Forced Running Endurance Is Influenced by Gene(s) on Mouse Chromosome 10

Acknowledgments The authors wish to acknowledge technical assistance from Mrs. Indrė Libnickienė and intellectual input from Dr. David A. Blizard. This research was funded by the European Social Fund under the Global Grant measure. Grant VP1-3.1-ŠMM-07-K-02-057 was awarded to AL.Peer reviewedPublisher PD

Genetic polymorphisms of muscular fitness in young healthy men.

The effects of genetic polymorphisms on muscle structure and function remain elusive. The present study tested for possible associations of 16 polymorphisms (across ten candidate genes) with fittness and skeletal muscle phenotypes in 17- to 37-year-old healthy Caucasian male endurance (n = 86), power/strength (n = 75) and team athletes (n = 60), and non-athletes (n = 218). Skeletal muscle function was measured with eight performance tests covering multiple aspects of muscular fitness. Along with body mass and height, the upper arm and limb girths, and maximal oxygen uptake were measured. Genotyping was conducted on DNA extracted from blood. Of the 16 polymorphisms studied, nine (spanning seven candidate genes and four gene families/signalling pathways) were independently associated with at least one skeletal muscle fitness measure (size or function, or both) measure and explained up to 4.1% of its variation. Five of the studied polymorphisms (activin- and adreno-receptors, as well as myosine light chain kinase 1) in a group of one to three combined with body height, age and/or group explained up to 20.4% of the variation of muscle function. ACVR1B (rs2854464) contributed 2.0-3.6% to explain up to 14.6% of limb proximal girths. The G allele (genotypes AG and GG) of the ACVR1B (rs2854464) polymorphism was significantly overrepresented among team (60.4%) and power (62.0%) athletes compared to controls (52.3%) and endurance athletes (39.2%), and G allele was also most consistently/frequently associated with muscle size and power. Overall, the investigated polymorphisms determined up to 4.1% of the variability of muscular fitness in healthy young humans

A modelling approach to disentangle the factors limiting muscle oxygenation in smokers

Cigarette smoking is associated with a lower exercise capacity and lower muscle fatigue resistance. This is at least partly attributable to carboxyhaemoglobin (HbCO) in the blood that via reduction in the oxygen-carrying capacity, and the left-shift of the Hb-dissociation curve would reduce tissue oxygenation. On the other hand, a reduced oxygen uptake due to mitochondrial dysfunction would result in improved oxygenation. We used previously collected capillarisation, myoglobin and estimated cellular maximal muscle oxygen consumption data derived from succinate dehydrogenase-stained sections from the vastus lateralis muscle from six smokers and five non-smokers. These data were fed into an expanded Krogh tissue oxygenation model to assess whether an impaired muscle fatigue resistance in smokers is primarily due to HbCO or impaired mitochondrial respiration. The model showed that in smokers with 6% and 20% HbCO (causing a left-shift of the Hb-dissociation curve) average muscle oxygenation was reduced by 1.9% and 7.2%, respectively. Muscle oxygenation was increased by 13.3% when maximal mitochondrial respiration was reduced by 29%. A combination of a 29% reduction in maximal mitochondrial respiration and 20% HbCO led to no significant difference in muscle oxygenation from that in non-smokers. This indicates that while HbCO may explain the reduced exercise capacity after just one smoking session, in chronic smokers impaired mitochondrial respiration appears more important in reducing oxygen extraction and exercise capacity with only a small contribution of the left-shift of the Hb-dissociation curve

Aerobic Capacity Is Related to Multiple Other Aspects of Physical Fitness: A Study in a Large Sample of Lithuanian Schoolchildren

This study evaluated how aerobic capacity is related to performance in other aspects of health-related physical fitness among schoolchildren. The study involved >15,200 schoolchildren of both genders aged 11–18 years, who were tested with a reliable tests from Eurofit battery for most important aspects of exercise capacity and anthropometrics from 1992 to 2012. The analysis showed that aerobic capacity was weakly but significantly positively related to all other aspects of exercise abilities tested in all age groups for both genders. Variance of performance in agility shuttle run and standing broad jump were each explained by aerobic capacity the strongest (>10%), followed by weaker but still significant positive relation of aerobic capacity with the abilities in bent arm hang and abdominal curl tests (aerobic capacity explaining ∼6.5% of the variance of the performance in these tests), as well as in balance and flexibility tasks (aerobic capacity significantly explaining ∼3% of the variance). Thus, while aerobic capacity in schoolchildren of all ages and both genders can explain the performance in other aspects of physical fitness and especially leg muscle power, the percent of explained variance in the results of any these tests was not high and therefore aerobic capacity should be tested as a separate important fitness parameter which cannot be substituted by other tests from the Eurofit battery

Regenerated soleus muscle shows reduced creatine kinase efflux after contractile activity in vitro

Date of Acceptance: 07/10/2014 Acknowledgements We are very grateful to Petras Jeneckas and Audrius Capskas for technical assistance. The study was supported by a grant (No. MIP-067/2012) from the Research Council of Lithuania.Peer reviewedPostprin

Myostatin dysfunction does not protect from fasting-induced loss of muscle mass in mice

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H55N polymorphism is associated with low citrate synthase activity which regulates lipid metabolism in mouse muscle cells

Funding: This work was supported, in whole or in part, by European Social Fund under the Global Grant measure Grant VP1-3.1-ŠMM-07-K-02-057 (to A.L.), European Foundation for the Study of Diabetes grant (to T.V.), NHS Grampian Endowment grant (to A.R. and S.R.G.), Kuwait Ministry of Health grant (to M.A.), Saudi Ministry of Higher Education grant (to Y.A.,) as well as Saltire scholarship, Wenner-Gren Foundation Postdoctoral Fellowship, Albert Renold Travel Fellowship and a Novo Nordisk Foundation Challenge Grant (to B.G.).Peer reviewedPublisher PD

Moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions differently affects muscle contractile function in young males

Background: We investigated the impact of moderate muscle cooling induced by single and intermittent/prolonged cold-water immersions (CWI) on muscle force and contractility in unfatigued state and during the development of fatigue resulting from electrically induced contractions.Methods: Twelve young males participated in this study consisting of two phases [single phase (SP) followed by intermittent/prolonged phase (IPP)], with both phases including two conditions (i.e., four trials in total) performed randomly: control passive sitting (CON) and cold-water immersions (10°C). SP-CWI included one 45 min-bath (from 15 to 60 min). IPP-CWI included three baths (45 min-bath from 15 to 60 min, and 15 min-baths from 165 to 180 min and from 255 to 270 min), with participants sitting at room temperature the rest of the time until 300 min. Blood pressure and intramuscular (Tmu) temperature were assessed, and neuromuscular testing was performed at baseline and 60 min after baseline during SP, and at baseline, 60, 90, 150 and 300 min after baseline during IPP. A fatiguing protocol (100 electrical stimulations) was performed after the last neuromuscular testing of each trial.Results: In unfatigued state, SP-CWI and IPP-CWI reduced electrically induced torque at 100 Hz (P100) but not at 20 Hz (P20), and increased P20/P100 ratio. The changes from baseline for P100 and P20/P100 ratio were lower in IPP-CWI than SP-CWI. Both cold-water immersion conditions slowed down muscle contraction and relaxation, and reduced maximal isokinetic contraction torque, but the changes from baseline were lower after IPP-CWI than SP-CWI. cold-water immersions did not impair maximal voluntary isometric contraction. During the fatiguing protocol, torque fatigue index and the changes in muscle contractile properties were larger after IPP-CWI than SP-CWI, but were in the same range as after CON conditions. The differences of muscle contractile function between SP-CWI and IPP-CWI were accompanied by a lower reduction of superficial Tmu and a smaller increase in systolic blood pressure after IPP-CWI than SP-CWI.Conclusion: IPP-CWI induces a less pronounced fast-to-slow contractile transition compared to SP-CWI, and this may result from the reduced vasoconstriction response and enhanced blood perfusion of the superficial muscle vessels, which could ultimately limit the reduction of superficial Tmu

Physiological comparison between non-athletes, endurance, power and team athletes.

We hypothesized that endurance athletes have lower muscle power than power athletes due to a combination of weaker and slower muscles, while their higher endurance is attributable to better oxygen extraction, reflecting a higher muscle oxidative capacity and larger stroke volume. Endurance (n = 87; distance runners, road cyclists, paddlers, skiers), power (n = 77; sprinters, throwers, combat sport athletes, body builders), team (n = 64; basketball, soccer, volleyball) and non-athletes (n = 223) performed a countermovement jump and an incremental running test to estimate their maximal anaerobic and aerobic power (VO2max), respectively. Dynamometry and M-mode echocardiography were used to measure muscle strength and stroke volume. The VO2max (L min-1) was larger in endurance and team athletes than in power athletes and non-athletes (p < 0.05). Athletes had a larger stroke volume, left ventricular mass and left ventricular wall thickness than non-athletes (p < 0.02), but there were no significant differences between athlete groups. The higher anaerobic power in power and team athletes than in endurance athletes and non-athletes (p < 0.001) was associated with a larger force (p < 0.001), but not faster contractile properties. Endurance athletes (20.6%) had a higher (p < 0.05) aerobic:anaerobic power ratio than controls and power and team athletes (14.0-15.3%). The larger oxygen pulse, without significant differences in stroke volume, in endurance than power athletes indicates a larger oxygen extraction during exercise. Power athletes had stronger, but not faster, muscles than endurance athletes. The similar VO2max in endurance and team athletes and similar jump power in team and power athletes suggest that concurrent training does not necessarily impair power or endurance performance

Regular endurance exercise of overloaded muscle of young and old male mice does not attenuate hypertrophy and improves fatigue resistance

It has been observed that there is an inverse relationship between fiber size and oxidative capacity due to oxygen, ADP, and ATP diffusion limitations. We aimed to see if regular endurance exercise alongside a hypertrophic stimulus would lead to compromised adaptations to both, particularly in older animals. Here we investigated the effects of combining overload with regular endurance exercise in young (12 months) and old (26 months) male mice. The plantaris muscles of these mice were overloaded through denervation of synergists to induce hypertrophy and the mice ran on a treadmill for 30 min per day for 6 weeks. The hypertrophic response to overload was not blunted by endurance exercise, and the increase in fatigue resistance with endurance exercise was not reduced by overload. Old mice demonstrated less hypertrophy than young mice, which was associated with impaired angiogenesis and a reduction in specific tension. The data of this study suggest that combining endurance exercise and overload induces the benefits of both types of exercise without compromising adaptations to either. Additionally, the attenuated hypertrophic response to overload in old animals may be due to a diminished capacity for capillary growth