Etudes Musculation : page 3.8

De nouvelles cellules souches découvertes dans les muscles

30/09/2016 | Echauffement et blessures et Etudes Musculation


The first characterization of a novel (non-satellite cell) stem cell population in human skeletal muscle
J.P. Nederveen     Appl. Physiol. Nutr. Metab. Vol. 41, 2016 S376

Skeletal muscle stem cells (satellite cells; SC) represent the primary
cell population responsible for muscle regeneration/repair. SC content
and activation has been show to increase in response to muscle
damaging exercise. However, non-satellite cell progenitors, under experimental
conditions in animals, have been identified to form skeletal
when the SC population is compromised. PW1+ interstitial
cells (PIC) have also been shown, experimentally, to contribute to
muscle repair in animals. This cell population, however, has never
been identified in humans. We sought to examine the changes in both
PIC and SC content following a single bout of eccentric exercise. Ten
sedentary males (24±3 years of age; mean±SEM) were recruited. Percutaneous
muscle biopsies from the vastus lateralis muscle were taken
prior to a bout of eccentric exercise (Pre), and 6h, 24h, and 72 h
post-exercise. Muscle fiber size, SC and PIC content were determined
via immunofluorescent microscopy. mRNA expression was assessed
by RT-PCR. The number of SC increased from Pre (10.3±0.8 Pax7+cells/
100 fibers) to 72h post-exercise (12.3±2.0 Pax7+cells/100 fibers, p<0.05).
Similarly, PW1+ cells increased from Pre (2.1±0.6 PW1+ cells/100 fibers)
to 72h post-exercise (6.8±2.5 PW1+ cells/100 fibers, p<0.05). PW1 mRNA
expression was significantly (p<0.05) increased 1.9-fold from Pre to
72h post-exercise. Here, for the first time in humans, we identify a
population of cells which are located in the interstitium that respond
to eccentrically-induced muscle damage in a similar fashion to SC.


Le sport élève ton niveau d’albumine…

30/06/2016 | Etudes cardio et Echauffement et blessures et Etudes Musculation et Etudes Anti-âge


Le sport élève ton niveau d’albumine…

Exercise-induced albuminuria is related to metabolic syndrome
Sharon Greenberg                 American Journal of Physiology - Renal Physiology Published 1 June 2016 Vol. 310 no. 11, F1192-F1196

Microalbuminuria (MA) is a known marker for endothelial dysfunction and future cardiovascular events. Exercise-induced albuminuria (EiA) may precede the appearance of MA. Associations between EiA and metabolic syndrome (MS) have not been assessed so far. Our aim was to investigate this association in a large sample of apparently healthy individuals with no baseline albuminuria. This was a cross-sectional study of 2,027 adults with no overt cardiovascular diseases who took part in a health survey program and had no baseline MA. Diagnosis of MS was based on harmonized criteria. All patients underwent an exercise test (Bruce protocol), and urinary albumin was measured before and after the examination. Urinary albumin-to-creatinine ratio (ACR) values before and after exercise were 0.40 (0.21–0.89) and 1.06 (0.43–2.69) mg/g for median (interquartile range) respectively. A total of 394 (20%) subjects had EiA; ACR rose from normal rest values (0.79 mg/g) to 52.28 mg/g after exercise (P < 0.001); this effect was not shown for the rest of the study population. EiA was related to higher prevalence of MS (13.8% vs. 27.1%, P < 0.001), higher metabolic equivalents (P < 0.001), higher baseline blood pressure (P < 0.001), and higher levels of fasting plasma glucose, triglycerides, and body mass index (P < 0.001). Multivariate binary logistic regression model showed that subjects with MS were 98% more likely to have EiA (95% confidence interval: 1.13–3.46, P = 0.016).

In conclusion, EiA in the absence of baseline MA is independently related to MS.

Deux lignes plus loin, on te montre le contraire

29/06/2016 | Etudes cardio et Etudes Musculation


pour le coup, j’ai nettement moins de mal à croire cette étude

Concurrent exercise incorporating high-intensity interval or continuous training modulates mTORC1 signaling and microRNA expression in human skeletal muscle
Jackson J. Fyfe           American Journal of Physiology - Regulatory, Integrative and Comparative Physiology Published 1 June 2016 Vol. 310 no. 11, R1297-R1311

We compared the effects of concurrent exercise, incorporating either high-intensity interval training (HIT) or moderate-intensity continuous training (MICT), on mechanistic target of rapamycin complex 1 (mTORC1) signaling and microRNA expression in skeletal muscle, relative to resistance exercise (RE) alone. Eight males (mean ± SD: age, 27 ± 4 yr; V̇o2 peak, 45.7 ± 9 ml·kg−1·min−1) performed three experimental trials in a randomized order: 1) RE (8 × 5 leg press repetitions at 80% 1-repetition maximum) performed alone and RE preceded by either 2) HIT cycling [10 × 2 min at 120% lactate threshold (LT); HIT + RE] or 3) work-matched MICT cycling (30 min at 80% LT; MICT + RE). Vastus lateralis muscle biopsies were obtained immediately before RE, either without (REST) or with (POST) preceding endurance exercise and +1 h (RE + 1 h) and +3 h (RE + 3 h) after RE. Prior HIT and MICT similarly reduced muscle glycogen content and increased ACCSer79 and p70S6KThr389 phosphorylation before subsequent RE (i.e., at POST). Compared with MICT, HIT induced greater mTORSer2448 and rps6Ser235/236 phosphorylation at POST. RE-induced increases in p70S6K and rps6 phosphorylation were not influenced by prior HIT or MICT; however, mTOR phosphorylation was reduced at RE + 1 h for MICT + RE vs. both HIT + RE and RE. Expression of miR-133a, miR-378, and miR-486 was reduced at RE + 1 h for HIT + RE vs. both MICT + RE and RE.

Postexercise mTORC1 signaling following RE is therefore not compromised by prior HIT or MICT, and concurrent exercise incorporating HIT, but not MICT, reduces postexercise expression of miRNAs implicated in skeletal muscle adaptation to RE.

Ca serait bien si c’était vrai

29/06/2016 | Etudes cardio et Etudes Musculation


c’est le gros problème de la “science”

Aerobic exercise augments muscle transcriptome profile of resistance exercise

Tommy R. Lundberg           American Journal of Physiology - Regulatory, Integrative and Comparative Physiology Published 1 June 2016 Vol. 310 no. 11, R1279-R1287

Recent reports suggest that aerobic exercise may boost the hypertrophic response to short-term resistance training. This study explored the effects of an acute aerobic exercise bout on the transcriptional response to subsequent resistance exercise. Ten moderately trained men performed ∼45 min cycling on one leg followed by 4 × 7 maximal knee extensions for each leg, 15 min later. Thus, one limb performed aerobic and resistance exercise (AE + RE) while the opposing leg did resistance exercise only (RE). Biopsies were obtained from the vastus lateralis muscle of each leg 3 h after the resistance exercise bout. Using DNA microarray, we analyzed differences [≥1.5-fold, false discovery rate (FDR) ≤10%] in gene expression profiles for the two modes of exercise. There were 176 genes up (127)- or downregulated (49) by AE + RE compared with RE. Among the most significant differentially expressed genes were established markers for muscle growth and oxidative capacity, novel cytokines, transcription factors, and micro-RNAs (miRNAs). The most enriched functional categories were those linked to carbohydrate metabolism and transcriptional regulation. Upstream analysis revealed that vascular endothelial growth factor, cAMP-response element-binding protein, Tet methylcytosine dioxygenase, and mammalian target of rapamycin were regulators highly activated by AE + RE, whereas JnK, NF-κβ, MAPK, and several miRNAs were inhibited. Thus, aerobic exercise alters the skeletal muscle transcriptional signature of resistance exercise to initiate important gene programs promoting both myofiber growth and improved oxidative capacity.

These results provide novel insight into human muscle adaptations to diverse exercise modes and offer the very first genomic basis explaining how aerobic exercise may augment, rather than compromise, muscle growth induced by resistance exercise.

L’entraînement au poids de corps ne serait-il que de la gonflette?

12/03/2016 | Etudes Musculation


N. JENKINS             Journal of Strength and Conditioning Research   2016   VOLUME 30 | SUPPLEMENT 1 | FEBRUARY | S47

However, it is unclear how muscle activation influences these adaptations.

Purpose: Therefore, the purpose of this study was to investigate electromyographic amplitude
(EMG AMP), EMG mean power frequency (MPF), muscle
cross sectional area (mCSA), exercise volume (VOL), total
work and muscle activation (iEMG), and time under concentric
tension (TUCT) during 3 sets to failure at 80% vs. 30% 1RM
leg extension resistance exercise in men and women.

Methods: Eleven men (mean 6 SD; age = 21.5 6 2.7 years; resistance
training per week = 6.6 6 3.7 hours) and 11 women
(age = 22.3 6 3.6 years; resistance training per week = 3.7 6
3.3 hours) completed 1RM testing, followed by 2 experimental
sessions during which they completed 3 sets to failure of leg
extension resistance exercise at 80 or 30% 1RM. EMG signals
were recorded from the 3 superficial quadriceps femoris
muscles of the dominant thigh. An electrogoniometer was
placed across the knee joint to measure joint angle (8). Exercises
were performed on a plate-loaded leg extension device
that was custom fitted with a load cell. Force, EMG AMP
(mV$s21), and EMG MPF (Hz) values were calculated from
signal epochs corresponding to the 608 range of motion occurring
between 1008 and 1608 of leg extension during the concentric
portion of each repetition (rep) based on the
electrogoniometer signal. The EMG AMP and MPF values from
the initial, middle, and last rep of each set were normalized to
a maximal voluntary isometric contraction (MVIC) and used for
analyses. Panoramic ultrasound imaging was used to assess
mCSA of the rectus femoris and vastus lateralis immediately
pre- and post-exercise. Exercise volume, total work, iEMG, and
TUCT were also quantified.

Results: The mean 6 SD for the
numbers of reps completed during sets 1, 2, and 3 were 8.9 6
2.7, 6.7 6 1.9, and 6.2 6 1.7 at 80% 1RM, and 45.6 6 14.3,
26.8 6 8.3, and 22.2 6 8.6 at 30% 1RM, respectively. EMG
AMP increased across reps and sets at 80 and 30% 1RM, but
was consistently greater for 80 than 30% 1RM. EMG MPF
decreased across reps at 80 and 30% 1RM, but decreased
to a greater extent and was lower for the last reps at 30 than
80% 1RM (71.6% vs. 78.1% MVIC). mCSA increased more
from pre-to post-exercise for 30% (20.2 cm2–24.1 cm2) than
80% 1RM (20.3 cm2–22.8 cm2). VOL, total work, iEMG and
TUCT were greater for 30 than 80% 1RM.

Conclusions: EMG AMP remained greater at 80 than 30% 1RM across all
repetitions and during all sets, despite 74 and 147% increases
in EMG AMP during the sets at 80 and 30% 1RM, respectively.
VOL, total work, iEMG, and TUCT were 18–202%
greater, and the decreases in EMG MPF were more pronounced
at 30% 1RM. Furthermore, the increases in mCSA
(i.e., muscle swelling) from pre-to post-exercise were greater at
30 than 80% 1RM.

Practical Applications: Muscle activation was greater during resistance exercise at 80 than 30% 1RM.
Therefore, muscle activation may not be responsible for the
similar hypertrophy observed after 30 vs. 80% 1RM training
to failure. Exercise volume, metabolic byproduct accumulation,
and muscle swelling, however, may be contributing factors.
Additional studies are needed to investigate the acute and
chronic neuromuscular responses to high-versus low-load
resistance training.

La brûlure musculaire est neuroprotectrice

20/02/2016 | Etudes cardio et Etudes Musculation et Etudes Anti-âge


L-Lactate protects neurons against excitotoxicity: implication of an ATP-mediated signaling cascade.
Sci Rep. 2016 Feb 19;6:21250.      Jourdain P

Converging experimental data indicate a neuroprotective action of L-Lactate. Using Digital Holographic Microscopy, we observe that transient application of glutamate (100 μM; 2 min) elicits a NMDA-dependent death in 65% of mouse cortical neurons in culture. In the presence of L-Lactate (or Pyruvate), the percentage of neuronal death decreases to 32%. UK5099, a blocker of the Mitochondrial Pyruvate Carrier, fully prevents L-Lactate-mediated neuroprotection. In addition, L-Lactate-induced neuroprotection is not only inhibited by probenicid and carbenoxolone, two blockers of ATP channel pannexins, but also abolished by apyrase, an enzyme degrading ATP, suggesting that ATP produced by the Lactate/Pyruvate pathway is released to act on purinergic receptors in an autocrine/paracrine manner. Finally, pharmacological approaches support the involvement of the P2Y receptors associated to the PI3-kinase pathway, leading to activation of KATP channels.

This set of results indicates that L-Lactate acts as a signalling molecule for neuroprotection against excitotoxicity through coordinated cellular pathways involving ATP production, release and activation of a P2Y/KATP cascade.

Connectivité intermusculaire

19/01/2016 | Echauffement et blessures et Etudes Musculation


Altered mechanical interaction between rat plantar flexors due to changes in intermuscular connectivity
M. Bernabei               Scandinavian Journal of Medicine & Science in Sports   2016   Early View (Online Version of Record published before inclusion in an issue)

Connective tissue formation following muscle injury and remedial surgery may involve changes in the stiffness and configuration of the connective tissues linking adjacent muscles. We investigated changes in mechanical interaction of muscles by implanting either a tissue-integrating mesh (n = 8) or an adhesion barrier (n = 8) to respectively increase or decrease the intermuscular connectivity between soleus muscle (SO) and the lateral gastrocnemius and plantaris complex (LG+PL) of the rat. As a measure of mechanical interaction, changes in SO tendon forces and proximal–distal LG+PL force differences in response to lengthening LG+PL proximally were assessed 1 and 2 weeks post-surgery. The extent of mechanical interaction was doubled 1 week post-implantation of the tissue-integrating mesh compared to an unaffected compartment (n = 8), and was more than four times higher 2 weeks post-surgery. This was found only for maximally activated muscles, but not when passive. Implanting the adhesion barrier did not result in a reduction of the mechanical interaction between these muscles.

Our findings indicate that the ratio of force transmitted via myofascial, rather than myotendinous pathways, can increase substantially when the connectivity between muscles is enhanced. This improves our understanding of the consequences of connective tissue formation at the muscle boundary on skeletal muscle function.

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