An Investigation into Reference Values for Ankle Muscle Strength Using the Cybex Norm Isokinetic Dynamometer

Introduction and purpose
The importance of measuring ankle muscle strength (AMS) has been demonstrated in a variety of research, clinical and sporting areas. Isokinetic dynamometry is a common method of AMS measurement and it has been demonstrated that the Cybex Norm isokinetic dynamometer is a reliable and valid measure of AMS. Reference values are commonly used to contextualise the understanding of measured values, however no AMS reference values
using the Cybex Norm exist.
Design / methodology
A systematic review identified sixty papers which used the Cybex Norm to measure AMS. From those papers eight common methodological variables were identified and a protocol was produced based on these. It was demonstrated that the protocol was reliable and was subsequently used to test 100 participants.
Results
A stepwise linear regression analysis based on height, body mass, age, gender and shoe size
was performed to produce a predictive model for each of the eight measures of AMS. The reference models were validated by accurately predicting AMS in a validation group.Furthermore, a t-test showed there was no statistical difference between the predicted and actual measures of AMS.
The validated equations were then used to predict AMS in elite football players. The results
indicated that concentric and eccentric eversion AMS was higher than the predicted normal
range in the footballers. All other measures were within the predicted range.
Applications / limitations
The limitations of the predicted values are in the absolute accuracy. Whilst the predictive
equations have been validated for small groups, it is not possible to predict an individual’s
normal range. Further research into variables that predict AMS would enable a more accurate set of equations to be produced. The eight reference value equations described could be used in a range of sporting and clinical settings. For example in 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 effectiveness of rehabilitation. Where reduced strength is due to disease rather than injury an AMS reference range could inform on the progress of disease.
The research presented here has demonstrated the importance of eight different variables
in terms of isokinetic testing of the ankle. It was concluded that all eight of these variables
should be addressed when measuring isokinetic ankle strength and, furthermore, should be
taken into consideration when comparing results.
Originality / value
This thesis has produced eight novel validated reference equations which can predict normal
average AMS in groups of individuals using the Cybex Norm isokinetic dynamometer. These
equations could aid the understanding of disease progression, injury, rehabilitation and
athletic performance.