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Daohang Sha, Christopher R. France, and James S. Thomas

The effect of target location, speed, and handedness on the average total mechanical energy and movement efficiency is studied in 15 healthy subjects (7 males and 8 females with age 22.9 ± 1.79 years old) performing full body reaching movements. The average total mechanical energy is measured as the time average of integration of joint power, potential energy, and kinetic energy respectively. Movement efficiency is calculated as the ratio of total kinetic energy to the total joint power and potential energy. Results show that speed and target location have significant effects on total mechanical energy and movement efficiency, but reaching hand only effects kinetic energy. From our findings we conclude that (1) efficiency in whole body reaching is dependent on whether the height of the body center of mass is raised or lowered during the task; (2) efficiency is increased as movement speed is increased, in part because of greater changes in potential energy; and (3) the CNS does not appear to use movement efficiency as a primary planning variable in full body reaching. It may be dependent on a combination of other factors or constraints.

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Matej Supej

An important question in alpine skiing is how to determine characteristics of well-performed ski turns, an issue that has become more crucial with the arrival of new carving skis. This article introduces a new method for estimating the quality of skiing at each point of observation based on mechanical energy behavior that can be measured using established motion analysis techniques. It can be used for single-or multiple-skier analyses for evaluation of skiing technique as well as racing tactics. An illustration of its use is shown by analyzing 16 top-level racers using a 3-D kinematical system and video recorded during an alpine ski world cup race. Based on energy behavior of several racers, it is demonstrated that the most direct line with shortest radius of turn is not necessarily the most effective strategy in contrast to what some coaches believe.

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Matthew K. Seeley, Iain Hunter, Thomas Bateman, Adam Roggia, Brad J. Larson, and David O. Draper


A novel spring-loaded-crutch design may provide patients additional forward velocity, relative to traditional axillary crutches; however, this idea has not yet been evaluated.


To quantify elastic potential energy stored by spring-loaded crutches during crutch–ground contact and determine whether this energy increases forward velocity for patients during crutch ambulation. Because elastic potential energy is likely stored by the spring-loaded crutch during ambulation, the authors hypothesized that subjects would exhibit greater peak instantaneous forward velocity during crutch–ground contact and increased preferred ambulation speed during spring-loaded-crutch ambulation, relative to traditional-crutch ambulation.




Biomechanics laboratory.


10 healthy men and 10 healthy women.


The independent variable was crutch type: Subjects used spring-loaded and traditional axillary crutches to ambulate at standardized and preferred speeds.

Main Outcome Measures:

The primary dependent variables were peak instantaneous forward velocity and preferred ambulation speed; these variables were quantified using high-speed videography and an optoelectronic timing device, respectively. Between-crutches differences for the dependent variables were evaluated using paired t tests (α = .05). Elastic potential energy stored by the spring-loaded crutches during crutch–ground contact was also quantified via videography.


Peak forward velocity during crutch–ground contact was 5% greater (P < .001) for spring-loaded-crutch ambulation than for traditional-crutch ambulation. Preferred ambulation speed, however, did not significantly differ (P = .538) between crutch types. The spring-loaded crutches stored an average of 2.50 ± 1.96 J of elastic potential energy during crutch–ground contact.


The spring-loaded crutches appear to have provided subjects with additional peak instantaneous forward velocity. This increased velocity, however, was relatively small and did not increase preferred ambulation speed.

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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.

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John R. Harry, Leland A. Barker, Jeffrey D. Eggleston, and Janet S. Dufek

peak vGRF and/or decreased loading time) mechanical stress. When evaluating the loading rate and similar loading parameters during landing, the ankle joint should be closely considered, as it is the first joint to contribute to mechanical energy absorption and force attenuation. 15 , 16 By increasing

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Mu Qiao

questions remain for how each leg joint contributes to the spring of the entire body (ie, virtual leg). If the leg joints are all torsional springs and change stiffness proportionally, they will store and return the same percentage of mechanical energy independently of hopping frequency. Alternatively, leg

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Alexis D. Gidley and Joshua P. Bailey

): 605 – 615 . doi: 10.1152/jn.2000.84.2.605 3. Minetti AE , Ardigo LP , Saibene F . Mechanical determinants of gradient walking energetics in man . J Physiol . 1993 ; 471 : 725 – 735 . doi: 10.1113/jphysiol.1993.sp019969 4. Gottschall JS , Kram R . Mechanical energy fluctuations during

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Teun van Erp, Carl Foster, and Jos J. de Koning

mean maximal power (MMP) of 413 (32) W or 5.55 (0.8) W/kg can be seen as a measure of their excellence. Kilojoules Spent For every training, road race, or TT, the total mechanical energy spent (in kilojoules [kJ]) was calculated from the PO as measure of external TL. PO was collected with the use of

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Jonathan K. Holm, Jonas Contakos, Sang-Wook Lee, and John Jang

This study investigated the energetics of the human ankle during the stance phase of downhill walking with the goal of modeling ankle behavior with a passive spring and damper mechanism. Kinematic and kinetic data were collected on eight male participants while walking down a ramp with inclination varying from 0° to 8°. The ankle joint moment in the sagittal plane was calculated using inverse dynamics. Mechanical energy injected or dissipated at the ankle joint was computed by integrating the power across the duration of the stance phase. The net mechanical energy of the ankle was approximately zero for level walking and monotonically decreased (i.e., became increasingly negative) during downhill walking as the slope decreased. The indication is that the behavior of the ankle is energetically passive during downhill walking, playing a key role in dissipating energy from one step to the next. A passive mechanical model consisting of a pin joint coupled with a revolute spring and damper was fit to the ankle torque and its parameters were estimated for each downhill slope using linear regression. The passive model demonstrated good agreement with actual ankle dynamics as indicated by low root-mean-square error values. These results indicate the stance phase behavior of the human ankle during downhill walking may be effectively duplicated by a passive mechanism with appropriately selected spring and damping characteristics.

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Robert Norman, Graham Caldwell, and Paavo Komi

Differences in the utilization of body segment movements between world-class and recreational cross-country skiers which result in a longer stride of the elite were studied using mechanical energy analyses. Nine world-class racers and six recreational skiers (novices) were filmed, the latter while they executed their fastest possible stable diagonal stride on a level track, and the former during competition. A 15-member linked segment model was digitized, the coordinate data filtered at 4.5 Hz and body segment energy curves; mechanical work output and mechanical energy transfers were calculated using the method described by Pierrynowski, Winter, and Norman (1980). The elite skiers exhibited larger exchanges between potential and kinetic energy in all segments during swing phases and all but the upper arm segment during pushing phases. Step-wise discriminant function analysis showed significant differences in the swinging foot, pushing foot, and pushing shank. The differences appear to be largely attributable to the higher leg swings of the experts, who prolong the glide and enhance step length, probably at a relatively lower metabolic cost by exploiting gravity to augment muscular force by generating pendulum-like movements.