Achilles tendinopathy, biomechanics with an adapted shoe

Shoe modification is one of the most common methods in prevention and treatment
of overuse injuries . Rocker bars are external shoe modifications which can be
prescribed for different ankle and foot pathologies.
Achilles tendinopathy is one of the most common overuse injuries, accounting
for 8-15% of all injuries in athletes . Achilles tendinopathy is characterized
by pain, tenderness and swelling of the Achilles tendon which is worse at the
beginning of and during sporting activity Some biomechanical risk factors such
as greater plantar flexion moment have been considered in developing of
Achilles tendinopathy . Rockered shoes by altering the motions and moments of
the ankle joint, could be a selective intervention for Achilles tendinopathy
During the push off phase of gait, calf muscles make a plantar flexion motion.
In response, ground reaction force (GRF) causes a dorsiflexion moment. The
hypothesis is that a proximally placed rockerbar makes the arm of the
external ankle moment shorter, resulting in less GRF and consequently decrease
in the amount of force on the calf muscles and the Achilles tendon . In case of
changes in ankle moment due to a rocker bar, the reduced propelling force which
normally is generated by calf muscles now should be compensated by other lower
extremity parts such as knee or hip muscles and this might also change the
angles of these joints.
It is also possible that with a proximally placed rockerbar the heel off phase
of gait cycle starts earlier and consequently, we expect that the calf muscles
will be active earlier as well. Besides that the amount of activity of the calf
muscles should be lower if our assumption is true. This question can be studied
by Electromyography (EMG).
Today, there are few of previously studies that investigate the kinetics and
kinematics changes of gait with rockered shoes. In two studies only normal
walking with rocker shoes has been investigated and there is only one study
focused on running biomechanics with rockered shoes but the control shoes used
are different brand
To our knowledge there is no study which investigates the biomechanical changes
of gait in response to a rockered shoe in patients with Achilles tendinopathy
and only one study has analyzed the effect of rocker bar on lower extremity
muscle activity by EMG.

Primary Objective: The primary goal of this research project is to evaluate the
effect of a rockered shoe on walking and running biomechanics in healthy
athletes and athletes with Achilles tendinopathy.
The reason for using a patient group is that people with Achilles tendinpathy
due to pain might adapt their walking or running patterns (biomechanics). Thus,
it is possible that people with Achilles tendinopathy show a different push off
than normal people. It is also possible that their basic gait pattern is not
changed, but that their adaptation to the proximally placed rockerbar is
different from healthy people.

Primary questions:
1. Does a rockered shoe change the external dorsi flexion moment of the ankle
during walking and running in healthy runners?
2. Does a rockered shoe change the external dorsi flexion moment of the ankle
during walking and running in runners with Achilles tendinopathy?

Secondary Objective(s): As secondary goals, we will investigate:
1) Muscle activity (m. Tibialis Anterior, lateral and medial m. Gastrocnemius)
changes in response to the rockered shoe
2) Changes in other biomechanical parameters of gait in ankle, knee and hip?
(Joint angles, forces, moments, power and Spatio-temporal parameters)

Two groups of subjects will be assessed separately and a within-group
comparison will be made. One group consists of 16 healthy active athletes and
one group consists of 16 athletes with Achilles tendinopathy. Subjects will
undergo kinetics and kinematics measurements in a single test session of about
1 hour. In this session, they will perform at least 3 walking and 3 running
trials with two pair of shoes (normal and Rockered shoes) in the Lab for
Movement Analysis of the Center for Rehabilitation at the University Medical
Center Groningen.

The entire study is only one session and will take about 1 hour. Each subject
will walk and run for 10 meters at a low a self selected speed in the Gait Lab.