| 1. |
- Bergh, U, et al.
(author)
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Maximal oxygen uptake "classical" versus "contemporary" viewpoints.
- 2000
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In: Medicine & Science in Sports & Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 32:1, s. 85-8
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Journal article (peer-reviewed)abstract
- In two articles Timothy Noakes proposes a new physiological model in which skeletal muscle recruitment is regulated by a central "govenor," specifically to prevent the development of a progressive myocardial ischemia that would precede the development of skeletal muscle anaerobiosis during maximal exercise. In this rebuttal to the Noakes' papers, we argue that Noakes has ignored data supporting the existing hypothesis that under normal conditions cardiac output is limiting maximal aerobic power during dynamic exercise engaging large muscle groups.
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| 2. |
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| 3. |
- Craig, Cora L, et al.
(author)
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International physical activity questionnaire : 12-country reliability and validity
- 2003
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In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 35:8, s. 1381-1395
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Journal article (peer-reviewed)abstract
- BACKGROUND: Physical inactivity is a global concern, but diverse physical activity measures in use prevent international comparisons. The International Physical Activity Questionnaire (IPAQ) was developed as an instrument for cross-national monitoring of physical activity and inactivity.METHODS: Between 1997 and 1998, an International Consensus Group developed four long and four short forms of the IPAQ instruments (administered by telephone interview or self-administration, with two alternate reference periods, either the "last 7 d" or a "usual week" of recalled physical activity). During 2000, 14 centers from 12 countries collected reliability and/or validity data on at least two of the eight IPAQ instruments. Test-retest repeatability was assessed within the same week. Concurrent (inter-method) validity was assessed at the same administration, and criterion IPAQ validity was assessed against the CSA (now MTI) accelerometer. Spearman's correlation coefficients are reported, based on the total reported physical activity.RESULTS: Overall, the IPAQ questionnaires produced repeatable data (Spearman's rho clustered around 0.8), with comparable data from short and long forms. Criterion validity had a median rho of about 0.30, which was comparable to most other self-report validation studies. The "usual week" and "last 7 d" reference periods performed similarly, and the reliability of telephone administration was similar to the self-administered mode.CONCLUSIONS: The IPAQ instruments have acceptable measurement properties, at least as good as other established self-reports. Considering the diverse samples in this study, IPAQ has reasonable measurement properties for monitoring population levels of physical activity among 18- to 65-yr-old adults in diverse settings. The short IPAQ form "last 7 d recall" is recommended for national monitoring and the long form for research requiring more detailed assessment.
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| 4. |
- Crenshaw, Albert G., et al.
(author)
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Reduced muscular oxygenation during computer mouse use with time pressure and precision demands
- 2004
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In: Conference proceedings at the American College of Sports Medicine (ACSM) 51st Annual Meeting. ; 35:5, s. S221-S222
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Conference paper (peer-reviewed)abstract
- Monitoring oxidative metabolic states may provide information on the mechanism behind computer use related musculoskeletal disorders. PURPOSE: To compare tissue oxygen saturation (Sat-O2) profiles in the forearm extensor carpi radialis (ECR) during computer mouse use with and without time pressure and precision demands. METHODS: Twenty-four healthy, right-handed subjects (12 females, 12 males; age 19-28 years) participated in the study. Subjects performed a 45-min mouse operated computer task on two occasions, separated by 3-5 days. The task consisted of painting squares that were presented on the screen. On one occasion, time pressure and precision demands were imposed by limiting the time available for painting a square and introducing a scoring system based on precision of painting (STRESS). On the other occasion, no such restraints were added (NON-STRESS). The order of the two task versions was randomized. During the task, Sat-O2 in the right ECR muscle was measured by near-infrared spectroscopy – NIRS (Inspectra, Hutchinson Technology). In addition, subjective ratings of tenseness and strain, and painting performance measures were recorded. RESULTS: A repeated measures ANOVA revealed a significant decline in Sat-O2 during the STRESS condition (p < 0.05), but no change for the NON-STRESS condition. A gender difference was apparent as females exhibited an overall lower Sat-O2 than males (p < 0.05); however, no interaction was found. Subjects’ ratings of tenseness and strain were significantly higher during the STRESS as compared to the NON-STRESS condition (p < 0.001). These data were paralleled by work pace (i.e. squares painted during STRESS = 119; NON-STRESS = 84, p < 0.001). Furthermore, accuracy of painting was greater for the STRESS as compared to the NON-STRESS condition (p < 0.01), i.e., number of times outside the square, STRESS = 2, NON-STRESS = 4. No gender differences in subjective ratings or performance variables were detected. CONCLUSIONS: Our finding of a change in local metabolic states under stressful conditions may shed light on the mechanism behind computer mouse related forearm muscular disorders. Furthermore, that females demonstrate a lower ECR Sat-O2 could give precedence to their higher incidence of disorders than males.
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| 5. |
- Ekelund, Ulf, 1960-, et al.
(author)
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Energy expenditure assessed by heart rate and doubly labeled water in young athletes
- 2002
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In: Medicine & Science in Sports & Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 34:8, s. 1360-1366
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Journal article (peer-reviewed)abstract
- PURPOSE: To compare total energy expenditure (TEE) estimated by the FLEX heart rate (HR) method with that measured by the doubly labeled water (DLW) technique in young speed skaters. We hypothesized that the accuracy of FLEX HR-estimated TEE would be affected by a) the definition of the FLEX HR and b) the type of training regimen.METHODS: Eight young athletes (mean age 18.2 +/- 1.3 yr) underwent measurements during two 10-d training periods: an off-season period with voluntary training (predominantly running) and a preseason period mainly focused on skating technique training. TEE was measured simultaneously by the DLW and FLEX HR methods. FLEX HR1 was defined as the mean of the HRs during all resting calibration activities and the lowest HR during exercising calibration activities. FLEX HR2 was defined as the mean of the highest HR during resting activities and the lowest HR during exercising.RESULTS: ANOVA showed that FLEX HR1 was significantly lower than FLEX HR2 (mean of both periods; 77 +/- 5 vs 84 +/- 6 beats.min(-1); P = 0.004). TEE values obtained by DLW were 16.8 +/- 3.8 and 16.9 +/- 2.9 MJ.d(-1) in the two periods, respectively. TEE values calculated from FLEX HR1 were 17.8 +/- 3.6 and 17.4 +/- 2.6 MJ.d(-1), and those from FLEX HR2 17.1 +/- 3.1 and 17.0 +/- 2.7 MJ.d-1, respectively. No significant period (P = 0.83) or method (P = 0.44) effect on TEE was observed.CONCLUSION: FLEX HR-estimated TEE was not affected by the definition of the FLEX HR or by the type of training regimen as compared with TEE measured by the DLW method in young athletes.
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| 6. |
- Ekelund, Ulf, 1960-, et al.
(author)
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Physical activity assessed by activity monitor and doubly labeled water in children
- 2001
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In: Medicine & Science in Sports & Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 33:2, s. 275-281
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Journal article (peer-reviewed)abstract
- PURPOSE: To validate the Computer Science and Application's (CSA) activity monitor for assessment of the total amount of physical activity during two school-weeks in 9-yr-old children and to develop equations to predict total energy expenditure (TEE) and activity energy expenditure (AEE) from activity counts and anthropometric variables.METHODS: A total of 26 children (15 boys and 11 girls, mean age 9.1 +/- 0.3 yr) were monitored for 14 consecutive days. TEE was simultaneously measured by the doubly labeled water method. Averaged activity counts (counts.min(-1)) were compared with data on: 1) TEE, 2) AEE = TEE minus basal metabolic rate (BMR; estimated from predictive equations), and 3) daily physical activity level (PAL = TEE/BMR).RESULTS: Physical activity determined by activity counts was significantly related to the data on energy expenditures: TEE (r = 0.39; P < 0.05), AEE (r = 0.54; P < 0.01), and PAL (r = 0.58; P < 0.01). Multiple stepwise regression analysis showed that TEE was significantly influenced by gender, body composition (body weight or fat free mass), and activity counts (R(2) = 0.54--0.60). AEE was significantly influenced by activity counts and gender (R(2) = 0.45). There were no significant differences between activity counts and PAL in discriminating among activity levels with "low" (PAL < 1.56), "moderate" (1.57 < or = PAL > or = 1.81), and "high" (PAL > 1.81) intensity.CONCLUSION: Activity counts from the CSA activity monitor seems to be a useful measure of the total amount of physical activity in 9-yr-old children. Activity counts contributed significantly to the explained variation in TEE and was the best predictor of AEE.
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| 7. |
- Hedelin, Rikard, et al.
(author)
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Cardiac autonomic imbalance in an overtrained athlete.
- 2000
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In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 32:9, s. 1531-1533
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Journal article (peer-reviewed)abstract
- PURPOSE: In order to investigate overtraining-related adaptations in the autonomic nervous system, cardiac autonomic activity was examined in a junior cross-country skier who presented with reduced performance in competitions, early breathlessness during training sessions, and accumulated central fatigue. METHODS: Power spectral analysis of heart rate variability (HRV) was performed before, when overtrained (OT), and after recovery (Rec). RESULTS: In the overtrained state, high frequency (HF) and total powers in the lying position were higher compared with before and after. In normalized units, the increased HF in OT was even more prominent and clearly higher than in any control subject, and it was reversed in Rec. Resting heart rate was slightly reduced in OT and returned to baseline in Rec. CONCLUSIONS: The shift toward increased heart rate variability, particularly in the HF range, together with a reduced resting heart rate suggest a cardiac autonomic imbalance with extensive parasympathetic modulation in this athlete when overtrained.
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| 8. |
- Hedelin, R, et al.
(author)
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Heart rate variability in athletes : relationship with central and peripheral performance.
- 2001
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In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 33:8, s. 1394-1398
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Journal article (peer-reviewed)abstract
- PURPOSE: To investigate relationships between heart rate variability (HRV) and peripheral and central performance measures, 17 cross-country (X-C) skiers and seven canoeists were studied before and after a training period of 7 months. METHODS: For the skiers and canoeists respectively, leg and arm peak torque (Tq), time to peak torque (TiTq), and total work (Wrk) were measured in an isokinetic dynamometer. Maximal oxygen uptakes (VO(2max)) were obtained from treadmill tests. Power spectral analysis of HRV was performed on electrocardiographic recordings in the resting supine position and after a tilt to yield power in the low-frequency (0.04--0.15 Hz) and high-frequency (0.15--0.45 Hz) components of HRV. RESULTS: The change in normalized LF-variability in standing (Delta LFnT) correlated (P < 0.01) with the changes in TiTq (r = 0.63), max lactate (r = -0.63), and VO(2max) (r = -0.53). The change in absolute LFT was inversely correlated with the change in Tq. Subjects who improved VO(2max) were characterized by consistently higher high-frequency and total HRV than subjects with deteriorated aerobic capacity (P < 0.05). CONCLUSION: The results suggest that improved measures of both peripheral and central (aerobic) work capacities were associated with a reduction of low-frequency HRV in the tilted position. High-frequency and total HRV did not change in proportion with changes in muscle performance or aerobic capacity, but the ability to further improve VO(2max) with training in these already fit subjects seemed to depend on their average levels of these HRV measures, interpreted to reflect parasympathetic activity.
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| 9. |
- Hedelin, Rikard, et al.
(author)
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Short-term overtraining : effects on performance, circulatory responses, and heart rate variability.
- 2000
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In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 32:8, s. 1480-1484
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Journal article (peer-reviewed)abstract
- PURPOSE AND METHODS: Nine elite canoeists were investigated concerning changes in performance, heart rate variability (HRV), and blood-chemical parameters over a 6-d training camp. The training regimen consisted of cross-country skiing and strength training, in total 13.0+/-1.6 h, corresponding to a 50% increase in training load. RESULTS: Time to exhaustion (RunT) decreased from 19.1+/-1.0 to 18.0+/-1.2 min (P < 0.05). VO2max and max lactate (La(max)) both decreased significantly (P < 0.05) over the training period (4.99+/-0.97 to 4.74+/-0.98 L x min(-1) and from 10.08+/-1.25 to 8.98+/-1.03 mmol x L(-1) respectively). Heart rates (HR) decreased significantly at all workloads. Plasma volume increased by 7+/-7% (P < 0.05). Resting cortisol, decreased from 677+/-244 to 492+/-222 nmol x L(-1) (P < 0.05), whereas resting levels of adrenaline and noradrenaline remained unchanged. The change between tests in RunT correlated significantly with the change in HRmax (r = 0.79; P = 0.01). There were no group changes in high or low frequency HRV, neither at rest nor following a tilt. CONCLUSIONS: The reduced maximal performance indicates a state of fatigue/overreaching and peripheral factors are suggested to limit performance even though HRmax and La(max) both were reduced. The reduced submaximal heart rates are probably a result of increased plasma volume. HRV in this group didn't seem to be affected by short-term overtraining.
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| 10. |
- Krustrup, Peter, et al.
(author)
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Slow-twitch fiber glycogen depletion elevates moderate-exercise fast-twitch fiber activity and O2 uptake.
- 2004
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In: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 36:6, s. 973-82
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Journal article (peer-reviewed)abstract
- PURPOSE: We tested the hypotheses that previous glycogen depletion of slow-twitch (ST) fibers enhances recruitment of fast-twitch (FT) fibers, elevates energy requirement, and results in a slow component of VO2 during moderate-intensity dynamic exercise in humans. METHODS: Twelve healthy, male subjects cycled for 20 min at approximately 50% VO2max with normal glycogen stores (CON) and with exercise-induced glycogen depleted ST fibers (CHO-DEP). Pulmonary VO2 was measured continuously and single fiber, muscle homogenate, and blood metabolites were determined repeatedly during each trial. RESULTS: ST fiber glycogen content decreased (P < 0.05) during CON (293 +/- 24 to 204 +/- 17 mmol x kg d.w.), but not during CHO-DEP (92 +/- 22 and 84 +/- 13 mmol x kg d.w.). FT fiber CP and glycogen levels were unaltered during CON, whereas FT fiber CP levels decreased (29 +/- 7%, P < 0.05) during CHO-DEP and glycogen content tended to decrease (32 +/- 14%, P = 0.07). During CHO-DEP, VO2 was higher (P < 0.05) from 2 to 20 min than in CON (0-20 min:7 +/- 1%). Muscle lactate, pH and temperature, ventilation, and plasma epinephrine were not different between trials. From 3 to 20 min of CHO-DEP, VO2 increased (P <0.05) by 5 +/- 1% from 1.95 +/- 0.05 to 2.06 +/- 0.08 L x min but was unchanged during CON. In this exercise period, muscle pH and blood lactate were unaltered in both trials. Exponential modeling revealed a slow component of VO2 equivalent to 0.12 +/- 0.04 L x min during CHO-DEP. CONCLUSION: This study demonstrates that previous glycogen depletion of ST fibers enhances FT fiber recruitment, elevates O2 cost, and causes a slow component of VO2 during dynamic exercise with no blood lactate accumulation or muscular acidosis. These findings suggest that FT fiber recruitment elevates energy requirement of dynamic exercise in humans and support an important role of active FT fibers in producing the slow component of VO2
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