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1.
Muscle time under tension during resistance exercise stimulates differential muscle protein sub-fractional synthetic responses in men.
Burd, NA, Andrews, RJ, West, DW, Little, JP, Cochran, AJ, Hector, AJ, Cashaback, JG, Gibala, MJ, Potvin, JR, Baker, SK, et al
The Journal of physiology. 2012;(2):351-62
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Abstract
We aimed to determine if the time that muscle is under loaded tension during low intensity resistance exercise affects the synthesis of specific muscle protein fractions or phosphorylation of anabolic signalling proteins. Eight men (24 ± 1 years (sem), BMI = 26.5 ± 1.0 kg m(-2)) performed three sets of unilateral knee extension exercise at 30% of one-repetition maximum strength involving concentric and eccentric actions that were 6 s in duration to failure (SLOW) or a work-matched bout that consisted of concentric and eccentric actions that were 1 s in duration (CTL). Participants ingested 20 g of whey protein immediately after exercise and again at 24 h recovery. Needle biopsies (vastus lateralis) were obtained while fasted at rest and after 6, 24 and 30 h post-exercise in the fed-state following a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine. Myofibrillar protein synthetic rate was higher in the SLOW condition versus CTL after 24-30 h recovery (P < 0.001) and correlated to p70S6K phosphorylation (r = 0.42, P = 0.02). Exercise-induced rates of mitochondrial and sarcoplasmic protein synthesis were elevated by 114% and 77%, respectively, above rest at 0-6 h post-exercise only in the SLOW condition (both P < 0.05). Mitochondrial protein synthesis rates were elevated above rest during 24-30 h recovery in the SLOW (175%) and CTL (126%) conditions (both P < 0.05). Lastly, muscle PGC-1α expression was increased at 6 h post-exercise compared to rest with no difference between conditions (main effect for time, P < 0.001). These data show that greater muscle time under tension increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust, but delayed stimulation of myofibrillar protein synthesis 24-30 h after resistance exercise.
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Effect of texture of plastic and elastic model foods on the parameters of mastication.
Foster, KD, Woda, A, Peyron, MA
Journal of neurophysiology. 2006;(6):3469-79
Abstract
Mastication is continually modified throughout the chewing sequence in response to the texture of the food. The aim of this work was to compare the effects of an increase in hardness of two model food types, presenting either elastic or plastic rheological properties, on mastication. Each model food type consisted of four products of different hardness. Sensory testing experiments conducted with one group of 14 subjects showed significant perceived differences between products in terms of their increasing hardness. Fifteen other volunteers were asked to chew three replicates of each elastic and plastic product during two sessions. EMGs of masseter and temporalis muscles were recorded simultaneously with jaw movement during chewing. Numerous variables were analyzed from these masticatory recordings. Multiple linear regression analyses were used to assess the respective effects of food hardness and rheological properties on variables characterizing either the whole masticatory sequence or different stages of the sequence. Muscle activities were significantly affected by an increase in hardness regardless of the food type, whereas the shape of the cycles depended on the rheological properties. The masticatory frequency was affected by hardness at the initial stage of the sequence but overall frequency adaptation was better explained by a change in rheological behavior, with plastic products being chewed at a slower frequency. A dual hypothesis was proposed, implicating first a cortical-brain stem preprogrammed mechanism to adapt the shape of the jaw movements to the rheological properties of the food, and second, a brain stem mechanism with mainly sensory feedback from the mouth to adapt muscle force to the food hardness.
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Glycogenin activity and mRNA expression in response to volitional exhaustion in human skeletal muscle.
Shearer, J, Graham, TE, Battram, DS, Robinson, DL, Richter, EA, Wilson, RJ, Bakovic, M
Journal of applied physiology (Bethesda, Md. : 1985). 2005;(3):957-62
Abstract
Glycogenolysis results in the selective catabolism of individual glycogen granules by glycogen phosphorylase. However, once the carbohydrate portion of the granule is metabolized, the fate of glycogenin, the protein primer of granule formation, is not known. To examine this, male subjects (n = 6) exercised to volitional exhaustion (Exh) on a cycle ergometer at 75% maximal O2 uptake. Muscle biopsies were obtained at rest, 30 min, and Exh (99 +/- 10 min). At rest, total glycogen concentration was 497 +/- 41 and declined to 378 +/- 51 mmol glucosyl units/kg dry wt following 30 min of exercise (P < 0.05). There were no significant changes in proglycogen, macroglycogen, glycogenin activity, or mRNA in this period (P > or = 0.05). Exh resulted in decreases in total glycogen, proglycogen, and macroglycogen as well as glycogenin activity (P < 0.05). These decrements were associated with a 1.9 +/- 0.4-fold increase in glycogenin mRNA over resting values (P < 0.05). Glycogenolysis in the initial exercise period (0-30 min) was not adequate to induce changes in glycogenin; however, later in exercise when concentration and granule number decreased further, decrements in glycogenin activity and increases in glycogenin mRNA were demonstrated. Results show that glycogenin becomes inactivated with glycogen catabolism and that this event coincides with an increase in glycogenin gene expression as exercise and glycogenolysis progress.
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Muscle sarcoplasmic reticulum Ca2+ cycling adaptations during 16 h of heavy intermittent cycle exercise.
Holloway, GP, Green, HJ, Duhamel, TA, Ferth, S, Moule, JW, Ouyang, J, Tupling, AR
Journal of applied physiology (Bethesda, Md. : 1985). 2005;(3):836-43
Abstract
The repetition-dependent effects of a repetitive heavy exercise protocol previously shown to alter muscle mechanic behavior (Green HJ, Duhamel TA, Ferth S, Holloway GP, Thomas MM, Tupling AR, Rich SM, and Yau JE. J Appl Physiol 97: 2166-2175, 2004) on muscle sarcoplasmic reticulum (SR) Ca2+-transport properties, measured in vitro, were examined in 12 untrained volunteers [peak aerobic power (VO2(peak)) = 44.3 +/- 0.66 ml x kg(-1) x min(-1)]. The protocol involved 6 min of cycle exercise performed at approximately 91% VO2(peak) once per hour for 16 h. Tissue samples were obtained from the vastus lateralis before (B) and after (A) exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). Reductions (P < 0.05) in maximal Ca2+-ATPase activity (Vmax) of 26 and 12% with exercise were only observed at R1 and R16, respectively. Vmax remained depressed (P < 0.05) at R2 (B) but not at R9 (B) and R16 (B). No changes were observed in two other kinetic properties of the enzyme, namely the Hill coefficient (defined as the slope of the relationship between Ca2+-ATPase activity and free Ca2+ concentration) and the Ca50 (defined as the free Ca2+ concentration needed to elicit 50% Vmax). Changes in Ca2+ uptake (measured at 2,000 nM) with exercise and recovery generally paralleled Vmax. The apparent coupling ratio, defined as the ratio between Ca2+ uptake and Vmax, was unaffected by the intermittent protocol. Reductions (P < 0.05) in phase 1 Ca2+ release (32%) were only observed at R1. No differences were observed between B and A for R2, R9, and R16 or between B and B for R1, R2, R9, and R16. The changes in phase 2 Ca2+ release were as observed for phase 1 Ca2+ release. It is concluded that the SR Ca2+-handling properties, in general, display rapid adaptations to repetitive exercise.
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Influence of muscle glycogen availability on ERK1/2 and Akt signaling after resistance exercise in human skeletal muscle.
Creer, A, Gallagher, P, Slivka, D, Jemiolo, B, Fink, W, Trappe, S
Journal of applied physiology (Bethesda, Md. : 1985). 2005;(3):950-6
Abstract
Two pathways that have been implicated for cellular growth and development in response to muscle contraction are the extracellular signal-regulated kinase (ERK1/2) and Akt signaling pathways. Although these pathways are readily stimulated after exercise, little is known about how nutritional status may affect stimulation of these pathways in response to resistance exercise in human skeletal muscle. To investigate this, experienced cyclists performed 30 repetitions of knee extension exercise at 70% of one repetition maximum after a low (2%) or high (77%) carbohydrate (LCHO or HCHO) diet, which resulted in low or high (approximately 174 or approximately 591 mmol/kg dry wt) preexercise muscle glycogen content. Muscle biopsies were taken from the vastus lateralis before, approximately 20 s after, and 10 min after exercise. ERK1/2 and p90 ribosomal S6 kinase phosphorylation increased (P < or = 0.05) 10 min after exercise, regardless of muscle glycogen availability. Akt phosphorylation was elevated (P < 0.05) 10 min after exercise in the HCHO trial but was unaffected after exercise in the LCHO trial. Mammalian target of rapamycin phosphorylation was similar to that of Akt during each trial; however, change or lack of change was not significant. In conclusion, the ERK1/2 pathway appears to be unaffected by muscle glycogen content. However, muscle glycogen availability appears to contribute to regulation of the Akt pathway, which may influence cellular growth and adaptation in response to resistance exercise in a low-glycogen state.
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Dietary protein intake impacts human skeletal muscle protein fractional synthetic rates after endurance exercise.
Bolster, DR, Pikosky, MA, Gaine, PC, Martin, W, Wolfe, RR, Tipton, KD, Maclean, D, Maresh, CM, Rodriguez, NR
American journal of physiology. Endocrinology and metabolism. 2005;(4):E678-83
Abstract
This investigation evaluated the physiological impact of different dietary protein intakes on skeletal muscle protein synthesis postexercise in endurance runners. Five endurance-trained, male runners participated in a randomized, crossover design diet intervention, where they consumed either a low (0.8 g/kg; LP)-, moderate (1.8 g/kg; MP)-, or high (3.6 g/kg; HP)-protein diet for 4 wk. Diets were designed to be eucaloric with carbohydrate, fat, and protein approximating 60, 30, and 10%; 55, 30, and 15%; and 40, 30, and 30% for LP, MP, and HP, respectively. Substrate oxidation was assessed via indirect calorimetry at 3 wk of the dietary interventions. Mixed-muscle protein fractional synthetic rate (FSR) was measured after an endurance run (75 min at 70% V(O2 peak)) using a primed, continuous infusion of [(2)H(5)]phenylalanine. Protein oxidation increased with increasing protein intake, with each trial being significantly different from the other (P < 0.01). FSR after exercise was significantly greater for LP (0.083%/h) and MP (0.078%/h) than for HP (0.052%/h; P < 0.05). There was no difference in FSR between LP and MP. This is the first investigation to establish that habitual dietary protein intake in humans modulates skeletal muscle protein synthesis after an endurance exercise bout. Future studies directed at mechanisms by which level of protein intake influences skeletal muscle turnover are needed.
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Dynamic interleaved 1H/31P STEAM MRS at 3 Tesla using a pneumatic force-controlled plantar flexion exercise rig.
Meyerspeer, M, Krssák, M, Kemp, GJ, Roden, M, Moser, E
Magma (New York, N.Y.). 2005;(5):257-62
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Abstract
OBJECTIVE To develop a measurement method for interleaved acquisition of 1H and 31 STEAM localised spectra of exercising human calf muscle. MATERIALS AND METHODS A non-magnetic exercise rig with a pneumatic piston and sensors for force and pedal angle was constructed to enable plantar flexion measured in the 3 T MR scanner, which holds the dual tuned (1H ,31P) surface coil used for signal transmission and reception. RESULTS (31) spectra acquired in interleaved mode benefit from higher Signal to noise ratio (factor of 1.34 +/-0.06 for PCr) compared to standard acquisition due to the Nuclear Overhauser effect and substantial PCr/P(i) changes during exercise can be observed in 31P spectra. 1H spectral quality is equal to that in single mode experiments and allows Cr2 changes to be monitored. CONCLUSION The feasibility of dynamic interleaved localised 1H and 31P spectroscopy during plantar flexion exercise has been demonstrated using a custom-built pneumatic system for muscle activation. This opens the possibility of studying the dynamics of metabolism with multi nuclear MRS in a single run.
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Myofibrillar and collagen protein synthesis in human skeletal muscle in young men after maximal shortening and lengthening contractions.
Moore, DR, Phillips, SM, Babraj, JA, Smith, K, Rennie, MJ
American journal of physiology. Endocrinology and metabolism. 2005;(6):E1153-9
Abstract
We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque = 225 +/- 7 N.m, means +/- SE) or lengthening contractions (LC; average peak torque = 299 +/- 18 N.m) with equivalent work performed in each mode. Eight healthy young men (21.9 +/- 0.6 yr, body mass index 24.9 +/- 1.3 kg/m2) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 +/- 0.7 vs. 10.9 +/- 0.8 kJ, P = 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g.kg(-1).h(-1) of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P < 0.01). The increases (P < 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC.
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Prolonged exercise to fatigue in humans impairs skeletal muscle Na+-K+-ATPase activity, sarcoplasmic reticulum Ca2+ release, and Ca2+ uptake.
Leppik, JA, Aughey, RJ, Medved, I, Fairweather, I, Carey, MF, McKenna, MJ
Journal of applied physiology (Bethesda, Md. : 1985). 2004;(4):1414-23
Abstract
Prolonged exhaustive submaximal exercise in humans induces marked metabolic changes, but little is known about effects on muscle Na+-K+-ATPase activity and sarcoplasmic reticulum Ca2+ regulation. We therefore investigated whether these processes were impaired during cycling exercise at 74.3 +/- 1.2% maximal O2 uptake (mean +/- SE) continued until fatigue in eight healthy subjects (maximal O2 uptake of 3.93 +/- 0.69 l/min). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45 min of exercise, and at fatigue. Muscle was analyzed for in vitro Na+-K+-ATPase activity [maximal K+-stimulated 3-O-methylfluorescein phosphatase (3-O-MFPase) activity], Na+-K+-ATPase content ([3H]ouabain binding sites), sarcoplasmic reticulum Ca2+ release rate induced by 4 chloro-m-cresol, and Ca2+ uptake rate. Cycling time to fatigue was 72.18 +/- 6.46 min. Muscle 3-O-MFPase activity (nmol.min(-1).g protein(-1)) fell from rest by 6.6 +/- 2.1% at 10 min (P <0.05), by 10.7 +/- 2.3% at 45 min (P <0.01), and by 12.6 +/- 1.6% at fatigue (P <0.01), whereas 3[H]ouabain binding site content was unchanged. Ca2+ release (mmol.min(-1).g protein(-1)) declined from rest by 10.0 +/- 3.8% at 45 min (P <0.05) and by 17.9 +/- 4.1% at fatigue (P < 0.01), whereas Ca2+ uptake rate fell from rest by 23.8 +/- 12.2% at fatigue (P=0.05). However, the decline in muscle 3-O-MFPase activity, Ca2+ uptake, and Ca2+ release were variable and not significantly correlated with time to fatigue. Thus prolonged exhaustive exercise impaired each of the maximal in vitro Na+-K+-ATPase activity, Ca2+ release, and Ca2+ uptake rates. This suggests that acutely downregulated muscle Na+, K+, and Ca2+ transport processes may be important factors in fatigue during prolonged exercise in humans.
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Effect of contraction frequency on energy expenditure and substrate utilisation during upper and lower body exercise.
Kang, J, Hoffman, JR, Wendell, M, Walker, H, Hebert, M
British journal of sports medicine. 2004;(1):31-5
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Abstract
OBJECTIVE To examine the effect of contraction frequency on energy expenditure and substrate utilisation during upper (UE) and lower (LE) body exercise. METHODS Twenty four college students were recruited: 12 were tested on an arm ergometer, and the other 12 were tested on a leg ergometer. Each subject underwent three experimental trials on three separate days, and the three trials were presented in a randomised order. Each trial consisted of 10 minutes of arm cranking or leg cycling at 40, 60, or 80 rev/min, with power output being kept constant at 50 W. Steady state oxygen uptake (VO(2)) and respiratory exchange ratio (RER) were measured during each exercise. Energy expenditure was calculated from the steady state VO(2) adjusted for substrate metabolism using RER. Carbohydrate and fat oxidation were calculated from VO(2) and RER based on the assumption that protein breakdown contributes little to energy metabolism during exercise. RESULTS Energy expenditure was greater (p<0.05) at 80 rev/min than at 40 rev/min. No difference was found between 40 and 60 rev/min and between 60 and 80 rev/min during both UE and LE. During LE, carbohydrate oxidation was also higher at 80 rev/min than at 40 rev/min, whereas no difference in fat oxidation was found among all three pedal rates. During UE, no speed related differences in either carbohydrate or fat utilisation were observed. CONCLUSIONS Pedalling at a greater frequency helped to maximise energy expenditure during exercise using UE or LE despite an unchanging power output. Whereas contraction frequency affects energy expenditure similarly during both UE and LE, its impact on carbohydrate utilisation appears to be influenced by exercise modality or relative exercise intensity.