Validity of an Inexpensive Hanging Scale During Isometric Shoulder Movements.

CONTEXT

Strength assessment is essential to prescribe exercise in sports and rehabilitation. Low-cost valid equipment may allow continuous monitoring of training.

OBJECTIVE

To examine the validity of a very low-cost hanging scale by comparing differences in the measures of peak force to a laboratory grade load cell during shoulder abduction, flexion, extension, and internal and external rotations.

DESIGN

Analytical study.

PARTICIPANTS

Thirty-two healthy subjects (18 women, age 26 [10] y, height 172 [8] cm, mass 69 [13] kg, body mass index 23 [4] kg/m2).

MAIN OUTCOME MEASURES

The dependent variable was the maximal peak force (in kilogram-force). The independent variable was the instrument (laboratory grade load cell and hanging scale).

RESULTS

No differences were observed while comparing the results. The intraclass correlation coefficients1,1 ranged from .96 to .99, showing excellent results. The Cronbach alpha test also returned >.99 for all comparisons. The SEM ranged from 0.02 to 0.04 kgf, with an averaged SD from 0.24 to 0.38 kgf. The correlation was classified as high for all tested movements (r > .99; P < .001), with excellent adjusted coefficients of determination (.96 < r2 < .99). Bland-Altman results showed high levels of agreement with bias ranging from 0.27 to 0.48.

CONCLUSIONS

Hanging scale provides valid measures of isometric strength with similar output measures as laboratory grade load cell.