Assessing isometric ankle abductor strength with a novel device: Reliability and electromyographic validation

Area of Science:

• Biomechanics
• Musculoskeletal Physiology

Background:

• Ankle abductor (ABD) strength is crucial for lateral ankle stability, primarily due to the peroneal muscles.
• Previous research has lacked reliable methods to measure isolated ABD strength and correlate it with peroneal muscle function.

Purpose of the Study:

• To evaluate the intra-session test-retest reliability of a novel isometric ankle ABD strength assessment device.
• To examine the construct validity of this device using surface electromyography (EMG) to assess peroneal muscle activation.

Main Methods:

• A custom-built, examiner-independent device was used for isometric ankle ABD strength testing in two independent samples (n=24 for reliability, n=15 for EMG validity).
• Reliability was assessed using Intraclass Correlation Coefficient (ICC), Standard Error of Measurement (SEM), and Minimal Detectable Change (MDC95).
• Surface EMG recorded activity of peroneus longus, peroneus brevis, and tibialis anterior during isometric ABD efforts at varying force levels (30%, 50%, 70% MVC).

Main Results:

• The novel device demonstrated good-to-excellent intra-session test-retest reliability (ICC: 0.82–0.94) with acceptable SEM and MDC95 values.
• EMG analysis revealed a clear, force-dependent activation pattern in the peroneal muscles (peroneus longus and brevis) during ankle ABD.
• Tibialis anterior muscle activity showed more variability and a less consistent force-dependent response compared to peroneal muscles.

Conclusions:

• The developed device provides reliable and consistent measurements of isometric ankle abductor strength.
• The device's ability to elicit specific peroneal muscle activation patterns validates its use in assessing lateral ankle stability.
• This tool supports clinical evaluation of ankle stabilizers and can inform rehabilitation strategies for ankle injuries.