In the high-velocity tennis serve, the contributions that the upper limb segments' anatomical rotations make to racket head speed at impact depend on both their angular velocity and the instantaneous position of the racket with respect to the segments' axes of rotation. Eleven high-performance tennis players were filmed at a nominal rate of 200 Hz by three Photosonics cameras while hitting a high-velocity serve. The three-dimensional (3-D) displacement histories of 11 selected landmarks were then calculated using the direct linear transformation approach, and 3-D individual segment rotations for the upper limb were calculated using vector equations (Sprigings, Marshall, Elliott, & Jennings, 1994). The major contributors to the mean linear velocity of the center of the racket head of 31.0 m · s-1 at impact were internal rotation of the upper arm (54.2%), flexion of the hand (31.0%), horizontal flexion and abduction of the upper arm (12.9%), and racket shoulder linear velocity (9.7%). Forearm extension at the elbow joint played a negative role (-14.4%) and reduced the forward velocity of the center of the racket at impact.
Bruce C. Elliott, Robert N. Marshall, and Guillermo J. Noffal
Robert N. Marshall, David J. Paterson, and Paul Glendining
Approximately 25 runners were filmed at the 24.9- and 41.0-km points in the 1987 Everest Marathon. Their finishing times ranged from 4:53:10 to 7:14:37. Leg length, step lengths, step frequencies, knee angles at impact, and ankle-to-hip angles at impact were determined for each runner who appeared in both films (N = 20). The slopes at the two filming sites were −21.8% and −26.8%, considerably steeper gradients than have previously been studied. When compared to data from other downhill running studies at −10% gradient, these athletes had slightly slower speeds, shorter step lengths, straighter legs on impact, and greater minimum knee angles during stance. The results suggest that the runners used a variety of techniques to minimize the effects of ground impact while still allowing for the competitive aspect of the race, considerable variation in footing and terrain, and personal safety.
Joseph P. Hunter, Robert N. Marshall, and Peter J. McNair
The literature contains some hypotheses regarding the most favorable ground reaction force (GRF) for sprint running and how it might be achieved. This study tested the relevance of these hypotheses to the acceleration phase of a sprint, using GRF impulse as the GRF variable of interest. Thirty-six athletes performed maximal-effort sprints from which video and GRF data were collected at the 16-m mark. Associations between GRF impulse (expressed relative to body mass) and various kinematic measures were explored with simple and multiple linear regressions and paired t-tests. The regression results showed that relative propulsive impulse accounted for 57% of variance in sprint velocity. Relative braking impulse accounted for only 7% of variance in sprint velocity. In addition, the faster athletes tended to produce only moderate magnitudes of relative vertical impulse. Paired t-tests revealed that lower magnitudes of relative braking impulse were associated with a smaller touchdown distance (p < 0.01) and a more active touchdown (p < 0.001). Also, greater magnitudes of relative propulsive impulse were associated with a high mean hip extension velocity of the stance limb (p < 0.05). In conclusion, it is likely that high magnitudes of propulsion are required to achieve high acceleration. Although there was a weak trend for faster athletes to produce lower magnitudes of braking, the possibility of braking having some advantages could not be ruled out. Further research is required to see if braking, propulsive, and vertical impulses can be modified with specific training. This will also provide insight into how a change in one GRF component might affect the others.