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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).

Purpose:

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.

Methods:

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.

Results:

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.

Conclusions:

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.

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Andrea Monte, Francesca Nardello and Paola Zamparo

Purpose:

The effects of different loads on kinematic and kinetic variables during sled towing were investigated with the aim to identify the optimal overload for this specific sprint training.

Methods:

Thirteen male sprinters (100-m personal best: 10.91 ± 0.14 s) performed 5 maximal trials over a 20-m distance in the following conditions: unloaded and with loads from 15% to 40% of the athlete’s body mass (BM). In these calculations the sled mass and friction were taken into account. Contact and flight times, stride length, horizontal hip velocity (vh), and relative angles of hip, knee, and ankle (at touchdown and takeoff) were measured step by step. In addition, the horizontal force (Fh) and power (Ph) and maximal force (Fh0) and power (Ph0) were calculated.

Results:

vh, flight time, and step length decreased while contact time increased with increasing load (P < .001). These variables changed significantly also as a function of the step number (P < .01), except between the 2 last steps. No differences were observed in Fh among loads, but Fh was larger in sled towing than in unloaded. Ph was unaffected by load up to +20%BM but decreased with larger loads. Fh0 and Ph0 were achieved at 20%BM. Up to 20%BM, no significant effects on joint angles were observed at touchdown and takeoff, while at loads >30%BM joint angles tended to decrease.

Conclusion:

The 20%BM condition represents the optimal overload for peak power production—at this load sprinters reach their highest power without significant changes in their running technique (eg, joint angles).

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Vagenas * Blaine Hoshizaki * 2 1992 8 1 11 29 10.1123/ijsb.8.1.11 A Perturbation Study of Lower Extremity Motion during Running Wilbert Van Woensel * Peter R. Cavanagh * 2 1992 8 1 30 47 10.1123/ijsb.8.1.30 Friction Measurement in Tennis on the Field and in the Laboratory Bart Van Gheluwe * Eric

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* Manssour H. Moeinzadeh * 2 1990 6 1 78 91 10.1123/ijsb.6.1.78 Technical Notes Measurement of Push-Off Force and Ice Friction during Speed Skating Hans Jobse * Ruud Schuurhof * Ferenc Cserep * A. Wim Schreurs * Jos J. de Koning * 2 1990 6 1 92 100 10.1123/ijsb.6.1.92 jab International Journal of

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Bocchinfuso * Michael R. Sitler * Iris F. Kimura * 5 1994 3 2 125 134 10.1123/jsr.3.2.125 Research Treatment of infrapatellar Tendinitis: A Combination of Modalities and Transverse Friction Massage versus Iontophoresis Geraldine L. Pellecchia * Holly Hamel * Peter Behnke * 5 1994 3 2 135 145 10

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Leigh J. Allin, Maury A. Nussbaum and Michael L. Madigan

compared with tripping or missteps among young and middle-aged adults. 3 Slipping while walking commonly occurs at heel contact when insufficient friction forces result in the foot translating forward over the support surface, and a recovery response is often needed to prevent a fall. This response often

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Iliotibial Band Friction Syndrome Elizabeth A. Racioppi MS, PT Dawn T. Gulick PhD, PT, ATC 9 1999 4 4 5 5 9 9 10 10 10.1123/att.4.5.9 Case Review Lateral Foot Pain Susanne Graner MA, ATC-L 9 1999 4 4 5 5 11 11 12 12 10.1123/att.4.5.11 Administratively Speaking Litigation and Athletic Trainers: Two

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Leadership: A Matter of Style? Michael G. Dolan MA, ATC 9 1997 2 2 5 5 17 17 17 17 10.1123/att.2.5.17 Injury Management Update Treating ITB Friction Syndrome Using Lontophoresis Paul Federici MEd, ATC John A. Norwig MEd, ATC 9 1997 2 2 5 5 22 22 23 23 10.1123/att.2.5.22 Case Review A Lis Franc Fracture

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ORIGINAL RESEARCH Coefficient of Friction at the Fingertips in Type II Diabetics Compared to Healthy Adults Beatriz H. Thames * Stacey L. Gorniak * 6 2017 26 06 2017 33 3 185 188 10.1123/jab.2016-0147 jab.2016-0147 The Advantages of Normalizing Electromyography to Ballistic Rather than

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24 34 10.1123/jab.24.1.24 Drag Characteristics of Competitive Swimming Children and Adults Per-Ludvik Kjendlie * Robert Keig Stallman * 2 2008 24 1 35 42 10.1123/jab.24.1.35 A Technique to Determine Friction at the Fingertips Adriana V. Savescu * Mark L. Latash * Vladimir M. Zatsiorsky * 2