Biceps brachii myoelectric and oxygenation changes during static and sinusoidal isometric exercises

Surface myoelectric signal changes occurring during sustained isometric contractions have been extensively studied with quantitative surface electromyography (sEMG) and are described by means of some sEMG global variables in time and frequency domain (such as the median power spectral frequency). Recently, the possibility of studying local muscle O₂ saturation during exercise using non-invasive methods has been enhanced thanks to the use of near-infrared spectroscopy (NIRS). The purpose of this work was to combine NIRS and sEMG techniques to analyze the relationship between modifications of sEMG parameters and the underlying metabolic status of the exercising biceps brachii muscle. This relationship was tested under different isometric contraction modalities, namely static (ST) at 20, 40, 60 and 80%MVC and sinusoidal (SIN) at 40 ± 20 and 60 ± 20%MVC. Results clearly indicated the presence of an initial fast phase of muscle O₂ desaturation followed by a slow phase, regardless of the contraction modality. Moreover, the initial rate of muscle O₂ desaturation was related to the level of force output (R = 0.92), but it was independent on the contraction modality (p < 0.05). Similarly, changes in sEMG parameters were related to force level (Conduction Velocity-CV vs. Force: R = 0.87; sEMG Median Frequency-MDF vs. Force: R = 0.86). The high correlation found between CV-MDF and Tissue Oxygenation Index (TOI) slope (R = 0.73 and 0.72, respectively) suggests a strong relationship between NIRS and sEMG data. This study indicates that muscle O₂ demand during isometric contractions from low to high force levels is influenced by the type of active motor units and not from the type of isometric exercise modality.     

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.     

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.     

Closed chain assessment of quadriceps activation using the superimposed burst technique

The superimposed burst technique is used to estimate quadriceps central activation ratio during a maximal voluntary isometric contraction, which is calculated from force data during an open-chain knee extension task. Assessing quadriceps activation in a closed-chain position would more closely simulate the action of the quadriceps during activity. Our aim was to determine the test–retest reliability of the quadriceps central activation ratio in the closed chain.MethodsTwenty-two healthy, active volunteers (13M/12F; age = 23.8 ± 3; height = 72.7 ± 14.5 cm; mass = 175.3 ± 9.6 kg) were recruited to participate. Knee extension MVIC torque and the peak torque during a superimposed electrical stimulus delivered to the quadriceps during an MVIC were measured to estimate quadriceps CAR. Interclass correlation coefficients were used to assess test–retest reliability between sessions, and Bland–Altman plots to graphically assess agreement between sessions.ResultsTest–retest reliability was fair for CAR (ICC_2,k = 0.68; P = 0.005), with a mean difference of −2.8 ± 10.3%, and limits of agreement ranging −23.1–18.1%.ConclusionsCAR calculated using the superimposed burst technique is moderately reliable in a closed-chain position using technique-based instruction. Although acceptable reliability was demonstrated, wide limits of agreement suggest high variability between sessions.     

The reliability of surface electromyography to assess quadriceps fatigue during multi joint tasks in healthy and painful knees

This study’s aim was to determine the between days reliability of surface EMG recordings from the superficial quadriceps during a multi joint sub-maximal fatiguing protocol. Three subject groups (healthy n = 29; patellofemoral pain syndrome n = 74; knee osteoarthritis n = 55) performed the task at 60 maximum voluntary isometric contraction on three separate days. Spectral and amplitude EMG parameters were recorded from vastus medialis oblique, vastus lateralis and rectus femoris and were analysed for between days reliability using intraclass correlation coefficient (ICC_(2,1)), the standard errors of measure and smallest detectable differences. For frequency results, initial and final frequency values had ‘good’ or ‘excellent’ reliability in all groups for all muscles. ICCs for median frequency slopes for vastus medialis oblique, vastus lateralis, and rectus femoris respectively, in the osteoarthritis group were 0.04, 0.55, and 0.72; in the patellofemoral pain group were 0.41, 0.17, and 0.33; in the healthy group were 0.68, 0.64, and 0.31. The standard errors of measurement and smallest detectable differences for all groups and for all muscles were unacceptably high. For amplitude results, ICC root mean squared initial and final values were ‘good’ to ‘excellent’ for all groups and all muscles, albeit with high measurement error. The ICCs for root mean squared slopes in all tests were ‘poor’ with extremely high measurement error. The poor between days reliability and high measurement error suggests that surface EMG should not be adopted to assess fatigue during multi joint sub-maximal isometric quadriceps testing.     

Diminished sub-maximal quadriceps force control in anterior cruciate ligament reconstructed patients is related to quadriceps and hamstring muscle dyskinesia

The aim of this study was to determine the effects of anterior cruciate ligament reconstruction (ACLR) on sub-maximal quadriceps force control with respect to quadriceps and hamstring muscle activity. Thirty ACLR individuals together with 30 healthy individuals participated. With real-time visual feedback of muscle force output and electromyographic electrodes attached to the quadriceps and hamstring muscles, subjects performed an isometric knee extension task where they increased and decreased their muscle force output at 0.128 Hz within a range of 5–30% maximum voluntary capacity. The ACLR group completed the task with more error and increased medial hamstring and vastus medialis activation (p < 0.05). Moderate negative correlations (p < 0.05) were observed between quadriceps force control and medial (Spearman’s rho = −0.448, p = 0.022) and lateral (Spearman’s rho = −0.401, p = 0.034) hamstring activation in the ACLR group. Diminished quadriceps sub-maximal force control in ACLR subjects was reflective of medial quadriceps and hamstring dyskinesia (i.e., altered muscle activity patterns and coordination deficits). Within the ACLR group however, augmented hamstring co-activation was associated with better quadriceps force control. Future studies should explore the convergent validity of quadriceps force control in ACLR patients.     

Measuring voluntary quadriceps activation: Effect of visual feedback and stimulus delivery

Introduction: Quadriceps voluntary activation, assessed via the superimposed burst technique, has been extensively studied in a variety of populations as a measure of quadriceps function. However, a variety of stimulus delivery techniques have been employed, which may influence the level of voluntary activation as calculated via the central activation ratio (CAR). The purpose was to determine the effect of visual feedback, stimulus delivery, and perceived discomfort on maximal voluntary isometric contraction (MVIC) peak torque and the CAR. Methods: Quadriceps CAR was assessed in 14 individuals on two days using three stimulus delivery methods; (1) manual without visual feedback, (2) manual with visual feedback, and (3) automated with visual feedback. Results: MVIC peak torque and the CAR were not different between the automated with visual feedback (MVIC = 3.25, SE = 0.14 N m/kg; CAR = 88.63, SE = 1.75%) and manual with visual feedback (MVIC = 3.26, SE = 0.13 N m/kg, P = 0.859; CAR = 89.06, SE = 1.70%, P = 0.39) stimulus delivery methods. MVIC (2.99, SE = 0.12 N m/kg) and CAR (85.32, SE = 2.10%) were significantly lower using manual without visual feedback compared to manual with visual feedback and automated with visual feedback (CAR P < 0.001; MVIC P < 0.001). Perceived discomfort was lower in the second session (P < 0.05). Conclusion: Utilizing visual feedback ensures participant MVIC, and may provide a more accurate assessment of quadriceps voluntary activation.     

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.     

Knee flexor strength and bicep femoris electromyographical activity is lower in previously strained hamstrings

The aim of this study was to determine if athletes with a history of hamstring strain injury display lower levels of surface EMG (sEMG) activity and median power frequency in the previously injured hamstring muscle during maximal voluntary contractions. Recreational athletes were recruited, 13 with a history of unilateral hamstring strain injury and 15 without prior injury. All athletes undertook isokinetic dynamometry testing of the knee flexors and sEMG assessment of the biceps femoris long head (BF) and medial hamstrings (MHs) during concentric and eccentric contractions at ±180 and ±60° s^?1. The knee flexors on the previously injured limb were weaker at all contraction speeds compared to the uninjured limb (+180° s^?1 p = 0.0036; +60° s^?1 p = 0.0013; ?60° s^?1 p = 0.0007; ?180° s^?1 p = 0.0007) whilst sEMG activity was only lower in the BF during eccentric contractions (?60° s^?1 p = 0.0025; ?180° s^?1 p = 0.0003). There were no between limb differences in MH sEMG activity or median power frequency from either BF or MH in the injured group. The uninjured group showed no between limb differences in any of the tested variables. Secondary analysis comparing the between limb difference in the injured and the uninjured groups, confirmed that previously injured hamstrings were mostly weaker (+180° s^?1 p = 0.2208; +60° s^?1 p = 0.0379; ?60° ^?1 p = 0.0312; ?180° s^?1 p = 0.0110) and that deficits in sEMG were confined to the BF during eccentric contractions (?60° s^?1 p = 0.0542; ?180° s^?1 p = 0.0473). Previously injured hamstrings were weaker and BF sEMG activity was lower than the contralateral uninjured hamstring. This has implications for hamstring strain injury prevention and rehabilitation which should consider altered neural function following hamstring strain injury.     

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.     

Effects of hand and knee positions on muscular activity during trunk extension exercise with the Roman chair

This experimental study was performed to investigate the effects of hand and knee positions on muscular activity during back extension exercises with the Roman chair. Eighteen asymptomatic male amateur athletes performed four prone back extension exercises with two hand positions (crossed-arms and behind-the-head), and two knee positions (extended knee and 90° flexed knee). Surface electromyography (sEMG) was performed to collect data from the lower trapezius (LT), latissimus dorsi (LD), erector spinae in the T12 paraspinal region (ES-T12), erector spinae at the L3 level (ES-L3), gluteus maximus (GM), and biceps femoris (BF). Two-way repeated analysis of variance with two within-subject factors (two hand positions and two knee positions) was used to determine the significance of differences between the exercise conditions, and which hand and knee positions resulted in greater activation with exercise variation. The root mean square sEMG values were normalized using the maximum voluntary isometric contraction (MVIC) and represented as the % of the maximum EMG (%mEMG). There was no significant interaction between knee and hand positions in the %mEMG data. The results showed that the hand position affected the normalized activation of LT; the behind-the-head position resulted in significantly greater muscle activation than the crossed-arms hand position (P < 0.05). The activations of the LD, ES-T10, ES-L4, and GM were greater in the 90° flexed-knee position compared to the extended-knee position (P < 0.05). Although back extension exercise using the Roman chair has been shown to effectively activate the extensor musculature, our results indicated that changing the knee and hand positions could activate specific muscles differently. To achieve greater activation of trunk extensor muscle during extension exercise with the Roman chair, the flexed-knee position is a useful means of increasing resistance.     

A new parameter for quantifying the variability of surface electromyographic signals during gait: The occurrence frequency

Natural variability of myoelectric activity during walking was recently analyzed considering hundreds of strides. This allowed assessing a parameter seldom considered in classic surface EMG (sEMG) studies: the occurrence frequency, defined as the frequency each muscle activation occurs with, quantified by the number of strides when a muscle is recruited with that specific activation modality. Aim of present study was to propose the occurrence frequency as a new parameter for assessing sEMG-signal variability during walking. Aim was addressed by processing sEMG signals acquired from Gastrocnemius Lateralis, Tibialis Anterior, Rectus Femoris and Biceps femoris in 40 healthy subjects in order to: (1) show that occurrence frequency is not correlated with ON/OFF instants (R_mean = 0.11 ± 0.07; P > 0.05) and total time of activation (R_mean = 0.15 ± 0.08; P > 0.05); (2) confirm the above results by two handy examples of application (analysis of gender and age) which highlighted that significant (P < 0.05) gender-related and age-related differences within population were detected in occurrence frequency, but not in temporal sEMG parameters. In conclusion, present study demonstrated that occurrence frequency is able to provide further information, besides those supplied by classical temporal sEMG parameters and thus it is suitable to complement them in the evaluation of variability of myoelectric activity during walking.     

The effect of perspiration on the sEMG amplitude and power spectrum

Sweat accumulation underneath surface EMG (sEMG) electrodes is a common problem in workplace studies which compromises electrode adherence to the skin as well as signal fidelity. In this study, the effect of sweat accumulation on signal amplitude and mean frequency (MF) was examined to determine if the sEMG signal becomes altered through the sweat layer and whether this effect can be avoided by interrupting the pool of sweat using a thin strip of medical adhesive between the electrode snaps. Nine males performed a maximum, isometric contraction of their right quadriceps as sEMG was collected. Skin conditions under the electrode were dry and wet in incremental layers of 0.02 mm of artificial sweat. The results demonstrated that sweat accumulation under sEMG electrodes dampens the amplitude of the EMG signal in a predictable way (r = .88 and .97 for double and single snap electrodes, respectively) with almost 2% and 3% deterioration for every 0.02 mm of sweat depending on the type of electrode used. The medical adhesive proved to be highly effective at preventing amplitude deterioration indicating that signal shunting can be prevented. MF was not influenced by sweat accumulation even under the extreme wet condition.     

Jogging gait kinetics following fatiguing lumbar paraspinal exercise

A relationship exists between lumbar paraspinal muscle fatigue and quadriceps muscle activation. The objective of this study was to determine whether hip and knee joint moments during jogging changed following paraspinal fatiguing exercise. Fifty total subjects (25 with self-reported history of low back pain) performed fatiguing, isometric lumbar extension exercise until a shift in EMG median frequency corresponding to a mild level of muscle fatigue was observed. We compared 3-dimensional external joint moments of the hip and knee during jogging before and after lumbar paraspinal fatigue using a 10-camera motion analysis system. Reduced external knee flexion, knee adduction, knee internal rotation and hip external rotation moments and increased external knee extension moments resulted from repetitive lumbar paraspinal fatiguing exercise. Persons with a self-reported history of LBP had larger knee flexion moments than controls during jogging. Neuromuscular changes in the lower extremity occur while resisting knee and hip joint moments following isolated lumbar paraspinal exercise. Persons with a history of LBP seem to rely more heavily on quadriceps activity while jogging.     

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.     

Nutrient concentrations in tidal creeks as indicators of the water quality role of mangrove wetlands in Southwest Florida

Coastal mangroves have the potential to improve the water quality of urban and rural runoff before it is discharged into adjacent coastal bays and oceans; but they also can be impaired by excessive pollutants from upstream. Nutrients (phosphorus and nitrogen), salinity, and other water quality parameters were measured in five mangrove tidal creeks in different hydrogeomorphic and urbanization settings during high and low tides over a calendar year of wet (June and August 2015) and dry (February and April 2016) seasons in the Greater Naples Bay area in Southwest Florida, USA. Nutrient concentrations (ave. ± std error) in the tidal creeks were 0.055 ± 0.008 mg-P/L for total phosphorus (TP) and 0.610 ± 0.020 mg-N/L for total nitrogen (TN), with an average N:P ratio of 11.4:1. Average wet season TP (0.075 ± 0.010 mg-P/L) was significantly higher than the dry season TP (0.033 ± 0.003 mg-P/L; p < 0.01, f = 15.17, f_crit = 3.89) and the average wet season TN (0.75 ± 0.03 mg-N/L) was significantly higher than dry season TN (0.52 ± 0.02 mg/L; p < 0.01, f = 64.14, f_crit = 3.89), suggesting that urban stormwater runoff is directly or indirectly affecting the nutrient conditions in these mangroves. Significant differences in nutrient concentrations between low tide and high tide were not found for either TP (p = 0.43, f = .63, f_crit = 3.88) or TN (p = 0.20, f = 1.66, f_crit = 3.89). These differences were confirmed by a PCA and cluster analyses, which found differences to be seasonal. We could not conclude from these results whether these five mangrove wetlands were sources nor sinks of nutrients based simply on the measurement of nutrient concentrations. But we illustrated that nutrient concentrations were indicators of the mangroves’ hydrogeomorphic settings, their tidal fluxes from Naples Bay, and the Bay's upstream watersheds, and less by direct urban runoff.     

Neuromuscular activation of vastus intermedius muscle during fatiguing exercise

The purpose of this study was to investigate neuromuscular activation of the vastus intermedius (VI) muscle during fatiguing contraction. Seven healthy men performed sustained isometric knee extension exercise at 50% of maximal voluntary contraction until exhaustion. During the fatiguing task, surface electromyograms (EMGs) were recorded from four muscle components of the quadriceps femoris muscle group: VI; vastus lateralis (VL); vastus medialis (VM); and rectus femoris (RF) muscles. For the VI muscle, our recently developed technique was used. Root mean square (RMS) and median frequency (MF) of the surface EMG signal were calculated and these variables were then normalized by the value at the beginning of the task. Normalized RMS of the VI muscle resembled those of the other three muscles at all given times. At 95% of exhaustion time, normalized MF of the VI muscle was significantly higher than that of the VL muscle (p < 0.05). These results suggested that neuromuscular activation is not consistent between the VI and VL muscles at the exhaustion for isometric submaximal contraction and this could reflect the dissimilar intramuscular metabolism between these muscles.     

The acute effects of local muscle vibration frequency on peak torque,rate of torque development,and EMG activity

PurposeVibratory stimuli enhance muscle activity and may be used for rehabilitation and performance enhancement. Efficacy of vibration varies with the frequency of stimulation, but the optimal frequency is unclear. The purpose of this study was to examine the effects of 30 Hz and 60 Hz local muscle vibration (LMV) on quadriceps function.MethodsTwenty healthy volunteers (age = 20.4 ± 1.4 years, mass = 68.1 ± 11.0 kg, height = 170.1 ± 8.8 cm, males = 9) participated. Isometric knee extensor peak torque (PT), rate of torque development (RTD), and electromyography (EMG) of the quadriceps were assessed followed by one of the three LMV treatments (30 Hz, 60 Hz, control) applied under voluntary contraction, and again immediately, 5, 15, and 30 min post-treatment in three counterbalanced sessions. Dependent variables were analyzed using condition by time repeated-measures ANOVA.ResultsThe condition × time interaction was significant for EMG amplitude (p = 0.001), but not for PT (p = 0.324) or RTD (p = 0.425). The increase in EMG amplitude following 30 Hz LMV was significantly greater than 60 Hz LMV and control.ConclusionsThese findings suggest that 30 Hz LMV may elicit an improvement in quadriceps activation and could be used to treat quadriceps dysfunction resulting from knee pathologies.     

Pyrrolidine analogs of GZ-793A: Synthesis and evaluation as inhibitors of the vesicular monoamine transporter-2 (VMAT2)

Central heterocyclic ring size reduction from piperidinyl to pyrrolidinyl in the vesicular monoamine transporter-2 (VMAT2) inhibitor GZ-793A and its analogs resulted in novel N-propane-1,2(R)-diol analogs 11a–i. These compounds were evaluated for their affinity for the dihydrotetrabenazine (DTBZ) binding site on VMAT2 and for their ability to inhibit vesicular dopamine (DA) uptake. The 4-difluoromethoxyphenethyl analog 11f was the most potent inhibitor of [³H]-DTBZ binding (K_i = 560 nM), with 15-fold greater affinity for this site than GZ-793A (K_i = 8.29 μM). Analog 11f also showed similar potency of inhibition of [³H]-DA uptake into vesicles (K_i = 45 nM) compared to that for GZ-793A (K_i = 29 nM). Thus, 11f represents a new water-soluble inhibitor of VMAT function.     

Paracellular absorption in laboratory mice: Molecule size-dependent but low capacity

Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems lower in nonfliers than in fliers, although that conclusion rests largely on a comparison of relatively larger nonflying mammals (> 155 g) and relatively smaller flying birds (< 155 g). We report on paracellular absorption in laboratory mice, the smallest nonflying mammal species studied to date. Using a standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption = f) of inert carbohydrate probes: l-arabinose (M_r = 150.13 Da) and cellobiose (342.3) that are absorbed exclusively by the paracellular route, and 3-O-methyl d-glucose (3OMD-glucose) (M_r = 194) absorbed both paracellularly and transcellularly. f was measured accurately in urine collection trials of 5–10 h duration. Absorption of 3OMD-glucose by mice was essentially complete (f = 0.95 ± 0.07) and much higher than that for l-arabinose (f = 0.21 ± 0.02), indicating that in mice, like other nonflying mammals, > 80% of glucose is absorbed by mediated process(es) rather than the passive, paracellular route. As in all other vertebrates, absorption of cellobiose (f = 0.13 ± 0.02) was even lower than that for l-arabinose, suggesting an equivalent molecular size cut-off for flying and nonflying animals and thus a comparable effective TJ aperture. An important ecological implication is that smaller water-soluble plant secondary metabolites that have been shown to be absorbed by the paracellular path in cell culture, such as phenolics and alkaloids, might be absorbed in substantial amounts by bats and small birds relative to nonflying mammals such as mice.