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- Norrbrand, Lena
(författare)
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Acute and early chronic responses to resistance exercise using flywheel or weights
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Resistance exercise using weights typically offers constant external load during coupled shortening (concentric) and lengthening (eccentric) muscle actions in sets of consecutive repetitions until failure. However, the constant external load and the inherent capability of skeletal muscle to produce greater force in the eccentric compared with the concentric action, would infer that most actions are executed with incomplete motor unit involvement. In contrast, use of the inertia of flywheels to generate resistance allows for maximal voluntary force to be produced throughout the concentric action, and for brief episodes of greater eccentric than concentric loading, i.e. “eccentric overload”. Thus, it was hypothesized that acute flywheel resistance exercise would induce greater motor unit and muscle use, and subsequent fatigue, compared with traditional weight stack/free weight resistance exercise. Furthermore, it was hypothesized that flywheel training would induce more robust neuromuscular adaptations compared with training using weights. A total of 43 trained and untrained men were investigated in these studies.Knee extensor muscle activation, fatigue response and muscle use were assessed during exercises by recording electromyographic signals and by means of functional magnetic resonance imaging, respectively. Flywheel resistance exercise provoked maximal or near maximal muscle activation from the first repetition, induced robust fatigue, and prompted more substantial motor unit and muscle use than weight stack/free weight resistance exercise in both novice and resistance trained men. Both prior to and following five weeks of unilateral knee extension training, the eccentric muscle activation was greater with flywheel than weight stack training. Furthermore, weight stack training generated greater increases of dynamic strength and neural adaptations, while flywheel training generated more prominent hypertrophy of individual quadriceps muscles and greater improvement of maximal isometric strength. Hence, due to the preferential metabolic cost of the concentric rather than eccentric actions, the maximal activation through the entire range of the concentric action within each repetition of a set during flywheel resistance exercise probably evoked the marked fatigue, and prompted more substantial muscle use than resistance exercise using weights. Furthermore, while any cause‐effect relationship remains to be determined, results of the pesent study suggest that brief episodes of “eccentric overload” amplify muscular adaptations following concentriceccentric resistance training.
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| 2. |
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| 3. |
- Aagaard, Per, 1957, et al.
(författare)
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Early repolarization in ECG. Definition, prevalence and prognostic significance
- 2015
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Ingår i: Läkartidningen. - 0023-7205. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- Early repolarization defined as antero-lateral ST-segment elevation exists in 1-2 % of the general population and has been considered a benign ECG finding for decades. However, early repolarization, defined as infero-lateral J-waves, has in recent studies been associated with an increased - albeit low - risk of sudden and cardiovascular death. This ECG pattern is present in 3-13% of the general population. However, exercise training can induce all types of early repolarization, and the prevalence in the athletic population rises to 20-90%. There is large variability between sports (higher in endurance athletes) and also throughout the season (higher during times of peak fitness). In athletes, early repolarization, regardless of type, is considered benign. In asymptomatic non-athletes, the absolute risk is too low to use this ECG finding in clinical practice. In individuals with J-wave syndrome, on the other hand, ICD implantation should be strongly considered to prevent sudden cardiac death.
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| 4. |
- Aagaard, Per, 1957, et al.
(författare)
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Heart Rate and Its Variability in Response to Running-Associations with Troponin
- 2014
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Ingår i: Medicine and Science in Sports and Exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131. ; 46:8, s. 1624-1630
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: The objective of this study is to investigate the time course of autonomic tone changes after a first-time endurance running race participation and associations with postexertional high-sensitivity troponin (hsTnT) levels in middle-aged males. Methods: Male (n = 42) first-time long-distance running race (Lidingoloppet 30 km) participants >= 45 yr (50.5 +/- 5) were examined. HR and HR variability (HRV) in the time domain (SDANN) was measured continuously from 2 d before to 4 d after the race using a wireless cardiovascular monitor that also recorded arrhythmia episodes. In addition, subjects were assessed pre- and postrace by medical history and physical examination, 12-lead ECG, blood tests including hsTnT, and echocardiography. Results: Compared with corresponding prerace values, nighttime (2: 00-4: 00 a.m.) HR was significantly elevated (63.6 +/- 9.4 vs 53.9 +/- 8.3 bpm, P < 0.001) on the first night postrace, whereas HRV remained reduced for a median of 64 h (interquartile range, 51-102 h). A prolonged HR recovery period (r = 0.48, P = 0.005) and a larger reduction in postrace HRV (r = -0.49, P = 0.003) correlated with higher postrace hsTnT levels. The association between reduced HRV and higher hsTnT remained significant after multivariate analysis (A = -0.48, P = 0.01). No sustained ventricular arrhythmias were recorded, but atrial fibrillation occurred in two subjects. Conclusion: Endurance running race participation caused a prolonged alteration of autonomic tone. More marked and prolonged changes were associated with higher levels of hsTnT, suggesting that the magnitude of troponin increase after strenuous exercise may reflect the magnitude of exercise-induced cardiovascular stress.
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| 5. |
- Aagaard, Per, 1957, et al.
(författare)
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Preparticipation Evaluation of Novice, Middle-Age Long-Distance Runners.
- 2013
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Ingår i: Medicine and science in sports and exercise. - 0195-9131 .- 1530-0315. ; 45:1, s. 130-137
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Tidskriftsartikel (refereegranskat)abstract
- Abstract PURPOSE: To assess the cardiovascular health and risk profile in middle-aged males making an entry to participate for their first time in a long-distance race. METHODS: Male first-time participants ≥45 years in the world's largest cross-country running race, the Lidingöloppet, were evaluated with a medical history and physical exam, European risk-SCORE, 12-lead ECG, echocardiography and blood tests. Further diagnostic work-up was performed when clinically indicated. RESULTS: Of 265 eligible runners, 153 (58%, age 51±5 y) completed the study. While the 10-year fatal cardiovascular event risk was low (SCORE: 1% (IQR: 0 - 1%)), mild abnormalities were common, e.g. elevated blood-pressure (19%), left ventricular hypertrophy (6%), elevated LDL cholesterol (5%). ECG changes compatible with "athlete's heart" were present in 82%, e.g. sinus bradycardia (61%) and/or early repolarization (32%). ECG changes considered training-unrelated were found in 24%, e.g. prolonged QTc: 13%; left axis deviation: 5.3%; left atrial enlargement: 4%). In 14 runners (9%) additional diagnostic work-up was clinically motivated, and 4 (2%) were ultimately discouraged from vigorous exercise due to QTc intervals >500 ms (n=2), symptomatic atrioventricular block (n=1), and a cardiac tumor (n=1). The physician exam and the ECG identified 12 of the 14 subjects requiring further evaluation. CONCLUSIONS: Cardiovascular evaluation of middle-aged men, including a physician exam and a 12-lead ECG, appears useful to identify individuals requiring further testing prior to vigorous exercise. The additional yield of routine echocardiography was small.
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| 6. |
- Bojsen-Møller, Jens, et al.
(författare)
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Differential displacement of the human soleus and medial gastrocnemius aponeuroses during isometric plantar flexor contractions in vivo.
- 2004
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Ingår i: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 97:5, s. 1908-14
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Tidskriftsartikel (refereegranskat)abstract
- The human triceps surae muscle-tendon complex is a unique structure with three separate muscle compartments that merge via their aponeuroses into the Achilles tendon. The mechanical function and properties of these structures during muscular contraction are not well understood. The purpose of the study was to investigate the extent to which differential displacement occurs between the aponeuroses of the medial gastrocnemius (MG) and soleus (Sol) muscles during plantar flexion. Eight subjects (mean +/- SD; age 30 +/- 7 yr, body mass 76.8 +/- 5.5 kg, height 1.83 +/- 0.06 m) performed maximal isometric ramp contractions with the plantar flexor muscles. The experiment was performed in two positions: position 1, in which the knee joint was maximally extended, and position 2, in which the knee joint was maximally flexed (125 degrees ). Plantarflexion moment was assessed with a strain gauge load cell, and the corresponding displacement of the MG and Sol aponeuroses was measured by ultrasonography. Differential shear displacement of the aponeurosis was quantified by subtracting displacement of Sol from that of MG. Maximal plantar flexion moment was 36% greater in position 1 than in position 2 (132 +/- 20 vs. 97 +/- 11 N.m). In position 1, the displacement of the MG aponeurosis at maximal force exceeded that of the Sol (12.6 +/- 1.7 vs. 8.9 +/- 1.5 mm), whereas in position 2 displacement of the Sol was greater than displacement of the MG (9.6 +/- 1.0 vs. 7.9 +/- 1.2 mm). The amount and "direction" of shear between the aponeuroses differed significantly between the two positions across the entire range of contraction, indicating that the Achilles tendon may be exposed to intratendinous shear and stress gradients during human locomotion.
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| 7. |
- Elam, Cecilia, et al.
(författare)
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Effects of age on muscle power, postural control and functional capacity after short-term immobilization and retraining.
- 2022
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Ingår i: Journal of musculoskeletal & neuronal interactions. - 1108-7161. ; 22:4, s. 486-497
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the effect of lower limb immobilization and retraining on postural control and muscle power in healthy old and young men.Twenty men, nine old (OM:67.3±4.4 years) and eleven young (YM:24.4±1.6 years) underwent 2 weeks of unilateral whole-leg casting, followed by 4 weeks of retraining. Measures included center of pressure (CoP) sway length and area during single- and double-leg stance, maximal leg extensor muscle power, habitual and maximal 10-m gait speed, sit-to-stand performance, and 2-min step test.After immobilization, leg extension muscle power decreased by 15% in OM (from 2.68±0.60 to 2.29±0.63 W/kg, p<0.05) and 17% in YM (4.37±0.76 to 3.63±0.69 W/kg, p<0.05). Double-leg CoP sway area increased by 45% in OM (218±82 to 317±145 mm2; p<0.05), with no change in YM (p=0.43). Physical function did not change after immobilization but sit-to-stand performance (+20%, p<0.05) and 2-min step test (+28%, p<0.05) increased in OM following retraining. In both groups, all parameters returned to baseline levels after retraining.Two weeks of lower limb immobilization led to decreases in maximal muscle power in both young and old, whereas postural control was impaired selectively in old men. All parameters were restored in both groups after 4 weeks of resistance-based retraining.
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| 8. |
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| 9. |
- Elam Edwén, Cecilia, 1970, et al.
(författare)
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Stretch-shortening cycle muscle power in women and men aged 18-81 years: Influence of age and gender
- 2014
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Ingår i: Scandinavian Journal of Medicine & Science in Sports. - : Wiley. - 0905-7188. ; 24:4, s. 717-726
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Tidskriftsartikel (refereegranskat)abstract
- This study explored the age-related deterioration in stretch-shortening cycle (SSC) muscle power and concurrent force-velocity properties in women and men across the adult life span. A total of 315 participants (women: n = 188; men: n = 127) aged 18-81 years performed maximal countermovement jumps on an instrumented force plate. Maximal SSC leg extension power expressed per kg body mass (Ppeak) was greater in men than in women across the adult age span (P < 0.001); however, this gender difference was progressively reduced with increasing age, because men showed an similar to 50% faster rate of decline in SSC power than women (P < 0.001). Velocity at peak power (VPpeak) was greater in men than in women (P < 0.001) but declined at a greater rate in men than in women (P = 0.002). Vertical ground reaction force at peak power (FPpeak) was higher in men than in women in younger adults only (P < 0.001) and the age-related decline was steeper in men than in women (P < 0.001). Men demonstrated a steeper rate of decline in Ppeak than women with progressive aging. This novel finding emerged as a result of greater age-related losses in men for both force and velocity. Consequently, maximal SSC power production was observed to converge between genders when approaching old age.
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| 10. |
- Estmark Kalinowski, Birgitta
(författare)
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Dissolution Kinetics and Alteration Products of Micas and Epidote in Acidic Solutions at Room Temperature
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The reaction kinetics of the weathering of several phyllosilicates and one sorosilicate were stud ied experimentally. The alteration products were characterised by various methods in clud ing XRD, HRTEM, SEM, FTIR, NMR and Mössbauer spectroscopy. Weathering of silicates is of particular concern to our knowledge of several areas in low temperature geochemistry, such as el e ment cy cling, ground water chemistry and soil formation. The importance of these processes ex tends to the long-term nutrient supply to forest ecosystems and control of soil and water acidity, es pe cial ly in Scandinavia.Several soil models designed to predict the impact of acid rain on the soil chemistry rely on kinetic data of mineral weathering. The reaction kinetics for minerals are used in such models to predict chang es in soil chem is try. This enables calculation of the effect of acid rain (i. e. critical load) in a 100-year per spec tive. For some minerals relatively little knowledge is available for the reaction kinetics. There fore the dissolution kinetics of muscovite, biotite, phlogopite, vermiculite and epi dote were studied over the pH range 1 to 6.5 at room temperature using flow-through reactors.Silica release rates based on specific surface area are about the same for as divers silicates as epidote (sorosilicate), K-feldspar (tectosilicate) and phlogopite (phyllosilicate). At pH 3 log R = -15.41, -15.5 and -15.46 respectively for these min er als. However, the framework of Si and Al is likely to determine with what ease cations positioned in between the conformation of Si and Al tetrahedra are re leased. For example, K in micas have transportation channels due to the layer struc ture and ought there fore to be released easier than in K-feldspar. In most cases Si is the most slowly released element in silicates, but in epidote, Si and Ca are the fastest released elements from the structure, while Al and Fe are retained. Leaching of inter framework cations creates strain and charge im bal ance in the silicate structure, causing Si to be more readily released in base cation containing silicates than in quartz. Released Si may repolymerise directly at the surface of silicates or interlayers. Amor phous silica gel has been detected, as a weathering product between packages of 2:1 layers in bi otite, using AEM. Iron(hydr)oxides have been found as the end-product of biotite weathering. Re sid u al layer calculations based on the solution composition show that Al and Fe form an enriched layer with a thickness of 1-2 nm at the surface of epidote.Biotite and phlogopite probably alter to trioctahedral vermiculite from the edges and inwards. Mössbauer spectroscopy shows that weathering of biotite as well as ver micu lite is accompanied by oxidation. Al-hydroxy polymers are introduced in the in ter lay er during weathering of phlogopite and vermiculite, which is supported by both XRD and 27Al MAS-NMR analyses. Additions of KCl and AlCl3 to the reactant solutions show that release rates, exfoliation and oxidation processes decrease with increased concentrations for both biotite and phlogopite. Leaching of interlayer cat i ons seems thus to initiate oxidation of ferrous iron.
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