A sit-ski design aimed at controlling centre of mass and inertia

Abstract

This article introduces a sit-ski developed for the Canadian Alpine Ski Team in view of the Vancouver 2010 Paralympic games. The design is predominantly based on controlling the mass distribution of the sit-ski, a critical factor in skiing performance and control. Both the antero-posterior location of the centre of mass and the sit-ski moment of inertia were addressed in our design. Our design provides means to adjust the antero-posterior centre of mass location of a sit-ski to compensate for masses that would tend to move the antero-posterior centre of mass location away from the midline of the binding area along the ski axis. The adjustment range provided is as large as 140 mm, thereby providing sufficient adaptability for most situations. The suspension mechanism selected is a four-bar linkage optimised to limit antero-posterior seat movement, due to suspension compression, to 7 mm maximum. This is about 5% of the maximum antero-posterior centre of mass control capacity (151 mm) of a human participant. Foot rest inclination was included in the design to modify the sit-ski inertia by as much as 11%. Together, these mass adjustment features were shown to drastically help athletes' skiing performance.

Biomechanical Analysis of the Stroking Cycle in the Sport of Sledge Hockey

“…Additionally, in a non-contractile system, a peak force-generating drop should occur slightly above the horizon with an extended arm. However, biomechanical analysis of double poling endorses shortening the lever arm (decrease angle at the elbow) during impact, then increasing the lever arm during force transfer and push-off [24], [25], [42], [44], [51], [54]. Lever arm (moment) length is a key parameter during investigation of impact forces and corresponding moments.…”

“…Torso angle and elbow angle range were established from alpine sit-ski literature investigating sit-ski design controlling and inertia, in conjunction with pilot on-ice sledge hockey investigations conducted by the author [23], [25]. Alpine sit-skiers require increased balance in the bucket, improving control as they produce highly explosive and agile poling motions, similar to sledge hockey [25].…”

“…Torso angle and elbow angle range were established from alpine sit-ski literature investigating sit-ski design controlling and inertia, in conjunction with pilot on-ice sledge hockey investigations conducted by the author [23], [25]. Alpine sit-skiers require increased balance in the bucket, improving control as they produce highly explosive and agile poling motions, similar to sledge hockey [25]. A sit-ski bucket has a very different design (chair-like with specific leg supports) compared to a sledge hockey sledge (seat with open leg supports); however, both sports utilize the same increased torso flexion during initiation of explosive poling bursts [23], [25].…”

“…Alpine sit-skiers require increased balance in the bucket, improving control as they produce highly explosive and agile poling motions, similar to sledge hockey [25]. A sit-ski bucket has a very different design (chair-like with specific leg supports) compared to a sledge hockey sledge (seat with open leg supports); however, both sports utilize the same increased torso flexion during initiation of explosive poling bursts [23], [25]. Therefore, − 80 was fastened to a sledge hockey sledge at a fixed hip angle +40° from the horizon, with weights placed in the bucket to stabilize the sledge.…”

“…Elbow angle range was developed from the same sit-ski literature. Using an elbow jointcentre screw, the elbow angle was set at 120°, 135°, or 150° (fully extended elbow equals 180°), creating flexed, middle, and extended experimental conditions, respectively [25].…”