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- Lund Ohlsson, Marie, et al.
(author)
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Evaulation of two sitting positions in Cross-Country Sit-Skiing
- 2016
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In: Abstract book of the 7th International Congress on Science and skiing. - 9783200048850
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Conference paper (other academic/artistic)abstract
- INTRODUCTION In cross-country sit-skiing (CCSS) athletes with reduced trunk control mainly sit with their knees higher than the hips (KH) to increase trunk stability. To improve the spine curvature by reducing kyphosis a new sitting position was created where the knees are lower than the hips by help of a forward trunk support (KL). The aim of this study was to evaluate the new KL position and compare it to KH in terms of physiological and biomechanical measurements as well as musculoskeletal simulations. METHODS Five abled-bodied female cross-country skiers (62.6±8.1kg, 1.67±0.05m) performed two sets of tests; one in each sitting position on a skiing ergometer (ThoraxTrainer A/S, Denmark). Each test comprised a 30s all-out test (AO), an incremental submaximal test (4 to 6 x 3 min, SUB1-SUB6) and a maximal time-trial test of 3 min (MAX). During SUB and MAX external power and kinematics were measured. Metabolic rates (MR) were calculated from oxygen consumption and lactate concentrations. The AnyBody Modelling system (AMS 6.0, Anybody Technology A/S, Denmark) were used to simulate full-body musculoskeletal models over 4 poling cycles of SUB2, SUB4 and MAX. From the simulations muscular metabolic rate (mMR) and musculo-skeletal efficiency (ME) were computed (Holmberg et al., 2013). RESULTS & DISCUSSION The performance (W/kg) was higher in KH (p < 0.01) in both AO (24%) and MAX (32%). KL had more flexed knee, more extended hip and less kyphosis in trunk, while KH had larger range of motion (ROM) in hip and larger flexion and ROM in spine at SUB4 and MAX. Gross efficiency (GE) was higher in KH than KL. The total MR and ratio of anaerobic MR to total MR were higher in KL at SUB3 and SUB4. Simulations showed that 4 subjects had higher ME in KH for both SUB4 and MAX, though no statistical significance were observed. mMR were higher for KL at SUB2 and SUB4 but it was higher for KH at MAX. The ratio of mMR in body parts to total mMR showed higher ratio for KL in arm-shoulders (6.7-9.1%) and higher ratio for KH in trunk (3.7-4.6%) and hip-legs (3.0-4.6%). CONCLUSION The physiological results were comparable to others (Lajunen, 2014 & Verellen et al, 2012) and the simulation results were novel by showing how the motion of the trunk contributes to the total metabolic rate. KH position showed higher performance and GE while the KL position indicated higher mMR for arm-shoulders, and had also higher anaerobic MR. Therefore the KH position is favorable for abled-bodied athletes because KL limits trunk motion. REFERENCES Holmberg, L. J. et al. (2013). Comput Methods Biomech Biomed Engin, 16(9), 987-992. Lajunen, K. (2014). Effect of sitting posture on sit-skiing economy. Bachelor’s thesis, University of Jyväskylä.Verellen, J. et al. (2012). Eur J Appl Physiol, 112(3), 983-989.
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| 2. |
- Lund Ohlsson, Marie, et al.
(author)
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On the effect of sitting position, in simulated cross-country sit-skiing
- 2016
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Conference paper (peer-reviewed)abstract
- IntroductionIn Cross-country sit-skiing (CCSS), athletes with severe reduced trunk control are mainly seated with the knees higher than the hip (KH; arm and trunk powered). However this posture is hypothesized to have high risk for lower back and shoulder injuries. Therefore, a new seat was created where the knees were lower than hip and the trunk frontal supported (KL), to improve spinal curvature. Thus, the aim of this study was to examine performance between these two different sitting positions.Methods10 female abled-bodied elite cross-country skiers (age 25.5 ± 3.8 years (mean ± standard deviation), height 1.65 ± 0.05 m and weight 61.1 ± 6.8 kg) were tested on a skiing ergometer (ThoraxTrainer, ThoraxTrainer A/S, Kokkedal, Denmark) in a 30 s all-out test (WIN), a submaximal incremental test with 3-6 levels of 3 min (SUB), and a maximal 3 min time-trial test (MAX). The SUB and MAX tests were monitored breath-by-breath with a stationary metabolimeter (Quark CPET, COSMED, Italy). Aerobic metabolism and gross efficiency were computed from oxygen uptake, and anaerobic metabolism were estimated from net blood lactate concentrations. Muscle oxygenation saturation (SmO2) in right vastus lateralis (VL) was monitored with NIRS methodology (Moxy Monitor, Fortiori Design LLC, Minnesota, USA).ResultsHigher performance (W·kg-1) was observed for KH both in WIN (KL: 1.13 ± 0.33, KH: 1.40 ± 0.30) and MAX (KL: 0.67 ± 0.14, KH: 0.88 ± 0.19) compared to KL (p < 0.01). No differences were observed in breathing rate, cycle rate, oxygen consumption or aerobic metabolic rate neither in SUB nor MAX. The KH position showed higher gross efficiency and lower anaerobic metabolic rate and minute ventilation. SmO2 was higher for KH compared to baseline bench (12.2 ± 7.2%) whereas no difference was observed between baseline and KL position (3.2 ± 5.5%). During SUB levels 1-4, higher SmO2 was observed for KH compared to KL when normalizing data with baseline bench (p < 0.05).DiscussionThis study showed that abled bodied athletes perform better and have higher efficiency in KH compared to KL. The position using larger part of the body (joint range of motion and amount of active muscle mass) have higher gross efficiency, lower lactate concentration and lower ventilation, also shown by Lajunen (2014). It was also concluded that SmO2 was higher in KH compared to KL, and thus there might be a smaller risk for injuries in the legs connected to circulation. This study of abled-bodied athletes have the potential to serve as a control for future studies of para-athletes. ReferencesLajunen K (2014). Effect of sitting posture on sit-skiing economy. Bachelor’s thesis, University of Jyväskylä.
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| 3. |
- Nieminen, Tuomo, et al.
(author)
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Global analysis of continental boundary layer new particle formation based on long-term measurements
- 2018
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In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 18:19, s. 14737-14756
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Journal article (peer-reviewed)abstract
- Atmospheric new particle formation (NPF) is an important phenomenon in terms of global particle number concentrations. Here we investigated the frequency of NPF, formation rates of 10 nm particles, and growth rates in the size range of 10-25 nm using at least 1 year of aerosol number size-distribution observations at 36 different locations around the world. The majority of these measurement sites are in the Northern Hemisphere. We found that the NPF frequency has a strong seasonal variability. At the measurement sites analyzed in this study, NPF occurs most frequently in March-May (on about 30 % of the days) and least frequently in December-February (about 10 % of the days). The median formation rate of 10 nm particles varies by about 3 orders of magnitude (0.01-10 cm(-3) s(-1)) and the growth rate by about an order of magnitude (1-10 nm h(-1)). The smallest values of both formation and growth rates were observed at polar sites and the largest ones in urban environments or anthropogenically influenced rural sites. The correlation between the NPF event frequency and the particle formation and growth rate was at best moderate among the different measurement sites, as well as among the sites belonging to a certain environmental regime. For a better understanding of atmospheric NPF and its regional importance, we would need more observational data from different urban areas in practically all parts of the world, from additional remote and rural locations in North America, Asia, and most of the Southern Hemisphere (especially Australia), from polar areas, and from at least a few locations over the oceans.
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