Search Results

You are looking at 1 - 10 of 16 items for :

  • "energy dissipation" x
Clear All
Restricted access

Matej Supej and Hans-Christer Holmberg

This study examined whether gate setup and turn radii influence energy dissipation in slalom skiing. 3D kinematical measurements were performed over two runs on the same slope in a WC slalom competition with two different gate setups: 1) open gates (OG) and 2) open gates with a delayed gate (DG). Using the arithmetic mean of the skis’ turn radii (R AMS) the slalom turns were divided into 1) initiation phase (R AMS > 15m) and steering phase (R AMS < 15m). The results show differences between OG and DG regarding: 1) the absolute center of gravity’s (CG) velocity, 2) absolute acceleration, 3) CG turn radii and R AMS, 4) ground reaction forces (F) and 5) energy dissipation during skiing (all p < .05). In both gate setups the highest F and the highest energy dissipation were present in the steering phase, whereas the correlation between R AMS and energy dissipation was low (OG: r = .364 and DG: r = .214, both p < .001). In summary, compared with plain open gates, an additional delayed gate prolonged the turn radii and decreased energy dissipation in the beginning of the initiation phase, despite the fact that the relative frequency of occurrence of the highest energy dissipation was higher in DG.

Restricted access

Matthew T.G. Pain and John H. Challis

The aims of this study were to quantify intrasegmental motion using an array of 28 surface-mounted markers to examine frequency and amplitude measurements of the intrasegmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One participant performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces, the muscle tension significantly affected the amount of intrasegmental motion. Tensing the arm reduced the intrasegmental motion by 50%. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intrasegmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70% of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intrasegment soft tissue motion can have on the kinetics of an impact.

Restricted access

Øyvind Sandbakk, Silvana Bucher Sandbakk, Matej Supej and Hans-Christer Holmberg

This study examined the influence of turn radius on velocity and energy profiles when skidding and step turning during more and less effective downhill turns while cross-country skiing. Thirteen elite female cross-country skiers performed single turns with a 9- or 12-m radius using the skidding technique and a 12- or 15-m radius with step turning. Mechanical parameters were monitored using a real-time kinematic Global Navigation Satellite System and video analysis. Step turning was more effective during all phases of a turn, leading to higher velocities than skidding (P < .05). With both techniques, a greater radius was associated with higher velocity (P < .05), but the quality of turning, as assessed on the basis of energy characteristics, was the same. More effective skidding turns involved more pronounced deceleration early in the turn and maintenance of higher velocity thereafter, while more effective step turning involved lower energy dissipation during the latter half of the turn. In conclusion, the single-turn analysis employed here reveals differences in the various techniques chosen by elite cross-country skiers when executing downhill turns of varying radii and can be used to assess the quality of such turns.

Restricted access

Matej Supej, Kim Hébert-Losier and Hans-Christer Holmberg

Purpose:

Numerous environmental factors can affect alpine-ski-racing performance, including the steepness of the slope. However, little research has focused on this factor. Accordingly, the authors’ aim was to determine the impact of the steepness of the slope on the biomechanics of World Cup slalom ski racers.

Methods:

The authors collected 3-dimensional kinematic data during a World Cup race from 10 male slalom skiers throughout turns performed on a relatively flat (19.8°) and steep (25.2°) slope under otherwise similar course conditions.

Results:

Kinematic data revealed differences between the 2 slopes regarding the turn radii of the skis and center of gravity, velocity, acceleration, and differential specific mechanical energy (all P < .001). Ground-reaction forces (GRFs) also tended toward differences (P = .06). Examining the time-course behaviors of variables during turn cycles indicated that steeper slopes were associated with slower velocities but greater accelerations during turn initiation, narrower turns with peak GRFs concentrated at the midpoint of steering, more pronounced lateral angulations of the knees and hips at the start of steering that later became less pronounced, and overall slower turns that involved deceleration at completion. Consequently, distinct energy-dissipation-patterns were apparent on the 2 slope inclines, with greater pregate and lesser postgate dissipation on the steeper slope. The steepness of the slope also affected the relationships between mechanical skiing variables.

Conclusions:

The findings suggest that specific considerations during training and preparation would benefit the race performance of slalom skiers on courses involving sections of varying steepness.

Restricted access

Anh-Dung Nguyen, Jeffrey B. Taylor, Taylor G. Wimbish, Jennifer L. Keith and Kevin R. Ford

.6.804 10.1123/jab.29.6.804 23434732 25. Winter DA . Biomechanics and Motor Control of Human Movement . 3rd ed. New York, NY : John Wiley & Sons, Inc ; 2005 . 26. Zhang SN , Bates BT , Dufek JS . Contributions of lower extremity joints to energy dissipation during landings . Med Sci Sports

Restricted access

Sarah C. Moudy, Neale A. Tillin, Amy R. Sibley and Siobhán Strike

BT , Dufek JS . Contributions of lower extremity joints to energy dissipation during landings . Med Sci Sports Exerc . 2000 ; 32 ( 4 ): 812 – 819 . PubMed ID: 10776901 doi: 10.1097/00005768-200004000-00014 28. Norcross MF , Lewek MD , Padua DA , Shultz SJ , Weinhold PS

Restricted access

Wing-Kai Lam, Winson Chiu-Chun Lee, Wei Min Lee, Christina Zong-Hao Ma and Pui Wah Kong

sprint performance, and (2) both medial plate and medial + lateral plates shoes would minimize the energy dissipation (ie, less power absorption) at the ankle and metatarsophalangeal joints. Methods Test Shoe Conditions Three identical pairs of US9.0 basketball shoes (Li Ning Yushuai 9, Beijing, China

Restricted access

Nicole C. George, Charles Kahelin, Timothy A. Burkhart and David M. Andrews

on ground reaction forces, joint torques and joint reaction forces in drop landings . J Biomech . 2006 ; 39 : 119 – 124 . PubMed doi:10.1016/j.jbiomech.2004.10.036 16271595 10.1016/j.jbiomech.2004.10.036 5. Schmitt S , Günther M . Human leg impact: energy dissipation

Restricted access

Caroline Lisee, Tom Birchmeier, Arthur Yan, Brent Geers, Kaitlin O’Hagan, Callum Davis and Christopher Kuenze

: 10.1177/0363546506293899 17092928 20. Yeow CH , Lee PVS , Goh JCH . An investigation of lower extremity energy dissipation strategies during single-leg and double-leg landing based on sagittal and frontal plane biomechanics . Hum Mov Sci . 2011 ; 30 ( 3 ): 624 – 635 . PubMed ID: 21411162

Restricted access

Akihiro Tamura, Kiyokazu Akasaka and Takahiro Otsudo

. Zhang SN , Bates BT , Dufek JS . Contributions of lower extremity joints to energy dissipation during landings . Med Sci Sports Exerc . 2000 ; 32 ( 4 ): 812 – 819 . PubMed ID: 10776901 doi: 10.1097/00005768-200004000-00014 10776901 12. DeVita P , Skelly WA . Effect of landing