Brandon Winward and Faculty Mentor: Ty Hopkins, Exercise Science Department
Inversion ankle sprains are common and are caused by sudden inversion
stresses during weight-bearing movement which causes the foot to roll under and
inward.1 Ankle sprains result in tearing or stretching of ligaments and muscles, which
reduces ankle stability.2 After a single ankle sprain, up to 80% of people suffer repeated
sprains, which often develop into chronic ankle instability (CAI).3 Research has shown
CAI patients often exhibit delayed lower leg muscle reaction time and restricted
dorsiflexion range of motion (DROM).2
Faster muscle reaction time to inversion stress may reduce tissue damage via
protective forces.4 We hypothesized that restricted DROM may contribute to slower
muscle reaction time. For example, forces experienced during an inversion ankle sprain
pull the talus forward relative to the tibia. This faulty ankle joint positioning limits DROM.
This may lead to greater risk of reinjury due to a shorter distance to reach maximum
inversion which ultimately means the body has a shorter time to respond. As such,
restricted DROM, defined as a strong predictor for ankle reinjury,9 would place the foot
in a more injury-prone position.8
Many muscle reaction time studies5-7 have used a standing inversion platform
with trap doors that fall to 30 degrees of inversion, however, these studies5-7 provide
limited information to understand dynamic characteristics of muscle reaction time
because ankle sprains more often occur during dynamic movement rather than
standing. To evaluate dynamic muscle reaction time to simulated ankle sprains, Dr.
Hopkins developed a walkway inversion platform (Fig. 1).4 Previous work4 compared
CAI patients to healthy controls. However, this common comparison does not consider
a between-patient variability in a CAI population. Since each CAI patient would have a
different level of deficits and/or severity after ankle injury, we determined it necessary to
consider subgroups of CAI. This speculation led us to consider the idea that some CAI
patients may not have restricted DROM as opposed to most other CAI patients. As
restricted DROM resulted in 5 times greater risk of ankle reinjury compared to normal
DROM,10 we sought to see whether restricted DROM in CAI patients would reveal
greater risks of ankle reinjury during walking. If this hypothesis is correct, clinicians will
need to approach this “homogenous” injured population differently for treatment.
This study was a controlled laboratory trial. We recruited 20 health controls (10
male, 10 female) and 45 CAI subjects (21 male, 24 female) to participate. Our sample
size was determined by power analysis, a priori, using previous data.4 Subject exclusion
criteria included lower limb surgery, fracture, and/or neurologic disorders in their lifetime
and sport-related injury in the past 3 months. Subject inclusion criteria included a history
of physical activity of at least 90 min/week in the past 3 months.
Each participant completed a survey that included two valid and reliable selfreported
disability questionnaires: Foot Ankle Ability Measure Activities of Daily Living
(FAAM ADL) and FAAM Sports. Healthy controls were defined as those with no
previous ankle injury and a normal score (100%) on both FAAM ADL and FAAM Sports.
CAI subjects were defined to have (i) at least 2 ankle sprains on the same side, (ii) a
score of ≤ 90% on the FAAM ADL, and (iii) a score of ≤ 75% on the FAAM Sports.
CAI subjects were assigned to either the limited DROM or normal DROM group
based on DROM during a weight-bearing lunge test. The cutoff score for group
assignment was determined to be 45 degrees of DROM, which is average for healthy
The aforementioned inversion walkway platform consists of seven 1.22-meter
segments. The central three segments feature bilateral trapdoors. Any one of the six
trapdoors can be triggered to fall to 30 degrees of inversion when stepped on (Fig. 1).
Subjects were provided headphones with a built-in metronome set to 110
beats/minute and were instructed to walk along the platform to the beat. During a trial
one or none of the six trapdoors was triggered. Data was collected for 14 successful
trials (seven for each leg) of stimulated inversion during walking.
Muscle reaction time was measured using EMG electrodes that sense changes
in voltage associated with muscle activation. Electrodes were placed on the muscle
bellies of the gastrocnemius, peroneus longus, peroneus brevis, tibialis anterior, gluteus
maximus, and gluteus medius based on SENIAM EMG guidelines.
For 3D joint kinematics, such as ankle joint angular velocities, we used 12 highspeed
cameras (Vicon, Oxford, UK; 1200 Hz) that tracked the movement of reflective
markers attached to anatomical landmarks on each subject. Visual 3D software was
used to calculate joint kinematics.
No results are currently available for this study. Prolonged IRB approval and
mechanical issues with the inversion platform resulted in unforeseeable delays. Data
collection is now complete, but additional time is needed for analysis and interpretation.
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