Limited data exists on knee biomechanics in alpine ski turns despite the high rate of injuries associated with this maneuver. The purpose of the current study was to compare knee joint loading between a carved and a skidded ski turn and between the inner and outer leg. Kinetic data were collected using Kistler mobile force plates. Kinematic data were collected with five synchronized, panning, tilting, and zooming cameras. Inertial properties of the segments were calculated using an extended version of the Yeadon model. Knee joint forces and moments were calculated using inverse dynamics analysis. The obtained results indicate that knee joint loading in carving is not consistently greater than knee joint loading in skidding. In addition, knee joint loading at the outer leg is not always greater than at the inner leg. Differentiation is required between forces and moments, the direction of the forces and moments, and the phase of the turn that is considered. Even though the authors believe that the analyzed turns are representative, results have to be interpreted with caution due to the small sample size.
Miriam Klous, Erich Müller and Hermann Schwameder
Michael Joch, Mathias Hegele, Heiko Maurer, Hermann Müller and Lisa K. Maurer
Motor learning can be monitored by observing the development of neural correlates of error processing. Among these neural correlates, the error- and feedback-related negativity (Ne/ERN and FRN) represent error processing mechanisms. While the Ne/ERN is more related to error prediction, the FRN is found after an error is manifested. The questions the current study strives to answer are: What information is needed by the system to make error predictions and how is this represented by the Ne/ERN and FRN in a complex motor task? We reduced the information and increased the difficulty level for the prediction in a semivirtual throwing task and found no Ne/ERN but a large FRN when the action result was finally observed (hitting or missing a target). We assume that uncertainty for error prediction was too high (either due to insufficient information or due to lacking prerequisites for prediction), such that error processing had to be mainly based on feedback. The finding is in line with the reinforcement theory of learning, after which Ne/ERN and FRN should behave complementary.
Gerda Strutzenberger, Adam Brazil, Timothy Exell, Hans von Lieres und Wilkau, John D. Davies, Steffen Willwacher, Johannes Funken, Ralf Müller, Kai Heinrich, Hermann Schwameder, Wolfgang Potthast and Gareth Irwin
Context: In sprint events, the first 2 steps are used to accelerate the center of mass horizontally and vertically. Amputee athletes cannot actively generate energy with their running-specific prosthesis. It is likely that sprint acceleration mechanics, including step asymmetry, are altered compared with able-bodied athletes. Purpose : To investigate spatiotemporal and kinetic variables of amputee compared with able-bodied sprinters. Methods: Kinematic and kinetic data of the first and second stance were collected from 15 able-bodied and 7 amputee sprinters (2 unilateral transfemoral, 4 unilateral transtibial, and 1 bilateral transtibial) with a motion-capture system (250 Hz) and 2 force plates (1000 Hz). In addition, bilateral asymmetry was quantified and compared between groups. Results: Compared with able-bodied athletes, amputee athletes demonstrated significantly lower performance values for 5- and 10-m times. Step length, step velocity, and step frequency were decreased and contact times increased. Peak horizontal force and relative change of horizontal velocity were decreased in both stances. Peak vertical force and relative change of vertical velocity were lower for the amputee than the able-bodied group during the first stance but significantly higher during the second stance. During the first stance, able-bodied and amputee sprinters displayed a similar orientation of the ground-reaction-force vector, which became more vertically orientated in the amputee group during second stance. Amputee sprinters showed significantly greater asymmetry magnitudes for vertical force kinetics compared with able-bodietd athletes. Conclusion: A running-specific prosthesis does not replicate the function of the biological limb well in the early acceleration phase.