Matheson L, Mooney V, Grant J, Lichter R. Reliability of the EPIC Lift Capacity Test. Unpublished research paper. Employment Potential Improvement Corporation, 1994.
Any test of lift capacity must meet the following standards for tests and measurement developed by professional and governmental entities:
- Safety: When used properly, the test must not be expected to lead to injury;
- Reliability: The test score must be dependable across evaluators, evaluees, and the date or time of test administration;
- Validity: The test score must measure what is intended to be measured and must either predict or reflect performance in a target task;
- Practicality: The direct and indirect costs of the test procedure must be reasonable;
- Utility: The test procedure must meet the needs of the evaluee, referrer, and payor.
The first four standards relate to each other in a dynamic manner. A decision to emphasize one of the standards usually will detrimentally affect one or more of the other standards. Without adequately addressing the first four standards, utility cannot be achieved.
Strength as an Indicator of Lift Capacity
The evaluation of strength has been used as an indicator or predictor of lift capacity based on the hypothesis that a “weak link” in the biomechanical system determines the impaired person’s maximum load and that the weak link is the impaired biomechanical segment. Although lift capacity is not simply a function of strength, tests of strength often are used to estimate and predict lift capacity. Strength has been defined as the maximum voluntary force a worker is willing to exert in a single attempt.
Isoinertial strength is measured in a dynamic test in which the muscle is contracted in order to move a constant mass that is incremented on a blind equal-interval basis. Isoinertial lift capacity is tested using an approach that involves progressive loading of a container moved by the evaluee at a set frequency over a set vertical range. Isoinertial testing is distinguished from psychophysical lift testing by the former test’s structured and progressive, equal-interval nature.
A New Test Design
The current authors surveyed available tests and found important objections to each. The psychophysical tests lacked adequate safeguards for use with impaired persons. The isometric and isokinetic tests required expensive equipment, lacked well-developed standardized instructions, or both. Although isoinertial tests appeared to be the most promising, available tests did not adequately address the professional standards. Given these concerns, a project to develop a new lift capacity test was undertaken.
The equipment that is required to administer the ELC can be built by the user. Commercial versions of the equipment are also available. The ELC requires a standardized lifting crate and a set of masked weights, a heart rate monitor, and sturdy shelves.
Every evaluation task must have clearly defined parameters. The key parameters are starting height and vertical displacement, frequency and pace, horizontal displacement and starting load. Each of these parameters is “designed in” to the protocol. Additional parameters include:
- Perceived Exertion: A “Rating of Perceived Load” scale rates “heaviness” with a low-end anchor that reflects perception and a high-end anchor that reflects safety.
- Heart Rate Performance Window: The ELC uses risk factor screening and a two-level heart rate performance system.
- Load Guidelines: There are twelve biomechanical guidelines. These are used to identify the point in the test at which the load exceeds an acceptable maximum.
Purpose of Current Research
Stability within the evaluee and across evaluators are fundamental requirements of a test. The purpose of Study #1 was to formally study intra-rater reliability of the ELC in a sample of healthy subjects (n = 26). The purpose of Study #2 was to study inter-rater reliability of the ELC test in a sample of subjects who were disabled (n = 14).
Procedures: On the first occasion of testing, all subjects were tested on the ELC using the standard procedures. There was no target load. Subjects returned for re-testing 5 days to 11 days after the initial test. For the disabled subjects, a different evaluator was used to allow inter-rater comparisons. After the retest, all subjects were contacted by telephone for next-day follow-up.
ELC Test Performance: None of the subjects terminated any test because of work behavior or inability to complete all task segments. Four of the disabled subjects stopped one or more tests in the battery because of heart rate limits while this occurred with only one healthy subject. The majority of the disabled subjects’ tests were terminated by self-perception report of maximum or achievement of the psychophysical rating scale maximum, frequently with concordance between these measures. None of the disabled subjects achieved the load guidelines. In contrast, 18 (69%) of the healthy subjects achieved or exceeded the load guidelines.
Test Safety: None of the subjects reported injuries as a consequence of participation in the test. Most reported next-day soreness in the hamstring muscles. These resolved with the use of non-prescription analgesics. None of the disabled subjects reported new symptoms.
Test-Retest Reliability: Reliability on a test-retest basis was evaluated through the use of Pearson product-moment correlations. These data are presented in Table 1.
|aTwo cases deleted with missing values.|
All correlations are statistically significant below p = .01. Through the use of Fisher r-to-Z transformation procedure to compare the two samples on each sub-test, none of the correlation coefficients was found to be significantly different.
The technical difficulties encountered in the evaluation of the lift capacity of adults with spinal impairment have been addressed in the development of the ELC by following published technical standards. The present studies considered the safety and reliability of the ELC.
In terms of safety, the current studies demonstrate that the ELC is acceptable. None of the healthy or disabled subjects who were formally studied in this research project reported new injuries or exacerbation of injuries. The current studies also demonstrate acceptable intra-rater reliability and inter-rater reliability within a laboratory setting.