Objective: The purpose of this study was to compare the firmness of used mattress coil springs from the areas bearing greatest body weight versus areas subjected to little compression.

Methods: Weight-bearing springs (WBS) extracted from the center of the mattresses (N = 32), and non-weight-bearing springs (NWBS) extracted from the head/foot were of the same mattresses. To determine spring weakness, a 1296-g ingot was placed on the coil, and the compression distance was measured (cm). In addition, a gauge was used to measure the amount of pressure required to compress the coil springs a distance of 2 cm. Comparison between WBS and NWBS data were statistically treated using independent t tests and a 1-way analysis of variance.

Results: There were no significant group differences in weight or height in unloaded coils. However, there were significant (P < .05) differences in coil spring compression distance under load (WBS = 2.78 ± 0.34 cm; NWBS = 1.52 ± 0.39 cm) and force gauge compression (WBS = 1090.51 ± 88.42 g; NWBS = 1213.12 ± 71.38 g) between groups.

Conclusion: This study found that WBSs were weaker when compressed than the NWBS from used mattresses, and such characteristics may not be visually apparent in a mattress when not in use. Thus, coil springs in bedding systems may eventually fail to provide the initial structural support after use. Such sagging may compromise sleep posture with accompanying poor sleep quality and quantity.