Predictive models for isokinetic ankle muscle strength relating to age, mass, stature, sex and shoe size

The importance of measuring ankle muscle strength (AMS) has been demonstrated in research, clinical practice and sporting performance. Reference values or ranges for other joints are commonly used in the literature, however, there are limited reference values for ankle muscle strength. Although literature concerning reference ranges for AMS is evident, reference ranges for all of the eight reciprocal isokinetic movements of the ankle complex are not considered (Benfica et al. Reference values for muscle strength: a systematic review with a descriptive meta-analysis. Brazilian Journal of Physical Therapy, 2018; 22(5), 355–369). Therefore, due to the limitations in the current literature, the aim of this study is to produce a comprehensive set of predictive models that will provide reference ranges for concentric and eccentric plantar flexion, dorsiflexion, inversion and eversion. Following institutional ethics approval, in the first part of the study dominant ankle muscle strength was measured for concentric and eccentric plantar flexion and dorsiflexion (60°/s-1), and inversion and eversion (120°/s-1) in 120 healthy adults. A stepwise linear regression analysis was performed using sex, stature, mass, age, and shoe size as variables. Based on the results of this analysis predictive models for each of the eight isokinetic muscle actions were generated. In the second part of the study these models were used to predict the average ankle muscle strength of 15 healthy adults. Each of the eight ankle muscle strength measures taken from the validation population fell within the calculated reference ranges. A paired samples t-test indicated that there was no significant difference between the predicted and measured results (P < 0.05). The isokinetic AMS models presented here can be used to predict muscle strength in plantar flexion and dorsiflexion measured at 60°/s-1 and inversion and eversion measured at 120°/s-1 . These models could be used in a range of sporting and clinical settings such as examining relationships between AMS and both falling episodes and functional movement in the elderly as well as general ankle stability. A reference range could be used as an indicator of the effectiveness of intervention strategies and the extent of rehabilitation. Where reduced strength is due to pathology rather than injury the validated AMS models produced here could be used to inform on the progress of disease.