Reliability of the Adapted Compensatory Arm and Leg Movements (A-CALM) Scale During Perturbation Treadmill Walking in Older Adults

Michael Schwenk^1*Mitzi Ramirez Mantilla¹Nina Marie Schmidt²Vanessa Haug³Christian Werner⁴Markus Gruber¹Michael Denkinger³Tim Fleiner⁵

• ¹Universitat Konstanz, Konstanz, Germany
• ²Carl von Ossietzky Universitat Oldenburg, Oldenburg, Germany
• ³Universitat Ulm, Ulm, Germany
• ⁴Universitat Heidelberg, Heidelberg, Germany
• ⁵Technische Hochschule Ulm, Ulm, Germany

Introduction: Reactive balance during walking is crucial for fall prevention, as it determines recovery from unexpected perturbations like slips and trips. Existing reactive balance assessments are complex and lab-based, lacking an easy-to-use alternative for broader application in clinical environments. The Adapted Compensatory Arm and Leg Movements (A-CALM) scale was developed to address this gap by providing an observer-based tool to evaluate compensatory balance reactions during perturbation treadmill walking. This study assessed its inter-and intra-rater reliability in fall-prone older adults. Methods: Eighteen participants aged 82 ± 7 years walked on the BalanceTutor® perturbation treadmill. Depending on assigned intensity levels, each received 8, 16, or 24 perturbations in mediolateral and anteroposterior directions. Compensatory balance reactions after each perturbation were video-recorded and evaluated by three trained raters using the A-CALM scale, capturing responses from minor adjustments to near-fall scenarios. Arm movements were rated on a five-point scale (1 = near fall, 5 = regular arm swing), while leg movements were rated on an eight-point scale (1 = near fall, 8 = normal walking), with intermediate scores reflecting varying recovery steps. Inter-rater reliability was assessed using Fleiss' Kappa, while intra-rater reliability over a two-week interval was evaluated using Cohen's Kappa. Results: Overall, 288 perturbations were recorded. The A-CALM scale demonstrated strong intra-rater reliability, with Kappa values of 0.85 (95%CI = 0.80 - 0.89) for arm scores, 0.80 (95%CI = 0.75 - 0.86) for leg scores, and 0.86 (95%CI = 0.83 - 0.90) for total scores, indicating a high level of consistency in the raters' assessments across time. Inter-rater reliability was substantial for arm scores (K = 0.67, 95%CI = 0.62 - 0.72) but moderate for leg scores (K = 0.48, 95%CI = 0.44 - 0.51) and total scores (K = 0.41, 95%CI = 0.38 - 0.44) with significant values in all analyses (p < 0.001). Conclusion: The A-CALM scale showed high intra-rater consistency and moderate-to-substantial inter-rater agreement, with greater reliability for arm than leg movements. Single-rater use is recommended to enhance stability, while future work should refine leg scoring and validate the scale in larger cohorts with outcomes like falls and functional decline.