable to complete the study. Subjects with low back pain had abdominal muscle strength 38.8 mmHg lower than healthy controls [F(1,62) = 72.84, P2 < 0.01]. Order of measurements was similar [F(2,62) = 1.19, P2 = 0.31]; instruments differed [F(2,62) = 27.94, P2 < 0.01]. Duplicate readings were similar (minimum P2 > 0.10); all 3 devices detected significant differences between the 2 groups (P2 < 0.01); mean measurement time was 19 s and time to measure with each device was similar (P2 = 0.70).

All 3 instruments performed equally well. Since the sphygomanometer is available at about 1/5 the cost of the vigorometer and 1/12 the cost of the myometer, it is the preferred instrument.