Learning effects associated with the least stable level of the biodex® stability system during dual and single limb stance.

The Biodex® Stability System (BSS) has high test-retest reliability when stable (high) resistance levels are used. However, reliability data for lower stability levels, associated with more pronounced learning curves, are rare in the existing literature. Thus, it is likely that BSS scores obtained from lower stability levels require greater familiarization (i.e. practice) to achieve a stable score both within and between test sessions. Therefore, the purpose of this investigation was to determine if a commonly reported 6 trial sequence (3 practice trials, 3 test trials) used with the BSS can achieve a stable within session score on the lowest stability level (i.e. level 1). The secondary purpose was to evaluate the test-retest reliability of the lowest BSS resistance level over a 10-week period. Twenty sedentary university students (11 male, 9 female; age: 21.5 ± 1.9 years, height: 1.7 ± 0.1 m, weight: 66.3 ± 12.1 kg, BMI: 22.4 ± 2.3) voluntarily participated. Participants completed two test sessions separated by 10-weeks. Twelve, 20-second trials (six dual limb stance, six single limb stance on the dominant limb) on the lowest stability level were completed during both test sessions by all participants. A stable within session dual and single limb stance score was achieved with a maximum of 3 familiarization trials. Reliability ranged between poor and good across all outcomes but all outcomes had large minimal detectable change scores. At least 3 stance specific familiarization trials are needed to achieve a stable BSS score within a single test session on the lowest resistance level. However, the inconsistent reliability and high minimal detectable changes scores suggest that the lowest resistance level should not be used as an objective marker of rehabilitation progress over extended periods of time (e.g. 10-weeks). Key pointsLevel 1 BSS scores should not be used as a test setting to assess rehabilitation.Familiarization trials should not be underestimated by researchers/clinicans.Lower stability levels on the BSS may not be appropriate for use as an objective marker of progression due to poor reliability of the scores over time.