Etudes Musculation

Etre bon en cardio enfant aide-t’il à prendre du muscle plus tard?

02/11/2018 | Etudes cardio et Etudes Musculation

 

Physiological adaptations to resistance training in rats selectively bred for low and high response to aerobic exercise training
Juha P. Ahtiainen         Experimental Physiology banner                 05 September 2018 https://doi.org/10.1113/EP087144

1 New Findings
What is the central question of this study?

Can phenotypic traits associated with low response to one mode of training be extrapolated to other exercise‐inducible phenotypes? The present study investigated whether rats that are low responders to endurance training are also low responders to resistance training.

What is the main finding and its importance?

After resistance training, rats that are high responders to aerobic exercise training improved more in maximal strength compared with low‐responder rats. However, the greater gain in strength in high‐responder rats was not accompanied by muscle hypertrophy, suggesting that the responses observed could be mainly neural in origin.

The purpose of this study was to determine whether rats selectively bred for low and high response to aerobic exercise training co‐segregate for differences in muscle adaptations to ladder‐climbing resistance training. Five high‐responder (HRT) and five low‐responder (LRT) rats completed the resistance training, while six HRT and six LRT rats served as sedentary control animals. Before and after the 6 week intervention, body composition was determined by dual energy X‐ray absorptiometry. Before tissue harvesting, the right triceps surae muscles were loaded by electrical stimulation. Muscle fibre cross‐sectional areas, nuclei per cell, phosphorylation status of selected signalling proteins of mTOR and Smad pathways, and muscle protein, DNA and RNA concentrations were determined for the right gastrocnemius muscle. The daily protein synthesis rate was determined by the deuterium oxide method from the left quadriceps femoris muscle. Tissue weights of fore‐ and hindlimb muscles were measured. In response to resistance training, maximal carrying capacity was greater in HRT (∼3.3 times body mass) than LRT (∼2.5 times body mass), indicating greater improvements of strength in HRT. However, muscle hypertrophy that could be related to greater strength gains in HRT was not observed. Furthermore, noteworthy changes within the experimental groups or differences between groups were not observed in the present measures. The lack of hypertrophic muscular adaptations despite considerable increases in muscular strength suggest that adaptations to the present ladder‐climbing training in HRT and LRT rats were largely induced by neural adaptations.

Toutes les techniques d’entraînement se valent t-elles chez le débutant?

18/10/2018 | Etudes Musculation

 

Load and time under tension do not determine motor unit
activation during resistance exercise performed to volitional
failure in young, healthy men

R.W. Morton   Appl. Physiol. Nutr. Metab. Vol. 43, 2018       S83

We aimed to determine if performing resistance exercise (RE) to volitional
failure with heavier or lighter loads and shorter or longer times
under tension would result in similar motor unit activation.

Ten recreationally
active young men performed three sets of unilateral knee
extension exercise that varied in speed of contraction and load:
80%RM Regular (80R; 1 eccentric: 1 pause: 1 concentric), 80%RM Slow
(80S; 3:1:3), 30%RM Regular (30R; 1:1:1) and 30%RM Slow (30S; 3:1:3).
Peak EMG amplitude increased in every condition but was higher in
the heavy-load conditions during the first and last repetitions of each
set. The integrated EMG signal was higher in the light-load conditions.
Maximum voluntary force decreased between each set in every condition
with no difference between conditions. At rest, type II muscle
fibres had more glycogen than type I fibres with no difference between
type IIA and type IIX fibres. There were no differences in glycogen
depletion between conditions; however, glycogen depletion was
greater in type II than type I fibres and type IIA fibres depleted more
than type IIX fibres.

We conclude that performing RE to volitional
failure results in significant fatigue and motor unit activation that is
similar regardless of load or speed of contraction.

Efficacité des repos extrêmes entre les séries?

18/10/2018 | Etudes cardio et Echauffement et blessures et Etudes Musculation

 

Sprint exercise snacks: A novel approach to increase aerobic
fitness

G. Jackson         Appl. Physiol. Nutr. Metab. Vol. 43, 2018

Sprint interval training (SIT) is a time-efficient way to improve aerobic
fitness. The purpose of this study was to determine if performing
isolated sprints throughout the day with longer (>1 hour) rest periods
(i.e., “sprint snacks”) could comparably improve aerobic capacity. In a
randomized pilot trial, healthy, young, inactive participants performed
six weeks of training (3 d/wk) as either sprint snacks (SS; 3x20
sec with 1-4-hour rest, n=12) or SIT (3x20 sec with 3-minute rest within
a 10-minute session, n=16).

The primary outcome was peak oxygen
uptake (V˙ O2peak) assessed before and after training. Absolute
V˙ O2peak increased by 4% after SS and 6% after SIT (main effect of
time P = 0.004) with no difference between groups (group X time
interaction, P = 0.559). In SIT, exercise enjoyment increased from the
first training session (3.8 ± 1.4) to final training session (5.2 ± 1.2)
whereas enjoyment of SS did not change (4.8 ± 1.9 to 4.5 ± 1.4) (group X
time interaction, P = 0.01). Performing three all-out intensity “sprint
snacks” spread throughout the day can lead to similar aerobic adaptations
when compared to a time-efficient SIT protocol involving the
same number and length of sprints.
Future research should examine
whether sprint snacks can be translated into an effective real-world
intervention.

Effet de l’exercice physique sur les niveaux de GDF-15

23/01/2018 | Etudes sur les hormones et Etudes Musculation

 

Exercise increases circulating GDF15 in humans
Maximilian Kleinert         Mol Met 2017.12.016


Highlights
•Circulating GDF15 increases during exercise and during recovery from exercise in humans.
•Skeletal muscle tissue appears not to be the source for this exercise-induced increase in GDF15 levels.

Objective
The growth differentiation factor 15 (GDF15) is a stress-sensitive circulating factor that regulates systemic energy balance. Since exercise is a transient physiological stress that has pleiotropic effects on whole-body energy metabolism, we herein explored the effect of exercise on a) circulating GDF15 levels and b) GDF15 release from skeletal muscle in humans.

Methods
Seven healthy males either rested or exercised at 67% of their VO2max for 1 h and blood was sampled from the femoral artery and femoral vein before, during, and after exercise. Plasma GDF15 concentrations were determined in these samples.

Results
Plasma GDF15 levels increased 34% with exercise (p < 0.001) and further increased to 64% above resting values at 120 min (p < 0.001) after the cessation of exercise. There was no difference between the arterial and venous GDF15 concentration before, during, and after exercise. During a resting control trial, GDF15 levels measured in the same subjects were unaltered.

Conclusions
Vigorous submaximal exercise increases circulating GDF15 levels in humans, but skeletal muscle tissue does not appear to be the source.

Rôle de l’ IL-15/IL dans la synthèse des protéines après la muscu

17/01/2018 | Etudes sur les hormones et Etudes Musculation

 

Skeletal muscle IL-15/IL-15Rα and myofibrillar protein synthesis after resistance exercise
Scandinavian Journal of Medicine & Science Sports 28, Issue 1 January 2018 Pages 116–125
A. Pérez-López

In vitro and in vivo studies described the myokine IL-15 and its receptor IL-15Rα as anabolic/anti-atrophy agents, however, the protein expression of IL-15Rα has not been measured in human skeletal muscle and data regarding IL-15 expression remain inconclusive. The purpose of the study was to determine serum and skeletal muscle IL-15 and IL-15Rα responses to resistance exercise session and to analyze their association with myofibrillar protein synthesis (MPS).

Fourteen participants performed a bilateral leg resistance exercise composed of four sets of leg press and four sets of knee extension at 75% 1RM to task failure. Muscle biopsies were obtained at rest, 0, 4 and 24 hours post-exercise and blood samples at rest, mid-exercise, 0, 0.3, 1, 2, 4 and 24 hours post-exercise. Serum IL-15 was increased by ~5.3-fold immediately post-exercise, while serum IL-15Rα decreased ~75% over 1 hour post-exercise (P

<.001). Skeletal muscle IL-15Rα mRNA and protein expression were increased at 4 hours post-exercise by ~2-fold (P<.001) and ~1.3-fold above rest (P=.020), respectively. At 24 hours post-exercise, IL-15 (P=.003) and IL-15Rα mRNAs increased by ~2-fold (P=.002). Myofibrillar fractional synthetic rate between 0-4 hours was associated with IL-15Rα mRNA at rest (r=.662, P=.019), 4 hours (r=.612, P=.029), and 24 hours post-exercise (r=.627, P=.029). Finally, the

muscle IL-15Rα protein up-regulation was related to Leg press 1RM (r=.688, P=.003) and total weight lifted (r=.628, P=.009). In conclusion, IL-15/IL-15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.

Effet de la respiration sur la pression intra-abdominale?

10/01/2018 | Etudes Musculation

 

Causal effect of intra-abdominal pressure on maximal voluntary isometric hip extension torque
European Journal of Applied Physiology January 2018, Volume 118, Issue 1, pp 93–99     Kota Tayashiki

Intra-abdominal pressure (IAP) has been recently shown to be associated specifically with maximal voluntary isometric contraction (MVC) torque of hip extension, although the causal relationship remains unclear. The present study aimed to elucidate whether IAP has a causal effect on hip extension MVC torque.

Methods
IAP during hip extension MVC was changed by controlling the lung volume (i.e., depth of inspiration). Twelve healthy males conducted MVCs of hip extension during breath-hold at full inspiration (inspiratory condition) or expiration (expiratory condition), or during normal breath-hold (normal condition). IAP during MVCs was measured a pressure transducer placed in the rectum.

Results
The IAP during hip extension MVC was significantly higher in inspiratory condition (132.0 ± 46.1 mmHg) than in the other two conditions and also higher in normal condition (104.6 ± 35.9 mmHg) than in expiratory condition (77.0 ± 39.1 mmHg). The hip extension MVC torque was significantly higher in inspiratory condition (297.7 ± 82.7 N m) than in expiratory condition (266.4 ± 84.5 N m). In each condition, the hip extension MVC torque correlated with IAP during the MVC task.

Conclusion
The current results suggest that IAP has a positive causal effect on hip extension MVC torque and that a sufficient increase in IAP directly leads to an enhancement of hip extension MVC torque.

Le mystère des courbatures…

26/12/2017 | Etudes Musculation

 

Muscle damage protective effect by two maximal isometric contractions on maximal eccentric exercise of the elbow flexors of the contralateral arm

Trevor C. Chen   Scandinavian Journal of Medicine & Science in Sports 23 December 2017

Muscle damage after 30 maximal eccentric contractions of the elbow flexors (30MVEC) is reduced when the same exercise is performed by the opposite arm, and when two maximal voluntary isometric contractions at a long muscle length (2MVIC) are performed prior to 30MVEC by the same arm. This study investigated the hypothesis that 2MVIC would attenuate muscle damage after 30MVEC performed by the opposite arm. Untrained young (20-25 y) men were placed into one of four experimental groups that performed 2MVIC at 1 (1d), 2 (2d), 4 (4d) or 7 days (7d) before 30 MVEC by the opposite arm, or one control group that performed 30MVEC only (n=13/group). Changes in indirect muscle damage markers after 30MVEC were compared among the groups by mixed-design two-way ANOVA. Maximal voluntary concentric contraction torque, range of motion, plasma creatine kinase activity and muscle soreness did not change significantly after 2MVIC. Changes in these variables after 30MVEC were smaller (p<0.05) for 1d (e.g., peak soreness: 45 ± 21 mm) and 2d groups (46 ± 20 mm) than control group (66 ± 18 mm), without significant differences between 1d and 2d groups. No significant differences in the changes were found among 4d, 7d and control groups, except for soreness showing smaller (P<0.05) increases for 4d group (54 ± 19 mm) than 7d (62 ± 17 mm) and control groups. These results supported the hypothesis, and showed that muscle damage induced by 30MVEC was reduced by 2MVIC performed 1-2 days prior to 30MVIC by the contralateral arm.

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