Basic science
Reliability and agreement between 2 strength devices used in the newly modified and standardized Constant score

https://doi.org/10.1016/j.jse.2014.04.011Get rights and content

Hypothesis

The new and standardized test protocol for the Constant score (CS) provides new methodology, but different devices are still used for shoulder strength testing. It was hypothesized that strength measurements using the IsoForceControl (IFC) dynamometer (MDS Medical Device Solutions, Oberburg, Switzerland) would provide results comparable with the IDO isometer (Innovative Design Orthopaedics, Redditch, UK).

Materials and methods

Sixty healthy subjects, aged 19 to 83 years, were studied, with 5 men and 5 women in each of 6 ten-year age groups. The IFC and IDO were used in randomized order with an 8-minute interval between testing. Subjects performed 3 successive trials with strong verbal encouragement, with 1 minute between trials. The best strength performance was used in the analysis. The rater and subjects were blinded to all results.

Results

The IFC produced 0.28-kg (0.62-lb) higher strength values on average than the IDO (P = .002). The intraclass correlation coefficient (ICC2,1) was 0.97 (95% confidence interval, 0.95-0.98), whereas the standard error of measurement and smallest real difference were 0.43 kg (0.95 lb) and 1.2 kg (2.63 lb), respectively. The total CS and strength reached mean values of 92.4 points (SD, 6.2 points) and 8.2 kg (SD, 2.6 kg) (18.0 lb [SD, 5.8 lb]), respectively, and were negatively associated with age (r > −0.407, P ≤ .001). The strength values decreased (P ≤ .001) by 1.3 CS points per decade, and women had strength values that were 8 CS points lower on average than those of men of the same age.

Conclusions

The relative (intraclass correlation coefficient) and absolute (standard error of measurement) reliability between the IFC and IDO is excellent, indicating that performances reported from settings using the IDO are comparable with those recorded with the IFC in other settings.

Section snippets

Material and methods

Sixty adult volunteers (30 women and 30 men, aged 19-83 years) from the Copenhagen area were tested within a 2-week period. The following inclusion criteria were used: age 18 years or older, ability to give informed consent, ability to speak and understand Danish, and no current shoulder problems. Subjects were recruited by telephone or E-mail, according to 6 prespecified age groups, with 10 subjects (5 women and 5 men) in each of the following 6 age groups: 18 to 29 years, 30 to 39 years, 40

Results

Of the 60 subjects, 15 were students (bachelor’s or higher level), 31 were working, and 14 were retired; 55 used the right arm as the dominant arm during testing; 48 reported that they were physically active; 9 reported a previous injury in the dominant shoulder; and the mean age for all subjects was 49.4 years (SD, 18.5 years). The 15 students, with a mean age of 29.6 years (SD, 7.4 years), presented significantly (P ≤ .02) higher total CS and strength values than the 14 retired subjects (mean

Discussion

This study, following the newly standardized guidelines for CS testing,2 found excellent relative reliability (ICC, 0.97) and very low measurement noise at a group level (<1 CS point) between the 2 strength devices examined: the IFC and the IDO. Thus, an increase or decrease by 1 or more CS strength points can be considered a true difference for a group of subjects, enabling comparison between data recorded with the IFC and IDO. Furthermore, we found that the total CS and both the raw and

Conclusions

The results of this study show that performances of the standardized strength test in the CS, carried out with the IFC and the IDO, are comparable at a group level because high relative reliability and very low measurement noise were found. It is recommended that an individual be tested with the same device to measure change over time. Our findings that age and especially sex affected strength values and thereby the total CS of healthy subjects are in accordance with results previously

Disclaimer

The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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