The Reliability and Validity of Two New Tests of Lifting Capacity. Alpert J, Matheson L, Beam W, Mooney V. Journal of Occupational Rehabilitation. 1991: 1(1).
Introduction
Machine-based tests of lifting-lowering capacity have become available in recent years and hold much promise. However, before any test can be used with confidence, its reliability and validity must be demonstrated.
The purpose of this study was to investigate the test-retest reliability of the isokinetic and gravity/inertia modes of the Lido Lift and of the EPIC progressive lifting capacity test (ELC #2). A second purpose was to investigate the validity of the Lido Lift tests by comparing them to the ELC #2.
Methods
Twenty-nine healthy male subjects employed in physically demanding occupations were tested on two separate occasions. Maximal lifting capacity tests were performed in the isokinetic and gravity/inertia modes on the Lido Lift and with the ELC #2. Pearson product-moment correlation coefficients were calculated to determine the test-retest reliabilities and to compare ELC #2 test values with isokinetic and gravity/inertia test values.
Results
Reliability for the Lido Lift isokinetic was r = .90 (p < .05), the Lido Lift gravity/inertia mode was r = .82 (p < .05), and the ELC #2 was r = .91 (p < .05). In terms of validity, the correlations between the isokinetic test, the gravity/inertial test, and the ELC #2 are presented in Table I.
| Type of Test | Absolute Value | Absolute / Body Mass | ||
|---|---|---|---|---|
| Test | Retest | Test | Retest | |
| Lido lift (isokinetic) | 0.64 | 0.72 | 0.68 | 0.73 |
| Lido lift (gravity/inertia) | 0.72 | 0.81 | 0.80 | 0.85 |
Because there was a relationship between body mass and strength in these subjects, body mass was used as a normalizing variable for both measures of lift capacity in subsequent regression analyses. The regression equations that describe these relationships are, for the isokinetic test, y = .44x + .445 (R-squared = .532) and, for the gravity/inertial test, y = .738x + .169 (R-squared = .755). The data on which these equations are based are presented in Table II.
Absolute lifting capacity values are classified by percentile for the test and retest in the isokinetic, gravity/inertia and ELC #2 tests in Table III. The average of the best three of the four peak force values that were obtained in the isokinetic test ranged from 47.3 to 125.0 kilograms, and at the retest ranged from 42.5 to 130.2 kilograms.
| %-ile Rank | LIDO Lift Isokinetic | LIDO Lift Gravity/Inertia | ELC #2 Isoinertial | |||
|---|---|---|---|---|---|---|
| Test | Retest | Test | Retest | Test | Retest | |
| 90th | 112.20 | 111.90 | 90.50 | 88.50 | 92.30 | 88.90 |
| 75th | 95.00 | 98.50 | 86.10 | 83.80 | 78.90 | 80.10 |
| 50th | 77.60 | 80.30 | 72.70 | 76.40 | 70.70 | 74.10 |
| 25th | 66.50 | 66.60 | 66.60 | 68.30 | 61.60 | 65.30 |
| 10th | 56.30 | 52.50 | 62.00 | 63.10 | 61.30 | 62.70 |
Discussion
The results of this study support the reliability of both Lido Lift tests and of the ELC #2. Test-retest correlations were sufficiently high to confirm the reliability of each test. Similarly, the correlations between each of the machine-based tests and the ELC #2, taken as a “gold standard” against which to compare machine performance, support the validity of the isokinetic and gravity/inertia tests. The strength of the relationship between the ELC #2 and each of the machine tests suggests that each can be used to cross-validate the other in a clinical setting.
The present study was the first to examine the reliability of the gravity/inertia and ELC #2 tests. The test-retest correlation coefficient was r = .81 for the gravity/inertia test and r = .90 for the ELC #2.
The test-retest correlation coefficient of r = .90 for the ELC #2 was higher than what was reported by Matheson and his colleagues (1990) for the original PLC (r=.77) and by Mayer (1988) for the PILE over this range (r =.87). The main difference in testing protocols for those tests and the tests used in the present study was the end-point criteria. There were three defined end-point criteria for the PLC I and for the PILE. These were 1) a psychophysical end-point, 2) an aerobic end-point, and 3) a percent of ideal body weight end-point. Subjects in the present study were instructed to continue until a “maximum safe lift” was reached which could be dependably reproduced 10 to 12 times per day. Each subject used his own perception of the load as a psychophysical end-point. There were no heart rate or ideal body weight constraints. The test-retest interval for the PILE was only one day, while the interval in the present study averaged 8 days. Also, as with the PLC I, in the ELC #2 the weights in the crate were masked and subjects were unable to visually evaluate the amount of each lift. It would seem unlikely that subjects were able to remember the amount of weight that was lifted during the initial test. Given the greater test-retest interval and the masked weights, the reliability of the ELC may actually be greater than the PILE.