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- Holmberg, L. Joakim, 1971-
(author)
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Musculoskeletal Biomechanics in Cross-country Skiing
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Why copy the best athletes? When you finally learn their technique, they may have already moved on. Using muscluloskeletal biomechanics you might be able to add the "know-why" so that you can lead, instead of being left in the swells.This dissertation presents the theoretical framework of musculoskeletal modeling using inverse dynamics with static optimization. It explores some of the possibilities and limitations of musculoskeletal biomechanics in cross-country skiing, especially double-poling. The basic path of the implementation is shown and discussed, e.g. the issue of muscle model choice. From that discussion it is concluded that muscle contraction dynamics is needed to estimate individual muscle function in double-poling. Several computer simulation models, using The Anybody Modeling System™, have been created to study different cross-country skiing applications. One of the applied studies showed that the musculoskeletal system is not a collection of discrete uncoupled parts because kinematic differences in the lower leg region caused kinetic differences in the other end of the body. An implication of the results is that the kinematics and kinetics of the whole body probably are important when studying skill and performance in sports. Another one of the applied studies showed how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Skiing efficiency was defined as skiing work divided by metabolic muscle work, performance was defined as forward impulse. A higher utilization of the lower-body increased the performance, but decreased the skiing efficiency. The results display the potential of musculoskeletal biomechanics for skiing efficiency estimations. The subject of muscle decomposition is also studied. It is shown both analytically and with numerical simulations that muscle force estimates may be affected by muscle decomposition depending on the muscle recruitment criteria. Moreover, it is shown that proper choices of force normalization factors may overcome this issue. Such factors are presented for two types of muscle recruitment criteria.To sum up, there are still much to do regarding both the theoretical aspects as well as the practical implementations before predictions on one individual skier can be made with any certainty. But hopefully, this disseration somewhat furthers the fundamental mechanistic understanding of cross-country skiing, and shows that musculoskeletal biomechanics will be a useful complement to existing experimental methods in sports biomechanics.
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| 2. |
- Holmberg, Joakim L., 1971-
(author)
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Computational Biomechanics in Cross-country Skiing
- 2008
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Licentiate thesis (other academic/artistic)abstract
- Traditionally, research on cross‐country skiing biomechanics is based mainly on experimental testing alone. Trying a different approach, this thesis explores the possibilities of using computational musculoskeletal biomechanics for cross‐country skiing. As far as the author knows, this has not been done before.Cross‐country skiing is both fast and powerful, and the whole body is used to generate movement. Consequently, the computational method used needs to be able to handle a full‐body model with lots of muscles. This thesis presents several simulation models created in the AnyBody Modeling System, which is based on inverse dynamics and static optimization. This method allows for measurementdriven full‐body models with hundreds of muscles and rigid body segments of all major body parts.A major result shown in the thesis is that with a good simulation model it is possible to predict muscle activation. Even though there is no claim of full validity of the simulation models, this result opens up a wide range of possibilities for computational musculoskeletal biomechanics in cross‐country skiing. Two example of new possibilities are shown in the thesis, finding antagonistic muscle pairs and muscle load distribution differences in different skiing styles. Being able to perform optimization studies and asking and answering “what if”‐questions really gives computational methods an edge compared to traditional testing.To conclude, a combination of computational and experimental methods seems to be the next logical step to increase the understanding of the biomechanics of crosscountry skiing.
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| 3. |
- Holmberg, L. Joakim, 1971-
(author)
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A simulation study on the necessity of muscle contraction dynamics in cross-country skiing
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Other publication (other academic/artistic)abstract
- Competitive cross-country skiing is considered to be a fast and powerful dynamic movement. It is unknown what level of complexity that is needed in a musculoskeletal model of a skiing movement, e.g. double-poling. Therefore, a simulation study is carried out to explore the influence of muscle model choice. The theoretical framework of two types of muscle models and their respective implementations are given. These models are a Hill-type model with contraction dynamics and a constant force model, respectively. Results show that it is necessary to incorporate muscle contraction dynamics to estimate individual muscle behaviour in double-poling. Moreover, it may be bad practice to model different body parts with different muscle models; the musculoskeletal system is not a collection of discrete uncoupled body parts and kinetic effects will propagate through the system.
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| 4. |
- Holmberg, L. Joakim, 1971-
(author)
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Biomekanisk simulering av längdskidåkning
- 2012
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In: Svensk idrottsmedicin. - Järna : Svensk Förening För Fysisk Aktivitet och Idrottmedicin. - 1103-7652. ; 31:3, s. 11-13
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Journal article (pop. science, debate, etc.)
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| 5. |
- Holmberg, L. Joakim, 1971-, et al.
(author)
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Can Simulations Assist in Classification Development?
- 2013
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In: Equipment and Technology in Paralympic Sports. - : International Paralympic Committee.
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Conference paper (other academic/artistic)abstract
- There is a critical need for research that describes the extent to which impairments of varying type, severity and distribution impact performance in Paralympic sports. It is important with evidence-based judgment on how the impairments aect performance. In the following, we present a complementary evidence-based tool for classication.Let us start with an example. We recently presented a study (Holmberg et al., 2012)1 that utilized two full-body musculoskeletal simulation models of cross-country skiing (double-poling). The models were identical except that one carried no muscles in the right lower leg and foot; thus mimicking a lower leg prosthesis. It was hypothesized that a lower leg prosthesis would inuence muscular work throughout the whole body. Results showed that to generate the same motion and external work, an able-bodied skier only had to produce about 80% metabolic muscle work compared to a disabled skier (with a non-active right lower leg prosthesis).In reality there is always psychological factors present and it is probably not possible to nd two human beings (one fully functional and one impaired) with the same tness, size, strength and technique. Thus, it is hard to nd the unbiased eect of an impairment on performance in a speci c sport. The example above shows the strength of using simulations because a musculoskeletal model yields quantitative data on the unbiased eect of dierent functional impairments.In cross-country skiing, athletes with functional impairments are, in 'competition format' classification, assigned to dierent categories with weight factors. Athletes perform their race and the result list is presented as race time multiplied by weight factor. In the future, musculoskeletal simulations may assist in answering how a specic functional impairment aects performance and thereby improve the fairness in assigning weight factors for classication.
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| 6. |
- Holmberg, L. Joakim, 1971-, et al.
(author)
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Muscle decomposition and recruitment criteria influence muscle force estimates
- 2012
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In: Multibody system dynamics. - : Springer. - 1384-5640 .- 1573-272X. ; 28:3, s. 283-289
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Journal article (peer-reviewed)abstract
- It has recently been pointed out that muscle decomposition influence muscle force estimates in musculoskeletal simulations. We show analytically and with numerical simulations that this influence depends on the recruitment criteria. Moreover, we also show that the proper choices of force normalization factors may overcome the issue. Such factors for the minmax and the polynomial criteria are presented.
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| 7. |
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| 8. |
- Rasmussen, John, et al.
(author)
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Performance optimization by musculoskeletal simulation
- 2012
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In: Movement & Sport Sciences – Science & Motricité. - Les Ulis, France : EDP Sciences. - 2118-5735 .- 2118-5743. ; 75, s. 73-83
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Journal article (peer-reviewed)abstract
- This paper uses two examples, from cross country skiing and badminton, to illustrate the idea of using musculoskeletal simulation as a tool to understand and ultimately optimize sports performance. The results show that the analysis provides insight into the performances that cannot be obtained by other means, and it is advocated that this insight ultimately can lead to better coaching. The importance of “know-why” over “know-how” is stressed, and it is hypothesized that this may enable athletes to learn difficult techniques faster.
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| 9. |
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| 10. |
- Rovan, Klemen, et al.
(author)
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The steps needed to perform acceleration and turning at different approach speeds
- 2014
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In: Kinesiologia Slovenica. - : University of Ljubljana. - 1318-2269 .- 2232-4062. ; 20:1, s. 38-50
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Journal article (peer-reviewed)abstract
- The aims of the study were to examine: how many and which steps are needed to initiate and complete accelerations and turnings at different angles at different approach speeds; and how an intended turning angle and approach speed influence the magnitude of the actual turning angle in each step. Eight soccer players participated in the study. They performed acceleration and turnings: 1) from a standstill; 2) while already jogging; and 3) while already running on an outdoor soccer field. The speeds and angles were calculated from the data obtained from the high-end Global Navigation Satellite System. The high correlation between the intended turning angle and actual turning angle indicated the major turning steps during a turn. The intended turning angle revealed a large effect on the magnitude of the turning angle during the side-step (r = 0.995, p < 0.01) and the following step (r = 0.950, p < 0.01) for acceleration and turning from a standstill, and during the first two steps following the side-step for starts made while already jogging (r= 0.919, p < 0.01; r = 0.952, p < 0.01) and running (r = 0.897, p < 0.01; r = 0.881, p < 0.01). Further, a major part of the turning began earlier at a lower approach speed, which allowed the turning to be more quickly completed. In conclusion, the effect of acceleration with turning on the turning angle could already be seen two steps before and up to two steps after the major turning steps during a turn.
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