1. The Shoulder Joint’s natural architecture produces
the largest range of motion. Mechanical design
warrants a reduction in structural integrity
throughout 3-dimensions with diminished
confidence to produce loadbearing stability. The
hip joint’s architecture promotes structural
compliancy through maximal loadbearing mobility.
.
INVESTIGATING THE SEATED DOUBLE POLING CYCLE
IDENTIFYING BASELINE MEASURES FOR THE PREPARATION PHASE
Gal A.M. 1, Chan A.D.C.1 & Hay D.C.2
INTRODUCTION PURPOSE
Figure 1: Sledge hockey players sit strapped into
a plastic/carbon-fibre bucket on top of 2 skate
blades, legs extended down an aluminum frame
to a footrest balanced by a triangular contact
point, the front. Miniature sticks consist of left
and right elongated blades with metal picks/
teeth at the opposite end to grip the contact
surface.
A previously validated methodology developed for the prototype (EX)
was used in conjunction with a Vicon motion capture system and
Kistler force-plate to investigate the downward movement and
contact force of the shoulder joint-centre (SJC) ; data were collected
at 200Hz and 800Hz, respectively. A velcro strap was attached to the
forearm’s centre-of-gravity (CoG), raised to test shoulder start angles
above, below and at the horizon. Markers were placed at the joint-
centres (shoulder & elbow), CoG (upper arm & forearm), anterior and
posterior wrist, and blade, joint and pick of the stick; markers were
14mm in diameter. Three useable trials investigating fixed joint angle
combinations at the elbow 120o , 135o and 150o , and wrist-stick at
45o were acquired and processed (time-normalized pre contact to the
initiation of stick recoil) using MATLab for both trajectory (zero-lag
fourth-order Butterworth LPF 12Hz) and force plate (no filter due to
rapid contact duration <5ms) data. A validated mathematical model
(CN) was used as a control (2-dimensional [x,z]).
Paralympic Sledge Hockey is a high-
velocity high-impact sport dependent
upon the shoulder’s structural
integrity in two ways:
1) the nature of the sport sanctions
full body-contact; the shoulder is the
most prominent exterior point of
contact constrained to withstand/
absorb impact forces
2) locomotion is produced solely
from the shoulder joint in a double
poling fashion where speed and
quickness are dependent upon force-
duration impact cycles (Impulse
[N∙s]).
Figure 2: Upright (top) and Seated (bottom) doubled poling consist of propulsion (PRO) the contact phase
picks with terrain; pick-plant to pick-off, and recovery (REC) return phase of the cycle; no direct contact with
terrain. Seated double poling introduces a third phase preparation (PREP); short pole length full arm
extension to pick-plant (sledge hockey/alpine sit-skiing) or longer pole length pick-off to initiation of return
of forward cycle (cross country sit-skiing). Direct biomechanical benefit for the addition of this phase into the
complete cycle is currently unknown warranting investigation.
RESULTS
CONCLUSION
Identify baseline measures for the preparation phase within the linear
stroking cycle for the sport of sledge hockey.
METHODOLODY
Figure 3. A solid-static prototype
(top – NOT test position)
architecturally designed from US
Marine Corp personnel data and
standardized parameters for
segment shape, length and mass
was built to represent a single
armed average adult male (80kg)
with dynamic shoulder joint. The
prototype was fastened to a
sledge hockey sledge (fixed hip
angle +40o from the horizon) and
weights placed in the bucket to
allow free stance. Two plastic
washers (4.00cm in diameter)
were used to decrease friction at
the dynamic joint. Two 1.30kg
wrist-weights were attached to
the upper arm in a stretched out
fashion (lateral & medial) with an
overlap at CoG mimicking arm
morphology. A 1.20kg ankle-
weight was attached to the lateral
forearm in a stretched out
fashion.
Obtaining baseline measures for
external forces concerning the
upper limb throughout this
downward movement allows for
comparison against internal forces
either supporting or dismissing
the assumptions required to be
made when investigating dynamic
movement.
Bernardi, M., Janssen, T., Bortolan L., Pellegrini, B., Fischer, G. & Schena, F. (2013). Kinematics of cross-country sit skiing during a paralympic race. Journal of Electromyography and
Kinesiology, 23, 94-101.
Gal AM, Hay DC & Chan ADC. (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.
Gal AM, Chan ADC & Hay DC. (2015). Validating a solid-static single-armed male prototype tasked to produce dynamic movement from the shoulder through the preparation phase.
IFMBE Proceedings.
Holmberg, H., Lindinger, S., Stoggl, T., Eitzlmair, E. & Muller, E. (2005). Biomechanical analysis of double poling in elite cross-country skiers. Medicine & Science in Sports & Exercise,
37(5):807-818.
Lomond, K. & Wiseman, R. (2003). Sledge hockey mechanics take toll on shoulders: Analysis of propulsion technique can help experts design training programs to prevent injury.
Journal of Bio-mechanics, 10( 3): 71-76.
Veeger, H.E.J., & van der Helm F.C.T. (2007). Shoulder function: The perfect compromise between mobility and stability. Journal of Biomechanics, 40, 2119-2129.
Acknowledgement M. Lamontagne (Human Movement Biomechanics Laboratory), B. Hallgrimsson (Industrial Design) & M. Haefele (Research Assistant)
1 2
Understanding baseline measures concerning the upper limb in this downward
moving phase of the cycle will provide an evaluation tool used in subsequent
research comparing musculoskeletal produced shoulder dependent locomotion
in the sport of sledge hockey. This study has determined that non-contractile
forces transferred onto the SJC were about 22X arm weight (5kg), near identical
to CN. Average RxnNet from EX was 1083N compared to CN 1080N; percent
difference equalling 0.28% suggesting all forces transfer onto the SJC. Further
investigation is required as each elbow angle ranked greatest; extended
forearm produced the largest RxnVert compared to a flexed forearm, highest
RxnHorz. Percent difference for RxnVert and RxnHorz between EX and CN were
2.01% and 0.32%, respectively, with EX producing slightly higher values. Finally,
45.3Nm of torque occurred anticlockwise about the SJC. Trauma to the shoulder
joint is inevitable for these athletes, however, understanding weight-bearing
shoulder produced locomotion will reduce the risk of overloading this highly
mobile joint in turn reinforcing structural integrity. From this evidence maximal
force transfer producing sledge propulsion will promote sport-specific
advancement in a necessary but basic skillset; the linear stroking cycle.
Figure 4: Peak RxnVert (red) for 120o (top left), 135o (top right) and 150o (bottom left) elbow angles were 860N, 810N and
1013N, respectively. Peak RxnHorz (green) for 120o, 135o and 150o were 716N, 571N and 629N, respectively. Peak RxnML
(blue) for 120o, 135o and 150o were 187N, 240N and 118N, respectfully. Peak RxnNet (bottom right) for 120o (__), 135o (--),
150o (-.-) were 1134N (23.1∙BW), 1119N (20.3 ∙ BW) and 997N (22.8 ∙ BW), respectfully. *BW = arm mass (49N)
REFERENCES & ACKNOWLEDGMENT