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.
Jeffrey R. Campbell, Irving S. Scher, David Carpenter, Bruce L. Jahnke and Randal P. Ching
ski boots and bindings have assured consumers that any alpine ski boot could be used appropriately in any alpine ski binding. Alpine touring (AT) is a subdiscipline of skiing in which the skier uses the skis to ascend, traverse, and descend snow-covered terrain, typically in the backcountry where
Walter Herzog and Lynda Read
The purpose of this study was to estimate cruciate ligament forces in Alpine skiing during a movement that has been associated with anterior cruciate ligament (ACL) tears. Resultant knee joint forces and moments were obtained from two skiers during a World Cup Downhill race using an inverse dynamics approach and a 2-D bilaterally symmetric system model. It was found that ACL forces were typically small for both skiers throughout the movement analyzed because quadriceps forces prevented anterior displacement of the tibia relative to the femur at the knee joint angles observed. However, for about 10 ms, loading conditions in the knee joint of Subject 2 (who displayed poor form) were such that large ACL forces may have been present. These particular loading conditions were never observed in Subject 1, who displayed good form. Since neither of the skiers was injured, it is not possible to draw firm conclusions about isolated ACL tears in Alpine skiing from the data at hand.
Andrew W. Subudhi, Scott L. Davis, Ronald W. Kipp and E. Wayne Askew
The goal of this field study was to assess antioxidant status and markers of oxidative damage in elite alpine ski racers during routine training. Subjects included 12 members of the U.S. Men’s Alpine Ski Team attending a 10-day summer training camp. Blood draws were collected at rest and after exercise: (a) prior to training, (b) following 2 days of dry land training, and (c) after 4 days of on-snow skiing. Seven measures of antioxidant status were determined using colorimetric and HPLC methods (Trolox “equivalent antioxidant capacity, uric acid, α-tocopherol, β-tocopherol, total glutathione, cytosolic glutathione peroxidase, and superoxide dismutase). Oxidative stress was assessed using 2 markers of lipid peroxidation (malondialdehyde and lipid hydroperoxides) and 2 markers of protein oxidation (carbonylated total proteins and carbonylated hemoglobin). The results of this study suggest that antioxidant status of elite alpine skiers may decline over a period of intense training. However, elevations in markers of oxidative stress were not evident.
Caroline Barelle, Anne Ruby and Michel Tavernier
Aerodynamic properties are one of the factors that determine speed performance in Alpine skiing. Many studies have examined the consequences of this factor in downhill skiing, and the impact of postural modifications on speed is now well established. To date, only wind tunnel tests have enabled one to measure aerodynamic drag values (a major component of the aerodynamic force in Alpine skiing). Yet such tests are incompatible with the constraints of a regular and accurate follow-up of training programs. The present study proposes an experimental model that permits one to determine a skier's aerodynamic drag coefficient (SCx) based on posture. Experimental SCx measurements made in a wind tunnel are matched with the skier's postural parameters. The accuracy of the model was determined by comparing calculated drag values with measurements observed in a wind tunnel for different postures. For postures corresponding to an optimal aerodynamic penetration (speed position), the uncertainty was 13%. Although this model does not permit an accurate comparison between two skiers, it does satisfactorily account for variations observed in the aerodynamic drag of the same skier in different postures. During Alpine ski training sessions and races, this model may help coaches assess the gain or loss in time induced by modifications in aerodynamic drag corresponding to different postures. It may also be used in other sports to help determine whether the aerodynamic force has a significant impact on performance.
Kevin Eseltine and Maury L. Hull
This article describes the design of a new binding for Alpine skiing wherein the release level of the toepiece in twist is modulated based on the level of neural stimulation of one of the vastii muscles in the quadriceps group. A conventional binding toepiece that relies on the force of a compressed spring to resist the release of the boot was modified. To modulate the release level to either a high or a low state, a special solenoid activated mechanism that alters the binding spring constant was designed. The design details of this special mechanism are described and the computations necessary to ensure reliable activation with a low force solenoid are summarized. Also described is the special circuitry that was designed to actuate the solenoid. To demonstrate the workability of both the mechanism and the circuitry, a prototype binding system was constructed and tested. The results of this testing are described as well.
Werner Nachbauer, Peter Kaps, Benno Nigg, Fritz Brunner, Alexander Lutz, Günter Obkircher and Martin Mössner
A video technique to obtain 3-D data in an Alpine skiing competition was investigated. The flight and landing phases of a jump were recorded during the 1994 Olympic combined downhill race. A direct linear transformation (DLT) implementation was applied, which computes the DLT parameters for each video image of each camera separately. As a consequence, one is able to pan and tilt the cameras and zoom the lenses. The problem of distributing control points in the large object space could be solved satisfactorily. The method proved to be suitable for obtaining 3-D data with reasonable accuracy, which is even sufficient for inverse dynamics. The computed resultant knee joint forces and moments compare well with results reported by other authors.
Lynda Read and Walter Herzog
The purpose of this study was to determine resultant knee joint forces and moments during a specific movement in Alpine ski racers. The movement analyzed consisted of a landing from a bump and the initiation of recovery (if necessary). Resultant loads were obtained using an inverse dynamics approach. Results of two specific skiers are contrasted, one skier landing in good form, the second skier landing in poor form. The skier landing in poor form exhibited larger knee flexion, and larger knee joint resultant forces and moments than the skier landing in good form. The movement of the skier landing in poor form has been associated with isolated anterior cruciate ligament (ACL) injury. However, the data obtained in this study do not indicate that either skier was in danger of ACL injury.
John G. Seifert, Ronald W. Kipp, Markus Amann and Oladele Gazal
This study examined energy and fluid supplementation on indices of muscle damage during alpine skiing. Skiers were assigned to a carbohydrate-protein (CP), placebo (PL), or no fluid (NF) group. CP and PL ingested 1.62 L during and after skiing. Myoglobin did not change from pre-skiing (PS) to 2 h post-skiing (2PS) for CP (24.8 ± 1.4 and 25.6 ± 1.6 ng/mL), but rose significantly from 26.4 ± 1.3 to 40.0 ± 2.8 ng/mL for PL and from 29.0 ± 1.3 to 82.9 ± 3.6 ng/mL for NF. Creatine kinase was maintained from PRE to 2 PS for CP, but increased significantly from 117 ± 7.2 to 174 ± 43.4 U/L for PL and from 126 ± 23.2 to 243 ± 34.3 U/L for NF. This study demonstrates that ingestion of a CP beverage minimized muscle damage indices during skiing compared to PL and NF and that ingesting fluids may also minimize muscle damage compared to a NF condition.
Andreas Krüger and Jürgen Edelmann-Nusser
This study aims at determining the accuracy of a full body inertial measurement system in a real skiing environment in comparison with an optical video based system. Recent studies have shown the use of inertial measurement systems for the determination of kinematical parameters in alpine skiing. However, a quantitative validation of a full body inertial measurement system for the application in alpine skiing is so far not available. For the purpose of this study, a skier performed a test-run equipped with a full body inertial measurement system in combination with a DGPS. In addition, one turn of the test-run was analyzed by an optical video based system. With respect to the analyzed angles, a maximum mean difference of 4.9° was measured. No differences in the measured angles between the inertial measurement system and the combined usage with a DGPS were found. Concerning the determination of the skier’s trajectory, an additional system (e.g., DGPS) must be used. As opposed to optical methods, the main advantages of the inertial measurement system are the determination of kinematical parameters without the limitation of restricted capture volume, and small time costs for the measurement preparation and data analysis.