In speed skating, performance is related to the product of the amount of work per stroke and the stroke frequency. Work per stroke is dependent on the component of the push-off force in the direction perpendicular to the gliding direction of the skate. The push-off force at different velocities was measured in three trained speed skaters. The results showed that the peak push-off force and mean force do not change at different velocities, and that the stroke time was decreased at higher velocities. It can be concluded that these speed skaters regulate their velocity not by changing the push-off force but by changing their stroke time. The shape of push-off–time curves is dependent on push-off technique and differs during straight lane and curve skating.
Jos J. de Koning, Ruud W. de Boer, Gert de Groot and Gerrit Jan van Ingen Schenau
Matthew J. Major, José L. Zavaleta and Steven A. Gard
longitudinal stiffness effects across different walking speeds. We hypothesized that decreased pylon stiffness would increase both collision and push-off work on the COM by the prosthetic limb across walking speeds. In accordance with theorized walking mechanics, 31 we also hypothesized that this increase in
Andrew D. Lyttle, Brian A. Blanksby, Bruce C. Elliott and David G. Lloyd
Thirty experienced male swimmers with body types ± 1 SD of the mean of selected body form parameters reported for elite male swimmers were recruited for the study. During three freestyle flip turns, selected kinetic, hydrodynamic, and kinematic variables of the push-off following a flip turn were recorded. Kinetics were recorded via a 2D vertically mounted forceplate that recorded peak push-off force and total impulse. The acceleration of each swimmer’s center of gravity and wall exit velocity were calculated from underwater videography. Hydrodynamic peak drag force and drag impulse were calculated from the kinetic and kinematic data using a derivative of Newton’s second law. A stepwise regression yielded peak drag force, peak propulsive force, and push-off time in the final regression equation (R = 0.80; R 2 = 0.64). Beta values indicated that the peak drag force carried the highest weighting of the three variables. The results of the stepwise regression indicated that a combination of a low peak drag force high peak propulsive force, and increased wall push-off time produced the fastest final push-off velocity.
Ruud W. de Boer, Gertjan J.C. Ettema, Hans van Gorkum, Gert de Groot and Gerrit Jan van Ingen Schenau
Characteristics of stroke mechanics of elite and trained speed skaters were measured during the skating of curves. Film and video analysis from the 5000-meter races at the Dutch National Championships yielded biomechanical variables that were correlated to performance. There are fundamental differences in push-off mechanics between skating the straight parts and skating the curves. The left stroke shows a more powerful push-off in the curve, caused by a greater push off angle compared to the right leg. The high speed and power output of the better skaters is a result of a high amount of work per stroke, caused by a short and effective directed push-off. These results strongly support the previous finding that skaters of different performance levels can be distinguished by differences in amount of work per stroke and not by differences in stroke frequency.
Ruud W. de Boer and Kim L. Nilsen
The 1988 Winter Olympic Games provided a unique opportunity to study large numbers of optimally prepared speed skaters during ideal ice and weather conditions for all the competitors (indoor Olympic Oval in Calgary). In this study a kinematic analysis was conducted of the gliding and push-off technique during the Men’s and Ladies' 1,500-m and 5,000-m races. Statistical analysis showed that factors such as trunk position, preextension knee angle, and peak knee and hip angular velocities failed to correlate with mean lap speed. Within such a homogeneous group of elite athletes it was found that the higher work per stroke of the faster skaters was correlated to a longer gliding phase and a more horizontally directed push-off. All skaters showed plantar flexion at the end of the stroke, which is undesirable and indicates the complex nature of the gliding and push-off technique in speed skating.
Hans Jobse, Ruud Schuurhof, Ferenc Cserep, A. Wim Schreurs and Jos J. de Koning
Portable equipment for active measurements of push-off force and ice friction was developed. The equipment consists of a pair of skates with three measuring elements between the shoe and the skate blade to register force in both fore/aft and normal direction. A portable computer samples the friction force and normal force signals during one or more strokes, calculates the mean coefficient of ice friction, and stores the sampled data in memory. The push-off force and ice friction force were measured. The peak push-off forces reach values of up to 140% of body weight. The magnitude of the coefficient of ice friction varies, depending on the weather conditions and preparatory method, generally between 0.003 and 0.007 when skating the straightaway. During the skating of the curves the coefficient of ice friction is 35% higher, most likely due to the different skating technique in the curves.
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.
Dionne A. Noordhof, Carl Foster, Marco J.M. Hoozemans and Jos J. de Koning
Speed skating posture, or technique, is characterized by the push-off angle or effectiveness (e), determined as the angle between the push-off leg and the ice; the preextension knee angle (θ 0); and the trunk angle (θ 1). Together with muscle-power output and environmental conditions, skating posture, or technique, determines velocity (v).
To gain insight into technical variables that are important to skate efficiently and perform well, e, θ 0, θ 1, and skating v were determined every lap during a 5000-m World Cup. Second, the authors evaluated if changes (Δ) in e, θ 0, and θ 1 are associated with Δv.
One camera filmed the skaters from a frontal view, from which e was determined. Another camera filmed the skaters from a sagittal view, from which θ 0 and θ 1 were determined. Radio-frequency identification tags around the ankles of the skaters measured v.
During the race, e progressively increased and v progressively decreased, while θ 0 and θ 1 showed a less consistent pattern of change. Generalized estimating equations showed that Δe is significantly associated with Δv over the midsection of the race (β = −0.10, P < .001) and that Δθ 0 and Δθ 1 are not significantly associated with Δv.
The decrease in skating v over the race is not due to increases in power losses to air friction, as knee and trunk angle were not significantly associated with changes in velocity. The decrease in velocity can be partly ascribed to the decrease in effectiveness, which reflects a decrease in power production associated with fatigue.
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.
Katie A. Conway and Jason R. Franz
Age-related mobility impairment and reduced independence arise in part from shorter steps and slower preferred speeds ( Beijersbergen, Granacher, Vandervoort, DeVita, & Hortobagyi, 2013 ). These changes likely arise from deficits in push-off intensity; compared with young adults, older adults walk