Development and Evaluation of a New Measure for Muscle Tone of Ankle Plantar Flexors: the Ankle Plantar Flexors Tone Scale

Abstract

Takeuchi N, Kuwabara T, Usuda S. Development and evaluation of a new measure for muscle tone of ankle plantar flexors: the Ankle Plantar Flexors Tone Scale. Objective To develop and evaluate the reliability and concurrent validity of a clinically feasible measure for muscle tone of the ankle plantar flexors. Design Cross-sectional reliability and validity study of the Ankle Plantar Flexors Tone Scale. Setting Department of rehabilitation in a general hospital. Participants Patients (N=74) with cerebrovascular disease. Interventions Not applicable. Main Outcome Measures Muscle tone of the ankle plantar flexors was measured using the Ankle Plantar Flexors Tone Scale, the Modified Ashworth Scale (MAS), quality of muscle reaction with the Modified Tardieu Scale, and passive resistive joint torque with a handheld dynamometer. Intrarater and interrater reliabilities were assessed using the Cohen kappa coefficient (κ). Internal consistency was assessed using the Cronbach alpha (α). Concurrent validity was assessed with the Spearman rank correlation coefficient (ρ). Results The Ankle Plantar Flexors Tone Scale included 3 items: stretch reflex, middle range resistance, and final range resistance. Intrarater and interrater reliabilities and internal consistency of the Ankle Plantar Flexors Tone Scale showed moderate to excellent agreement (κ=.63–.94; α=.81). Concurrent validity of the Ankle Plantar Flexors Tone Scale was low to very high among the 3 items of the Ankle Plantar Flexors Tone Scale and existing measures. The Spearman rank correlation coefficient showed high to very high correlation between stretch reflex and quality of muscle reaction as indices of the central component (ρ=.85–.94). Middle range resistance and final range resistance as indices of the peripheral component had low to moderate correlation with passive resistive joint torque using a handheld dynamometer and MAS (ρ=.44–.68). Conclusions The Ankle Plantar Flexors Tone Scale allows measurement of ankle plantar flexor tone in greater detail than existing subjective measures and provides a reliable and valid method for research and clinical use.