1. Shoulder Joint Produced Weight-Bearing Mobility: Defining Gait
Gal, A,M., Chan, A.D.C. and Hay, D.C.
Hip joint weight-bearing contralateral mobility has been extensively studied providing generalized
results known as gait (Kirtley, 2006). In today's society special populations dependent upon the
shoulder joint (SJ) for primary weight-bearing mobility has become more prominent; ranging from
wounded Veterans to rising life expectancy; advanced pediatric surgeries to the introduction of para-
sports. A level of evidence describing SJ produced gait with equivalent reliability and validity to that of
the hip joint would provide this special population positive life-changing knowledge regarding
individualized muscular activation-relaxation, transferred reaction forces (GRF) from contact to the
point of rotation, gait cycle phases with initial/final contact locations, and biomechanical trends within
these phases. The purpose of this study is to define gait for the SJ using a double poling (DP) technique
found commonly in para-sports such as sledge hockey and sit-skiing (Gal, Hay & Chan, 2014). This
bilateral forward cyclical motion is similar to wheelchair propulsion (O'Connor & Robertson, 1998);
the addition of the shortened pole to the investigation allows for localized data acquisition through the
contact phase known as propulsion. Additionally, a rapidly developing para-sport will gain much
needed sport-specific evidence. The linear stroking cycle will be investigated using 3-dimensional
motion capture, surface electromyography for the SJ's primary superficial movers/stabilizers, and force
plate acquisition for left pick, right pick and sledge GRF. Participants will be tasked to contact the force
plates mid-cycle and from a static-start both at submaximal and maximal efforts. This study developed
and validated an anatomically correct solid-static prototype mimicking the average male torso with a
single arm having fixed elbow and wrist-stick joint angles with a sole dynamic SJ. The purpose of the
prototype is to identify baseline measures (BM) through the preparation phase and initial pick-plant
within the seated DP cycle; upright DP does not identify this additional phase within its cycle. BM will
be compared to musculoskeletal produced preparation phases of task-naive able bodied males and task-
experts physically disabled males. Dynamic movement investigations require assumptions to be made
involving internal forces; BM assist in their validation or rejection (Robertson et al., 2004).
Specifically, BM for preparation will provide evidence in determining the direct biomechanical
importance of this phase to the complete seated cycle. Pilot study findings (single task-naive abled
male) have suggested that SJ produced gait is a posteriorly driven motion; rotator cuff contributions
cannot be investigated due to their deep location within the SJ, however, are considered to be the
primary stabilizers (Veeger & van der Helm, 2007). Peak impact GRF are suggested to be produced late
propulsion phase with elevated initial impact GRF from pick-plant (Gal et al., 2014). Collectively, this
data will illustrate seated SJ gait outlining static-start, start cycle and the remaining phases with their
key components. Understanding biomechanical functions for SJ weight-bearing mobility will aid in the
prevention of trauma induced from overuse/overloading thus protecting the joint's structural integrity.
Evidence will provide knowledge improving muscular development and training, rehabilitation and
sport-specific growth having positive life-changing effects for this entire special population; pediatrics
to aging Veterans.
References:
Gal, A.M., Hay, D.C. and Chan, A.D.C. (2014). 2 and 3-dimensional analysis of the linear stroking
cycle in the sport of sledge hockey: Glenohumeral joint kinematic, kinetic and surface EMG muscle
modelling on and off ice. 13th 3D AHM, :108-111 ISBN 9782880748562.
Kirtley, C. (2006). Clinical gait analysis: Theory and practice. UK: Elsevier Churchill Livingstone.

2. O'Connor, T.J. and Robertson, R.N. (1998). Three-dimensional kinematic analysis and physiological
assessment of racing wheel-chair propulsion. APAQ Human Kinetics, 15:1-14.
Robertson, G.E., Caldwell, G.E., Hamill, J., Kamen, G. And Whittlesey, S.N. (2004). Research
methods in biomechanics. Human Kinetics, US.
Veeger, H.E.J. and van der Helm, F.C.T. (2007). Shoulder function: The perfect compromise between
mobility and stability. J Biomechanics, 40, 2119-2129.