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- Ekblom, Örjan B, 1971-, et al.
(author)
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Cross-sectional trends in cardiovascular fitness in Swedish 16-year-olds between 1987 and 2007.
- 2011
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In: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 100:4, s. 565-9
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Journal article (peer-reviewed)abstract
- AIM: We sought to investigate the temporal trends in estimated maximal aerobic capacity in adolescents (mean age 16.1).METHODS: Analyses were based on data from three population-based samples, collected in 1987 (n=221), 2001 (n=537) and 2007 (n=265). Subjects underwent sub-maximal ergometer testing. Absolute and relative aerobic capacities were estimated using the Åstrand-Ryhming nomogram.RESULTS: Compared to 1987, values for estimated relative and absolute maximal aerobic capacities were lower in 2001 and 2007, and values in 2007 were lower compared to 2001, in both boys and girls, except for absolute capacity between 1987 and 2001 in girls. The differences over time did not differ between genders. Absolute values changed from 3.0 and 2.5 L/min in 1987 to 2.5 and 2.2 L/min in 2007, for boys and girls, respectively. Relative values changed from 46.5 and 45.9 mL/min/kg in 1987 to 35.0 and 36.6 mL/min/kg, in 2007, for boys and girls, respectively.CONCLUSION: Based on earlier reports on the relationship between aerobic capacity and metabolic risk, the results from the present study provide argument that future public health will be affected negatively.
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- Psilander, Niklas, et al.
(author)
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Effects of training, detraining, and retraining on strength, hypertrophy, and myonuclear number in human skeletal muscle
- 2019
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In: Journal of Applied Physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 126:6, s. 1636-1645
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Journal article (peer-reviewed)abstract
- Previously trained mouse muscles acquire strength and volume faster than naive muscles; it has been suggested that this is related to increased myonuclear density. The present study aimed to determine whether a previously strength-trained leg (mem-leg) would respond better to a period of strength training than a previously untrained leg (con-leg). Nine men and 10 women performed unilateral strength training (T1) for 10 wk, followed by 20 wk of detraining (DT) and a 5-wk bilateral retraining period (T2). Muscle biopsies were taken before and after each training period and analyzed for myonuclear number, fiber volume, and cross-sectional area (CSA). Ultrasound and one repetition of maximum leg extension were performed to determine muscle thickness (MT) and strength. CSA (similar to 17%), MT (similar to 10%), and strength (similar to 20%) increased during T1 in the mem-leg. However, the myonuclear number and fiber volume did not change. MT and CSA returned to baseline values during DT, but strength remained elevated (similar to 60%), supporting previous findings of a long-lasting motor learning effect. MT and strength increased similarly in the mem-leg and con-leg during T2, whereas CSA, fiber volume, and myonuclear number remained unaffected. In conclusion, training response during T2 did not differ between the mem-leg and con-leg. However, this does not discount the existence of human muscle memory. since no increase in the number of myonuclei was detected during T1 and no clear detraining effect was observed for cell size during DT; thus, the present data did not allow for a rigorous test of the muscle memory hypothesis. NEW & NOTEWORTHY If a long-lasting intramuscular memory exists in humans. this will affect strength-training advice for both athletes and the public. Based on animal experiments, we hypothesized that such a memory exists and that it is related to the myonuclear number. However, a period of unilateral strength training, followed by detraining, did not increase the myonuclear number. The training response, during a subsequent bilateral retraining period, was not enhanced in the previously trained leg.
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4. |
- Brink-Elfegoun, T., et al.
(author)
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Neuromuscular and circulatory adaptation during combined arm and leg exercise with different maximal work loads
- 2007
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In: European Journal of Applied Physiology. - : Springer Science and Business Media LLC. - 1439-6319 .- 1439-6327. ; 101:5, s. 603-611
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Journal article (peer-reviewed)abstract
- Cardiopulmonary kinetics and electromyographic activity (EMG) during exhausting exercise were measured in 8 males performing three maximal combined arm + leg exercises (cA+L). These exercises were performed at different rates of work (mean ± SD; 373 ± 48, 429 ± 55 and 521 ± 102 W) leading to different average exercise work times in all tests and subjects. reached a plateau versus work rate in every maximal cA+L exercise (range 6 min 33 s to 3 min 13 s). The three different exercise protocols gave a maximal oxygen consumption of 4.67 ± 0.57, 4.58 ± 0.52 and 4.66 ± 0.53 l min−1 (P = 0.081), and a maximal heart rate (HRmax) of 190 ± 6, 189 ± 4 and 189 ± 6 beats min−1 (P = 0.673), respectively. Root mean square EMG (EMGRMS) of the vastus lateralis and the triceps brachii muscles increased with increasing rate of work and time in all three cA+L protocols. The study demonstrates that despite different maximal rates of work, leading to different times to exhaustion, the circulatory adaptation to maximal exercise was almost identical in all three protocols that led to a plateau. The EMGRMS data showed increased muscle recruitment with increasing work rate, even though the HRmax and was the same in all three cA+L protocols. In conclusion, these findings do not support the theory of the existence of a central governor (CG) that regulates circulation and neuronal output of skeletal muscles during maximal exercise. Thibault Brink-Elfegoun and Hans-Christer Holmberg contributed equally to this article.
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5. |
- Brink-Elfegoun, Tibault, et al.
(author)
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Maximal oxygen uptake is not limited by a central nervous system governor.
- 2007
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In: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 102:2, s. 781-6
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Journal article (peer-reviewed)abstract
- We tested the hypothesis that the work of the heart was not a limiting factor in the attainment of maximal oxygen uptake (VO2 max). We measured cardiac output (Q) and blood pressures (BP) during exercise at two different rates of maximal work to estimate the work of the heart through calculation of the rate-pressure product, as a part of the ongoing discussion regarding factors limiting VO2 max. Eight well-trained men (age 24.4 +/- 2.8 yr, weight 81.3 +/- 7.8 kg, and VO2 max 59.1 +/- 2.0 ml x min(-1) x kg(-1)) performed two maximal combined arm and leg exercises, differing 10% in watts, with average duration of time to exhaustion of 4 min 50 s and 3 min 40 s, respectively. There were no differences between work rates in measured VO2 max, maximal Q, and peak heart rate between work rates (0.02 l/min, 0.3 l/min, and 0.8 beats/min, respectively), but the systolic, diastolic, and calculated mean BP were significantly higher (19, 5, and 10 mmHg, respectively) in the higher than in the lower maximal work rate. The products of heart rate times systolic or mean BP and Q times systolic or mean BP were significantly higher (3,715, 1,780, 569, and 1,780, respectively) during the higher than the lower work rate. Differences in these four products indicate a higher mechanical work of the heart on higher than lower maximal work rate. Therefore, this study does not support the theory, which states that the work of the heart, and consequently VO2 max, during maximal exercise is hindered by a command from the central nervous system aiming at protecting the heart from being ischemic.
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- Ekblom, Björn, et al.
(author)
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Effect of changes in arterial oxygen content on circulation and physical performance.
- 1975
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In: Journal of applied physiology. - 0021-8987. ; 39:1, s. 71-5
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Journal article (peer-reviewed)abstract
- To evaluate the effect of different levels of arterial oxygen content on hemodynamic parameters during exercise nine subjects performed submaximal bicycle or treadmill exercise and maximal treadmill exercise under three different experimental conditions: 1) breathing room air (control); 2) breathing 50% oxygen (hyperoxia); 3) after rebreathing a carbon monoxide gas mixture (hypoxia). Maximal oxygen consumption (Vo2 max) was significantly higher in hyperoxia (4.99 1/min) and significantly lower in hypoxia (3.80 1/min) than in the control experiment (4.43 1/min). Physical performance changes in parallel with Vo2 max. Maximal cardiac output (Qmax) was similar in hyperoxia as in control but was significantly lower in hypoxia mainly due to a decreased stroke volume. A correlation was found between Vo2 max and transported oxygen, i.e., Cao2 times Amax, thus suggesting that central circulation is an important limiting factor for human maximal aerobic power. During submaximal work HR was decreased in hyperoxia and increased in hypoxia. Corresponding Q values were unchanged except for a reduction during high submaximal exercise in hyperoxia.
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8. |
- Ivarsson, Niklas, et al.
(author)
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SR Ca2+ leak in skeletal muscle fibers acts as an intracellular signal to increase fatigue resistance.
- 2019
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In: The Journal of General Physiology. - : Rockefeller University Press. - 0022-1295 .- 1540-7748. ; 151:4, s. 567-577
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Journal article (peer-reviewed)abstract
- Effective practices to improve skeletal muscle fatigue resistance are crucial for athletes as well as patients with dysfunctional muscles. To this end, it is important to identify the cellular signaling pathway that triggers mitochondrial biogenesis and thereby increases oxidative capacity and fatigue resistance in skeletal muscle fibers. Here, we test the hypothesis that the stress induced in skeletal muscle fibers by endurance exercise causes a reduction in the association of FK506-binding protein 12 (FKBP12) with ryanodine receptor 1 (RYR1). This will result in a mild Ca2+ leak from the sarcoplasmic reticulum (SR), which could trigger mitochondrial biogenesis and improved fatigue resistance. After giving mice access to an in-cage running wheel for three weeks, we observed decreased FKBP12 association to RYR1, increased baseline [Ca2+]i, and signaling associated with greater mitochondrial biogenesis in muscle, including PGC1α1. After six weeks of voluntary running, FKBP12 association is normalized, baseline [Ca2+]i returned to values below that of nonrunning controls, and signaling for increased mitochondrial biogenesis was no longer present. The adaptations toward improved endurance exercise performance that were observed with training could be mimicked by pharmacological agents that destabilize RYR1 and thereby induce a modest Ca2+ leak. We conclude that a mild RYR1 SR Ca2+ leak is a key trigger for the signaling pathway that increases muscle fatigue resistance.
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9. |
- Mandroukas, A, et al.
(author)
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Deltoid muscle characteristics in wrestlers.
- 2010
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In: International Journal of Sports Medicine. - : Georg Thieme Verlag KG. - 0172-4622 .- 1439-3964. ; 31:3, s. 148-53
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Journal article (peer-reviewed)abstract
- The purpose of the present study was to investigate the deltoid muscle characteristics of wrestlers. Nine Greco-Roman competitive male wrestlers (mean age 20.1+/-2.7 yrs, height 175+/-0.6 cm, weight 83.2+/-12.5 kg, years of training 7.6+/-2.7 yrs) participated in this study. Six male healthy sedentary students (mean age 21.2+/-0.9 yrs, height 180+/-0.3 cm, weight 80.1+/-9.4 kg) served as controls. Muscle fibre distribution, cross-sectional area (CSA), as well as satellite cells, myonuclei and capillary density per muscle fibre area were determined by immunohistochemistry. Myosin heavy chain MHC isoform composition of single fibres was determined with protein electrophoresis. Immunohistochemical analysis showed that muscle fibre distribution of the MHC I and IIA were significantly higher in wrestlers than in controls (p<0.05). Electrophoretic analysis of single fibres revealed a significantly higher proportion of fibres containing MHC I and IIC in wrestlers (p<0.05). The mean CSA of type IIA fibres and the number of myonuclei per type II was significantly higher in wrestlers (p<0.05). We also found that the number of satellite cells was 2.5 fold higher in wrestlers than in the control group. This study suggests that the observed muscle fibre profile in the deltoid of wrestlers may represent an adaptation based on the specific mechanical and biochemical demands of the long-term training in Greco-Roman wrestling.
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10. |
- Mandroukas, A, et al.
(author)
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Deltoid muscle fiber characteristics in adolescent and adult wrestlers.
- 2010
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In: Journal of Sports Medicine and Physical Fitness. - 0022-4707 .- 1827-1928. ; 50:2, s. 113-20
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Journal article (peer-reviewed)abstract
- Our findings suggest that the observed muscle fiber profile in the deltoid muscle of wrestlers may represent an adaptation based on the mechanical and biochemical demands of the long-term training. Such adaptations are linked to the specific characteristics of the training program, the level and the previous training experience of the wrestlers.
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