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Han Houdijk, Jos J. de Koning, Maarten F. Bobbert and Gert de Groot

In speed skating, the conventional skate has been replaced by the klapskate, in which the shoe can rotate around a hinge between shoe and blade. It has been hypothesized that the improved performance with klapskates vs. conventional skates can be attributed to the difference in the anterior/posterior position of the foot’s center of rotation relative to the ice. This study investigated the effect of the position of the foot’s center of rotation on push-off mechanics in speed skating. Eight elite speed skaters skated four 2000-m trials on instrumented klapskates at a fixed velocity. In each trial the hinge was placed at a different position between the 5th metatarso-phalangeal joint and the tip of the toes. 3-D kinematics and pushoff forces were measured to analyze push-off kinematics and kinetics. Shifting the hinge from the most posterior to the more anterior positions resulted in a delayed onset of foot rotation and longer duration of push-off. This delay coincided with an increase in angular displacement and peak angular velocity of the knee and hip joint, an increase in the flexing knee joint moment at the end of the push-off, and a reduction in work generated at the knee joint. Total work per stroke was similar for the various hinge positions. Besides the similar work per stroke, the observed effects are in accordance with the differences between klapskating and conventional skating. It was concluded that the position of the foot’s center of rotation affects the timing of foot rotation, and therefore the balanced pattern of segmental rotations. Although it could not be proven in this study, it was shown that this constraint could affect work per stroke and might explain the difference between klapskates and conventional skates.

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Maarten F. Bobbert, Han Houdijk, Jos J. de Koning and Gert de Groot

To gain a better understanding of push-off mechanics in speed skating, forward simulations were performed with a model comprising four body segments and six muscles. We started with a simulated maximum height one-legged jump, obtained by optimization of muscle stimulation time histories. The simulated jump was very similar to one-legged jumps produced by a human, indicating that the model was realistic. We subsequently studied how performance was affected by introducing four conditions characteristic of speed skating: (a) We changed the initial position from that in jumping to that at the start of the push-off phase in skating. This change was accommodated by a delay in stimulation onset of the plantar flexors in the optimal solution. (b) The friction between foot and ground was reduced to zero. As a result, maximum jump height decreased by 1.2 cm and performance became more sensitive to errors in muscle stimulation. The reason is that without surface friction, the foot had to be prevented from slipping away, which constrained the solution space and reduced the tolerance to errors in stimulation. (c) We introduced the requirement to maintain the upper body in a more or less horizontal position. This change could be accommodated by a delay in stimulation onset of the hamstrings, which inevitably caused a reduction in maximum jump height by 11.6 cm. (d) We increased the effective foot length from 16.5 cm, representative of jumping, to 20.5 cm, representative of skating with klapskates. At the 20.5-cm foot length, rotation of the foot did not start during the buildup of plantar flexion moment as it did at smaller foot lengths, but was delayed until hip and knee extension moments decreased. This caused an unbalanced increase in segment angular velocities and muscle shortening velocities, leading to a decrease in muscle force and muscle work and a further decrease in maximum jump height by approximately 5 cm. Qualitatively, these findings help clarify why and how performance of speed skaters depends on the location of the hinge of their skate.

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Sonja de Groot, Linda J. Valent, Richard Fickert, Babette M. Pluim and Han Houdijk

Purpose:

To determine the relationship between outcomes of the shuttle wheel test (SWT) and peak oxygen uptake (VO2peak) during that test and whether SWT and VO2peak can discriminate between different skill levels of wheelchair tennis players.

Methods:

Fifteen wheelchair tennis players performed an SWT on a tennis court while VO2 was measured continuously. Outcome measures were VO2peak and achieved stage. Relations between outcomes and Dutch wheelchair tennis ranking were calculated with Spearman correlation. Independent t tests were used to test for differences between national and international players.

Results:

Moderate correlations were found between VO2peak and SWT outcome (r = .40–.47). The tennis ranking correlated weakly with VO2peak (r = –.35) and strongly with SWT outcome (r = –.80). A significant difference was found between national and international players for achieved stage (P = .027) and VO2peak (P = .027).

Conclusions:

The SWT outcome only explained a small part of the variance in VO2peak among players, so it cannot be considered a valid test for aerobic capacity. However, SWT outcomes are related to the skill level of the player and give a good indication of the overall peak wheelchair performance.

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Astrid C.J. Balemans, Han Houdijk, Gilbert R. Koelewijn, Marjolein Piek, Frank Tubbing, Anne Visser-Meily and Olaf Verschuren

Background: It is questionable whether postures that are regarded as sedentary behavior in able-bodied persons evoke comparable physiological responses in adults with stroke or cerebral palsy (CP). This study aimed to compare metabolic demand and muscle activity in healthy controls, adults with stroke, and adults with CP during sedentary behavior and light physical activities. Methods: Seventy-one adults (45.6 [18.9] y, range 18–86) participated in this study, of which there were 18 controls, 31 with stroke, and 22 with CP. The metabolic equivalent of task (MET) and level of muscle activation were assessed for different sedentary positions (sitting supported and unsupported) and light physical activities (standing and walking). Results: During sitting supported and unsupported, people with mild to moderate stroke and CP show comparable MET and electromyographic values as controls. While sitting unsupported, people with severe stroke show higher METs and electromyographic values (P < .001), and people with severe CP only show higher METs compared with controls (P < .05) but all below 1.5 METs. Standing increased electromyographic values in people with severe stroke or CP (P < .001) and reached values above 1.5 METs. Conclusions: Physiologic responses during sedentary behavior are comparable for controls and adults with mild to moderate stroke and CP, whereas higher metabolic demands and muscle activity (stroke only) were observed in severely affected individuals.