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Sledge hockey is the fastest growing parasport since its Paralympic debut in 1994; it is full body contact seated hockey having very limited scientific evidence supporting the high-velocity high- impact nature, none involving its biomechanics or how to move. Propulsion in sledge hockey is very similar to double-poling in cross country skiing. Previous investigations have suggested double-poling consists of two phases: 1) propulsion picks in contact with surface, and 2) recovery picks not in contact with the surface. Seated double-poling introduces a third phase, the location of this phase is sport dependent and determined by pole/stick length: 3) preparation full arm extension to initial pick contact for shorter stick lengths such as in sledge hockey. Why is the phase location sport dependent? Why is there a third phase sitting and not standing? These answers are unknown ; suggestions lead us to believe there is a change in biomechanical parameters like limb movement and muscular activation. Do you understand how you walk, or do you just assume the body knows what it is doing? How we move or produce locomotion has been of high interest to biomechanist and kinesiologist since the early 1900’s. Over the years research has been collected, shared and combined to create the gold standard for hip produced locomotion commonly known as gait (Fig 1). This gold standard identifies key components throughout the gait cycle assisting in the explanation of this primary means of movement or what exactly happens when we walk. ABSTRACT SLEDGE HOCKEY This study will define gait for shoulder produced locomotion using a double-poling technique from the sport of sledge hockey; an illustration similar to the gold standard will be developed (Fig 5). Additionally, the importance of the preparation phase to the overall cycle will be determined. PURPOSE Figure 1. The gold standard for analyzing gait produced from the hip joint; within this illustration bone, muscle and outer skin movements are tracked throughout the cycle demonstrating the importance of internal contributions to the observable external movement as a whole. This illustration is a representation of the foundation used to develop this study’s investigative purposes (Wolters Kluwer Health, 2011). Participants in the study are healthy elite adult male sledge hockey players medically diagnosed with a physical impairment (task-experts), and a control group of healthy able-bodied physically active adult males with no or limited knowledge of the physical tasks (task-naive). An indoor 3- dimensional motion capture system (Vicon) will be used in conjunction with surface electromyography (sEMG) electrodes and force plates (Fig 6). Primary superficial movers and stabilizers for shoulder-dependent weight-bearing locomotion includes the biceps brachii, deltoid threesome (anterior, medial, posterior), latissimus dorsi, pectoralis major, trapezius and triceps brachii. A note should be made that the rotator cuff is ultimately the primary stabilizer for the shoulder joint; however the deep location of this four muscle cuff presents issues for sEMG acquisition during dynamic movements. Ground reaction forces from pick-plant to pick-off will be acquired from force plates in an offset ‘t’ formation isolating the left and right sticks, and sledge/participant data. Anthropometric measurements for 3-dimensional reconstruction, and impairment history will be collected for categorization purposes. METHODOLOGY REFERENCES & ACKNOWLEDGMENT Acknowledgment: M. Lamontagne (Human Movement Biomechanics Laboratory), B. Hallgrimsson (Industrial Design) and M. Haefele (Research Assistant) 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. 13 th 3D AHM, 108-111. ISBN 9782880748562. Gastaldi L, Pastorelli S & Frassinelli S. (2012). A biomechanical approach to paralympic cross-country sit-ski racing. Clin J Sports Med, 22, 58-64. Goosey VL, Campbell IG & Fowler NE. (2000). Effect of push frequency on the economy of wheelchair racers. Med Sci Sprts Exerc, 32(1), 174-181. Holmberg H, et al. (2005). Biomechanical analysis of double poling in eltie cross-country skiers. Med & Sci in Sports & Exerc, 37(5), 807-818. Kirtley C (2006). Clinical gait analysis: Theory and practice, UK: Elsevier Churchill Livingstone. 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. J Biomechanics, 10(3), 71-76. Plexus Performance & Rehabilitation. (2013). [Graphic illustration gait Mar 17, 2014]. Wolters Kluwer Health, 2011. Retrieved from http://plexuspandr.co.uk/uncategorized/gait-a-simple-break-down/ O'Connor TJ & Robertson RN. (1998). Three-dimensional kinematic analysis and physiological assessment of racing wheelchair propulsion. APAQ Human Kinetics, 15, 1-14. Robertson GE et al. (2004). Research methods in biomechanics. US: Human Kinetics. Veeger HEJ & van der Helm FCT. (2007). Shoulder function: The perfect compromise between mobility and stability. J Biomechanics, 40, 2119-2129. A sub-study designed, implemented, and validated a methodology to be used to determine baseline measures during the preparation phase of seated weight-bearing locomotion. A subsequent sub-study used this methodology to examine baseline measures throughout the identified range of elbow angles 120 o , 135 o and 150 o . Understanding external forces at baseline measures (solid body weight and gravity) allows for valid assumptions to be made or dismissed concerning internal forces within the human body (bone and muscle movement). Dynamic biomechanical analysis requires assumptions involving internal and external parameters when producing a movement; it is unclear about what happens under the skin. In order to determine baseline measures of external movement produced by the shoulder joint, a solid-static anatomically correct (80kg male) prototype was tasked to produce the preparation phase with dynamic shoulder start angles (-10 o ,0 o and +10 o to the horizon). The prototype was fastened to a sledge hockey sledge with fixed hip angle (40 o ) from the horizon and weights placed in the bucket to off-set the balance allowing free stance; a velcro strap was attached to the forearm’s centre-of-gravity (CoG) and raised to where the neck would be located, then released allowing the arm to drop down and pick to contact the force plate (Fig 7b). Three useable trials where collected for each start angle and elbow angle. 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 with an overlap at CoG mimicking arm morphology, and a 1.20kg ankle-weight was attached to the forearm. BASELINE MEASURES Trajectory and reaction forces created through preparation for baseline measures were evaluated using a standard Newton-Euler mathematical model in conjunction with the 3- dimensional motion capture system and force plate (Fig 7). Trajectory data illustrated similar curvature for all respective elbow angles showing a decrease in arc-slope as the elbow angle increased (Fig 8); similar to shortening the radius of a pendulum. Reaction forces were determined to produced torque in an anticlockwise direction about the shoulder; initial impact pushes the arm back up into the shoulder joint (Fig 9). Average vertical reaction forces indicated that the lower the start angle the greater the reaction force 273.7N, 553.9N and 716.9N for +10 o , 0 o and -10 o , respectfully for all three elbow angles (Fig 10). From this baseline evidence preparation initiation should begin slightly below the horizon in order to produce the greatest non-contracting force to propel the sledge. Focus on muscular activity from the primary locomotors has determined that propulsion is a bilateral, posterior musculoskeletal dominant movement. Segmented phase data suggests that the double-poling is a 'push' motion executed by the triceps as the dominant muscular force, followed by the latissimus dorsi then the posterior deltoid. Peak reaction force is suggested to be produced late contact phase causing clockwise torque about the shoulder; the largest reaction force pushes the arm forward and up into the shoulder joint (Fig 9). RESULTS &DISCUSSION Preparation Phase • Start Location • What does it do? Contact Phase • Initial Contact • Peak Reaction Force • Push Off Recovery Phase Did you know that on average there are 86 000 Canadians with spinal cord injuries with an estimated 4300 new cases each year? How do they walk? Shoulder produced locomotion has not been as extensively studied leaving a gap of unknown information. Wheelchair propulsion occurs in a forward cyclical pattern very similar to walking (Fig 2). Since gait is the pattern of limb movement a connection is created and shoulder gait can be investigated and defined. Using the gold standard developed for hip gait, this study identified key components for investigation (Fig 3). First, there must be a contact phase to allow for a change in momentum, Newton’s First Law of Motion – Law of Inertia; during this phase there must be an initial contact, peak reaction force and push off. These are investigated using Newton’s Second and Third Laws of Motion – Law of Acceleration and Law of Motion (equal opposite reaction), by observing the reaction forces throughout the contact phase. Next the cycle must return in a contact free phase, sometimes this phase is known as recovery. However, it is difficult to evaluate a rolling wheel; wouldn’t it be much simpler if there was a focused contact point? The sport of sledge hockey uses this same forward cyclical pattern to produce movement from two miniature sticks, picks at one end and blades the other (Fig 4). Figure 3. Key components outlined from the gold standard of hip produced gait for this study assisting in defining shoulder produced gait; evaluation of these components integrates Newton’s 3 Laws of Motion (Inertia, Acceleration and Motion). Figure 2. Wheelchair propulsion cycle for a standard and racing chair (Goosey, Campbell & Fowler 2000) (←). Figure 4. Sledge hockey propulsion cycle; double-poling stroke uses two miniature sticks with picks allowing for a focused contact point (→). Figure 5. This study’s current definition of shoulder produced gait; previous research has identified that the start-cycle occurs twice as long as the remaining cycles, further investigation is currently being conducted for this cycle. Participants propel themselves through the 3x3x2 m capture zone on a modified indoor wheeled sledge, making precise force plate contact with submaximal and maximal efforts, followed by stationary start-propulsion on the force plates through the remaining capture space, again with submaximal and maximal efforts. A minimum of 3 useable trials are required for each of the four tests, and a minimum of 2 minutes rest is allotted between trials. Baseline parameters are defined by a using a validated solid-static prototype mimicking the average male upper torso with a single arm; the shoulder joint being the only dynamic element. Figure 6. a) sEMG placement for anterior movers and stabilizers left vs right; biceps brachii (A), pectoralis major (B), anterior deltoid (C) and medial deltoid (D) b) sEMG placement for posterior movers and stabilizers left vs right; triceps brachii (E), latissimus dorsi (F), posterior deltoid (G) and trapezius (H) c) Marker placement for motion capture data; wheeled sledge for indoor analysis d) Reconstructed 3-dimensional image created from Fig 6c motion capture data. A B C D E F G H Figure 7. a) Architectural drawing of the prototype during validation; mathematical model points (*) b) The anatomically correct prototype used to determine baseline measure for the average 80kg male (not test positon) c) 3-dimensional reconstruction of the prototype during a single trial; initial contact reaction force vector (red arrow) and marker trajectory (blue lines). Figure 8. The calculated average for the three elbow angle trajectories for the pick (time- normalized); arc-slope decreased as elbow angle increased; +10 o (-), 0 o (--) and -10 o (..) start angles. Figure 10. The combined average of the three elbow angles producing average reaction force in each direction, for each of the start angles; Total Average black (---) Hip joint weight-bearing contralateral mobility has been extensively studied and summarized 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; from increased surviving Veterans to increased human mortality rates; advanced pediatric surgeries to the introduction of parasports. 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 from contact to the point of rotation, gait cycle phases with initial and 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 parasports such as sledge hockey and sit-skiing (Gal, Hay & Chan 2014). This forward cyclical motion is similar to wheelchair propulsion (O’Connor & Robertson 1998); the addition of the shortened pole to the investigation allows for the collection of localized data through the contact phase known as propulsion. Additionally, a rapidly developing parasport will gain much needed sport-specific evidence. The linear stroking cycle will be investigated using 3- dimensional motion capture, surface electromyography electrodes and force plate acquisition for left pick, right pick and sledge reaction forces. Participants will be tasked to contact the force plates mid-cycle and from a static-start at both submaximal and maximal efforts. This study developed and validated a 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 (Gastaldi, Pastorelli & Frassinelli 2012; Holmberg et al. 2005). BM will be compared to musculoskeletal produced preparation phases of task-naive able bodied males and task-experts physically disabled males. The importance of BM concerning external forces allows for a validation or rejection of the internal assumptions required during dynamic movement investigation (Robertson et al. 2004). Specifically, BM for preparation will provide evidence in determining the direct biomechanical importance for the addition of this phase to the complete seated cycle. Pilot study findings from a single task-naive abled male have suggested that SJ produced gait is a posteriorly driven motion with the triceps, latissimus dorsi and posterior deltoid ranking dominantly (Gal et al. 2014). Further investigation regarding the minimal contribution from the biceps is required. Muscular hierarchy is expected to alter due to the addition of trapezius data; 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 reaction forces are suggested to be produced late propulsion phase with elevated initial impact reaction forces from pick-plant (Gal et al. 2014). Collectively, this data will be illustrated as a complete seated gait outlining static-start, start cycle and the remaining phases (Gal et al. 2014). This evidence will provide knowledge improving muscular development and training, rehabilitation and sport-specific growth having positive life-changing effects for this entire special population. BACKGROUND & DEVELOPMENT In conclusion, this data will illustrate the complete seated gait outlining static-start, start cycle and the remaining phases. Propulsion in sledge hockey is posteriorly driven with peak impact thrusting the arm up and back into the socket followed by a peak reaction force thrusting the arm up and forward. This evidence will provide knowledge improving muscular development and training, rehabilitation and sport-specific growth having positive life-changing effects for this CONCLUSION • Location • Magnitude • Direction Start Cycle Vs Remaining Cycles Figure 9. The reaction forces onto the shoulder from peak impact (red) followed by peak reaction force (green) late in the contact phase; a rapid shift within a socket not designed for weight-bearing structural integrity.
