The influence of chronic training status on the mechanical behavior of the vastus lateralis during repetitive trapezoidal contractions

Objectives:To examine maximal strength and fatigability of the knee extensors, and mechanomyographic amplitude (MMG_RMS)–force relationships of the vastus lateralis (VL) during repetitive muscle actions for 5 aerobically-(AT), 5 resistance-trained-(RT), and 5 sedentary (SED) individuals.Methods:Participants performed maximal voluntary contractions before (MVC_PRE) and after (MVC_POST) attempting 20 isometric trapezoidal muscle actions at 50% MVC_PRE. MMG was recorded from the VL. b terms (slopes) were calculated from the natural log-transformed MMG_RMS-force relationships for each participant (increasing and decreasing segments). MMG_RMS was averaged during steady force.Results:RT had greater MVC_PRE (P<0.001) and MVC_POST (P=0.001–0.004) than AT and SED. Only AT completed 20 muscle actions and exhibited no decrease in MVC_POST (P=0.149). The b terms were greater for RT than AT during the increasing segment of the first contraction (P=0.001) and decreasing segment of the last contraction (P=0.033). The b terms were also greater for RT (P=0.006) during the increasing than decreasing segment for the first contraction. MMG_RMS during steady force was greater during the last contraction when collapsed across training status (P=0.021).Conclusion:Knee extensor MVC and fatigability, and motor unit control strategies for the VL during a series of repetitive contractions were influenced by chronic training status.     

Relationships between skinfold thickness and electromyographic and mechanomyographic amplitude recorded during voluntary and non-voluntary muscle actions

IntroductionThe purpose of this study was to examine possible correlations between skinfold thicknesses and the a terms from the log-transformed electromyographic (EMG_RMS) and mechanomyographic amplitude (MMG_RMS)-force relationships, EMG M-Waves, and MMG gross lateral movements (GLM).MethodsForty healthy subjects performed a 6-s isometric ramp contraction from 5% to 85% of their maximal voluntary contraction with EMG and MMG sensors placed on the vastus lateralis (VL) and rectus femoris (RF). A single electrical stimulus was applied to the femoral nerve to record the EMG M-waves and MMG GLMs. Skinfold thickness was assessed at the site of each electrode. Pearson’s product correlation coefficients were calculated comparing skinfold thicknesses with the a terms from the log-transformed EMG_RMS-and MMG_RMS-force relationships, EMG M-waves, and MMG GLMs.ResultsThere were no significant cor1relations (p > 0.05) between the a terms and skinfold thicknesses for the RF and VL from the EMG_RMS and MMG_RMS-force relationships. However, there were significant correlations (p < 0.05) between skinfold thicknesses and the EMG M-waves and MMG GLMs for the RF (r = −0.521, −0.376) and VL (r = −0.479, −0.484).DiscussionRelationships were only present between skinfold thickness and the amplitudes of the EMG and MMG signals during the non-voluntary muscle actions.     

Electromyographic,but not mechanomyographic amplitude–force relationships,distinguished differences in voluntary activation capabilities between individuals

The purpose of the present study was to examine the influence of activation capabilities on the electromyography (EMG_RMS) and mechanomyography amplitude (MMG_RMS)–force relationships of the vastus lateralis (VL) and rectus femoris (RF). Thirteen men (mean ± SD; age = 22 ± 3 year) performed nine submaximal contractions (10–90% maximal voluntary contraction [MVC]) with the interpolated twitch technique performed during a separate contraction at 90% MVC to calculate percent voluntary activation (%VA). Nine participants with >90% VA were categorized into the high-activated group with the remaining categorized into the moderate-activated group. Slopes (b terms) were calculated from the log-transformed EMG_RMS and MMG_RMS–force relationships. The b terms (collapsed across the VL and RF) for the EMG_RMS–force relationships were greater for the high- (1.29 ± 0.31) than the moderate-activated (1.10 ± 0.20) group. In contrast, there were no differences in the b terms for the MMG_RMS–force relationships between the high- and moderate-activated groups. For the EMG_RMS and MMG_RMS–force relationships, the b terms were greater for the RF (1.38 ± 0.30, 0.81 ± 0.20) than the VL (1.08 ± 0.19, 0.60 ± 0.13) collapsed across groups. The b terms from the EMG_RMS–force relationships, but not the MMG_RMS–force relationships, reflected differences in %VA.     

Mechanomyography is more sensitive than EMG in detecting age-related sarcopenia

The aim of this work was to investigate the effects of age-related sarcopenia on the time and frequency domain properties of lower extremity muscles’ electromyographic and mechanomyographic activities. Healthy elderly (n=10, 64.5±4.5 yr) and young (n=10, 22.6±2.8 yr) were recruited as participants. Participants’ lean thigh volumes (LTV) and 1 RM (one repetition maximum) leg strength of quadriceps and maximum speed knee extension with different load levels (45%, 60% and 75% 1 RM) were recorded. The root mean square (RMS) and the mean frequency (MF) of the surface electromyography (EMG_RMS, EMG_MF) and mechanomyography (MMG_RMS, MMG_MF) signals were collected at vastus lateralis during concentric contraction with different intensity levels. Compared to the young, the elderly had significantly less LTV, absolute and relative maximal force, as well as absolute and relative maximal power (p<.05). EMG_MF of the elderly and the young increased monotonically from 45% to 75% 1 RM testing conditions. While the MMG_RMS of the young increased with testing intensities, the MMG_RMS of the elderly increased only from 45% to 60% but leveled off from 60% to 75% 1 RM testing conditions. The results indicate the declines of muscle mass, force and power production capacity with aging. The observations could be explained by neuromuscular performance and change of MU activation patterns may result from age-related sarcopenia. Aging affected muscle power more than muscle strength, which could be due to fast fiber reduction. This is supported by our observations that the MMG_RMS differences between the young and the elderly across all three intensity level where EMG_RMS was only different at the greatest intensity. We suggest that MMG could be used as an important measurement in studying muscle contraction in age-related sarcopenia.     

The influence of myosin heavy chain isoform content on mechanical behavior of the vastus lateralis in vivo

This study examined correlations between type I percent myosin heavy chain isoform content (%MHC) and mechanomyographic amplitude (MMG_RMS) during isometric muscle actions. Fifteen (age = 21.63 ± 2.39) participants performed 40% and 70% maximal voluntary contractions (MVC) of the leg extensors that included increasing, steady force, and decreasing segments. Muscle biopsies were collected and MMG was recorded from the vastus lateralis. Linear regressions were fit to the natural-log transformed MMG_RMS–force relationships (increasing and decreasing segments) and MMG_RMS was selected at the targeted force level during the steady force segment. Correlations were calculated among type I%MHC and the b (slopes) terms from the MMG_RMS–force relationships and MMG_RMS at the targeted force. For the 40% MVC, correlations were significant (P < 0.02) between type I%MHC and the b terms from the increasing (r = −0.804) and decreasing (r = −0.568) segments, and MMG_RMS from the steady force segment (r = −0.606). Type I%MHC was only correlated with MMG_RMS during the steady force segment (P = 0.044, r = −0.525) during the 70% MVC. Higher type I%MHC reduced acceleration in MMG_RMS (b terms) during the 40% MVC and the amplitude during the steady force segments. The surface MMG signal recorded during a moderate intensity contraction provided insight on the contractile properties of the VL in vivo.     

Differences in the log-transformed electromyographic–force relationships of the plantar flexors between high- and moderate-activated subjects

The present study examined the log-transformed electromyographic amplitude (EMG) versus force relationships for the medial gastrocnemius (MG) and soleus (SOL) in high- and moderate-activated subjects. Twenty-five (age = 21 ± 2 year; mass = 62 ± 12 kg) participants performed six submaximal contractions (30–90% maximal voluntary contraction [MVC]) with the interpolated twitch technique (ITT) performed at 90% MVC to calculate percent voluntary activation (% VA). Sixteen participants with > 90% VA at 90% MVC were categorized high-activated group; the remaining nine were the moderate-activated group. Linear regression models were fit to the log-transformed EMG–force relationships. The slope (b value) and the antilog of the Y-intercept (a value) were calculated. The b values from the MG EMG–force relationships were higher (P < 0.05) for the high-activated group (1.27 ± 0.13) than the moderate-activated group (0.88 ± 0.06). The a values and p–p M-wave amplitude values (collapsed across twitches [superimposed and potentiated]) were larger (P < 0.05) for the MG (1.17 ± 0.40 and 8.98 ± 0.46 mV) than the SOL (0.24 ± 0.07 and 4.48 ± 0.20 mV) when collapsed across groups. The b value from the log-transformed EMG–force relationships is an attractive model to determine if a subject has the ability to achieve high activation of their MG without muscle or nerve stimulation.     

History dependence of the electromyogram: Implications for isometric steady-state EMG parameters following a lengthening or shortening contraction

Residual force enhancement (RFE) and force depression (FD) refer to an increased or decreased force following an active lengthening or shortening contraction, respectively, relative to the isometric force produced at the same activation level and muscle length. Our intent was to determine if EMG characteristics differed in the RFE or FD states compared with a purely isometric reference contraction for maximal and submaximal voluntary activation of the adductor pollicis muscle. Quantifying these alterations to EMG in history-dependent states allows for more accurate modeling approaches for movement control in the future. For maximal voluntary contractions (MVC), RFE was 6–15% (P < 0.001) and FD was 12–19% (P < 0.001). The median frequency of the EMG was not different between RFE, FD and isometric reference contractions for the 100% and 40% MVC intensities (P > 0.05). However, root mean square EMG (EMG_RMS) amplitude for the submaximal contractions was higher in the FD and lower in the RFE state, respectively (P < 0.05). For maximal contractions, EMG_RMS was lower for the FD state but was the same for the RFE state compared to the isometric reference contractions (P > 0.05). Neuromuscular efficiency (NME; force/EMG) was lower in the force depressed state and higher in the force enhanced state (P < 0.05) compared to the isometric reference contractions. EMG spectral properties were not altered between the force-enhanced and depressed states relative to the isometric reference contractions, while EMG amplitude measures were.     

Early vs. late rate of torque development: Relation with maximal strength and influencing factors

We re-examined the relationship between rate of torque development (RTD) and maximal voluntary contractions (MVC) torque, and investigated some possible neuromuscular determinants of early (≤100 ms) and late (≥200 ms) RTD. Seventeen healthy men performed maximal explosive isometric knee extensions at five joint angles, from which MVC torque, RTD at different time intervals (50–250 ms), and early quadriceps EMG activity (EMG₅₀) were evaluated. Quadriceps muscle thickness (MT) was quantified by longitudinal ultrasonography. The relationship between MVC torque, EMG₅₀ and MT against RTD was assessed with Pearson’s and repeated measures correlation coefficients. Moderate-to-strong correlation coefficients were observed between MVC torque and RTD (r = 0.50–0.88, p < 0.001), with stronger relationships for late RTD than for early RTD. Weak-to-strong correlation coefficients were observed amongst RTD and EMG₅₀ (r = 0.37–0.83, p < 0.001), with stronger relationships for early RTD than for late RTD. Only late RTD was significantly correlated with MT, though only moderately (r = 0.50–0.52, p < 0.05). These findings suggest that early and late knee extension RTD are potentially governed by different neuromuscular factors. Neuromuscular activation seems to have a greater influence on early RTD than on late RTD, and vice versa for muscle mass.     

EMG amplitude and frequency parameters of muscular activity: Effect of resistance training based on electromyographic fatigue threshold

The present study aimed to evaluate the effect of a resistance training program based on the electromyographic fatigue threshold (EMG_FT, defined as the highest exercise intensity performed without EMG alterations), on the EMG amplitude (root mean square, RMS) and frequency (median frequency, MF) values for biceps brachii (BB), brachioradialis (BR), triceps brachii (TB) and multifidus (MT). Twenty healthy male subjects, (training group [TG], n = 10; control group [CG], n = 10), firstly performed isometric contractions, and after this, dynamic biceps curl at four different loads to determine the EMG_FT. The TG training program used the BB EMG_FT value (8 weeks, 2 sessions/week, 3 exhaustive bouts/session, 2 min rest between bouts). No significant differences were found for the isometric force after the training. The linear regression slopes of the RMS with time during the biceps curl presented significant decrease after training for the BB, BR and TB muscles. For the MT muscle, the slope and MF intercept values changed with training. The training program based on the EMG_FT influenced EMG the amplitude more than EMG frequency, possibly related to the recruitment patterns of the muscles, although the trunk extensor muscles presented changes in the frequency parameter, showing adaptation to the training program.     

Extinction coefficients of chlorophyll a and B in n,n-dimethylformamide and 80% acetone

We found inconsistencies in the commonly used data for chlorophyll analysis in 80% acetone. Recently developed extinction coefficients for chlorophyll b in N,N-dimethylformamide (DMF) based on values from 80% acetone are low as a result of these inconsistencies. We determined extinction coefficients of chlorophyll a (Chl a) and chlorophyll b (Chl b) in DMF for wavelengths of 618 to 665 nanometers. The simultaneous equations necessary for quantifying Chl a, Chl b, or total Chl in DMF in the absence of other chlorophyllous pigments are: Chl a = 12.70A_664.5 - 2.79A₆₄₇; Chl b = 20.70 A₆₄₇ - 4.62A_664.5; total Chl = 17.90A₆₄₇ + 8.08A_664.5, where A = absorbance in 1.00 centimeter cuvettes and Chl = milligrams per liter.

N,N-Dimethylformamide is a very convenient solvent for Chl extraction since it is effective on intact plant parts and Chl is quite stable in DMF. There was no difference in the amount of Chl extracted when plant tissue was stored for 1 or 3 days at three temperatures, with or without solvent added.

     

Conformations and interactions of pectins: I. X-ray diffraction analyses of sodium pectate in neutral and acidified forms

X-ray diffraction patterns of uniaxially oriented, polycrystalline fibers of neutral sodium pectate can be indexed on the basis of an orthogonal unit cell with dimensions a = 0.84 nm, b = 1.43 nm, c (fiber axis) = 1.34 nm, which contains trisaccharide fragments of two polygalacturonic chains of opposite sense. The polysaccharide chains have 3₁ screw symmetry but are arranged in a lattice that has space group symmetry P2₁ (unique axis b). There are three sodium ions in each crystal asymmetric unit. They are all octahedrally co-ordinated to oxygen atoms of the galacturonan chains or of water molecules. Every oxygen atom is involved also in at least one hydrogen bond. Sodium pectate can be partially converted to pectic acid whose polysaccharide chains preserve the 3₁ pectate conformation, are packed in an orthogonal unit cell also with P2₁ symmetry but with quite different dimensions a = 0.99 nm, b (unique 2₁ axis) = 1.23 nm, c (fiber axis) = 1.33 nm. In this lattice, the polygalacturonic acid chains form corrugated sheets in which alternate molecules have opposite sense and are extensively hydrogen-bonded through their carboxyl groups.     

Rational design,synthesis, anti-HIV-1 RT and antimicrobial activity of novel 3-(6-methoxy-3,4-dihydroquinolin-1(2H)-yl)-1-(piperazin-1-yl)propan-1-one derivatives

In the present study, fifteen novel 3-(6-methoxy-3,4-dihydroquinolin-1(2H)-yl)-1-(piperazin-1-yl)propan-1-one (6a-o) derivatives were designed as inhibitor of HIV-1 RT using ligand based drug design approach and in-silico evaluated for drug-likeness properties. Designed compounds were synthesized, characterized and in-vitro evaluated for RT inhibitory activity against wild HIV-1 RT strain. Among the tested compounds, four compounds (6a, 6b, 6j and 6o) exhibited significant inhibition of HIV-1 RT (IC₅₀ ⩽ 10 μg/ml). All synthesized compounds were also evaluated for anti-HIV-1 activity as well as cytotoxicity on T lymphocytes, in which compounds 6b and 6l exhibited significant anti-HIV activity (EC₅₀ values 4.72 and 5.45 μg/ml respectively) with good safety index.Four compounds (6a, 6b, 6j and 6o) found significantly active against HIV-1 RT in the in-vitro assay were in-silico evaluated against two mutant RT strains as well as one wild strain. Further, titled compounds were evaluated for in-vitro antibacterial (Escherichia coli, Pseudomonas putida, Staphylococcus aureus and Bacillus cereus) and antifungal (Candida albicans and Aspergillus niger) activities.     

Kinetic analysis of biphasic protein modification reactions cooperative effects

A mathematical treatment of protein modification reactions is presented, and it is shown thai in these cases protein modification is described by a summation of exponential functions of reaction time, the number of exponentials being equal to the number of modified protein species. It is shown that in cases of protein modification cooperativity, there is a strict dependence of the coefficients of the multiexponential modification equation on the constants of the same equation. The conditions necessary for a reduction of a multiexponential protein modification equation to one of a summation of two exponentials only are examined. The possible formulae for the coefficients of a two-exponential-summation equation, used to describe the modification of protein models with two, three or four modifiable residues (as well as some aspects of models with five and six modifiable residues) per protein molecule are derived. It is seen that the number of such coefficients is severely limited. The most frequently obtained formula for the lower stoichiomelric coefficient of a 'wo-exponential-summation equation is Ak_a/(k_a-k_b). where k_b and k_b are the constants of the two exponentials of the equation, and A is a constant. The value most frequently arrived at for A is (n?1)/n, where n is the number of modifiable residues per protein molecule, while values such as 1/n, or a/n (where a is an integer, and also where a < n) are also possible. In most of the cooperative protein modification models worked out, k_a is identical with k_n, viz., k_a is identical with the rate constant for the first stoichiometric protein modification.     

Cube law, condition factor and weight–length relationships: history, meta-analysis and recommendations

This study presents a historical review, a meta‐analysis, and recommendations for users about weight–length relationships, condition factors and relative weight equations. The historical review traces the developments of the respective concepts. The meta‐analysis explores 3929 weight–length relationships of the type W = aL^b for 1773 species of fishes. It shows that 82% of the variance in a plot of log a over b can be explained by allometric versus isometric growth patterns and by different body shapes of the respective species. Across species median b = 3.03 is significantly larger than 3.0, thus indicating a tendency towards slightly positive‐allometric growth (increase in relative body thickness or plumpness) in most fishes. The expected range of 2.5 < b < 3.5 is confirmed. Mean estimates of b outside this range are often based on only one or two weight–length relationships per species. However, true cases of strong allometric growth do exist and three examples are given. Within species, a plot of log a vs b can be used to detect outliers in weight–length relationships. An equation to calculate mean condition factors from weight–length relationships is given as K_mean = 100aL^b?3. Relative weight W_rm = 100W/(a_mL^bm) can be used for comparing the condition of individuals across populations, where a_m is the geometric mean of a and b_m is the mean of b across all available weight–length relationships for a given species. Twelve recommendations for proper use and presentation of weight–length relationships, condition factors and relative weight are given.     

New cholesterol esterase inhibitors based on rhodanine and thiazolidinedione scaffolds

We present a new class of inhibitors of pancreatic cholesterol esterase (CEase) based on ‘priviledged’ 5-benzylidenerhodanine and 5-benzylidene-2,4-thiazolidinedione structural scaffolds. The lead structures (5-benzylidenerhodanine 4a and 5-benzylidene-2,4-thiazolidinedione 4b) were identified in an in-house screening and these inhibited CEase with some selectivity over another serine hydrolase, acetylcholinesterase (AChE) (4a, CEase IC₅₀ = 1.76 μM vs AChE IC₅₀ = 5.14 μM and 4b, CEase IC₅₀ = 5.89 μM vs AChE IC₅₀ >100 μM). A small library of analogs (5a–10a) containing a core amino acid in place of the glycerol group of the lead structures, was prepared to explore other potential binding interaction with CEase. These analogs inhibited CEase with IC₅₀ values ranging from 1.44 to 85 μM, with the majority exhibiting some selectivity for CEase versus AChE. The most potent compound of the library (10a) had 17-fold selectivity over AChE. We also report molecular docking (with CEase) and detailed kinetic analysis on the amino acid analogs to further understand the associated structure–activity relationships.     

Design,synthesis and evaluation of 2-(indolylmethylidene)-2,3-dihydro-1-benzofuran-3-one and 2-(indolyl)-4H-chromen-4-one derivatives as novel monoamine oxidases inhibitors

A series of 2-(indolylmethylidene)-2,3-dihydro-1-benzofuran-3-ones (aurone-indole hybrids) and 2-(indolyl)-4H-chromen-4-ones (flavone-indole hybrids) were designed, synthesized, and their monoamine oxidase (MAO) A and B inhibitory activities were evaluated. Compounds 5b and 11b showed potent inhibitory activities against MAO-A, comparable to that of pargyline used as a positive control, and most of the compounds, except for 2a and 10b, showed potent inhibitory activities against MAO-B. Compound 9a was the most potent and highly selective inhibitor of MAO-B (IC₅₀ value for MAO-B: 0.0026 μM, and MAO-A: >100 μM). Comparison of the inhibitory activities of 1a vs. 9a vs. 13a and 1b vs. 7b vs. 11b suggested that methoxy substitution at R¹ on the A-rings of flavonoids increases MAO-A inhibition whereas methoxy substitution at R² increased MAO-B inhibition. Comparison of 4a vs. 10a, 6a vs. 11a, 3b vs. 8b and 4b vs. 9b showed incremental increases in MAO-B inhibitory activity by R² substitution on the A ring. Comparison of the MAO-B inhibitory effects of the flavone-indole hybrids and aurone-indole hybrids showed that most of the aurone-indole hybrids were stronger inhibitors than the corresponding flavone-indole hybrids. Molecular docking analysis of compounds 1a and 9a with MAO-B further supported the above structural effects of these compounds on MAO-B inhibitory activity.This is the first report identifying aurone-indole hybrids as potent MAO-B inhibitors. The results reported here suggest that 2-(1H-indol-1-ylmethylene)-6-methoxy-3(2H)-benzofuranone (9a) might be a useful lead for the design and development of novel MAO-B inhibitors     

The effectiveness of stretch–shortening cycling in upper-limb extensor muscles during elite cross-country skiing with the double-poling technique

This investigation was designed to evaluate the effectiveness of stretch–shortening cycling (SSC_EFF) in upper-limb extensor muscles while cross-country skiing using the double-poling technique (DP). To this end, SSC_EFF was analyzed in relation to DP velocity and performance. Eleven elite cross-country skiers performed an incremental test to determine maximal DP velocity (V_max). Thereafter, cycle characteristics, elbow joint kinematics and poling forces were monitored on a treadmill while skiing at two sub-maximal and racing velocity (85% of V_max). The average EMG activities of the triceps brachii and latissimus dorsi muscles were determined during the flexion and extension sub-phases of the poling cycle (EMG_FLEX, EMG_EXT), as well as prior to pole plant (EMG_PRE). SSC_EFF was defined as the ratio of aEMG_FLEX to aEMG_EXT. EMG_PRE and EMG_FLEX increased with velocity for both muscles (P < 0.01), as did SSC_EFF (from 0.9 ± 0.3 to 1.3 ± 0.5 for the triceps brachii and from 0.9 ± 0.4 to 1.5 ± 0.5 for the latissimus dorsi) and poling force (from 253 ± 33 to 290 ± 36 N; P < 0.05). Furthermore, SSC_EFF was positively correlated to V_max, to EMG_PRE and EMG_FLEX (P < 0.05). The neuromuscular adaptations made at higher velocities, when more poling force must be applied to the ground, exert a major influence on the DP performance of elite cross-country skiers.