The jump protocol with analysis of time to stabilization (TTS) can discriminate between persons with and those without functional ankle instability (FAI), according to researchers in the Department of Sport and Exercise Science at the University of Auckland in New Zealand. Persons with FAI have delayed trunk muscle reflexes to a sudden perturbation, supporting theoretical and experimental descriptions of proximal adaptations associated with ankle injury.
The researchers evaluated differences in measures of trunk and ankle stability between 12 study participants with FAI and 12 without, who were assessed for self-rated disability, TTS, and muscle reflex responses to sudden trunk perturbation. TTS results were calculated with an unbounded third-order polynomial, and trunk reflexes to a sudden unloading task were tested during flexion and extension movements.
Participants with FAI had worse perceptions of their ankle disability than those without but had the same vertical jump height. Their TTS times were delayed and their trunk muscle onsets were delayed in both flexion and extension. X-axis TTS times were identified by regression and analysis as significantly associated with extension latency times.
Delayed trunk reflexes have been shown to predispose persons to low back pain, the authors noted, although a cause-and-effect relationship between trunk and ankle instability was not established in this study.