Validity and reliability of a new device to simulate upper extremity work demands

Simulated work performance tasks in persons with neuropathic and myopathic weakness

OBJECTIVES

To determine the test-retest reliability of selected simulated work performance tasks in persons with neuropathic and myopathic weakness and control subjects, and the association between muscular performance during these work tasks and conventional isolated muscle group testing.

DESIGN

Measurement of three tasks performed on a work simulation device on two different days separated by 1 week. Associations between work task performance and previously reported strength measures in six muscle groups by hand-held dynamometry (HHD) were examined.

SETTING

Human performance laboratory of a university.

PARTICIPANTS

Convenience sample of ambulatory outpatients with hereditary motor and sensory neuropathy, type I (n = 9), myotonic muscular dystrophy (n = 10), and able-bodied controls (n = 11).

MAIN OUTCOME MEASURES

For work simulation, isokinetic peak torque and total work; and for HHD, maximal isometric torque.

RESULTS

Mean between-session differences for work simulation tasks ranged from -11% to +4% for peak torque and from -12% to +12% for total work; test sessions did not differ significantly for either patient or control groups. All groups had between-session intraclass correlation coefficients usually >.80, indicating good consistency. In general, correlations between peak torque during work simulation and HHD were strongest in the control group.

CONCLUSION

Persons with neuromuscular weakness reliably performed the simulated work tasks examined in this investigation. Work simulation tasks may be a useful tool to assess muscular performance in persons with neuromuscular weakness.

Reliability of isometric wrist extension torque using the LIDO WorkSET for late follow-up of postoperative wrist patients

The objectives of this study were to determine interobserver, intraobserver, and overall reliability of isometric wrist extension torque using the LIDO WorkSET and then to estimate the minimal level of detectable change using the standard error of measurement. A generalizability study was conducted on 18 postoperative patients. Primary outcome was mean torque of three trials. Variance components were used to calculate generalizability coefficients for intraobserver (G = 0.96), interobserver (G = 0.94), and overall reliability (G = 0.92). When the same therapist is evaluating a patient on different days, a change of more than 16 inch-lb is needed to be 90% confident that true change has occurred. A greater value for change (23 inch-lb) is required when different therapists evaluate a patient on different days. The LIDO WorkSET measures wrist torque in a reproducible manner in an applied setting. The testing protocol is sensitive to differences in wrist torque between individuals and tolerated in the late postoperative period.

Relationships among grip strength, work capacity, and recovery

The relationship between strength, fatigue, and work capacity is a central issue for occupational rehabilitation. Musculoskeletal impairments often are expressed functionally as a loss of strength. For work tasks that require strength, such impairments may have a detrimental effect on work capacity that is sufficient to be disabling. How important is strength as a component of work capacity? How do work capacity and strength affect recovery time from repetitive forceful upper extremity work ? A sample of 40 healthy subjects comprised of 20 males and 20 females was studied in a model that used the isotonic strength of each subject to set exercise levels for subsequent forceful repetitive gripping tasks. Resistance levels of 75%, 50%, and 25% of maximum were used for one-per-second repetitions until the subject could not maintain that pace. Isometric grip strength was measured after 1 minute of rest and after 5, 10, and 20 minutes. Results indicate that males and females do not differ in terms of their rate of recovery and that the best predictor of recovery time is the immediate measurement of strength loss following cessation of work activity.