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Glenn M. Street and Robert W. Gregory

While the scientific literature has confirmed the importance of high maximal aerobic power to successful cross-country skiing performance, the same cannot be said of skiing technique or gliding characteristics of skis. The purpose of this study was to determine whether glide speed was related to Olympic race performance. Male competitors in the 50-km freestyle event were videotaped during the 1992 Winter Olympic Games. Glide speeds of the entire field were measured through a 20-m flat section at the bottom of a 150-m, 12° downhill. A significant correlation (r = -.73) was found between finish time and glide speed, showing that the more successful competitors tended to have faster glide speeds through this section of the course. A predictive model of glide speed suggested that the faster glide speeds were due primarily to differences in friction. There was little evidence to suggest that differences in air drag, body mass, or initial speed accounted for the major differences in glide speeds.

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Robert W. Gregory, Sean E. Humphreys and Glenn M. Street

The women's 30-km freestyle cross-country race at the 1992 Winter Olympic Games was selected to determine the kinematic differences between more and less successful skiers. Three-dimensional filming techniques were used to capture the movement patterns on level terrain of 8 skiers who placed in the top 50% (Group 1) and 8 skiers who placed in the bottom 50% (Group 2) of the field. The mean cycle velocity for Group 1 was significantly faster (p < .005) than the velocity for Group 2. Significant correlations (p < .05) were found between race velocity and cycle velocity (r = .89) and between cycle length and cycle rate (r = -.82). Group 1 had significantly greater (p < .03) weak-side elbow flexion at pole plant, as well as less (p < .01) weak-side elbow extension and more (p < .05) trunk flexion during poling. The mean cycle velocity differences between Groups 1 and 2 may have been the result of smaller resistive and/or larger propulsive forces.

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Benjamin W. Stroube, Gregory D. Myer, Jensen L. Brent, Kevin R. Ford, Robert S. Heidt Jr. and Timothy E. Hewett

Context:

Anterior cruciate ligament (ACL) injuries are prevalent in female athletes. Specific factors have possible links to increasing a female athlete’s chances of suffering an ACL injury. However, it is unclear if augmented feedback may be able to decrease possible risk factors.

Objective:

To compare the effects of task-specific feedback on a repeated tuck-jump maneuver.

Design:

Double-blind randomized controlled trial.

Setting:

Sports-medicine biodynamics center.

Patients:

37 female subjects (14.7 ± 1.5 y, 160.9 ± 6.8 cm, 54.5 ± 7.2 kg).

Intervention:

All athletes received standard off-season training consisting of strength training, plyometrics, and conditioning. They were also videotaped during each session while running on a treadmill at a standardized speed (8 miles/h) and while performing a repeated tuck-jump maneuver for 10 s. The augmented feedback group (AF) received feedback on deficiencies present in a 10-s tuck jump, while the control group (CTRL) received feedback on 10-s treadmill running.

Main Outcome Measures:

Outcome measurements of tuck-jump deficits were scored by a blinded rater to determine the effects of group (CTRL vs AF) and time (pre- vs posttesting) on changes in measured deficits.

Results:

A significant interaction of time by group was noted with the task-specific feedback training (P = .03). The AF group reduced deficits measured during the tuck-jump assessment by 23.6%, while the CTRL training reduced deficits by 10.6%.

Conclusions:

The results of the current study indicate that task-specific feedback is effective for reducing biomechanical risk factors associated with ACL injury. The data also indicate that specific components of the tuck-jump assessment are potentially more modifiable than others.