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| 2. |
- Bjornsen, T., et al.
(författare)
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Frequent blood flow restricted training not to failure and to failure induces similar gains in myonuclei and muscle mass
- 2021
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Ingår i: Scandinavian Journal of Medicine & Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 31:7, s. 1420-1439
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the present study was to compare the effects of short-term high-frequency failure vs non-failure blood flow-restricted resistance exercise (BFRRE) on changes in satellite cells (SCs), myonuclei, muscle size, and strength. Seventeen untrained men performed four sets of BFRRE to failure (Failure) with one leg and not to failure (Non-failure; 30-15-15-15 repetitions) with the other leg using knee-extensions at 20% of one repetition maximum (1RM). Fourteen sessions were distributed over two 5-day blocks, separated by a 10-day rest period. Muscle samples obtained before, at mid-training, and 10-day post-intervention (Post10) were analyzed for muscle fiber area (MFA), myonuclei, and SC. Muscle size and echo intensity of m.rectus femoris (RF) and m.vastus lateralis (VL) were measured by ultrasonography, and knee extension strength with 1RM and maximal isometric contraction (MVC) up until Post24. Both protocols increased myonuclear numbers in type-1 (12%-17%) and type-2 fibers (20%-23%), and SC in type-1 (92%-134%) and type-2 fibers (23%-48%) at Post10 (p < 0.05). RF and VL size increased by 5%-10% in both legs at Post10 to Post24, whereas the MFA of type-1 fibers in Failure was decreased at Post10 (-10 +/- 16%; p = 0.02). Echo intensity increased by similar to 20% in both legs during Block1 (p < 0.001) and was similar to 8 to 11% below baseline at Post24 (p = 0.001-0.002). MVC and 1RM decreased by 5%-10% after Block1, but increased in both legs by 6%-11% at Post24 (p < 0.05). In conclusion, both short-term high-frequency failure and non-failure BFRRE induced increases in SCs, in myonuclei content, muscle size, and strength, concomitant with decreased echo intensity. Intriguingly, the responses were delayed and peaked 10-24 days after the training intervention. Our findings may shed light on the mechanisms involved in resistance exercise-induced overreaching and supercompensation.
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| 3. |
- Bjornsen, T., et al.
(författare)
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High-frequency blood flow-restricted resistance exercise results in acute and prolonged cellular stress more pronounced in type I than in type II fibers
- 2021
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Ingår i: Journal of Applied Physiology. - Rockville : American Physiological Society. - 8750-7587 .- 1522-1601. ; 131:2, s. 643-660
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Tidskriftsartikel (refereegranskat)abstract
- Myocellular stress with high-frequency blood flow-restricted resistance exercise (BFRRE) was investigated by measures of heat shock protein (HSP) responses, glycogen content, and inflammatory markers. Thirteen participants [age: 24 +/- 2 yr (means +/- SD), 9 males] completed two 5-day blocks of seven BFRRE sessions, separated by 10 days. Four sets of unilateral knee extensions to failure at 20% of one-repetition maximum (1RM) were performed. Muscle samples obtained before, 1 h after the first session in the first and second block (acute 1 and acute 2), after three sessions (day 4), during the "rest week," and at 3 (post 3) and 10 days postintervention (post 10) were analyzed for HSP70, alpha beta-crystallin, glycogen [periodic acid-Schiff (PAS) staining], mRNAs, miRNAs, and CD68(+) (macrophages) and CD661D(+) (neutrophils) cell numbers. alpha beta-crystallin translocated from the cytosolic to the cytoskeletal fraction after acute 1 and acute 2 (P < 0.05) and immunostaining revealed larger responses in type I than in type II fibers (acute 1, 225 +/- 184% vs. 92 +/- 81%, respectively, P = 0.001). HSP70 was increased in the cytoskeletal fraction at day 4 and post 3, and immunostaining intensities were more elevated in type I than in type II fibers at day 4 (206 +/- 84% vs. 72 +/- 112%, respectively, P <0.001), during the rest week (98 +/- 66% vs. 42 +/- 79%, P < 0.001), and at post 3 (115 +/- 82% vs. 28 +/- 78%, P = 0.003). Glycogen content was reduced in both fiber types, but most pronounced in type I, which did not recover until the rest week (-15% to 29%, P <= 0.001). Intramuscular macrophage numbers were increased by similar to 65% postintervention, but no changes were observed in muscle neutrophils. We conclude that high-frequency BFRRE with sets performed till failure stresses both fiber types, with type I fibers being most affected. NEW & NOTEWORTHY BFRRE has been reported to preferentially stress type I muscle fibers, as evidenced by HSP responses. We extend these findings by showing that the HSP responses occur in both fiber types but more so in type I fibers and that they can still be induced after a short-term training period. Furthermore, the reductions in glycogen content of type I fibers after strenuous frequent BFRRE in unaccustomed subjects can be prolonged (>= 5 days), probably due to microdamage.
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| 4. |
- Bjørnsen, Thomas, et al.
(författare)
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Delayed myonuclear addition, myofiber hypertrophy and increases in strength with high-frequency low-load blood flow restricted training to volitional failure.
- 2019
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 126:3, s. 578-592
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Tidskriftsartikel (refereegranskat)abstract
- To investigate muscle hypertrophy, strength, myonuclear and satellite cell (SC) responses to high-frequency blood flow restricted resistance exercise (BFRRE).Thirteen individuals (24±2 years [mean ± SD], 9 males) completed two 5-day-blocks of 7 BFRRE sessions, separated by a 10-day rest period. Four sets of unilateral knee extensions to voluntary failure at 20% of 1RM were conducted with partial blood flow restriction (90-100 mmHg). Muscle samples obtained before-, during, 3- and 10 days after training were analyzed for muscle fiber area (MFA), myonuclei, SC, and mRNA and miRNA expression. Muscle size was measured by ultrasonography and magnetic resonance imaging, and strength with 1RM knee-extension.With the first block of BFRRE, SC number increased in both fiber types (70-80%, p<0.05), while type I and II MFA decreased by 6±7% and 15±11% (p<0.05), respectively. With the second block of training, muscle size increased by 6-8%, while the number of SC (type I: 80±63%, type II 147±95%), myonuclei (type I: 30±24%, type II: 31±28%) and MFA (type I: 19±19%, type II: 11±19%) peaked 10 days after the second block of BFRRE, whereas strength peaked after 20 days of detraining (6±6%, p<0.05). Pax7- and p21 mRNA expression were elevated during the intervention, while myostatin, IGF1R, MyoD, myogenin, cyclinD1 and -D2 mRNA did not change until 3-10 days post intervention.High frequency low-load BFRRE induced robust increases in SC, myonuclei and muscle size, but modest strength gains. Intriguingly, the responses were delayed and peaked 10-20 days after the training intervention, indicating overreaching.
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| 5. |
- Bjørnsen, Thomas, et al.
(författare)
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Type 1 Muscle Fiber Hypertrophy after Blood Flow-restricted Training in Powerlifters.
- 2019
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Ingår i: Medicine and science in sports and exercise. - 1530-0315. ; 51:2, s. 288-298
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Tidskriftsartikel (refereegranskat)abstract
- To investigate the effects of blood flow restricted resistance exercise (BFRRE) on myofiber areas (MFA), number of myonuclei and satellite cells (SC), muscle size and strength in powerlifters. METHODSSeventeen national level powerlifters (25±6 yrs [mean±SD], 15 men) were randomly assigned to either a BFRRE group (n=9) performing two blocks (week 1 and 3) of five BFRRE front squat sessions within a 6.5-week training period, or a conventional training group (Con; n=8) performing front squats at ~70% of one-repetition maximum (1RM). The BFRRE consisted of four sets (first and last set to voluntary failure) at ~30% of 1RM. Muscle biopsies were obtained from m. vastus lateralis (VL) and analyzed for MFA, myonuclei, SC and capillaries. Cross sectional areas (CSA) of VL and m. rectus femoris (RF) were measured by ultrasonography. Strength was evaluated by maximal voluntary isokinetic torque (MVIT) in knee extension and 1RM in front squat.BFRRE induced selective type I fiber increases in MFA (BFRRE: 12% vs. Con: 0%, p<0.01) and myonuclear number (BFRRE: 17% vs. Con: 0%, p=0.02). Type II MFA was unaltered in both groups. BFRRE induced greater changes in VL CSA (7.7% vs. 0.5%, p=0.04), which correlated with the increases in MFA of type I fibers (r=0.81, p=0.02). No group differences were observed in SC and strength changes, although MVIT increased with BFRRE (p=0.04), whereas 1RM increased in Con (p=0.02).Two blocks of low-load BFRRE in the front squat exercise resulted in increased quadriceps CSA associated with preferential hypertrophy and myonuclear addition in type 1 fibres of national level powerlifters.
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| 6. |
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| 7. |
- Eftestøl, Einar, et al.
(författare)
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Muscle memory : Are myonuclei ever lost?
- 2020
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 128, s. 456-457
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Ellefsen, S., et al.
(författare)
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Blood flow-restricted strength training displays high functional and biological efficacy in women: a within-subject comparison with high-load strength training
- 2015
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Ingår i: American Journal of Physiology-Regulatory Integrative and Comparative Physiology. - : American Physiological Society. - 0363-6119 .- 1522-1490. ; 309:7
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Tidskriftsartikel (refereegranskat)abstract
- Limited data exist on the efficacy of low-load blood flow-restricted strength training (BFR), as compared directly to heavy-load strength training (HST). Here, we show that 12 wk of twice-a-week unilateral BFR [30% of one repetition maximum (1RM) to exhaustion] and HST (6-10RM) of knee extensors provide similar increases in 1RM knee extension and cross-sectional area of distal parts of musculus quadriceps femoris in nine untrained women (age 22 +/- 1 yr). The two protocols resulted in similar acute increases in serum levels of human growth hormone. On the cellular level, 12 wk of BFR and HST resulted in similar shifts in muscle fiber composition in musculus vastus lateralis, evident as increased MyHC2A proportions and decreased MyHC2X proportions. They also resulted in similar changes of the expression of 29 genes involved in skeletal muscle function, measured both in a rested state following 12 wk of training and subsequent to singular training sessions. Training had no effect on myonuclei proportions. Of particular interest, 1) gross adaptations to BFR and HST were greater in individuals with higher proportions of type 2 fibers, 2) both BFR and HST resulted in approximately four-fold increases in the expression of the novel exercise-responsive gene Syndecan-4, and 3) BFR provided lesser hypertrophy than HST in the proximal half of musculus quadriceps femoris and also in CSA(peak), potentially being a consequence of pressure from the tourniquet utilized to achieve blood flow restriction. In conclusion, BFR and HST of knee extensors resulted in similar adaptations in functional, physiological, and cell biological parameters in untrained women.
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| 9. |
- Hammarsten, Ola, et al.
(författare)
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How is cardiac troponin released from cardiomyocytes?
- 2022
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Ingår i: European heart journal. Acute cardiovascular care. - : Oxford University Press (OUP). - 2048-8726 .- 2048-8734. ; 11:9, s. 718-720
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Hammarsten, Ola, et al.
(författare)
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The ratio of cardiac troponin T to troponin I may indicate non-necrotic troponin release among COVID-19 patients
- 2022
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Ingår i: Clinica Chimica Acta. - : Elsevier. - 0009-8981 .- 1873-3492. ; 527, s. 33-37
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Tidskriftsartikel (refereegranskat)abstract
- Background: Although cardiac troponin T (cTnT) and troponin I(cTnI) are expressed to similar amount in cardiac tissue, cTnI often reach ten-times higher peak levels compared to cTnT in patients with myocardial necrosis such as in acute myocardial infarction (MI). In contrast, similar levels of cTnT and cTnI are observed in other situations such as stable atrial fibrillation and after strenuous exercise.Objective: Examine cTnT and cTnI levels in relation to COVID-19 disease and MI. Methods: Clinical and laboratory data from the local hospital from an observational cohort study of 27 patients admitted with COVID-19 and 15 patients with myocardial infarction (MI) that were analyzed with paired cTnT and cTnI measurement during hospital care.Results: Levels of cTnI were lower than cTnT in COVID-19 patients (TnI/TnT ratio 0.3, IQR: 0.1-0.6). In contrast, levels of cTnI were 11 times higher compared to cTnT in 15 patients with MI (TnI/TnT ratio 11, IQR: 7-14). The peak cTnI/cTnT ratio among the patients with MI following successful percutaneous intervention were 14 (TnI/ TnT ratio 14, IQR: 12-23). The 5 COVID-19 patient samples collected under possible necrotic events had a cTnI/ cTnT ratio of 5,5 (IQR: 1,9-8,3).Conclusions: In patients with COVID-19, cTnT is often elevated to higher levels than cTnI in sharp contrast to patients with MI, indicating that the release of cardiac troponin has a different cause in COVID-19 patients.
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