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- Björklund, Glenn, 1972-, et al.
(författare)
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Biomechanical influenced differences in O2 extraction in diagonal skiing: arm versus leg
- 2010
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Ingår i: Medicine & Science in Sports & Exercise. - : Lippincott Williams & Wilkins. - 0195-9131 .- 1530-0315. ; 42:10, s. 1899-1908
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Tidskriftsartikel (refereegranskat)abstract
- Biomechanically Influenced Differences in O-2 Extraction in Diagonal Skiing: Arm versus Leg. Med. Sci. Sports Exerc., Vol. 42, No. 10, pp. 1899-1908, 2010. Purpose: This study aimed to determine whether the differences in oxygen extraction and lactate concentration in arms and legs during cross-country skiing are related to muscle activation or force production and how these differences are influenced by a reduction in exercise intensity. Methods: Nine well-trained male cross-country skiers (age = 22 +/- 3 yr, (V) over dotO(2max) = 5.3 +/- 0.3 L.min(-1) and 69 +/- 3 mL.kg(-1).min(-1)) performed diagonal skiing on a treadmill for 3 min at 90% followed by 6 min at 70% of (V) over dotO(2max). During the final minute of each workload, arterial, femoral, and subclavian venous blood was collected for determination of blood gases, pH, and lactate. EMG was recorded from six upper-and lower-body muscles, and leg and pole forces were measured. Cardiorespiratory variables were monitored continuously. Results: Oxygen extraction in the legs was higher than that in the arms at both 90% and 70% of (V) over dotO(2max) (92% +/- 3% vs 85% +/- 6%, P < 0.05 and 90% +/- 3% vs 78% +/- 8%, P < 0.001). This reduction with decreased workload was more pronounced in the arms (-9.8% +/- 7.7% vs -3.2% +/- 3.2%, P < 0.01). EMGRMS for the arms was higher, and pole ground contact time was greater than the corresponding values for the legs (both P < 0.01). At both intensities, the blood lactate concentration was higher in the subclavian than that in the femoral vein but was lowered more in the subclavian vein when intensity was reduced (all P < 0.001). Conclusions: The higher muscle activation (percentage of maximal voluntary isometric contraction) in the arms and the longer ground contact time of the poles than the legs contribute to the lower oxygen extraction and elevated blood lactate concentration in the arms in diagonal skiing. The better lactate recovery in the arms than that in the legs is aided by greater reductions in muscle activation and pole force when exercise intensity is reduced.
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| 2. |
- Björklund, Glenn, et al.
(författare)
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Blood lactate recovery and respiratory responses during diagonal skiing of variable intensity
- 2011
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Ingår i: European Journal of Sport Science. - : Informa UK Limited. - 1746-1391 .- 1536-7290. ; 11:5, s. 317-326
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Tidskriftsartikel (refereegranskat)abstract
- The aims of the study were to investigate blood lactate recovery and respiratory variables during diagonal skiing of variable intensity in skiers at different performance levels. Twelve male cross-country skiers classified as elite (n=6; VO2max=73±3 ml. kg-1. min-1) or moderately trained (n=6; VO2max=61±5 ml. kg-1. min-1) performed a 48-min variable intensity protocol on a treadmill using the diagonal stride technique on roller skis, alternating between 3 min at 90% and 6 min at 70% of VO2max. None of the moderately trained skiers were able to complete the variable intensity protocol and there was a difference in time to exhaustion between the two groups (elite: 45.0±7.3 min; moderately trained: 31.4±10.4 min) (P<0.05). The elite skiers had lower blood lactate concentrations and higher blood base excess concentrations at all 70% workloads than the moderately trained skiers (all P<0.05). In contrast, VE/VO2 and VE/VCO2 at the 70% VO2max workloads decreased independently of group (P<0.05). Partial correlations showed that VO2max was related to blood lactate at the first and second intervals at 70% of VO2max (r=-0.81 and r=-0.82; both P<0.01) but not to VE/VO2, VE/VCO2 or the respiratory exchange ratio. Our results demonstrate that during diagonal skiing of variable intensity, (1) elite skiers have superior blood lactate recovery compared with moderately trained skiers, who did not show any lactate recovery at 70% of VO2max, suggesting it is an important characteristic for performance; and (2) the decreases in respiratory exchange ratio, VE/VO2, and VE/VCO2 do not differ between elite and moderately trained skiers.
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| 3. |
- Björklund, Glenn, 1972-, et al.
(författare)
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Låt underlaget bestämma löpsteget
- 2014
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Ingår i: Svensk Idrottsforskning. - 1103-4629. ; :4, s. 8-11
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Björklund, Glenn, 1972-
(författare)
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Metabolic and Cardiovascular Responses During Variable Intensity Exercise
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Previous research investigating endurance sports from a physiological perspectivehas mainly used constant or graded exercise protocols, although the nature ofsports like cross-country skiing and road cycling leads to continuous variations inworkload. Current knowledge is thus limited as regards physiological responses tovariations in exercise intensity. Therefore, the overall objective of the present thesiswas to investigate cardiovascular and metabolic responses to fluctuations inexercise intensity during exercise. The thesis is based on four studies (Studies I-IV);the first two studies use a variable intensity protocol with cardiorespiratory andblood measurements during cycling (Study I) and diagonal skiing (Study II). InStudy III one-legged exercise was used to investigate muscle blood flow duringvariable intensity exercise using PET scanning, and Study IV was performed toinvestigate the transition from high to low exercise intensity in diagonal skiing,with both physiological and biomechanical measurements. The current thesisdemonstrates that the reduction in blood lactate concentration after high-intensityworkloads is an important performance characteristic of prolonged variableintensity exercise while cycling and diagonal skiing (Studies I-II). Furthermore,during diagonal skiing, superior blood lactate recovery was associated with a highaerobic power (VO2max) (Study II). Respiratory variables such as VE/VO2, VE/VCO2and RER recovered independently of VO2max and did not reflect the blood lactate oracid base levels during variable intensity exercise during either cycling or diagonalskiing (Studies I-II). There was an upward drift in HR over time, but not inpulmonary VO2, with variable intensity exercise during both prolonged cyclingand diagonal skiing. As a result, the linear HR-VO2 relationship that wasestablished with a graded protocol was not present during variable intensityexercise (Studies I-II). In Study III, blood flow heterogeneity during one-leggedexercise increased when the exercise intensity decreased, but remained unchangedbetween the high intensity workloads. Furthermore, there was an excessiveincrease in muscular VO2 in the consecutive high-intensity workloads, mainlyexplained by increased O2 extraction, as O2 delivery and blood flow remainedunchanged. In diagonal skiing (Study IV) the arms had a lower O2 extraction thanthe legs, which could partly be explained by their longer contact phase along withmuch higher muscle activation. Furthermore, in Study IV, the O2 extraction in botharms and legs was at the upper limit during the high intensity workload with nofurther margin for increase. This could explain why no excessive increase inpulmonary VO2 occurred during diagonal skiing (Study II), as increased O2extraction is suggested to be the main reason for this excessive increase in VO2(Study III).
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| 8. |
- Laaksonen, Marko, 1975-, et al.
(författare)
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Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise
- 2010
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Ingår i: Clinical Physiology and Functional Imaging. - 1475-0961 .- 1475-097X. ; 30:4, s. 241-249
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Tidskriftsartikel (refereegranskat)abstract
- The association between muscle oxygen uptake (VO2) and perfusion or perfusion heterogeneity (relative dispersion, RD) was studied in eight healthy male subjects during intermittent isometric (1 s on, 2 s off) one-legged knee-extension exercise at variable intensities using positron emission tomography and a-v blood sampling. Resistance during the first 6 min of exercise was 50% of maximal isometric voluntary contraction force (MVC) (HI-1), followed by 6 min at 10% MVC (LOW) and finishing with 6 min at 50% MVC (HI-2). Muscle perfusion and O2 delivery during HI-1 (26 ± 5 and 5·4 ± 1·0 ml 100 g−1 min−1) and HI-2 (28 ± 4 and 5·8 ± 0·7 ml 100 g−1 min−1) were similar, but both were higher (P<0·01) than during LOW (15 ± 3 and 3·0 ± 0·6 ml 100 g−1 min−1). Muscle VO2 was also higher during both HI workloads (HI-1 3·3 ± 0·4 and HI-2 4·1 ± 0·6 ml 100 g−1 min−1) than LOW (1·4 ± 0·4 ml 100 g−1 min−1; P<0·01) and 25% higher during HI-2 than HI-1 (P<0·05). O2 extraction was higher during HI workloads (HI-1 62 ± 7 and HI-2 70 ± 7%) than LOW (45 ± 8%; P<0·01). O2 extraction tended to be higher (P = 0·08) during HI-2 when compared to HI-1. Perfusion was less heterogeneous (P<0·05) during HI workloads when compared to LOW with no difference between HI workloads. Thus, during one-legged knee-extension exercise at variable intensities, skeletal muscle perfusion and O2 delivery are unchanged between high-intensity workloads, whereas muscle VO2 is increased during the second high-intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O2 delivery and uptake. We propose that the excess muscle VO2 during the second high-intensity workload is derived from working muscle cells.
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| 9. |
- Löfgren, Ragnhild, et al.
(författare)
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Exploratory talk in science education : Inquiry-based learning and communicative approach in primary school
- 2013
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Ingår i: Journal of Baltic Science Education. - : Scientific Methodical Center. - 1648-3898 .- 2538-7138. ; 12:4, s. 482-496
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Tidskriftsartikel (refereegranskat)abstract
- Recent research on science education has increasingly focused on the role of exploratory talk for learning science in school. This study was conducted in third grade in the Swedish compulsory school and shows how difficult exploratory talk in science is to achieve. The recordings of each lesson focused mainly on the teacher but included the pupils as the teacher interacted with them. The empirical material was analysed from two different perspectives: ways of communicating the science content and communicative approach. The analysis of the classroom practice showed that scientific descriptions were dominating ways of communication. Only in a few cases explanations of scientific phenomena were in focus. Those situations caused turning points into more interactive/dialogic communications or exploratory talk. One main conclusion is that exploratory talk and scientific explanations are not easily achieved when working in primary school. These skills are not automatically attained by the use of inquiry-based material - it needs to be trained!
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| 10. |
- Löfgren, Ragnhild, et al.
(författare)
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Kommunicera naturvetenskap i skolan – exempel från årskurs 3.
- 2011
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Ingår i: Ämnesdidaktik<em> -- dåtid, nutid och framtid</em>.. - Linköping : Linköping University Electronic Press. - 9789173931823 ; , s. 51-62
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Bokkapitel (refereegranskat)abstract
- Kapitlet handlar det om kommunikation och interaktion mellan lärare och elever.Löfgren m.fl. prövar ett analysverktyg för att studera dialog- eller interaktionstyperi klassrummet. Har samtalet om ämnet någon betydelse ochvilka olika typer av elev- lärar-interaktion kan finnas? Samtalet är enligtförfattarna kontextbundet till respektive ämnes diskurs. Inom naturvetenskaputgörs diskursen främst av beskrivningar, generaliseringar och förklaringar,med andra ord hur läraren får eleverna att tillägna sig och användanaturvetenskapliga begrepp. De visar på mönster i interaktionenmellan lärare och elev och genom framför allt sociokulturella teorier omlärande analyserar de vilken typ av interaktion som bäst främjar begreppsutveckling.
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