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Metabolic and Cardiovascular Responses During Variable Intensity Exercise
Mid Sweden University, Faculty of Human Sciences, Department of Health Sciences.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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).

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet , 2010.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 86
Keywords [en]
cross-country skiing, cycling, heart rate, lactate, O2 extraction, O2 uptake, performance, ventilation
National Category
Sport and Fitness Sciences
Identifiers
URN: urn:nbn:se:miun:diva-11744ISBN: 978-91-86073-76-3 (print)OAI: oai:DiVA.org:miun-11744DiVA, id: diva2:325875
Public defence
2010-06-16, Q221, Östersund, 10:30 (English)
Available from: 2010-07-01 Created: 2010-06-21 Last updated: 2013-11-21Bibliographically approved
List of papers
1. Performance predicting factors in prolonged exhausting exercise of varying intensity
Open this publication in new window or tab >>Performance predicting factors in prolonged exhausting exercise of varying intensity
2007 (English)In: European Journal of Applied Physiology, ISSN 1439-6319, E-ISSN 1439-6327, Vol. 99, no 4, p. 423-429Article in journal (Refereed) Published
Abstract [en]

Several endurance sports, e.g. road cycling, have a varying intensity profile during competition. At present, few laboratory tests take this intensity profile into consideration. Thus, the purpose of this study was to examine the prognostic value of heart rate (HR), lactate (La−1), potassium (K+), and respiratory exchange ratio (RER) performance at an exhausting cycling exercise with varying intensity. Eight national level cyclists performed two cycle tests each on a cycle ergometer: (1) a incremental test to establish VO2max, maximum power (W max), and lactate threshold (VO2LT), and (2) a variable intensity protocol (VIP). Exercise intensity for the VIP was based upon the VO2max obtained during the incremental test. The VIP consisted of six high intense (HI) workloads at 90% of VO2max for 3 min each, interspersed by five middle intense (MI) workloads at 70% of VO2max for 6 min each. VO2 and HR were continuously measured throughout the tests. Venous blood samples were taken before, during, and after the test. Increases in HR, La-, K+, and RER were observed when workload changed from MI to HI workload (P < 0.05). Potassium and RER decreased after transition from HI to MI workloads (P < 0.05). There was a negative correlation between time to exhaustion and decrease in La- concentration during the first MI (r = −0.714; P = 0.047). Furthermore, time to exhaustion correlated with VO2LT calculated from the ramp test (r = 0.738; P = 0.037). Our results suggest that the magnitude of decrease of La−1 between the first HI workload and the consecutive MI workload could predict performance during prolonged exercise with variable intensity

Keywords
Cycling, Exercise, Lactate, Potassium, Idrottsvetenskap
National Category
Sport and Fitness Sciences Microbiology
Identifiers
urn:nbn:se:miun:diva-4539 (URN)10.1007/s00421-006-0352-0 (DOI)000243963000011 ()2-s2.0-33846872580 (Scopus ID)5629 (Local ID)5629 (Archive number)5629 (OAI)
Note

VR-Medicine, External

Available from: 2008-09-30 Created: 2009-06-07 Last updated: 2017-12-12Bibliographically approved
2. Blood lactate recovery and respiratory responses during diagonal skiing of variable intensity
Open this publication in new window or tab >>Blood lactate recovery and respiratory responses during diagonal skiing of variable intensity
2011 (English)In: European Journal of Sport Science, ISSN 1746-1391, E-ISSN 1536-7290, Vol. 11, no 5, p. 317-326Article in journal (Refereed) Published
Abstract [en]

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&lt;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&lt;0.05). In contrast, VE/VO2 and VE/VCO2 at the 70% VO2max workloads decreased independently of group (P&lt;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&lt;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.

Keywords
Exercise, Lactate, Oxygen uptake, Ventilatory equivalents
National Category
Sport and Fitness Sciences
Identifiers
urn:nbn:se:miun:diva-15361 (URN)10.1080/17461391.2010.521580 (DOI)000299419700003 ()2-s2.0-80052293601 (Scopus ID)
Available from: 2011-12-18 Created: 2011-12-18 Last updated: 2017-12-08Bibliographically approved
3. Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise
Open this publication in new window or tab >>Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise
Show others...
2010 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 30, no 4, p. 241-249Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
blood flow, knee extension, oxygen delivery, positron emission tomography, skeletal muscle
National Category
Physiology
Identifiers
urn:nbn:se:miun:diva-10421 (URN)10.1111/j.1475-097X.2010.00934.x (DOI)000278564500004 ()20491840 (PubMedID)2-s2.0-77954093861 (Scopus ID)
Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2018-01-12Bibliographically approved
4. Biomechanical influenced differences in O2 extraction in diagonal skiing: arm versus leg
Open this publication in new window or tab >>Biomechanical influenced differences in O2 extraction in diagonal skiing: arm versus leg
2010 (English)In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 42, no 10, p. 1899-1908Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Lippincott Williams & Wilkins, 2010
Keywords
CROSS-COUNTRY SKIING, EMG, FORCE, LACTATE, OXYGEN CONSUMPTION
National Category
Sport and Fitness Sciences Physiology
Identifiers
urn:nbn:se:miun:diva-10877 (URN)10.1249/MSS.0b013e3181da4339 (DOI)000282188300013 ()20216469 (PubMedID)2-s2.0-77957333501 (Scopus ID)
Projects
Integrative Human PhysiologyIntegrative Physiologi & Biomechanics
Available from: 2010-01-06 Created: 2010-01-06 Last updated: 2018-01-12Bibliographically approved

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