Isotonic and isoelectric endurance tests for the upper trapezius muscle

As an alternative to a conventional endurance electromyogram (EMG) test for assessment of muscle capacity in the upper trapezius muscle (isotonic test, IT), an isoelectric test (IE) has been investigated. Nine subjects performed the two endurance tests. The tests were performed with a straight horizontal arm in the plane of the scapula. In IE, EMG amplitude was fed back to the subject and the subject was instructed to maintain a constant EMG activity equal to the level with the arm unsupported. Subjective ratings of local fatigue were obtained during the experiments. The EMG recordings from both tests were analysed for the root mean square value as well as according to the mean power frequency (MPF) technique. All the subjects endured maximal 15?min IE while in IT the median endurance was 11.9 min. Average subjective ratings of perceived fatigue increased more in IT compared to IE. The average normalised MPF curve from IT increased while that from IE was unaffected. There was a significant difference between the MPF results at 6 and 8 min. It is noteworthy that the MPF was higher in IT in spite of a higher accumulated biomechanical load. It was concluded from these studies that the interpretation of decreased MPF as an indicator of increased local muscle fatigue is doubtful at low contraction levels. It is suggested that an IE is a more appropriate method for the functional evaluation of low threshold motor units of the upper trapezius muscle in research into occupational disorders.     

Caffeine affects cardiovascular and neuroendocrine activation at work and home

OBJECTIVE: This study investigated the effects of moderate doses of caffeine on ambulatory blood pressure and heart rate, urinary excretion of epinephrine, norepinephrine, and cortisol, and subjective measures of stress during normal activities at work and at home in the evening. METHODS: Healthy, nonsmoking, habitual coffee drinkers (N = 47) participated in 3 days of ambulatory study. After a day of ad lib caffeine consumption, caffeine (500 mg) and placebo were administered double-blind in counter-balanced order on separate workdays. Ambulatory blood pressure and heart rate were monitored from the start of the workday until bedtime. Urinary excretion of catecholamines and cortisol was assessed during the workday and evening. RESULTS: Caffeine administration significantly raised average ambulatory blood pressure during the workday and evening by 4/3 mm Hg and reduced average heart rate by 2 bpm. Caffeine also increased by 32% the levels of free epinephrine excreted during the workday and the evening. In addition, caffeine amplified the increases in blood pressure and heart rate associated with higher levels of self-reported stress during the activities of the day. Effects were undiminished through the evening until bedtime. CONCLUSIONS: Caffeine has significant hemodynamic and humoral effects in habitual coffee drinkers that persist for many hours during the activities of everyday life. Furthermore, caffeine may exaggerate sympathetic adrenal-medullary responses to the stressful events of normal daily life. Repeated daily blood pressure elevations and increases in stress reactivity caused by caffeine consumption could contribute to an increased risk of coronary heart disease in the adult population.     

Neck muscle fatigue affects postural control in man

We hypothesised that, since anomalous neck proprioceptive input can produce perturbing effects on posture, neck muscle fatigue could alter body balance control through a mechanism connected to fatigue-induced afferent inflow. Eighteen normal subjects underwent fatiguing contractions of head extensor muscles. Sway during quiet stance was recorded by a dynamometric platform, both prior to and after fatigue and recovery, with eyes open and eyes closed. After each trial, subjects were asked to rate their postural control. Fatigue was induced by having subjects stand upright and exert a force corresponding to about 35% of maximal voluntary effort against a device exerting a head-flexor torque. The first fatiguing period lasted 5 min (F1). After a 5-min recovery period (R1), a second period of fatiguing contraction (F2) and a second period of recovery (R2) followed. Surface EMG activity from dorsal neck muscles was recorded during the contractions and quiet stance trials. EMG median frequency progressively decreased and EMG amplitude progressively increased during fatiguing contractions, demonstrating that muscle fatigue occurred. After F1, subjects swayed to a larger extent compared with control conditions, recovering after R1. Similar findings were obtained after F2 and after R2. Although such behaviour was detectable under both visual conditions, the effects of fatigue reached significance only without vision. Subjective scores of postural control diminished when sway increased, but diminished more, for equal body sway, after fatigue and recovery. Contractions of the same duration, but not inducing EMG signs of fatigue, had much less influence on body sway or subjective scoring. We argue that neck muscle fatigue affects mechanisms of postural control by producing abnormal sensory input to the CNS and a lasting sense of instability. Vision is able to overcome the disturbing effects connected with neck muscle fatigue.     

A non-invasive method for measuring inspiratory muscle fatigue during progressive isocapnic hyperventilation in man

Summary Eleven normal adults each performed a ten minute progressive isocapnic hyperventilation (PIHV) test in which ventilatory levels were increased every two minutes. All subjects exhibited mechanical fatigue by failing to maintain the target of 80% of maximum voluntary ventilation (MVV). The mean ventilation at this level was 67.5±1.4 %MVV. This fatigue was accompanied by a fall in transdiaphragmatic pressure. During the test the EMG of the sternomastoid (SM) was monitored by surface electrodes and was analyzed using fast-fourier transform. The centroid frequency (Fc) fell as ventilation increased, and correlated negatively with the inability to achive target ventilation (r=–0.99, p<0.015). Five subjects performed the test while the diaphragmatic EMG was recorded from an oesophageal electrode (DIes) and from surface electrodes (DIs). The Fc of DIes fell with increasing ventilation levels (r=–0.95, p<0.05) and there was a correlation beween the Fc changes of both DIes and the SM (r=0.92, p<0.001). The Fc of DIs did not correlate with either mechanical performance or the Fc of DIes, because of contamination of surface signals by signals from expiratory muscles. It is concluded that the PIHV along with surface monitoring of EMG activity from the sternomastoid can serve as a non-invasive method for evaluating inspiratory muscle fatigue.     

Static and dynamic myoelectric measures of shoulder muscle fatigue during intermittent dynamic exertions of low to moderate intensity

Despite extensive research on muscular fatigue during prolonged static efforts, there have been relatively few studies of more complex tasks (dynamic and intermittent). A laboratory study of overhead work tasks was conducted to investigate whether electromyographic (EMG) measures can potentially serve as indicators of fatigue, particularly for ergonomic tasks analysis. Sixteen participants performed the tasks until they either developed substantial discomfort or reached a 3-h limit. EMG signals were obtained at intervals throughout the experiment from four shoulder muscles, both statically (during fixed-level test contractions) and dynamically (during task performance). Both EMG root mean square (RMS) amplitude and spectral content (mean and median power frequencies) were examined and compared in terms of their variability and sensitivity. In addition, a new fatigue index was developed to allow for the estimation of substantial fatigue onset. Variability was found to differ significantly between muscles and EMG measures, and was generally lowest for mean power frequencies obtained during static test contractions. Sensitivity was typically greatest for RMS versus spectral measures, and slightly higher for median than mean power frequencies. The results suggest that fatigue during dynamic tasks, while a complex phenomenon, can be monitored and quantified using EMG. Electronic Publication     

Effects of body-mind training and relaxation stretching on persons with chronic toxic encephalopathy

The purpose of this project was to investigate the psychological and physical effects of training of body awareness and slow stretching on persons with chronic toxic encephalopathy (CTE). In the present study, a method of self-regulation, a body-mind training, is presented. The body-mind training used was a guided relaxation technique combined with meditative stretching. The techniques are introduced and the psychological and physiological effects of the training is presented. Eight subjects with CTE, 48.5 years, were trained for 8 weeks. Outcome measures were percentage alpha brain waves (alpha%), electromyography (EMG) on the frontalis muscle, state-trait anxiety (STAI), creativity (RAT), and mood measured as anxiousness, humour and mental fatigue. The mean alpha% increased 52% during the training period (P < 0.01), and the EMG decreased 31% (P < 0.001. State anxiety decreased 22% during the training period (P < 0.01), but no changes were observed in trait anxiety and in the creativity score. The level of anxiousness and fatigue before a training session decreased during the training period. In conclusion, the body-mind training resulted in an improved ability for physical and mental relaxation as indicated from the lower EMG, the higher alpha% and the decrease in state anxiety.     

Changes in Motor Unit Activity and Metabolism in Human Skeletal Muscle during and after Repeated Eccentric and Concentric Contractions

This study was designed to investigate electromyographic (EMG), muscle glycogen and blood lactate changes in quadriceps muscle group during repeated 40 maximal eccentric and concentric contractions, and to follow the recovery in EMG, muscle glycogen and serum creatine kinase values during a 4 day period following the work test. The subjects were normal males and the test order (eccentric or concentric) was randomly selected. The results indicated first, that the EMG parameters (IEMG, AMUP), muscle glycogen and blood lactate changed in a similar manner during the both fatigue loads. Despite the high tension work no selective depletion of glycogen could be observed in the slow or fast twitch muscle fibres in either type of work. The restoring of muscle glycogen occurred in a similar manner after the both fatigue loads, and no significant differences were present between eccentric and concentric works in the serum creatine kinase levels for a 2 days period. The eccentric work was associated with muscle soreness, which was strongest during the second day after the termination of the work test. The recovery of the EMG parameters were also delayed in eccentric fatigue. After concentric fatigue EMG-activity returned to normal values within 2 days.     

Trunk muscle fatigue and associated EMG changes during a dynamic iso-inertial test

This study was designed to investigate the relationship between trunk muscle fatigue and associated changes in the electromyographic (EMG) signals during a dynamic iso-inertial test. Eleven subjects performed dynamic trunk flexion/extension movements against 40% maximum voluntary contraction (MVC) torque until exhaustion in a tri-axial trunk dynamometer. EMG parameters in the time and frequency domain were studied by analysing changes of the signal amplitudes and the spectral density (using the zero-crossing-rate and the median frequency). The kinematics of the movement were analysed according to the movement velocities and the deviations from the required movement plane. The flexion and extension velocities decreased from the beginning to the end of the test. Movement deviations from the sagittal plane into the frontal and transverse plane increased with increasing test duration, as did the EMG amplitude. The median frequency during periods with maximum muscle activity decreased, as did the zero-crossing-rate. The increase in amplitude and decrease in median frequency were more pronounced in the trunk flexors than in the trunk extensors. The parameters of median frequency, zero-crossing-rate and amplitude seem to be sensitive identifiers of muscle fatigue during well-controlled dynamic contractions. While the kinematic data did not yield any information on the mechanisms of the fatigue, changes in the EMG parameters demonstrated that the duration of the test was limited by the fatigue of the trunk flexors.     

Temporal profile of prolonged, night-time driving performance: breaks from driving temporarily reduce time-on-task fatigue but not sleepiness

Breaks are often used by drivers to counteract sleepiness and time-on-task fatigue during prolonged driving. We examined the temporal profile of changes in driving performance, electroencephalogram (EEG) activity and subjective measures of sleepiness and fatigue during prolonged nocturnal driving in a car simulator. In addition, the study examined the impact of regular breaks from driving on performance, sleepiness and fatigue. Healthy volunteers (n=12, 23-45 years) maintained a regular sleep-wake pattern for 14 days and were then in a laboratory from 21:00 to 08:30 hours. The driving simulator scene was designed to simulate monotonous night-time rural driving. Participants drove 4 × 2-h test sessions, with a break from driving of 1 h between each session. During the break participants performed tests assessing sleepiness and fatigue, and psychomotor performance (~30 mins), and then were permitted to sit quietly. They were monitored for wakefulness, and not permitted to nap or ingest caffeine. EEG was recorded during the driving task, and subjective assessments of sleepiness and fatigue were obtained at the start and completion of each session. We found that driving performance deteriorated (2.5-fold), EEG delta, theta and alpha activity increased, and subjective sleepiness and fatigue ratings increased across the testing period. Driving performance and fatigue ratings improved following the scheduled breaks from driving, while the breaks did not affect EEG activity and subjective sleepiness. Time-on-task effects increased through the testing period, indicating that these effects are exacerbated by increasing sleepiness. Breaks from driving without sleep temporarily ameliorate time-on-task fatigue, but provide little benefit to the sleepy driver.     

Relaxation training affects success and activation on a teaching test

We studied the effects of an audiocassette-relaxation training period (ART) and its timing on success at a teaching test (lecture type), on observed tension and on a number of physiological responses. The electrical activity of the upper trapezius muscle (EMG), heart rate (HR) and blood pressure (BP), of female and male instructor candidates, were examined before, during and after the teaching test as well as during its critique. The relaxation period (18 min) was presented either on the preceding night (ARTnt) or immediately before the teaching test (ARTimm). The influence of personality (types A-B and extrovert-introvert) was also studied. ART improved success at the teaching test in both sexes. In males (but not in females), ARTimm decreased EMG level during the test, but ARTnt increased EMG at the test period as compared to the control group. In females, both ARTnt and ARTimm lowered HR more than in the control group. ARTimm lowered systolic BP in both sexes. Personality types affected the ART responses; ART was more beneficial for type A than B subjects.     

Signal characteristics of EMG during fatigue

Summary Electromyographic (EMG) activity of m. rectus femoris muscle was registered from young male and female subjects during maintained isometric knee extension at 60% of maximal voluntary contraction. The following EMG parameters were analyzed for the entire fatigue time: integrated EMG (IEMG), averaged motor unit potential (AMUP) and power spectral density function (PSDF). The results indicated a slight but continuous rise of IEMG during the fatigue period. AMUP showed sensitivity to fatigue with increase in amplitude, rise time, and number of spikes counted. PSDF was also easily affected by fatigue so that the total power density curve was shifted towards lower frequencies with a high frequency decay. The mean power frequency decreased linearily as a function of fatigue time. The findings suggest that in addition to natural recruitment of new motor units the fatigue is characterized by marked reduction in the conduction velocities of action potential along the used muscle fibers.     

Electromyogram as an indicator of neuromuscular fatigue during incremental exercise

This study analysed the changes in the electromyographic activity (EMG) of the vastus lateralis muscle (VL) during an incremental maximal oxygen uptake test on a treadmill. A breakpoint in the integrated electromyogram (iEMG)-velocity relationship has already been interpreted in two ways: either as a sign of neuromuscular fatigue or as an expression of the iEMG-velocity relationship characteristics. The aim of this study was to test a method of distinguishing fatigue effects from those due to increases in exercise power. Eight well-trained male runners took part in the study. They completed a running protocol consisting of 4-min stages of increments in power output. Between each stage (about 15?s after the start of a minute at rest), the subjects had to maintain a standard effort: a 10-s isometric leg extension contraction [50% isometric maximal voluntary contraction (IMVC)]. The EMG was recorded during the running and isometric protocols, a change in the EMG signal during the isometric exercise being considered as the sign of fatigue. The iEMG-velocity relationships were strongly fitted by a second-order polynomial function for data taken at both the start (r?=?0.98) and the end (r?=?0.98) of the stage. Based on the stability of the 50%IMVC-iEMG relationship noted between stages, the start-iEMG has been identified as expressing the iEMG-velocity relationship without fatigue. The stage after which end-iEMG increased significantly more steeply than start-iEMG was considered as the iEMG threshold and was simultaneous with the ventilatory equivalent for carbon dioxide threshold. The parallel changes of minute ventilation and iEMG would suggest the existence of common regulation stimuli linked either to effort intensity and/or to metabolic conditions. The fall in intracellular [K⁺] has been discussed as being one of the main factors in regulating ventilation.     

Back and neck extensor loading and back pain provocation in urban bus drivers with and without low back pain

This study assessed low back and trapezius muscle activity in bus drivers, with or without recurrent low back pain (LBP), during the long term driving. In addition, low back and neck–shoulder pain intensities and fatigue were measured and the effect of low back support was observed. Also the possible source of LBP was attempted to assess by vibration pain provocation test and lumbar MRI.

Forty bus drivers (recurrent LBP n = 25) participated in this study. Low back and neck–shoulder pain and subjective fatigue intensity was assessed by visual analogue scales (VAS) before and after driving. Lumbar paraspinal and trapezius muscle activation during driving was measured by surface EMG. Vibration pain provocation test was applied for all subjects.

Average paraspinal myoelectric activity during driving was approximately 1% of MVC in both groups. Average trapezius myoelectric activity during driving was from 2 to 4% of MVC. Trapezius muscle activity was higher in back healthy drivers than in those with LBP. The low back support had no effect either on paraspinal or trapezius EMG activity. Low back and neck–shoulder fatigue increased during driving in both groups especially in those subjects with positive vibration pain provocation. The neck–shoulder pain and fatigue were more severe in drivers suffering from LBP. Low back support had no effect on low back and neck–shoulder subjective fatigue and neck–shoulder pain but tended to limit the LBP increase during driving. Paraspinal muscle loading in urban bus drivers was very limited and either LBP or ergonomic low back support had no effect on it. Trapezius muscle seemed to be less active in drivers suffering from recurrent LBP. Internal disc disruptions may expose to pain and fatigability during driving.     

A Multiple-Response Evaluation of EMG Biofeedback Performance During Training and Stress-Induction Conditions

The present study evaluated multiple system physiological responding which accompanied EMG biofeedback performance under two conditions—during EMG biofeedback training sessions, and during the utilization of that training in the presence of a stressor. Twelve subjects were randomly assigned to one of two groups: 1) an EMG biofeedback group, or 2) a false-EMG biofeedback group. During the training sessions, significant frontalis EMG decreases were produced by the biofeedback group. This performance was associated with a concomitant decrease in heart rate and respiration rate, but an increase in skin conductance level. The biofeedback group was also able to maintain a low level of EMG activity during a stress-induction procedure. However, this low level of activity did not generalize to other physiological responses. Heart rate and skin conductance levels both increased, which coincided with the subjects' self-report of anxiety during this phase of the study. These data clearly demonstrate that single-system arousal reduction produced by EMG biofeedback training, rather than producing cross-system arousal reduction, produces specificity of a single response change under a stress-inducing situation.     

Effect of body tilt angle on fatigue and EMG activities in lower limbs during cycling

This study compared the rate of fatigue and lower limb EMG activities during high-intensity constant-load cycling in upright and supine postures. Eleven active males performed seven cycling exercise tests: one upright graded test, four fatigue tests (two upright, two supine) and two EMG tests (one upright, one supine). During the fatigue tests participants initially performed a 10 s all-out effort followed by a constant-load test with 10 s all-out bouts interspersed every minute. The load for the initial two fatigue tests was 80% of the peak power (PP) achieved during the graded test and these continued until failure. The remaining two fatigue tests were performed at 20% PP and were limited to the times achieved during the 80% PP tests. During the EMG tests subjects performed a 10 s all-out effort followed by a constant-load test to failure at 80% PP. Normalised EMG activities (% maximum, NEMG) were assessed in five lower limb muscles. Maximum power and maximum EMG activity prior to each fatigue and EMG test were unaffected by posture. The rate of fatigue at 80% PP was significantly higher during supine compared with upright posture (−68 ± 14 vs. −26 ± 6 W min⁻¹, respectively, P < 0.05) and the divergence of the fatigue responses occurred by the second minute of exercise. NEMG responses were significantly higher in the supine posture by 1–4 min of exercise. Results show that fatigue is significantly greater during supine compared with upright high-intensity cycling and this effect is accompanied by a reduced activation of musculature that is active during cycling.     

EMG characteristics of low back and lower limb muscles during forward bending posture

The study observed forward bending posture and evaluated its effect on muscular activity. The Muscular activity was monitored through the Electromyography (EMG). The objective was to extend the evaluation method of EMG due to muscular load in maintaining the posture and to investigate the existence of muscular coordination between low back and lower limb muscles during the posture. Twelve male subjects were asked to maintain the postures of six stages in bending angles from 0 to 180 degrees. The EMG of erector spinae (ES) at L1 and L5 levels, hamstrings, and gastrocnemius were recorded and analyzed by power spectral density. The characteristics of muscular activities were observed through the EMG power spectrum and the frequency. The activity changes were normalized by the relative presentation and the standardization. The relative presentation showed the level of activity changes in each posture by taking the activity during upright standing as a reference posture, and the standardization was applied to overcome the dependence of the power spectrum and the frequency upon the high standard deviation. A t test with the paired data was also applied to compare the values of EMG of the respective stages of the posture. The results showed that the activity of ES significantly increased during bending posture with an angle up to 45 degrees, and reached silent activity at 90 degrees of flexion. On the other hand, the activity of the hamstrings and gastrocnemius were recognized even when ES activity started and reached the silent activity. The lower limb muscles were considered to be always active during all stages of the posture, and they provided a greater contribution when the ES was in the silent activity.     

Psychophysiological activity and neuropsychological test performance in alcoholics.

This study examined electromyogram (EMG) and skin conductance level (SCL) as mediators of neuropsychological test performance of alcoholics. Alcoholics and controls with high EMG performed less well than low EMG subjects on 12 measures of neuropsychological performance. For SCL, the alcoholics and controls in the Low Group did not differ from those in the High Group on any measure. Analyses that used information intake (Low EMG and High SCL) and rejection (High EMG and Low SCL) information postures (IPs) demonstrated that the intake group outperformed the rejection group on 10 neuropsychological measures. Subjects with intake IPs reported more stimulation, concentration, and interest during the tasks than did subjects with rejection IPs. Results suggest that IPs can be used to identify alcoholics with neuropsychological deficits.     

Fatigue and EMG of Repeated Fast Voluntary Contractions in Man

A fatigue test consisting of repeated fast maximal contractions of the left quadriceps muscle in an isokinetic apparatus was performed by 12 healthy male subjects (19–25 yrs). EMG signals were recorded from the surface of the left vastus lateralis muscle, from which also biopsies were obtained for muscle fibre classification. Only minor changes were observed in the EMG variables despite a decrease in muscle strength performance, in terms of peak torque, work and power to about 50% of initial values after 100 contractions. The concomitantly obtained positive correlation between the increase in EMG/torque ratio and the individual percentage of fast twitch (FT) muscle fibres indicated that local factors in the muscle, primarily in the FT fibres, were causing the development of fatigue during repeated dynamic contractions with high power outputs.     

Performance on the Balance Error Scoring System Decreases After Fatigue

OBJECTIVE: To determine the immediate effects of a whole-body fatigue protocol on performance of the Balance Error Scoring System (BESS), a postural-stability test commonly used as part of a concussion-assessment battery. DESIGN AND SETTING: Subjects were assigned to a fatigue or control group and were assessed before and immediately after a 20-minute fatigue protocol or rest period. SUBJECTS: Fourteen fatigue subjects and 13 control subjects participated in this study. All subjects were male and free of vestibular disorders, and none had suffered a mild head injury or lower extremity injury in the preceding 6 months, as described through self-report. MEASUREMENTS: We measured performance on the BESS for 9 stance-surface conditions and summed each condition to obtain a total score. Using the Borg scale, we also measured ratings of perceived exertion before, during, and after the fatigue protocol or rest period. RESULTS: We found a significant increase in total errors from pretest to posttest in the fatigue group (14.36 +/- 4.73 versus 16.93 +/- 4.32), a significant decrease in errors in the control group (13.32 +/- 3.77 versus 11.08 +/- 3.88), and a significant difference between groups on the posttest. The rating of perceived exertion scores were significantly different between the fatigue and control groups at the middle (13.29 +/- 1.59 versus 6.23 +/- 0.83) and end (15.86 +/- 2.38 versus 6.15 +/- 0.55) of the fatigue or rest period. CONCLUSIONS: The BESS error scores increased immediately after the fatigue protocol, demonstrating that balance ability diminished. Clinicians who use the BESS as part of their sideline assessment for concussion should not administer the test immediately after a concussion due to the effects of fatigue.     

Inter-relationship between muscle morphology, mechanical output and electromyographic activity during fatiguing dynamic knee-extensions in untrained females

Changes in mechanical performance and electromyographic activity during fatiguing dynamic knee-extensions were evaluated with respect to muscle fibre type composition of the vastus lateralis muscle in nine sedentary female [23 (3) years] volunteers. The subjects performed 150 repetitive maximum knee-extensions using a Cybex dynamometer at 1.57?rad?·?s^?1. EMG activity was recorded from the vastus lateralis, the vastus medialis and the rectus femoris muscles. For each contraction, mean power frequency (MPF) and the root mean square (RMS) of the EMG were calculated, simultaneously with the peak torque (PT), contractional work (CW) and the mean power (MP). The MPF showed an initial decrease followed by a stable phase. The RMS increased during the initial seven contractions, after which a period of variability was displayed until about the 60th contraction. At the plateau level (last 50 contractions) the relative RMS values were not significantly different from the initial values. The PT, CW and MP increased during the initial five to ten contractions, after which a two-phase pattern was displayed, with a gradual decline followed by a stable phase. The absolute plateau level of MPF for the vastus lateralis muscle showed a significant negative correlation with the area percentage of type-1 fibres (r?=??0.71). Significant correlations were also demonstrated to occur between the absolute plateau levels of PT, CW and MP and the relative proportion of type-1 fibres (r?=?0.80, r?=?0.82 and r?=?0.82 respectively). Thus, in female subjects the mechanical performance and the MPF during fatigue are at least partly determined by muscle morphology.