Comparison of Fourier and wavelet transform procedures for examining the mechanomyographic and electromyographic frequency domain responses during fatiguing isokinetic muscle actions of the biceps brachii.

The primary purpose of the present study was to compare the fast Fourier transform (FFT) with the discrete wavelet transform (DWT) for determining the mechanomyographic (MMG) and electromyographic (EMG) center frequency [mean power frequency (mpf), median frequency (mdf), or wavelet center frequency (cf)] patterns during fatiguing isokinetic muscle actions of the biceps brachii. Seven men (mean+/-SD age=23+/-3 years) volunteered to perform 50 consecutive maximal, concentric isokinetic muscle actions of the dominant forearm flexors at a velocity of 180 degrees s(-1). Non-parametric "run" tests indicated significant (p<0.05) trends in the MMG and EMG signals for the 5th, 25th, and 45th muscle actions for all subjects, thereby confirming non-stationarity of the MMG and EMG signals. There were significant (p<0.05) correlations among the average normalized mpf, mdf, and cf values for contractions 1-50 for both MMG (r=0.671-0.935) and EMG (r=0.956-0.987). Polynomial regression analyses demonstrated quadratic decreases in normalized MMG mpf (R2=0.439), MMG mdf (R2=0.258), MMG cf (R2=0.359), EMG mpf (R2=0.952), EMG mdf (R2=0.914) and EMG cf (R2=0.888) across repetitions. The primary finding of this study was the similarity in the mpf, mdf, and cf patterns for both MMG and EMG, which suggested that, despite the concerns over non-stationarity, Fourier based methods are acceptable for determining the patterns for normalized MMG and EMG center frequency during fatiguing dynamic muscle actions at moderate velocities.     

Removing ECG contamination from EMG recordings: a comparison of ICA-based and other filtering procedures

Trunk muscle electromyography (EMG) is often contaminated by the electrocardiogram (ECG), which hampers data analysis and potentially yields misinterpretations. We propose the use of independent component analysis (ICA) for removing ECG contamination and compared it with other procedures previously developed to decontaminate EMG. To mimic realistic contamination while having uncontaminated reference signals, we employed EMG recordings from peripheral muscles with different activation patterns and superimposed distinct ECG signals that were recorded during rest at conventional locations for trunk muscle EMG. ICA decomposition was performed with and without a separately collected ECG signal as part of the data set and contaminated ICA modes representing ECG were identified automatically. Root mean squared relative errors and correlations between the linear envelopes of uncontaminated and contaminated EMG were calculated to assess filtering effects on EMG amplitude. Changes in spectral content were quantified via mean power frequencies. ICA-based filtering largely preserved the EMG's spectral content. Performance on amplitude measures was especially successful when a separate ECG recording was included. That is, the ICA-based filtering can produce excellent results when EMG and ECG are indeed statistically independent and when mode selection is flexibly adjusted to the data set under study.     

The relationship between narrow and wide bandwidth filter settings during an EMG scanning procedure

This study examined the correlation between EMG values measured with wide (25-1000 Hz) and narrow (100-200 Hz) band-width filters. An EMG diagnostic scan was conducted on 32 chronic pain patients admitted to an inpatient treatment unit. EMG readings were taken from a total of 44 sites (11 sites X 2 sides X 2 postures). Each EMG measure was passed in parallel through a narrow and wide band-pass filter and the stable readings were recorded. Correlated t tests and Pearson correlations were used to compare the data from the narrow and wide filter settings. The measures from the wide filter were significantly higher than the measures from the narrow filter. In addition, 61% of the correlations were greater than .90. The majority of the correlations below the median (.93) occurred in the neck region and the abdomen. The implications of the findings are discussed.     

The effect of sampling frequency on EMG measures of occupational mechanical exposure.

The purpose of the present study was to determine how much it is possible to downsample EMG without loosing the accuracy of some EMG measures of occupational mechanical exposure frequently used in the literature. The EMG signals of four muscles (two trapezius, right deltoid and right extensor digitorum) were collected (sampling frequency: 1024 Hz) from 20 subjects while performing a 20 min computer work task. The EMG RMS amplitude was computed from 0.125 s successive time-windows for the original (1024 Hz) and four additional digitally resampled (at 512, 256, 128 and 64 Hz) EMG signals. Three of the most frequently used data reduction methods (1. gaps analysis, 2. amplitude probability distribution function and 3. exposure variation analysis) were used to summarise the 20 min EMG activation profiles. The results from the exposure variation analysis were summarized into three variables using a new method detailed here. In general, the ANOVA for repeated measures demonstrated that a decrease of the sampling frequency significantly changed the EMG measures (relative to the 1024 Hz sampling condition) most of the time at 64 and 128 Hz, occasionally at 256 Hz, but practically never at 512 Hz. An analysis of the maximal errors (relative to the 1024 Hz condition) across all subjects supported these findings. Consequently, it was concluded that 512 Hz is quite conservative and should practically never lead to invalid EMG parameters estimations. Conversely, 256 Hz represents the lowest limit tolerable for some EMG parameters (gaps analysis, amplitude probability distribution function) while it is unacceptable for others (modified exposure variation analysis).     

Power output,mechanomyographic, and electromyographic responses to maximal,concentric, isokinetic muscle actions in men and women

The purpose of this study was to examine the responses of peak torque (PT), mean power output (MP), mechanomyographic (MMG) and electromyographic (EMG) amplitudes, and mean power frequencies (MPFs) of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) in men and women during dynamic muscle actions. Twelve women (mean +/- SD age = 22 +/- 3 years) and 11 men (22 +/- 3 years) performed maximal, concentric, isokinetic leg extensions at velocities of 60, 120, 180, 240, and 300 degrees x s(-1) on a Cybex 6000 dynamometer. Piezoelectric MMG-recording sensors and bipolar surface EMG electrodes were placed over the VL, RF, and VM muscles. No sex-related differences were found among the velocity-related patterns for PT, MP, MMG amplitude, MMG MPF, or EMG MPF. There were, however, sex-related differences in the patterns of EMG amplitude across velocity. The results indicated similar velocity-related patterns of increase of MP and MMG amplitude for all 3 muscles and of EMG amplitude for the VL and VM in the women. Velocity-related decreases (p 0.05) across velocity. MMG MPF increased (p < or = 0.05) only between 240 and 300 degrees x s(-1). Overall, these findings suggested that there were sex- and muscle-specific, velocity-related differences in the associations among motor unit activation strategies (EMG amplitude and MPF) and the mechanical aspects of muscular activity (MMG amplitude and MPF). With additional examination and validation, however, MMG may prove useful to practitioners for monitoring training-induced changes in muscle power output.     

Influences of experimental factors on spinal stretch reflex latency and amplitude in the human triceps surae.

The spinal stretch reflex (SSR) is commonly assessed via electromyographic (EMG) analysis of joint perturbations inducing changes in muscle length. Previous literature indicates that when large experimental changes in magnitude of agonist background EMG, perturbation velocity, and perturbation amplitude are employed, SSR latency and amplitude are significantly altered. The purpose of this investigation was to evaluate the relative dependence of SSR latency and amplitude on inherent variability in these experimental variables. Soleus SSR latency and amplitude were assessed in 40 healthy subjects following dorsiflexion perturbation under an active state ( approximately 14% MVC). Experimental variables displayed limited variability (means +/- SD): soleus background EMG (13.47 +/- 7.08% MVC), perturbation velocity (96.1 +/- 30 degrees /s), and perturbation amplitude (4 +/- 1 degrees ). SSR latency was not significantly related to soleus background EMG (r = 0.189), perturbation velocity (r = 0.213), or perturbation amplitude (r = 0.202). Similarly, SSR amplitude was not significantly related to soleus background EMG (r = 0.306), perturbation velocity (r = 0.053), or perturbation amplitude (r = 0.056). Variability in experimental variables was much smaller than what has been reported in the literature to significantly impact SSR characteristics. These results suggest that SSR latency and amplitude are independent of agonist background EMG, perturbation velocity, and perturbation amplitude when experimental variability is relatively limited.     

External-internal relationships in humeri of modern human females

With data from an early twentieth century human skeletal collection, this exploratory study investigates associations between inner cortical and medullary cavity structures and outer shaft and epiphyseal features of a long bone. Humeri are measured directly in both whole bone and transverse section contexts; data along 2 axes at 2 sites are obtained. Twenty-two probable females, with an age range concentrated in middle adulthood, comprise the sample. Correlations between multiple external and internal bone measurements are analyzed, with the aim of yielding information on the physical nature of bone and on the effects of different measurement types, locations, and orientations for bone relationships. The study also examines whether prediction of inner humeral dimensions from outer measurements would be appropriate. Results indicate biepicondylar width and maximum length as the strongest external correlates of cortical dimensions. Contrasting with studies on the proximal femur, the humeral head shows external size changeability, mostly in the transverse plane, in response to modeling forces shared with the shaft. Epiphyseal measures are more highly associated with absolute rather than percent, and areal rather than linear, cortical variables. Medullary cavity dimensions are not significantly correlated with whole bone measures. Most associations demonstrate shape or proportion influences rather than a shared effect of linear body size. Regarding location and orientation, the distal site and medial-lateral axis display the strongest correlations among external and internal bone dimensions. In light of the demonstrated correlation patterns, prediction of humeral cortical quantity from external bone measures in living and skeletal populations would benefit from utilizing (1) biepicondylar width and maximum length; (2) an absolute, areal cortical measure; (3) a distal location; and (4) a medial-lateral orientation.     

The relationship between narrow and wide bandwidth filter settings during an EMG scanning procedure

This study examined the correlation between EMG values measured with wide (25–1000 Hz) and narrow (100–200 Hz) band-width filters. An EMG diagnostic scan was conducted on 32 chronic pain patients admitted to an inpatient treatment unit. EMG readings were taken from a total of 44 sites (11 sites×2 sides×2 postures). Each EMG measure was passed in parallel through a narrow and wide band-pass filter and the stable readings were recorded. Correlatedt tests and Pearson correlations were used to compare the data from the narrow and wide filter settings. The measures from the wide filter were significantly higher than the measures from the narrow filter. In addition, 61% of the correlations were greater than .90. The majority of the correlations below the median (.93) occurred in the neck region and the abdomen. The implications of the findings are discussed.This research was sponsored by the Swedish Hospital Pain Clinic.     

Cardiorespiratory fitness, different measures of adiposity, and total cancer mortality in women

The objective was to examine associations among cardiorespiratory fitness (CRF), adiposity, and cancer mortality in women. Healthy women (N = 14,256) without cancer history completed a baseline health examination 1970-2005. Measures included BMI, percent body fat (%Fat), and CRF quantified as duration of a maximal treadmill test. CRF was classified as low (quintile 1), moderate (Q2-3), and high fit (Q4-5) by age. Standard BMI cutpoints were used, while participants were classified by %Fat quintiles. Cancer mortality rates were calculated following age, exam year, and smoking adjustment. During a mean follow-up period of 15.2 ± 9.4 years, 250 cancer deaths occurred. Adjusted mortality rates across BMI groups were 4.6, 5.7, and 8.8 (P trend 0.08); %Fat 3.0, 4.9, 2.9, 3.8, and 6.9 (P trend 0.17); and CRF 7.9, 5.5, and 2.9 (P trend 0.003). When grouped into categories of fit and unfit (upper 80% and lower 20% of CRF distribution), and using BMI as the adiposity exposure, cancer mortality rates of unfit-obese women were significantly higher than fit-normal weight women (9.8 vs. 4.1 deaths/10,000 woman-years; P = 0.02), while fit-overweight and fit-obese women had no greater risk of mortality than fit-normal weight women. Using %Fat as the adiposity exposure, unfit-obese women tended to have higher cancer mortality than fit-normal weight women (7.0 vs. 3.3 deaths/10,000 woman-years, P = 0.10). Higher levels of CRF are associated with lower cancer mortality risk in women and attenuate the risk of cancer mortality in overweight women. Using adiposity measures to estimate cancer mortality risk in women can be potentially misleading unless CRF is considered.     

Electromyographic indices, orofacial myofunctional status and temporomandibular disorders severity: A correlation study

This study examined whether there is an association between surface electromyography (EMG) of masticatory muscles, orofacial myofunction status and temporomandibular disorder (TMD) severity scores. Forty-two women with TMD (mean 30 years, SD 8) and 18 healthy women (mean 26 years, SD 6) were examined. According to the Research Diagnostic Criteria for TMD (RDC/TMD), all patients had myogenous disorders plus disk displacements with reduction. Surface EMG of masseter and temporal muscles was performed during maximum teeth clenching either on cotton rolls or in intercuspal position. Standardized EMG indices were obtained. Validated protocols were used to determine the perception severity of TMD and to assess orofacial myofunctional status. TMD patients showed more asymmetry between right and left muscle pairs, and more unbalanced contractile activities of contralateral masseter and temporal muscles (p<0.05, t-test), worse orofacial myofunction status and higher TMD severity scores (p<0.05, Mann-Whitney test) than healthy subjects. Spearman coefficient revealed significant correlations between EMG indices, orofacial myofunctional status and TMD severity (p<0.05). In conclusion, these methods will provide useful information for TMD diagnosis and future therapeutic planning.     

A preliminary analysis of correlations between chewing motor patterns and mandibular morphology across mammals

The establishment of a publicly-accessible repository of physiological data on feeding in mammals, the Feeding Experiments End-user Database (FEED), along with improvements in reconstruction of mammalian phylogeny, significantly improves our ability to address long-standing questions about the evolution of mammalian feeding. In this study, we use comparative phylogenetic methods to examine correlations between jaw robusticity and both the relative recruitment and the relative time of peak activity for the superficial masseter, deep masseter, and temporalis muscles across 19 mammalian species from six orders. We find little evidence for a relationship between jaw robusticity and electromyographic (EMG) activity for either the superficial masseter or temporalis muscles across mammals. We hypothesize that future analyses may identify significant associations between these physiological and morphological variables within subgroups of mammals that share similar diets, feeding behaviors, and/or phylogenetic histories. Alternatively, the relative peak recruitment and timing of the balancing-side (i.e., non-chewing-side) deep masseter muscle (BDM) is significantly negatively correlated with the relative area of the mandibular symphysis across our mammalian sample. This relationship exists despite BDM activity being associated with different loading regimes in the symphyses of primates compared to ungulates, suggesting a basic association between magnitude of symphyseal loads and symphyseal area among these mammals. Because our sample primarily represents mammals that use significant transverse movements during chewing, future research should address whether the correlations between BDM activity and symphyseal morphology characterize all mammals or should be restricted to this "transverse chewing" group. Finally, the significant correlations observed in this study suggest that physiological parameters are an integrated and evolving component of feeding across mammals.     

Family studies of tooth size factors in the permanent dentition.

Correlations between dimensions of the permanent teeth in Australian Aboriginals were studied by factor analysis to disclose the main sources of shared variability. Findings indicated that in both males and females most of the common variability in the tooth dimensions could be accounted for by factors representing mesiodistal size of anterior teeth, buccolingual size of anterior teeth, generalized size of the premolars and generalized size of the molars. Factor scores derived from the analysis were used to calculate intraclass correlations among brothers and among sisters. These correlations tended to be higher for the factors contributing most to the common variability indicating that the factors might represent fields under direct genetic control. There was no trend for intraclass correlations among siblings derived from multivariate scores to be consistently higher than those based on observed tooth dimensions. The main advantage to the user of factor analysis is the ability to interpret associations between interrelated variables more objectively than is possible by conventional correlation methods.     

Correlation between EMG and COP onset latency in response to a horizontal platform translation

This study examined the relationship between onset latencies estimates from EMG and center of pressure (COP) in young (five female, five male; mean=24.2+/-2.3 years) and older (six female, four male; 78.4+/-2.3 years) subjects during anterior or posterior platform translations. The latencies to onset of activity were estimated for the tibialis anterior (TA; mean=119.8 ms across both age groups) and COP (mean=139.7 ms across both groups) for anterior translations, and the soleus (SOL; mean=122.4 ms across both groups), gastrocnemius (GAS; mean=126.0 ms for young, and 115.9 ms for old subjects) and COP (mean=160.0 ms across both groups) for posterior translations. Average within-subject correlations (r') among these measures showed a high correlation between TA and COP onset latency (r'=0.667, young; r'=0.482, old), and relatively low correlations between the plantar flexors (SOL and GAS) and COP onset latencies (SOL: r'=0.292 for young, r'=0.249 for old; GAS: r'=0.126 for young, r'=0.143 for old). The SOL and GAS onset latencies correlated well with each other, especially in the older subjects (r'=0.762), suggesting that the contribution of two muscles creates some variability in the relationship with COP onset latency. The strong correlation between TA and COP for anterior perturbations, coupled with the weaker correlations for the plantar flexors suggest that the COP method may be preferable for studies interested in determining timing of postural responses to multidirectional perturbations.     

The effects of electrode placement and innervation zone location on the electromyographic amplitude and mean power frequency versus isometric torque relationships for the vastus lateralis muscle.

The purposes of this investigation were to examine the effects of electrode placement and innervation zone (IZ) location on: (a) the torque-related patterns of responses for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) and (b) the mean absolute and normalized EMG amplitude and MPF values. In addition, the present study examined the variability between subjects for the location of the IZ for the vastus lateralis (VL). Eight men (mean+/-SD age=23.0+/-4.3yr) performed submaximal to maximal isometric muscle actions of the dominant leg extensors. During each muscle action, fifteen channels of bipolar surface EMG signals were detected from the vastus lateralis using a linear electrode array aligned with the long axis of the muscle fibers. The results indicated that there were differences among channels 1-15 for the patterns of responses and mean values for absolute and normalized EMG amplitude and MPF versus isometric torque. Thus, normalized EMG amplitude and MPF values from different individuals cannot be compared if the EMG signals were detected from different locations over the muscle. In addition, absolute and relative (to femur length) estimates of IZ location for the VL resulted in similar inter-subject variability.     

Relationship between sprint times and the strength/power outputs of a machine squat jump

Strength testing is often used with team-sport athletes, but some measures of strength may have limited prognostic/diagnostic value in terms of the physical demands of the sport. The purpose of this study was to investigate relationships between sprint ability and the kinetic and kinematic outputs of a machine squat jump. Thirty elite level rugby union and league athletes with an extensive resistance-training background performed bilateral concentric-only machine squat jumps across loads of 20% to 90% 1 repetition maximum (1RM), and sprints over 10 meters and 30 or 40 meters. The magnitudes of the relationships were interpreted using Pearson correlation coefficients, which had uncertainty (90% confidence limits) of approximately +/-0.3. Correlations of 10-meter sprint time with kinetic and kinematic variables (force, velocity, power, and impulse) were generally positive and of moderate to strong magnitude (r = 0.32-0.53). The only negative correlations observed were for work, although the magnitude was small (r = -0.18 to -0.26). The correlations for 30- or 40-meter sprint times were similar to those for 10-meter times, although the correlation with work was positive and moderate (r = 0.35-0.40). Correlations of 10-meter time with kinetic variables expressed relative to body mass were generally positive and of trivial to small magnitude (r = 0.01-0.29), with the exceptions of work (r = -0.31 to -0.34), and impulse (r = -0.34 to -0.39). Similar correlations were observed for 30- and 40-meter times with kinetic measures expressed relative to body mass. Although correlations do not imply cause and effect, the preoccupation with maximizing power output in this particular resistance exercise to improve sprint ability appears problematic. Work and impulse are potentially important strength qualities to develop in the pursuit of improved sprinting performance.     

Blood mercury concentrations in common bottlenose dolphins from the Indian River Lagoon,Florida: Patterns of social distribution

Social network analysis has been shown to be effective in studying the social structure of cetacean populations. Common bottlenose dolphins (Tursiops truncatus) inhabiting the Indian River Lagoon (IRL), Florida, have among the highest concentrations of total mercury (THg) in blood reported worldwide. The purpose of this study was to examine the relationship between THg concentrations in IRL dolphins and their social affiliations. Whole blood samples from 98 dolphins with photo‐identification sighting histories were collected between 2003–2007 and 2010–2012. Dolphins were categorized into approximate tertiles of low (mean 199.7 μg/L), medium (mean 366.8 μg/L), and high (mean 990.5 μg/L) THg exposure. Social associations between individual dolphins were defined by the proportion of sightings documented with another known individual. Social network measures of individuals and associations between dyads were examined to determine differences among THg categories. Strong social affiliations of individuals within the highest category of THg were found (P = 0.04), suggesting shared exposures among dolphins foraging in specific areas of the estuary. Network measures of strength and affinity were significantly higher in the highest exposure category. This report used social network analysis as a novel way to examine patterns of exposure to an environmental contaminant in a cetacean population.     

Relative importance of strength, power, and anthropometric measures to jump performance of elite volleyball players

The purpose of this investigation was to examine the potential strength, power, and anthropometric contributors to vertical jump performances that are considered specific to volleyball success: the spike jump (SPJ) and counter-movement vertical jump (CMVJ). To assess the relationship among strength, power, and anthropometric variables with CMVJ and SPJ, a correlation and regression analysis was performed. In addition, a comparison of strength, power, and anthropometric differences between the seven best subjects and the seven worst athletes on the CMVJ test and SPJ test was performed. When expressed as body mass relative measures, moderate correlations (0.53-0.65; p < or = 0.01) were observed between the 1RM measures and both relative CMVJ and relative SPJ. Very strong correlations were observed between relative (absolute height-standing reach height) depth jump performance and relative SPJ (0.85; p < or = 0.01) and relative CMVJ (0.93; p 相似文献   

Absolute vs. relative machine strength as predictors of function in older adults

This study examined the relationship between absolute and relative (1 repetition maximum/LBM) strength vs. 13 different functional measurements in 143 older adults (mean = 70.28, standard deviation = 7.90 years). Strength for 11 machine lifts was determined using a predicted 1-repetition maximal strength measurement. Zero-order correlation results between absolute and relative strength vs. function measures demonstrated very weak to moderate correlations in the range of 0.02-0.57 and 0.01-0.44, respectively, with the lowest correlations present between strength and balance measures and the highest correlations present between strength and the carrying task (p 相似文献   

The comparison of trunk muscles EMG activation between subjects with and without chronic low back pain during flexion-extension and lateral bending tasks.

The purpose of the study was to compare the electromyographic (EMG) activity of the trunk muscles between normal subjects and chronic low back pain (CLBP) patients during standardized trunk movements. Thirty-three male subjects (18 normals, 15 suffering from non specific CLBP) aged between 35 and 45 yr participated. A biomechanical analysis involving the recording of EMG signals from 12 trunk muscles, the kinematics of trunk segments and the computation of L5/S1 moments was performed. The subjects performed flexion-extension and lateral bending (left and right) tasks (three complete cycles) with and without a 12 kg load. Between group comparisons were performed on the full cycle average pattern of all biomechanical variables for each task. The reliability of EMG variables was evaluated for 10 subjects (5 normals and 5 CLBP) who performed the tasks on three different days. The reliability of EMG amplitude values was generally excellent for agonist muscles but poor to moderate for antagonists. The EMG amplitude analysis revealed significant differences between groups for some muscles (left lumbar and thoracic erector spinae). The abnormal (asymmetric) EMG patterns detected among CLBP patients were not explained by postural asymmetries.