| 1. |
- Siebenmann, Christoph, et al.
(författare)
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Hypoxia increases exercise heart rate despite combined inhibition of beta-adrenergic and muscarinic receptors
- 2015
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Ingår i: American Journal of Physiology. Heart and Circulatory Physiology. - : American Physiological Society. - 0363-6135 .- 1522-1539. ; 308:12, s. H1540-H1546
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Tidskriftsartikel (refereegranskat)abstract
- Hypoxia increases the heart rate response to exercise, but the mechanism(s) remains unclear. We tested the hypothesis that the tachycardic effect of hypoxia persists during separate, but not combined, inhibition of beta-adrenergic and muscarinic receptors. Nine subjects performed incremental exercise to exhaustion in normoxia and hypoxia (fraction of inspired O-2 = 12%) after intravenous administration of 1) no drugs (Cont), 2) propranolol (Prop), 3) glycopyrrolate (Glyc), or 4) Prop + Glyc. HR increased with exercise in all drug conditions (P < 0.001) but was always higher at a given workload in hypoxia than normoxia (P < 0.001). Averaged over all workloads, the difference between hypoxia and normoxia was 19.8 +/- 13.8 beats/min during Cont and similar (17.2 +/- 7.7 beats/min, P = 0.95) during Prop but smaller (P < 0.001) during Glyc and Prop + Glyc (9.8 +/- 9.6 and 8.1 +/- 7.6 beats/min, respectively). Cardiac output was enhanced by hypoxia (P < 0.002) to an extent that was similar between Cont, Glyc, and Prop + Glyc (2.3 +/- 1.9, 1.7 +/- 1.8, and 2.3 +/- 1.2 l/min, respectively, P > 0.4) but larger during Prop (3.4 +/- 1.6 l/min, P = 0.004). Our results demonstrate that the tachycardic effect of hypoxia during exercise partially relies on vagal withdrawal. Conversely, sympathoexcitation either does not contribute or increases heart rate through mechanisms other than beta-adrenergic transmission. A potential candidate is beta-adrenergic transmission, which could also explain why a tachycardic effect of hypoxia persists during combined beta-adrenergic and muscarinic receptor inhibition.
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| 2. |
- Nordsborg, N. B., et al.
(författare)
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Oxidative capacity and glycogen content increase more in arm than leg muscle in sedentary women after intense training
- 2015
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Ingår i: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 119:2, s. 116-123
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Tidskriftsartikel (refereegranskat)abstract
- The hypothesis that the adaptive capacity is higher in human upper- than lower-body skeletal muscle was tested. Furthermore, the hypothesis that more pronounced adaptations in upper-body musculature can be achieved by "low-volume high-intensity" compared with "high-volume low-intensity" exercise training was evaluated. A group of sedentary premenopausal women aged 45 +/- 6 yr (+/- SD) with expected high adaptive potential in both upper- and lower-extremity muscle groups participated. After random allocation to high-intensity swimming (HIS, n = 21), moderate-intensity swimming (MOS, n = 21), soccer (SOC, n = 21) or a nontraining control group (CON, n = 20), the training groups completed three workouts per week for 15 wk. Resting muscle biopsies were obtained from the vastus lateralis muscle and deltoideus muscle before and after the intervention. After the training intervention, a larger (P < 0.05) increase existed in deltoideus muscle of the HIS group compared with vastus lateralis muscle of the SOC group for citrate synthase maximal activity (95 +/- 89 vs. 27 +/- 34%), citrate synthase protein expression (100 +/- 29 vs. 31 +/- 44%), 3-hydroxyacyl-CoA dehydrogenase maximal activity (35 +/- 43 vs. 3 +/- 25%), muscle glycogen content (63 +/- 76 vs. 20 +/- 51%), and expression of mitochondrial complex II, III, and IV. Additionally, HIS caused higher (P < 0.05) increases than MOS in deltoideus muscle citrate synthase maximal activity, citrate synthase protein expression, and muscle glycogen content. In conclusion, the deltoideus muscle has a higher adaptive potential than the vastus lateralis muscle in sedentary women, and "high-intensity low-volume" training is a more efficient regime than "low-intensity high-volume" training for increasing the aerobic capacity of the deltoideus muscle.
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| 3. |
- Bonne, T. C., et al.
(författare)
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Phlebotomy eliminates the maximal cardiac output response to six weeks of exercise training
- 2014
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Ingår i: American Journal of Physiology-Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 306:10
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Tidskriftsartikel (refereegranskat)abstract
- With this study we tested the hypothesis that 6 wk of endurance training increases maximal cardiac output (Q(max)) relatively more by elevating blood volume (BV) than by inducing structural and functional changes within the heart. Nine healthy but untrained volunteers (Vo(2max) 47 +/- 5 ml.min(-1).kg(-1)) underwent supervised training (60 min; 4 times weekly at 65% Vo(2max) for 6 wk), and Q(max) was determined by inert gas rebreathing during cycle ergometer exercise before and after the training period. After the training period, blood volume (determined in duplicates by CO rebreathing) was reestablished to pretraining values by phlebotomy and Q(max) was quantified again. Resting echography revealed no structural heart adaptations as a consequence of the training intervention. After the training period, plasma volume (PV), red blood cell volume (RBCV), and BV increased (P < 0.05) by 147 +/- 168 (5 +/- 5%), 235 +/- 64 (10 +/- 3%), and 382 +/- 204 ml (7 +/- 4%), respectively. Vo(2max) was augmented (P < 0.05) by 10 +/- 7% after the training period and decreased (P < 0.05) by 8 +/- 7% with phlebotomy. Concomitantly, Q(max) was increased (P < 0.05) from 18.9 +/- 2.1 to 20.4 +/- 2.3 l/min (9 +/- 6%) as a consequence of the training intervention, and after normalization of BV by phlebotomy Q(max) returned to pretraining values (18.1 +/- 2.5 l/min; 12 +/- 5% reversal). Thus the exercise training-induced increase in BV is the main mechanism increasing Q(max) after 6 wk of endurance training in previously untrained subjects.
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| 4. |
- Connolly, L. J., et al.
(författare)
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Low-volume high-intensity swim training is superior to high-volume low-intensity training in relation to insulin sensitivity and glucose control in inactive middle-aged women
- 2016
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Ingår i: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 116:10, s. 1889-1897
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Tidskriftsartikel (refereegranskat)abstract
- We tested the hypothesis that low-volume high-intensity swimming has a larger impact on insulin sensitivity and glucose control than high-volume low-intensity swimming in inactive premenopausal women with mild hypertension. Sixty-two untrained premenopausal women were randomised to an inactive control (n = 20; CON), a high-intensity low-volume (n = 21; HIT) or a low-intensity high-volume (n = 21; LIT) training group. During the 15-week intervention period, HIT performed 3 weekly 6-10 x 30-s all-out swimming intervals (average heart rate (HR) = 86 +/- 3 % HRmax) interspersed by 2-min recovery periods and LIT swam continuously for 1 h at low intensity (average HR = 73 +/- 3 % HRmax). Fasting blood samples were taken and an oral glucose tolerance test (OGTT) was conducted pre- and post-intervention. After HIT, resting plasma [insulin] was lowered (17 +/- 34 %; P < 0.05) but remained similar after LIT and CON. Following HIT, 60-min OGTT plasma [insulin] and [glucose] was lowered (24 +/- 30 % and 10 +/- 16 %; P < 0.05) but remained similar after LIT and CON. Total area under the curve for plasma [glucose] was lower (P < 0.05) after HIT than LIT (660 +/- 141 vs. 860 +/- 325 mmol min L-1). Insulin sensitivity (HOMA-IR) had increased (P < 0.05) by 22 +/- 34 % after HIT, with no significant change after LIT or CON, respectively. Plasma soluble intracellular cell adhesion molecule 1 was lowered (P < 0.05) by 4 +/- 8 and 3 +/- 9 % after HIT and CON, respectively, while plasma soluble vascular cell adhesion molecule 1 had decreased (P < 0.05) by 8 +/- 23 % after HIT only. These findings suggest that low-volume high-intensity intermittent swimming is an effective and time-efficient training strategy for improving insulin sensitivity, glucose control and biomarkers of vascular function in inactive, middle-aged mildly hypertensive women.
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| 5. |
- Mohr, Magni, 1973, et al.
(författare)
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High-Intensity intermittent swimming improves cardiovascular health status for women with mild hypertension
- 2014
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Ingår i: BioMed Research International. - : Hindawi Publishing Corporation. - 2314-6133 .- 2314-6141. ; 2014
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Tidskriftsartikel (refereegranskat)abstract
- To test the hypothesis that high-intensity swim training improves cardiovascular health status in sedentary premenopausal women with mild hypertension, sixty-two women were randomized into high-intensity (n = 21; HIT), moderate-intensity (n = 21; MOD), and control groups (n = 20; CON). HIT performed 6-10 × 30 s all-out swimming interspersed by 2 min recovery and MOD swam continuously for 1 h at moderate intensity for a 15-week period completing in total 44 ± 1 and 43 ± 1 sessions, respectively. In CON, all measured variables were similar before and after the intervention period. Systolic BP decreased (P < 0.05) by 6 ± 1 and 4 ± 1 mmHg in HIT and MOD; respectively. Resting heart rate declined (P < 0.05) by 5 ± 1 bpm both in HIT and MOD, fat mass decreased (P < 0.05) by 1.1 ± 0.2 and 2.2 ± 0.3 kg, respectively, while the blood lipid profile was unaltered. In HIT and MOD, performance improved (P < 0.05) for a maximal 10 min swim (13 ± 3 % and 22 ± 3 %), interval swimming (23 ± 3 % and 8 ± 3 %), and Yo-Yo IE1 running performance (58 ± 5 % and 45 ± 4 %). In conclusion, high-intensity intermittent swimming is an effective training strategy to improve cardiovascular health and physical performance in sedentary women with mild hypertension. Adaptations are similar with high- and moderate-intensity training, despite markedly less total time spent and distance covered in the high-intensity group. © 2014 Magni Mohr et al.
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| 6. |
- Mohr, Magni, 1973, et al.
(författare)
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Muscle ion transporters and antioxidative proteins have different adaptive potential in arm than in leg skeletal muscle with exercise training
- 2017
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Ingår i: Physiological Reports. - : Wiley. - 2051-817X. ; 5:19
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Tidskriftsartikel (refereegranskat)abstract
- It was evaluated whether upper-body compared to lower-body musculature exhibits a different phenotype in relation to capacity for handling reactive oxygen species (ROS), H+, La-, Na+, K+ and also whether it differs in adaptive potential to exercise training. Eighty-three sedentary premenopausal women aged 45 +/- 6 years (mean +/- SD) were randomized into a high-intensity intermittent swimming group (HIS, n = 21), a moderate-intensity swimming group (MOS, n = 21), a soccer group (SOC, n = 21), or a control group (CON, n = 20). Intervention groups completed three weekly training sessions for 15 weeks, and pre- and postintervention biopsies were obtained from deltoideus and vastus lateralis muscle. Before training, monocarboxylate transporter 4 (MCT4), Na+/K+ pump alpha(2), and superoxide dismutase 2 (SOD2) expressions were lower (P < 0.05) in m. deltoideus than in m. vastus lateralis, whereas deltoid had higher (P < 0.05) Na+/H+ exchanger 1 (NHE1) expression. As a result of training, Na+/K+ pump alpha(2) isoform expression was elevated only in deltoideus muscle, while upregulation (P < 0.05) of the alpha(1) and beta(1) sub-units, phospholemman (FXYD1), NHE1, and superoxide dismutase 1 expression occurred exclusively in vastus lateralis muscle. The increased (P < 0.05) expression of MCT4 and SOD2 in deltoid muscle after HIS and vastus lateralis muscle after SOC were similar. In conclusion, arm musculature displays lower basal ROS, La-, K+ handling capability but higher Na+-dependent H+ extrusion capacity than leg musculature. Training-induced changes in the ion-transporting and antioxidant proteins clearly differed between muscle groups.
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| 7. |
- Nordsborg, N B, et al.
(författare)
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Erythropoietin does not reduce plasma lactate, H(+) , and K(+) during intense exercise.
- 2015
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 25:6, s. e566-e575
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Tidskriftsartikel (refereegranskat)abstract
- It is investigated if recombinant human erythropoietin (rHuEPO) treatment for 15 weeks (n = 8) reduces extracellular accumulation of metabolic stress markers such as lactate, H(+) , and K(+) during incremental exhaustive exercise. After rHuEPO treatment, normalization of blood volume and composition by hemodilution preceded an additional incremental test. Group averages were calculated for an exercise intensity ∼80% of pre-rHuEPO peak power output. After rHuEPO treatment, leg lactate release to the plasma compartment was similar to before (4.3 ± 1.6 vs 3.9 ± 2.5 mmol/min) and remained similar after hemodilution. Venous lactate concentration was higher (P < 0.05) after rHuEPO treatment (7.1 ± 1.6 vs 5.2 ± 2.1 mM). Leg H(+) release to the plasma compartment after rHuEPO was similar to before (19.6 ± 5.4 vs 17.6 ± 6.0 mmol/min) and remained similar after hemodilution. Nevertheless, venous pH was lower (P < 0.05) after rHuEPO treatment (7.18 ± 0.04 vs 7.22 ± 0.05). Leg K(+) release to the plasma compartment after rHuEPO treatment was similar to before (0.8 ± 0.5 vs 0.7 ± 0.7 mmol/min) and remained similar after hemodilution. Additionally, venous K(+) concentrations were similar after vs before rHuEPO (5.3 ± 0.3 vs 5.1 ± 0.4 mM). In conclusion, rHuEPO does not reduce plasma accumulation of lactate, H(+) , and K(+) at work rates corresponding to ∼80% of peak power output.
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