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.

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INVESTIGATING THE SEATED DOUBLE POLING CYCLEIDENTIFYING BASELINE MEASURES FOR THE PREPARATION PHASE

Gal A.M. 1, Chan A.D.C. 1 & Hay D.C. 2

INVESTIGATING THE SEATED DOUBLE POLING CYCLEIDENTIFYING 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 forces2) 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)

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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