Additional Muscle Mass Research Articles

Added mass in rat plantaris muscle causes a reduction in mechanical work.

Most of what we know about whole muscle behaviour comes from experiments on single fibres or small muscles that are scaled up in size without considering the effects of the additional muscle mass. Previous modelling studies have shown that tissue inertia acts to slow the rate of force development and maximum velocity of muscle during shortening contractions and decreases the work and power per cycle during cyclic contractions; however, these results have not yet been confirmed by experiments on living tissue. Therefore, in this study we conducted in situ work-loop experiments on rat plantaris muscle to determine the effects of increasing the mass of muscle on mechanical work during cyclic contractions. We additionally simulated these experimental contractions using a mass-enhanced Hill-type model to validate our previous modelling work. We found that greater added mass resulted in lower mechanical work per cycle relative to the unloaded trials in which no mass was added to the muscle (P=0.041 for both 85 and 123% increases in muscle mass). We additionally found that greater strain resulted in lower work per cycle relative to unloaded trials at the same strain to control for length change and velocity effects on the work output, possibly due to greater accelerations of the muscle mass at higher strains. These results confirm that tissue mass reduces muscle mechanical work at larger muscle sizes, and that this effect is likely amplified for lower activations.

Perceptions of Body Mass Index as a Valid Indicator of Weight Status among Adults in the United States

Background: Being overweight or obese increases risk for heart disease, stroke, type 2 diabetes, joint disease, and certain cancers. The Body Mass Index (BMI) is commonly used to determine weight status. As rates of overweight and obesity have risen sharply in the United States over the past 30 years, perceptions of a “normal” or healthy weight are subject to change. The purpose of this study was to analyze perceptions of BMI as an indicator of weight status. Methods: An online survey was administered to 376 US adults. The survey collected demographic information including height, weight, and perceived weight status (underweight, healthy weight, overweight and obese). The survey software calculated and presented participants with their personal BMI values. Participants then answered questions about their perception of the BMI as a valid indicator of weight status. Results: More participants reported a healthy weight status (51.6%) than were classified as such according to their computed BMI (43.6%). The majority of the sample (85.1%) considered BMI to be a valid indicator of weight status, although perceptions of validity varied by weight status. Participants that perceived BMI to be invalid most commonly cited incongruence with one’s perception of their own body weight, no accounting for unique body shapes, and no accounting for additional muscle mass. Conclusion: BMI is generally perceived to be a valid indicator of weight status. These perceptions of validity can vary depending on the individuals’ actual weight status. In instances where perceptions are not favorable toward BMI, it is largely attributable to opinions of incongruence with BMI and body shape, type, or composition. Continued use of BMI as a preliminary tool for determining weight status appears to be accepted. Efforts to increase BMI-related awareness and education may be necessary for individuals that currently see it as invalid.

Factors affecting running performance in 6-12-year-olds: The Health Oriented Pedagogical Project (HOPP).

The purpose of this study was to examine factors affecting running performance in children. A cross-sectional study exploring the relationships between height, weight, waist circumference, muscle mass, body fat percentage, relevant biomarkers, and the Andersen intermittent running test in 2272 children aged 6 to 12 years. Parental education level was used as a non-physiological explanatory variable. Mean values (SD) and percentiles are presented as reference values. Height (β = 6.4, p < .0001), high values of haemoglobin (β = 18, p = .013) and low percentage of body fat (β = -7.5, p < .0001) showed an association with results from the running test. In addition, high parental education level showed a positive association with the running test. Boys display better running performance than girls at all age ages, except 7 years old, probably because of additional muscle mass and less fatty tissue. Height and increased level of haemoglobin positively affected running performance. Lower body fat percentage and high parental education level correlated with better running performance.

Ractopamine Influences Muscle Proteome Profile of Postmortem Beef Longissimus Lumborum

ObjectivesRactopamine is a β-adrenergic agonist approved for use in cattle and pigs as a repartitioning agent to increase muscle deposition and potentially limit fat deposition. While the effects of ractopamine on proteome profile of postmortem pork muscles have been examined recently, its influence on beef muscle proteome has not been evaluated. Therefore, the objective of this study was to examine the effects of ractopamine on muscle proteome of postmortem longissimus lumborum (LL) from beef cattle.Materials and MethodsCrossbred steers housed in pens were fed either a corn-based basal diet (CON) or a diet top-dressed with Optaflexx 45 (Elanco Animal Health) to provide 400 mg of ractopamine hydrochloride/steer per day (RAC). Ractopamine was fed the last 28 d before slaughter. Steers were harvested, and carcasses were chilled. The LL muscle samples were obtained from the carcasses of 9 (n = 9) RAC and CON steers 24 h postmortem. The muscle samples were individually vacuum-packaged and frozen at –80°C for proteome analysis. Whole-muscle proteome was analyzed using 2-dimensional electrophoresis, and the digital gel images were analyzed. The protein spots exhibiting more than 1.5-fold intensity differences (P < 0.10) between RAC and CON were subjected to in-gel tryptic digestion and were identified by tandem mass spectrometry.ResultsFive differentially abundant protein spots identified were of greater (P < 0.10) abundance in LL samples from RAC compared to those from CON. The proteins identified were F-actin-capping protein subunit β2, PDZ and Lim domain protein-3, heat shock protein β-1, myoglobin, and L-lactate dehydrogenase A chain. The differentially abundant proteins belong to 4 functional groups; i.e., skeletal muscle organization (F-actin-capping protein subunit β2, and PDZ and LIM domain protein-3), chaperone activity (heat shock protein β-1), oxygen transportation (myoglobin), and energy metabolism (L-lactate dehydrogenase A chain).The over-abundance of F-actin-capping protein subunit β2 as well as PDZ and LIM domain protein-3 in RAC may be attributed to the increase in myofibrillar protein synthesis and increase in muscle mass as a result of ractopamine feeding. Heat shock protein β-1 is a chaperone that protects muscle proteins, and its increased abundance in RAC compared to CON may be due to the increased muscle protein synthesis. The over-abundance of myoglobin could possibly result from the increased oxygen consumption due to additional muscle mass accretion in RAC compared to CON, whereas the increased levels of L-lactate dehydrogenase A chain in RAC could potentially be due to the shift of muscle fiber type.ConclusionThe findings indicated that feeding ractopamine to steers influences the abundance of proteins involved in skeletal muscle organization, chaperone activity, oxygen transportation, and energy metabolism in postmortem beef LL muscle.

Surgical efficacy of the ankle tourniquet for forefoot surgery.

For precise, safe and proficient procedures haemostasis is critical. For forefoot surgery, the customary thigh tourniquet is commonly accepted for this role as the additional muscle mass and minimal bony prominences in the thigh avert neuromuscular and skin injury. However, for patients with pathophysiological issues that may be exacerbated by a thigh tourniquet, application of an ankle tourniquet may decrease the risks and increase cuff tolerance as the volume of ischaemic tissue is reduced.

Effect of a 12-Week Conditioning Period on Nitrogen Balance in Horses

Fourteen horses were used in two 12-week experiments. Horses were fed to meet crude protein needs for exercising horses and participated in light-to-moderate exercise. Total feces and urine output were measured in 4-day collections at the beginning and the end of each experiment. Fecal nitrogen (FN) and urine nitrogen (UN) were used to calculate nitrogen balance and digestibility. Nitrogen intake (NI) was higher in the end collection (P = .001). Fecal nitrogen expressed as a daily amount or as a percentage of NI was not different (P = .63 and .39, respectively). Nitrogen digestibility was not different (P = .39); however, the amount of nitrogen absorbed (NA) was lower in the initial collection (P = .001). Urine nitrogen was lower in the end collection when expressed as a total loss per day (P = .041), percent of NI (P = .001), or as a percent of NA (P = .001). Daily nitrogen retention (NR), NR expressed as a percentage of NI and as a percentage of NA, was higher in the end collection (P = .001). The improvement in NR in the end collection is due to the reduction in UN loss. This suggests more efficient use of dietary protein because there was no difference in FN loss; but without a significant change in body weight or body condition score, it cannot be concluded that the additional retained nitrogen was because of a need to support additional muscle mass.

Cardiovascular risk and androgenic anabolic steroids

Although several drugs are purported to improve exercise performance, androgenic anabolic steroids (AAS) are the most widespread. Furthermore, unlike other drugs, their use has expanded beyond competition, to non-competitive and recreational athletes. Correspondingly health professionals are more likely to come into contact with users of AAS than with users of other performance-enhancing drugs. While there are numerous reports outlining serious cardiovascular consequences to high-dose AAS abuse, this evidence is often limited by difficulties in gaining access to users due to the legal status of AAS. Additionally the co-abuse of other substances (as additional muscle mass enhancers, or to mitigate possible side effects) is a further confounding factor. This review examines the evidence for AAS having a negative effect on the cardiac and vascular tissue and the corresponding risk of developing cardiovascular disease. Possible mechanisms of action by which AAS bring about these changes are also discussed.

Pico de velocidade de crescimento como alternativa para classificação maturacional associada ao desempenho motor

Adolescence is a phase characterized by important physical and maturational alterations, with individuals of the same chronological age, but who are more mature, may present sportive advantages because of greater force gain and additional muscle mass. Thus, in studies evaluating motor skills of children and adolescents, maturational classification should be an efficient and easily applicable tool in order to facilitate the interpretation of the true relationship between maturation and motor performance. Therefore, the objective of this study was to compare the relationship between motor performance and different types of classification of biological maturation in 209 boys aged to 17 years (11.59 ± 2.57) practicing soccer. Anthropometric variables were obtained according to the ISAK criteria. Biological maturation was determined based on age at peak height velocity (PHV) and also by self-assessment of sexual maturation (genitalia and pubic hair). Motor performance was evaluated by sit-and-reach tests, horizontal jump, modified push-ups, 50-m run, and 9/12-min run/walk. The results showed progression in the variables analyzed as the subjects reached maturity. Correlation analysis and the egression values indicated higher consistency for the PHV classification, which better explained motor performance according to maturational status, exceeding the values obtained by comparison according to age or sexual maturation. Thus, the use of PHV as a classification instrument is preferably recommended for youngsters with haracteristics similar to those of the present sample.

Peak height velocity as an alternative for maturational classification associated with motor performance

Adolescence is a phase characterized by important physical and maturational alterations, with individuals of the same chronological age, but who are more mature, may present sportive advantages because of greater force gain and additional muscle mass. Thus, in studies evaluating motor skills of children and adolescents, maturational classification should be an efficient and easily applicable tool in order to facilitate the interpretation of the true relationship between maturation and motor performance. Therefore, the objective of this study was to compare the relationship between motor performance and different types of classification of biological maturation in 209 boys aged to 17 years (11.59 ± 2.57) practicing soccer. Anthropometric variables were obtained according to the ISAK criteria. Biological maturation was determined based on age at peak height velocity (PHV) and also by self-assessment of sexual maturation (genitalia and pubic hair). Motor performance was evaluated by sit-and-reach tests, horizontal jump, modified push-ups, 50-m run, and 9/12-min run/walk. The results showed progression in the variables analyzed as the subjects reached maturity. Correlation analysis and the egression values indicated higher consistency for the PHV classification, which better explained motor performance according to maturational status, exceeding the values obtained by comparison according to age or sexual maturation. Thus, the use of PHV as a classification instrument is preferably recommended for youngsters with haracteristics similar to those of the present sample.

Mechanical and energetic factors underlying gait transitions in bluegill sunfish (Lepomis macrochirus)

As their swimming speed increased, bluegill sunfish (Lepomis macrochirus) switched from pectoral-fin-powered labriform swimming to undulations of the body axis. This gait transition occurred at a mean swimming speed of 0.24+/-0.01 m s(-1) and a pectoral fin beat frequency of 2.79+/-0.11 Hz (mean +/- s.e.m., N=6). The power output available from the main upstroke (adductor profundus) and downstroke (abductor superficialis) muscles, measured using the work-loop technique was maximal at the gait transition point. The cost of transport, measured by respirometry, increased as the fish switched from labriform to undulatory swimming. Our data show that bluegill changed gait as swimming speed increased to recruit additional muscle mass, rather than to maximize economy, as is the case for many terrestrial animals.

Measuring Up in the Bedroom: Muscle, Thinness, and Men's Sex Lives

Research has shown men often desire additional muscle mass, a trait related to masculine personality characteristics. While some research has suggested men lacking in muscle may believe themselves to be sexually undesirable to women, little research has been done in this area, especially when compared to the strong literature connecting women’s drive for thinness to female sexual behavior. The present study sought to determine the connection between men’s body image and men’s perceived sexual efficacy and attractiveness. Male undergraduates (N = 105) completed a novel scale of sexual efficacy and attractiveness, in addition to questions relating to self-esteem, sexual behaviors and milestones, desire for muscle, and desire for thinness. Sexual efficacy and attractiveness was positively related to self-esteem, and mediated drive for muscle’s negative relationship to self-esteem. Drive for thinness was negatively related to self-esteem, but unrelated to any sexual indices. Results suggest the presence of two types of body image dissatisfaction in men—thinness and muscle—but only the culturally demanded body dimension impacts sexual variables. Implications for future research are discussed.

Consequences of Ankle Joint Fixation on FES Cycling Power Output: A Simulation Study

During fixed-ankle FES cycling in paraplegics, in which the leg position is completely determined by the crank angle, mechanical power output is low. This low power output limits the cardiovascular load that could be realized during FES ergometer cycling, and limits possibilities for FES cycling as a means of locomotion. Stimulation of ankle musculature in a released-ankle setup might increase power output. However, releasing the ankle joint introduces a degree of freedom in the leg that has to be controlled, which imposes constraints on the stimulation pattern. In this study, a forward dynamics modeling/simulation approach was used to assess the potential effect of releasing the ankle on the maximal mechanical power output. For the released-ankle setup, the optimal stimulation pattern was found to be less tightly related to muscle shortening/lengthening than for the fixed-ankle setup, which indicates the importance of the constraints introduced by releasing the ankle. As a result, the maximal power output for 45-RPM cycling in the released-ankle setup was found to be about 10% lower than with a fixed ankle, despite the additional muscle mass available for stimulation. Power output for the released-ankle setup can be improved by tuning the point of contact between the foot and pedal to the relative strength of the ankle plantar flexors. For the model used, power output was 14% higher than for the fixed-ankle setup when this point of contact was moved posteriorly by 0.075 m. Releasing the ankle joint and stimulating the triceps surae and tibialis anterior is expected to result in a modest increase in power output at best.

Contraction-induced increases in Na+-K+-ATPase mRNA levels in human skeletal muscle are not amplified by activation of additional muscle mass

The present study tested the hypothesis that exercise with a large compared with a small active muscle mass results in a higher contraction-induced increase in Na(+)-K(+)-ATPase mRNA expression due to greater hormonal responses. Furthermore, the relative abundance of Na(+)-K(+)-ATPase subunit alpha(1), alpha(2), alpha(3), alpha(4), beta(1), beta(2), and beta(3) mRNA in human skeletal muscle was investigated. On two occasions, eight subjects performed one-legged knee extension exercise (L) or combined one-legged knee extension and bilateral arm cranking (AL) for 5.00, 4.25, 3.50, 2.75, and 2.00 min separated by 3 min of rest. Leg exercise power output was the same in AL and L, but heart rate at the end of each exercise interval was higher in AL compared with L. One minute after exercise, arm venous blood lactate was higher in AL than in L. A higher level of blood epinephrine and norepinephrine was evident 3 min after exercise in AL compared with L. Nevertheless, none of the exercise-induced increases in alpha(1), alpha(2), beta(1), and beta(3) mRNA expression levels were higher in AL compared with L. The most abundant Na(+)-K(+)-ATPase subunit at the mRNA level was beta(1), which was expressed 3.4 times than alpha(2). Expression of alpha(1), beta(2), and beta(3) was less than 5% of the alpha(2) expression, and no reliable detection of alpha(3) and alpha(4) was possible. In conclusion, activation of additional muscle mass does not result in a higher exercise-induced increase in Na(+)-K(+)-ATPase subunit-specific mRNA.

Kinetics of oxygen uptake during arm cranking with the legs inactive or exercising at moderate intensities

The purpose of this study was to compare the kinetics of oxygen uptake (VO(2)) during arm cranking with the legs inactive or exercising. Each subject (n = 8) performed three exercise protocols: 6-min arm cranking at an intensity of 60% of peak oxygen uptake (VO(2peak), AC(60)) and 6-min combined arm cranking and leg cycling in which AC(60) was added to on-going leg cycling at an intensity of 20% or 40% of VO(2peak) (LC(20) and LC(40): AC(60)LC(20) and AC(60)LC(40), respectively). After the onset of arm cranking, VO(2) tended to increase until the end of arm cranking in all of the three exercise modes. The amplitudes of this increase in VO(2) were 0.98 (0.18), 0.93 (0.16) and 0.84 (0.12) l.min(-1) during AC(60), AC(60)LC(20) and AC(60)LC(40), respectively, and there were significant differences between values for each exercise. The data are presented as means and standard deviations. There were no significant differences in the effective VO(2) time constant, partial O(2) deficit, and the difference between the values of VO(2) measured at 3 and 6 min in the three exercise modes. The present results indicate that the amplitude of the increase in VO(2) is reduced during arm cranking with the legs exercising, that this reduction becomes greater with increases in the intensity of leg cycling, and that the rate of increase in VO(2) is not affected by the additional muscle mass of the legs exercising below moderate intensities. The decrease in the amplitude of increase in VO(2) might be caused by reduction in oxygen supply to the exercising arms due to large muscle mass and/or overlaps of activity of stabilizing muscles during combined arm and leg exercise.

SIMULTANEOUS MEASUREMENT OF CEREBRAL AND MUSCLE TISSUE OXYGENATION USING NIRS.

The simultaneous measurement of cerebral and muscle oxygenation (OX) and blood volume (BV) has not been studied during exercise using non-invasive near infrared spectroscopy (NIRS) when additional muscle mass is added to ongoing steady state exercise. This could provide some indication on how blood flow is redistributed when performing multi-exercise tasks. PURPOSE To examine the simultaneous measurement of OX and BV changes in the forearm flexor digitorum (OXf; BVf), vastus lateralis (OXv; BVv), and cerebral-frontal lobe (OXc; BVc) tissue using NIRS. METHODS Nine well-trained male cyclists (VO2max =69.2 ± 9.5 mL×kg−1×min−1) performed steady state cycle ergometry for 5 min below (BVT) and above (AVT) the ventilation threshold. Maximal rhythmical hand-grip exercise was performed for one min with the right hand during the last minute at each exercise intensity. Cardiorespiratory measurements were also recorded simultaneously. RESULTS The results indicated that OXc and BVc increased systematically during cycling exercise (r=0.975) and demonstrated an additional increase during maximal hand-grip exercise. However, BVT there was an increased OXv (10%; i.e. reduced deoxygenation) and a levelling-off of BVv in relation to the steady state exercise, while OXf [91%; (i.e. greater deoxygenation)] and BVf (35%) decreased. Similar trends were noted AVT but to a lesser degree. Whole body VO2 was significantly correlated to OX and BV changes BVT and AVT in all tissues monitored (r=0.64–0.98). CONCLUSION These results indicate that: (1) addition of maximal hand-grip exercise during submaximal cycling increases cerebral hemodynamcis, most likely due to increased cortical activation, and (2) OX and BV can be compromised in the vastus lateralis muscle during cycling exercise at intensities below and above the ventilatory threshold. Support by Faculty Research Fund, VP Research, UNB.

Lower extremity muscle activation during horizontal and uphill running

To provide more comprehensive information on the extent and pattern of muscle activation during running, we determined lower extremity muscle activation by using exercise-induced contrast shifts in magnetic resonance (MR) images during horizontal and uphill high-intensity (115% of peak oxygen uptake) running to exhaustion (2.0-3.9 min) in 12 young women. The mean percentage of muscle volume activated in the right lower extremity was significantly (P <0.05) greater during uphill (73 +/- 7%) than during horizontal (67 +/- 8%) running. The percentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphill running. During horizontal running, the muscles or groups most activated were the adductors (90 +/- 5%), semitendinosus (86 +/- 13%), gracilis (76 +/- 20%), biceps femoris (76 +/- 12%), and semimembranosus (75 +/- 12%). During uphill running, the muscles most activated were the adductors (83 +/- 8%), biceps femoris (79 +/- 7%), gluteal group (79 +/- 11%), gastrocnemius (76 +/- 15%), and vastus group (75 +/- 13%). Compared with horizontal running, uphill running required considerably greater activation of the vastus group (23%) and soleus (14%) and less activation of the rectus femoris (29%), gracilis (18%), and semitendinosus (17%). We conclude that during high-intensity horizontal and uphill running to exhaustion, lasting 2-3 min, muscles of the lower extremity are not maximally activated, suggesting there is a limit to the extent to which additional muscle mass recruitment can be utilized to meet the demand for force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.

High muscle blood flows are not attenuated by recruitment of additional muscle mass.

Recent studies have demonstrated that single-leg knee extensor (KE) exercise elicits high mass-specific blood flow (Q) which, if incremented toward maximum, in the presence of additional muscle recruitment would soon outstrip the heart's pumping capacity and blood pressure would fall. Thus incremental KE exercise provides the opportunity to determine the intensity at which, if at all, quadriceps muscle hemodynamics are altered during incremental exercise that involves a substantially greater muscle mass. Leg Q was measured during incremental KE exercise and again with superimposed incremental two-legged knee extensor exercise with incremental arm cranking (A+L) in trained subjects (n = 5). Leg Q and vascular conductance (VC) increased with work rate (WR) to reach high levels [Q = 385.7 +/- 26 and 342.3 +/- 15 ml.min-1.100 g-1 for KE and A+L exercise, respectively; VC at 90% of maximum WR (WRmax) = 79 +/- 5 and 75 +/- 6 ml.min-1. mmHg-1 for KE and A+L exercise, respectively], but the Q/WR and VC/WR relationships in KE and A+L exercise were not different. Maximum O2 consumption (VO2max) and the VO2max/WR relationship of the quadriceps were also unaffected by the additional muscle mass recruited. Despite a significantly greater net femoral venous norepinephrine (NE) outflow at both 90 and 100% of WRmax in A+L exercise (WRmax = 4,216 +/- 1,601 and 901 +/- 99 ng/ml for A+L and KE exercise, respectively; P < 0.05), leg Q continued to rise linearly with WR.(ABSTRACT TRUNCATED AT 250 WORDS)