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- 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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- Boushel, Robert, et al.
(författare)
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Low-intensity training increases peak arm VO2 by enhancing both convective and diffusive O2 delivery.
- 2014
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 211:1, s. 122-134
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Tidskriftsartikel (refereegranskat)abstract
- AIM: It is an ongoing discussion the extent to which oxygen delivery and oxygen extraction contribute to an increased muscle oxygen uptake during dynamic exercise. It has been proposed that local muscle factors including the capillary bed and mitochondrial oxidative capacity play a large role in prolonged low-intensity training of a small muscle group when the cardiac output capacity is not directly limiting. The purpose of this study was to investigate the relative roles of circulatory and muscle metabolic mechanisms by which prolonged low-intensity exercise training alters regional muscle VO2 .METHODS: In nine healthy volunteers (seven males, two females), haemodynamic and metabolic responses to incremental arm cycling were measured by the Fick method and biopsy of the deltoid and triceps muscles before and after 42 days of skiing for 6 h day(-1) at 60% max heart rate.RESULTS: Peak pulmonary VO2 during arm crank was unchanged after training (2.38 ± 0.19 vs. 2.18 ± 0.2 L min(-1) pre-training) yet arm VO2 (1.04 ± 0.08 vs. 0.83 ± 0.1 L min(1) , P < 0.05) and power output (137 ± 9 vs. 114 ± 10 Watts) were increased along with a higher arm blood flow (7.9 ± 0.5 vs. 6.8 ± 0.6 L min(-1) , P < 0.05) and expanded muscle capillary volume (76 ± 7 vs. 62 ± 4 mL, P < 0.05). Muscle O2 diffusion capacity (16.2 ± 1 vs. 12.5 ± 0.9 mL min(-1) mHg(-1) , P < 0.05) and O2 extraction (68 ± 1 vs. 62 ± 1%, P < 0.05) were enhanced at a similar mean capillary transit time (569 ± 43 vs. 564 ± 31 ms) and P50 (35.8 ± 0.7 vs. 35 ± 0.8), whereas mitochondrial O2 flux capacity was unchanged (147 ± 6 mL kg min(-1) vs. 146 ± 8 mL kg min(-1) ).CONCLUSION: The mechanisms underlying the increase in peak arm VO2 with prolonged low-intensity training in previously untrained subjects are an increased convective O2 delivery specifically to the muscles of the arm combined with a larger capillary-muscle surface area that enhance diffusional O2 conductance, with no apparent role of mitochondrial respiratory capacity.
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- Calbet, J.A.L., et al.
(författare)
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Chronic hypoxia increases arterial blood pressure and reduces adenosine and ATP induced vasodilatation in skeletal muscle in healthy humans
- 2014
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Ingår i: Acta Physiologica. - : Wiley. - 1748-1708 .- 1748-1716. ; 211:4, s. 574-584
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Tidskriftsartikel (refereegranskat)abstract
- Aims: To determine the role played by adenosine, ATP and chemoreflex activation on the regulation of vascular conductance in chronic hypoxia. Methods: The vascular conductance response to low and high doses of adenosine and ATP was assessed in ten healthy men. Vasodilators were infused into the femoral artery at sea level and then after 8-12 days of residence at 4559 m above sea level. At sea level, the infusions were carried out while the subjects breathed room air, acute hypoxia (FIO2 = 0.11) and hyperoxia (FIO2 = 1); and at altitude (FIO2 = 0.21 and 1). Skeletal muscle P2Y2 receptor protein expression was determined in muscle biopsies after 4 weeks at 3454 m by Western blot. Results: At altitude, mean arterial blood pressure was 13% higher (91 ± 2 vs. 102 ± 3 mmHg, P < 0.05) than at sea level and was unaltered by hyperoxic breathing. Baseline leg vascular conductance was 25% lower at altitude than at sea level (P < 0.05). At altitude, the high doses of adenosine and ATP reduced mean arterial blood pressure by 9-12%, independently of FIO2. The change in vascular conductance in response to ATP was lower at altitude than at sea level by 24 and 38%, during the low and high ATP doses respectively (P < 0.05), and by 22% during the infusion with high adenosine doses. Hyperoxic breathing did not modify the response to vasodilators at sea level or at altitude. P2Y2 receptor expression remained unchanged with altitude residence. Conclusions: Short-term residence at altitude increases arterial blood pressure and reduces the vasodilatory responses to adenosine and ATP. © 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.
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- Harridge, SDR, et al.
(författare)
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Sprint training, in vitro and in vivo muscle function, and myosin heavy chain expression
- 1998
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Ingår i: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 84:2, s. 442-449
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Tidskriftsartikel (refereegranskat)abstract
- Harridge, S. D. R., R. Bottinelli, M. Canepari, M. Pellegrino, C. Reggiani, M. Esbjörnsson, P. D. Balsom, and B. Saltin. Sprint training, in vitro and in vivo muscle function, and myosin heavy chain expression. J. Appl. Physiol. 84(2): 442–449, 1998.—Sprint training represents the condition in which increases in muscle shortening speed, as well as in strength, might play a significant role in improving power generation. This study therefore aimed to determine the effects of sprint training on 1) the coupling between myosin heavy chain (MHC) isoform expression and function in single fibers, 2) the distribution of MHC isoforms across a whole muscle, and 3) in vivo muscle function. Seven young male subjects completed 6 wk of training (3-s sprints) on a cycle ergometer. Training was without effect on maximum shortening velocity in single fibers or in the relative distribution of MHC isoforms in either the soleus or the vastus lateralis muscles. Electrically evoked and voluntary isometric torque generation increased ( P < 0.05) after training in both the plantar flexors (+8% at 50 Hz and +16% maximal voluntary contraction) and knee extensors (+8% at 50 Hz and +7% maximal voluntary contraction). With the shortening potential of the muscles apparently unchanged, the increased strength of the major lower limb muscles is likely to have contributed to the 7% increase ( P < 0.05) in peak pedal frequency during cycling.
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- Hattel, H. B., et al.
(författare)
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Lifelong endurance training keeps the mitochondria young.
- 2014
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Ingår i: Proceedings of the Physiological Society 2014. ; , s. 276P-277P
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Konferensbidrag (refereegranskat)abstract
- It is an ongoing debate whether mitochondrial function deteriorates with aging. Some studies demonstrate metabolic dysfunction and increased ROS production (Squier, 2001) while others find no bioenergetics alterations (Rasmussen, et al., 2003). The extent to which exercise maintains or restores mitochondrial function is unknown. Methods: A unique group of elderly lifelong trained males (64±2 yr, BMI=24.5±0.4 kg/m2, VO2max=3.5±0.07 L/min), who maintained road cycling training ~250 km/week 50 years were recruited for the experiment (group ET) along with a group of healthy age matched untrained males (age 65±2 yr, BMI=27±1, VO2max=2.4±0.1), who lived a sedentary lifestyle (group UT). A biopsy was obtained from Vastus lateralis under local anaesthesia. 15-25 mg muscle was immediately prepared and permeabilized for High Resolution Respirometry as previously described (Boushel, et al., 2011). LEAK respiration was assessed by addition of malate (2 mM) and octanoyl-carnitine (0.2 mM). Coupled ADP-stimulated respiration (OXPHOS) of complex I was assessed with pyruvate (5mM) and glutamate (10 mM), and ADP (5 mM). Maximal OXPHOS was determined by addition of succinate (10 mM) for convergent electron input to both complexes I and II. The isolated activity of cytochrome c oxidase (COX), was determined in a redox reaction with TMPD (N,N,N,N-tetramethyl-p-phenylenediamine dihydrochloride) (0.5 mM) and ascorbate (2mM) after blockade of electron flow through complex III with antimycin A (2.5μM) followed by sodium azide (100 mM). Findings: All values are mean±S.E.M. Preliminary findings show that mitochondrial OXPHOS capacity for CI (PI) is substantially higher (50±3 vs. 30±1 pmol.sec-1.mg-1, p<0.0001) in the ET compared to the UT, and maximal OXPHOS with CI+CII (PI+PII) was 2-fold higher (103±3 vs. 51±2 pmol.sec-1.mg-1, p<5*10-5). The higher substrate control ratio (CI+II/CI) in ET (2.05±0.09) compared to UT (1.7±0.06) suggests less substrate competition at the mitochondrial level. These findings indicate that exercise training throughout life induces both regulatory and mitochondrial density changes that optimize mitochondrial function. The observed OXPHOS capacities in the ET subjects are fully comparable to values reported in young elite trained subjects (Jacobs & Lundby, 2013), illustrating no mitochondrial age-related deteriorating in these subjects.
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- Jensen-Urstad, K, et al.
(författare)
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Pronounced resting bradycardia in male elite runners is associated with high heart rate variability.
- 1997
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 7:5, s. 274-8
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Tidskriftsartikel (refereegranskat)abstract
- Forty-eight hour Holter monitoring was undertaken of 16 male elite middle- and long-distance runners, age 25 +/- 3 years, with peak oxygen uptake 4.83 +/- 0.43 1 O2/min or 73.0 +/- 3.9 ml O2/kg/min. The athletes had pronounced bradycardia during the night-time, with heart rate calculated from four RR intervals < 30 beats/min in five runners. Twelve of 16 runners had RR intervals > 2 s. Of those, 10 runners had sinus pauses exceeding 2 s, the longest being 3.06 s. Three runners had AV block II, two with Mobitz type 1, and one with both Mobitz type 1 and 2. Autonomic function was estimated by time domain and power spectral analysis of heart rate variability. The runners were compared with a control group of 13 sedentary or moderately active subjects. The runners had a mean of 14 b.p.m. lower heart rate at night than the controls. The runners had higher heart rate variability in all spectral bands. In the time domain pNN50 and rMSSD, which are considered to reflect strongly vagal tone, were markedly higher in the runners than the controls. The findings suggest that an increased parasympathetic tone might at least partly explain the pronounced resting sinus bradycardias found in endurance-trained runners.
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- Koh, HE, et al.
(författare)
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Pronounced limb and fibre type differences in subcellular lipid droplet content and distribution in elite skiers before and after exhaustive exercise
- 2017
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Ingår i: Journal of Physiology. - 0022-3751 .- 1469-7793. ; 595:17, s. 5781-5795
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Tidskriftsartikel (refereegranskat)abstract
- KEY POINTS:Although lipid droplets in skeletal muscle are an important energy source during endurance exercise, our understanding of lipid metabolism in this context remains incomplete. Using transmission electron microscopy, two distinct subcellular pools of lipid droplets can be observed in skeletal muscle - one beneath the sarcolemma and the other between myofibrils. At rest, well-trained leg muscles of cross-country skiers contain 4- to 6-fold more lipid droplets than equally well-trained arm muscles, with a 3-fold higher content in type 1 than in type 2 fibres. During exhaustive exercise, lipid droplets between the myofibrils but not those beneath the sarcolemma are utilised by both type 1 and 2 fibres. These findings provide insight into compartmentalisation of lipid metabolism within skeletal muscle fibres.ABSTRACT:Although the intramyocellular lipid pool is an important energy store during prolonged exercise, our knowledge concerning its metabolism is still incomplete. Here, quantitative electron microscopy was used to examine subcellular distribution of lipid droplets in type 1 and 2 fibres of the arm and leg muscles before and after 1 h of exhaustive exercise. Intermyofibrillar lipid droplets accounted for 85-97% of the total volume fraction, while the subsarcolemmal pool made up 3-15%. Before exercise, the volume fractions of intermyofibrillar and subsarcolemmal lipid droplets were 4- to 6-fold higher in leg than in arm muscles (P < 0.001). Furthermore, the volume fraction of intermyofibrillar lipid droplets was 3-fold higher in type 1 than in type 2 fibres (P < 0.001), with no fibre type difference in the subsarcolemmal pool. Following exercise, intermyofibrillar lipid droplet volume fraction was 53% lower (P = 0.0082) in both fibre types in arm, but not leg muscles. This reduction was positively associated with the corresponding volume fraction prior to exercise (R2 = 0.84, P < 0.0001). No exercise-induced change in the subsarcolemmal pool could be detected. These findings indicate clear differences in the subcellular distribution of lipid droplets in the type 1 and 2 fibres of well-trained arm and leg muscles, as well as preferential utilisation of the intermyofibrillar pool during prolonged exhaustive exercise. Apparently, the metabolism of lipid droplets within a muscle fibre is compartmentalised.
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- Nielsen, J., et al.
(författare)
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Human skeletal muscle glycogen utilization in exhaustive exercise : Role of subcellular localization and fibre type
- 2011
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Ingår i: Journal of Physiology. - : Wiley. - 0022-3751 .- 1469-7793. ; 589:11, s. 2871-2885
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Tidskriftsartikel (refereegranskat)abstract
- Although glycogen is known to be heterogeneously distributed within skeletal muscle cells, there is presently little information available about the role of fibre types, utilization and resynthesis during and after exercise with respect to glycogen localization. Here, we tested the hypothesis that utilization of glycogen with different subcellular localizations during exhaustive arm and leg exercise differs and examined the influence of fibre type and carbohydrate availability on its subsequent resynthesis. When 10 elite endurance athletes (22 ± 1 years, = 68 ± 5 ml kg-1 min-1, mean ± SD) performed one hour of exhaustive arm and leg exercise, transmission electron microscopy revealed more pronounced depletion of intramyofibrillar than of intermyofibrillar and subsarcolemmal glycogen. This phenomenon was the same for type I and II fibres, although at rest prior to exercise, the former contained more intramyofibrillar and subsarcolemmal glycogen than the latter. In highly glycogen-depleted fibres, the remaining small intermyofibrillar and subsarcolemmal glycogen particles were often found to cluster in groupings. In the recovery period, when the athletes received either a carbohydrate-rich meal or only water the impaired resynthesis of glycogen with water alone was associated primarily with intramyofibrillar glycogen. In conclusion, after prolonged high-intensity exercise the depletion of glycogen is dependent on subcellular localization. In addition, the localization of glycogen appears to be influenced by fibre type prior to exercise, as well as carbohydrate availability during the subsequent period of recovery. These findings provide insight into the significance of fibre type-specific compartmentalization of glycogen metabolism in skeletal muscle during exercise and subsequent recovery. © 2011 The Authors. Journal compilation © 2011 The Physiological Society.
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