In this paper, we present an analysis to identify a sensor location for an inertial measurement unit (IMU) on the body of a skier and propose the best location to capture turn motions for training. We also validate the manner in which the data from the IMU sensor on the proposed location can characterize ski turns and performance with a series of statistical analyses, including a comparison with data collected from foot pressure sensors. The goal of the study is to logically identify the ideal location on the skier’s body to attach the IMU sensor and the best use of the data collected for the skier. The statistical analyses and the hierarchical clustering method indicate that the pelvis is the best location for attachment of an IMU, and numerical validation shows that the data collected from this location can effectively estimate the performance and characteristics of the skier. Moreover, placement of the sensor at this location does not distract the skier’s motion, and the sensor can be easily attached and detached. The findings of this study can be used for the development of a wearable device for the routine training of professional skiers.
Problem definition: We study a product-line design problem in which customer choice among multiple products is given by a multinomial logit (MNL) model. A firm determines product quality and prices in an evolving product line to maximize profit. In particular, given the prices and quality of products that already exist in a product line, the firm optimizes prices and/or quality of the new products. Academic/practical relevance: We extend the literature on discrete choice models to include the interaction between product quality and product price and consider two variations of the problem, each mirroring a relevant decision setting found in practice: Variation i is a price-optimization problem in which the firm determines prices of the new products given the quality. Variation ii is a joint price and quality optimization of the new products. Methodology: We apply convex optimization techniques and analyze properties of optimal solutions. Results: We establish concavity of the profit function under price optimization and present tractable solution approaches for the joint quality–price optimization. For each problem variation, we characterize the optimal solution and develop efficient algorithms. We show that the interaction of price and quality is central not only to reconciling the divergence of the existing literature’s equal-markup price prediction from differentiated markups observed in practice, but also for explaining differentiated quality measures across products; this empirically observed strategy can now be quantified and optimized with the model developed in this paper. In addition, we show that the presence of existing products tends to drive the firm to offer new products with both higher quality and prices because of the price–quality interaction. Managerial implications: Findings of this paper offer not only managerial guidelines, but also tools for decision support because of the wide empirical applicability of the MNL model. An important managerial implication is that the lack of realism in the linear utility of the MNL model can be addressed by including price–quality interaction, which is central to understanding the quality and price decision in product-line design. The interaction rationalizes the matching of high markup with high quality and justifies differentiated offering of new products in the presence of existing products.
[Purpose] The purpose of this study was to examine the effect of a 40-minute race on muscle activity and spatiotemporal cycle variables at four-time points during a 12-km roller skiing test using the double-poling technique. [Subjects and Methods] Five elite cross-country (XC) skiers on the Korean National reserve team participated in the study. Part of a biathlon course that consisted of both flat land and slopes was selected, and three measurements were recorded after every 4-km lap. Spatiotemporal variables, mean frequency and mean amplitude of 6 muscles were the chosen computational parameters. [Results] Significant differences were observed in cycle time and rate. The mean frequency of the upper-body muscles exhibited declining trends, with statistically significant differences for the triceps brachii. In addition, there were significant differences in the mean amplitude of the tibialis anterior and gastrocnemius. The activity of the triceps brachii, tibialis anterior, and gastrocnemius showed some degree of dependence on the technique. [Conclusion] Training and race strategies that improve the function of elbow extensors and ankle dorsiflexors are important in XC skiing; the application of roller-ski training research to actual XC skiing competitions is needed.
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