Onset Of EMG Activity Research Articles

Crossed Corticospinal Facilitation Between Arm and Trunk Muscles Correlates With Trunk Control After Spinal Cord Injury.

Objective: To investigate whether crossed corticospinal facilitation between arm and trunk muscles is preserved following spinal cord injury (SCI) and to elucidate these neural interactions for postural control during functional arm movements.Methods: Using transcranial magnetic stimulation (TMS) in 22 subjects with incomplete SCI motor evoked potentials (MEPs) in the erector spinae (ES) muscle were examined when the contralateral arm was at rest or performed 20% of maximal voluntary contraction (MVC) of biceps brachii (BB) or triceps brachii (TB). Trunk function was assessed with rapid shoulder flexion and forward-reaching tasks.Results: MEP amplitudes in ES were increased during elbow flexion in some subjects and this facilitatory effect was more prominent in subjects with thoracic SCI than in the subjects with cervical SCI. Those who showed the increased MEPs during elbow flexion had faster reaction times and quicker anticipatory postural adjustments of the trunk in the rapid shoulder flexion task. The onset of EMG activity in ES during the rapid shoulder flexion task correlated with the trunk excursion in forward-reaching.Conclusions: Our findings demonstrate that crossed corticospinal facilitation in the trunk muscles can be preserved after SCI and is reflected in trunk control during functional arm movements.

Feedforward activation of the quadratus lumborum during rapid shoulder joint abduction

This study aimed to clarify the difference in the onset of EMG activity between eight trunk muscles, including the anterior (QL-a) and posterior (QL-p) layers of the quadratus lumborum during rapid shoulder joint abduction. Thirteen healthy men participated in this study. Electromyography of the QL-a, QL-p, transversus abdominis (TrA), internal oblique (IO), external oblique (EO), rectus abdominis (RA), lumbar multifidus (LMF), lumbar erector spinae (LES) on non-movement side, and middle deltoid (MD) on the movement side were measured. Subjects who were standing in a relaxed position performed rapid shoulder abduction with the dominant hand after light stimulus with or without a 3 kg wrist weight. Two-way ANOVA (muscles × weight conditions) was used to compare the onset of trunk muscles relative to that of MD. There was a significant main effect of the muscles. The onset of the QL-a, QL-p, and TrA was significantly earlier than that of the IO, EO, LMF, and LES (P < 0.01). This result suggests that the activities of the QL-a, QL-p, and TrA have a crucial role in controlling the center of mass within the base of support and stabilizing the lumbar spine in the coronal plane during shoulder abduction.

Recruitment of rat diaphragm motor units across motor behaviors with different levels of diaphragm activation

Phrenic motor neurons are recruited across a range of motor behaviors to generate varying levels of diaphragm muscle (DIAm) force. We hypothesized that DIAm motor units are recruited in a fixed order across a range of motor behaviors of varying force levels, consistent with the Henneman Size Principle. Single motor unit action potentials and compound DIAm EMG activities were recorded in anesthetized, neurally intact rats across different motor behaviors, i.e., eupnea, hypoxia-hypercapnia (10% O2 and 5% CO2), deep breaths, sustained airway occlusion, and sneezing. Central drive [estimated by root-mean-squared (RMS) EMG value 75 ms after the onset of EMG activity (RMS75)], recruitment delay, and onset discharge frequencies were similar during eupnea and hypoxia-hypercapnia. Compared with eupnea, central drive increased (∼25%) during deep breaths, and motor units were recruited ∼12 ms earlier (P < 0.01). During airway occlusion, central drive was ∼3 times greater, motor units were recruited ∼30 ms earlier (P < 0.01), and motor unit onset discharge frequencies were significantly higher (P < 0.01). Recruitment order of motor unit pairs observed during eupnea was maintained for 98%, 87%, and 84% of the same pairs recorded during hypoxia-hypercapnia, deep breaths, and airway occlusion, respectively. Reversals in motor unit recruitment order were observed primarily if motor unit pairs were recruited <20 ms apart. These results are consistent with DIAm motor unit recruitment order being determined primarily by the intrinsic size-dependent electrophysiological properties of phrenic motor neurons.

Low-power polling mode of the next-generation IMES2 implantable wireless EMG sensor.

The IMES1 Implantable MyoElectric Sensor device is currently in human clinical trials led by the Alfred Mann Foundation. The IMES is implanted in a residual limb and is powered wirelessly using a magnetic field. EMG signals resulting from the amputee's voluntary movement are amplified and transmitted wirelessly by the IMES to an external controller which controls movement of an external motorized prosthesis. Development of the IMES technology is on-going, producing the next-generation IMES2. Among various improvements, a new feature of the IMES2 is a low-power polling mode. In this low-power mode, the IMES2 power consumption can be dramatically reduced when the limb is inactive through the use of a polled sampling. With the onset of EMG activity, the IMES2 system can switch to the normal higher sample rate to allow the acquisition of high-fidelity EMG data for prosthesis control.

A laser-supported lowerable surface setup to study the role of ground contact during stepping

We introduce a laser-supported setup to study the influence of afferent input on muscle activation during walking, using a movable ground platform. This approach allows investigating if and how the activity of stance phase muscles of an insect (e.g. stick insect) responds to a missing ground contact signal. The walking surface consists of a fixed and a lowerable part, which can be lowered to defined levels below the previous ground level at any time point during a walking sequence. As a consequence, the leg under investigation finds either a lower ground level or no ground support at all. The lowerable walking surface consists of a 49mm×34mm stainless steel surface, made slippery and equipped for tarsal contact monitoring, similar to the system that was described by Gruhn and colleagues (Gruhn et al., 2006). The setup controller allows pneumatic lowering of the surface and subsequent detection of tarsal entry into the previous ground level with the help of a thin sheet of laser light and a corresponding detector. Here, we describe basic properties of the new setup and show the results of first experiments to demonstrate its use for the study of sensory and central influences in stepping of a small animal. In the experiments, we compare the effect of ground-support (“control”) with either steps into the hole (SiH), ground support at a lower surface level, or the amputation of the tarsus on the onset of EMG activity in the flexor tibiae muscle of the stick insect.

Non-stationarity and power spectral shifts in EMG activity reflect motor unit recruitment in rat diaphragm muscle

We hypothesized that a shift in diaphragm muscle (DIAm) EMG power spectral density (PSD) to higher frequencies reflects recruitment of more fatigable fast-twitch motor units and motor unit recruitment is reflected by EMG non-stationarity. DIAm EMG was recorded in anesthetized rats during eupnea, hypoxia-hypercapnia (10% O2–5% CO2), airway occlusion, and sneezing (maximal DIAm force). Although power in all frequency bands increased progressively across motor behaviors, PSD centroid frequency increased only during sneezing (p<0.05). The non-stationary period at the onset of EMG activity ranged from ∼80ms during airway occlusion to ∼150ms during eupnea. Within the initial non-stationary period of EMG activity 80–95% of motor units were recruited during different motor behaviors. Motor units augmented their discharge frequencies progressively beyond the non-stationary period; yet, EMG signal became stationary. In conclusion, non-stationarity of DIAm EMG reflects the period of motor unit recruitment, while a shift in the PSD towards higher frequencies reflects recruitment of more fatigable fast-twitch motor units.

Spinal inhibition of descending command to soleus motoneurons is removed prior to dorsiflexion

It has recently been demonstrated that soleus motor-evoked potentials (MEPs) are facilitated prior to the onset of dorsiflexion. The purpose of this study was to examine if this could be explained by removal of spinal inhibition of the descending command to soleus motoneurons. To test this, we investigated how afferent inputs from the tibialis anterior muscle modulate the corticospinal activation of soleus spinal motoneurons at rest, during static contraction and prior to movement. MEPs activated by transcranial magnetic stimulation (TMS) and Hoffmann reflexes (H-reflexes), activated by electrical stimulation of the posterior tibial nerve (PTN), were conditioned by prior stimulation of the common peroneal nerve (CPN) at a variety of conditioning-test (CT) intervals. MEPs in the precontracted soleus muscle were inhibited when the TMS pulse was preceded by CPN stimulation with a CT interval of 35 ms, and they were facilitated for CT intervals of 50-55 ms. A similar inhibition of the soleus H-reflex was not observed. To investigate which descending pathways might be responsible for the afferent-evoked inhibition and facilitation, we examined the effect of CPN stimulation on short-latency facilitation (SLF) and long-latency facilitation (LLF) of the soleus H-reflex induced by a subthreshold TMS pulse at different CT intervals. SLF is known to reflect the excitability of the fastest conducting, corticomotoneuronal cells whereas LLF is believed to be caused by more indirect descending pathways. At CT intervals of 40-45 ms, the LLF was significantly more inhibited compared to the SLF when taking the effect on the H-reflex into account. Finally, we investigated how the CPN-induced inhibition and facilitation of the soleus MEP were modulated prior to dorsiflexion. Whereas the late facilitation (CT interval: 55 ms) was similar prior to dorsiflexion and at rest, no inhibition could be evoked at the earlier latency (CT interval: 35 ms) prior to onset of dorsiflexion. The observation that the CPN-induced inhibition of soleus MEPs disappears prior to onset of dorsiflexion may explain why soleus MEPs are facilitated prior to onset of dorsiflexion contraction. A possible mechanism involves the removal of inhibition of the descending command to the motoneurons at a spinal interneuronal level because the inhibition was seen in LLF and not in SLF, and the MEP inhibition was not observed in the H-reflex. The data illustrate that spinal interneuronal pathways modify descending commands to human spinal motoneurons and influence the size of MEPs elicited by TMS.

Efeito de diferentes calçados no ínicio da atividade eletromiográfica dos músculos estabilizadores da patela

Introdução: A síndrome da dor femoropatelar (SDFP) é caracterizada por uma dor difusa na região retopatelar. A SDFP tem maior prevalência em mulheres jovens e sua etiologia não é totalmente conhecida. Objetivo: O objetivo desse trabalho foi comparar a porcentagem de disparo inicial (PDI) dos músculos vasto medial oblíquo (VMO) e vasto lateral longo (VLL) de mulheres saudáveis com disfunção femoropatelar (SDFP) ao sentar e levantar de um banco, calçando sapatos de salto alto, tênis e descalças. Métodos: Vinte mulheres foram divididas em dois grupos: controle e SDFP. O início da atividade EMG dos músculos VMO e VLL foi registrada durante a realização das tarefas, executadas com diferentes calçados. Para a comparação das PDIs foi utilizado o teste Qui-quadrado com p0,05. Resultados: Verificou-se que o uso do tênis e do salto alto proporcionaram aumento da PDI no grupo controle. No entanto, nenhuma diferença foi observada no grupo SDFP. Conclusão: Os resultados sugerem que os indivíduos com SDFP não apresentam respostas adaptativas ao uso de diferentes calçados.

Does a SLAP lesion affect shoulder muscle recruitment as measured by EMG activity during a rugby tackle?

BackgroundThe study objective was to assess the influence of a SLAP lesion on onset of EMG activity in shoulder muscles during a front on rugby football tackle within professional rugby players.MethodsMixed cross-sectional study evaluating between and within group differences in EMG onset times. Testing was carried out within the physiotherapy department of a university sports medicine clinic. The test group consisted of 7 players with clinically diagnosed SLAP lesions, later verified on arthroscopy. The reference group consisted of 15 uninjured and full time professional rugby players from within the same playing squad. Controlled tackles were performed against a tackle dummy. Onset of EMG activity was assessed from surface EMG of Pectorialis Major, Biceps Brachii, Latissimus Dorsi, Serratus Anterior and Infraspinatus muscles relative to time of impact. Analysis of differences in activation timing between muscles and limbs (injured versus non-injured side and non injured side versus matched reference group).ResultsSerratus Anterior was activated prior to all other muscles in all (P = 0.001-0.03) subjects. In the SLAP injured shoulder Biceps was activated later than in the non-injured side. Onset times of all muscles of the non-injured shoulder in the injured player were consistently earlier compared with the reference group. Whereas, within the injured shoulder, all muscle activation timings were later than in the reference group.ConclusionsThis study shows that in shoulders with a SLAP lesion there is a trend towards delay in activation time of Biceps and other muscles with the exception of an associated earlier onset of activation of Serratus anterior, possibly due to a coping strategy to protect glenohumeral stability and thoraco-scapular stability. This trend was not statistically significant in all cases

An electrophysiological approach to the diagnosis of neurogenic dysphagia: implications for botulinum toxin treatment

Objectives:Botulinum toxin (BTX) injection into the cricopharyngeal (CP) muscle has been proposed for the treatment of neurogenic dysphagia due to CP hyperactivity. The aim was to determine whether an electrophysiological...

Electromyographic analysis of selected shoulder muscles during a rugby football tackle

BackgroundEpidemiological studies have shown that the incidence of shoulder injuries is increasing in rugby and the majority are related to the contact/tackle phase of play. However, no data currently exists that describes preparatory muscle activity during tackle. This information could aid in guiding training and rehabilitation, if available. The purpose of the study was to assess the sequence of onset of EMG activity of selected scapulohumeral muscles during rugby tackle. 15 healthy professional rugby players participated in the study. Surface EMG activity was assessed for timing of onset relative to time of impact during a modified tackle activity in pectorialis major, biceps brachii, latissimus dorsi, serratus anterior and infraspinatus muscles.ResultsOnset of activity occurred in all muscles prior to impact. Factorial ANOVA showed significant differences between muscles in activation timing (p = 0.0001), paired t-tests revealed that serratus anterior was activated prior to all other muscles tested (p < 0.04, for all comparisons), with comparison between all other muscles showing no significant differences (p > 0.05), except pectorialis major on all comparisons showed significantly later activation timing than all other muscles (p < 0.001).ConclusionMuscle activation timing may if not properly balanced around the shoulder girdle expose the glenohumeral joint to excessive load and stress. This paper demonstrates a simple method which sets out some preliminary normative data in healthy players. Further studies relating these data to injured players are required.

Task-dependent modulation of primary afferent depolarization in cervical spinal cord of monkeys performing an instructed delay task.

Task-dependent modulation of primary afferent depolarization (PAD) was studied in the cervical spinal cord of two monkeys performing a wrist flexion and extension task with an instructed delay period. We implanted two nerve cuff electrodes on proximal and distal parts of the superficial radial nerve (SR) and a recording chamber over a hemi-laminectomy in the lower cervical vertebrae. Antidromic volleys (ADVs) in the SR were evoked by intraspinal microstimuli (ISMS, 3-10 Hz, 3-30 microA) applied through a tungsten microelectrode, and the area of each ADV was measured. In total, 434 ADVs were evoked by ISMS in two monkeys, with onset latency consistently shorter in the proximal than distal cuffs. Estimated conduction velocity suggest that most ADVs were caused by action potentials in cutaneous fibers originating from low-threshold tactile receptors. Modulation of the size of ADVs as a function of the task was examined in 281 ADVs induced by ISMS applied at 78 different intraspinal sites. The ADVs were significantly facilitated during active movement in both flexion and extension (P<0.05), suggesting an epoch-dependent modulation of PAD. This facilitation started 400-900 ms before the onset of EMG activity. Such pre-EMG modulation is hard to explain by movement-induced reafference and probably is associated with descending motor commands.

Motor Adaptation during Slip-Perturbed Gait in Older Adults

[Purpose] The purpose of this study was to investigate adaptations to slip perturbations using a customized separated-belt treadmill in older adults. [Subjects] Forty-five healthy older subjects participated in this study. [Methods] Participants were requested to continue to walk against 20 slip perturbations during a 5-minute period. The magnitudes of the reactive responses were evaluated with the use of a tri-axial accelerometer attached to the subject's pelvis. Also, the latency to the onset of EMG activity and the magnitude of EMG activity were measured using surface electrodes placed on both sides of the erector spinae, rectus abdominis, biceps femoris, vastus medialis (VM), gastrocnemius medialis (GM), and tibialis anterior muscles. [Results] The magnitude of the reactive response in the second half of the perturbed walk was significantly more decreased than during the first half (p < 0.01). Decreases in the magnitude of EMG were also observed from VM and GM muscles (p < 0.01, p < 0.05, respectively), but the latency of each of the muscles was unchanged. [Conclusion] In conclusion, adaptations that may have contributed to the prevention of falls occurred in older adults. These adaptations might have been accomplished by a change in magnitude of muscle activity rather than by a change in timing.

Electrophysiologic patterns of oral-pharyngeal swallowing in parkinsonian syndromes

To assess the presence, severity, and differences in dysphagia in Parkinson disease (PD), Parkinson variant of multiple system atrophy (MSA-P), and progressive supranuclear palsy (PSP), and to study the pathophysiology of swallowing abnormalities in these disorders. We applied an electrophysiologic method to evaluate oral-pharyngeal swallowing. We analyzed the following measures: duration of EMG activity of suprahyoid/submental muscles (SHEMG-D); duration of laryngeal-pharyngeal mechanogram (LPM-D); duration of the inhibition of the cricopharyngeal muscle activity (CPEMG-ID); interval between onset of EMG activity of suprahyoid/submental muscles and onset of laryngeal-pharyngeal mechanogram (I-SHEMG-LPM); and swallowing reaction time (SRT). The prolongation of I-SHEMG-LPM was more typical in PD, whereas the most distinctive finding both in patients with PSP and MSA-P was the reduction or the absence of CPEMG-ID early in the course of the disease. Involvement of the peduncolo-pontine tegmental nucleus, with subsequent dysfunction of basal ganglia and of the medullary central pattern generator of swallowing, may account for the abnormalities detected in these parkinsonian syndromes. The method described was able to identify swallowing abnormalities also in patients without symptoms of dysphagia and to evaluate dysphagia severity in all patients.

Electromyographic analysis of the tackle within rugby football

EMG has previously been used to analyse muscle activation during shoulder rehabilitation programmes and during sports related activities There are no reports on the muscle activity around the shoulder during a standard tackle within rugby football, although there is epidemiological evidence stating that the incidence of injuries to the shoulder within professional rugby is between 0.5 and 1.0 per 1000 playing hours with several studies have highlighted the tackle as being the major cause of all injuries within rugby. The purpose of this study was to define the sequence of muscular activity in selected gleno and scapulo humeral muscles during a front on rugby football tackle. It is hoped then that this information can be utilised to develop muscle specific training and rehabilitation protocols, which may, ultimately minimise the incidence of injury, enhance sports-specific performance, and the career span of professional rugby players. Five healthy asymptomatic experienced Rugby Union players were examined. Surface EMG activity was assessed during a modified tackle activity against a tackle dummy. Onset of EMG activity was assessed in Pectorialis Major, Biceps Brachii, Latissimus Dorsi, Serratus Anterior and Infraspinatus relative to time of impact in the tackle. Onset of activity occurred in all muscles prior to impact. One way ANOVA showed significant differences between muscles in activation timing ( p = 0.0001 ), paired t -tests (with Bonferroni corrections) revealed that Serratus Anterior was activated prior to all other muscles tested ( p p > 0.05 ). These findings indicate consistent early activation of Serratus Anterior prior to impact, ahead of other muscles. Previous literature has reported decreased or inconsistent Serratus Anterior recruitment in swimmers with shoulder pathology, further research is required to discover if altered recruitment of Serratus Anterior is also related to shoulder injuries in rugby.

FC14.4 Short-latency intracortical inhibition preceding movement: Different time-course of modulation during simple and choice reaction time

Background: Motor preparation is associated with excitability changes along the corticospinal tract. In simple reaction time task (SRT), the motor-evoked potentials (MEP) to transcranial magnetic stimulation (TMS) are facilitated before onset of EMGactivity (EMGonset), and the short-latency intracortical inhibition (SICI) is reduced preceding the facilitatory changes.We examined the timing of those neural processes in choice reaction time task (CRT). Aim: To identify potential differences in SICI during SRT and CRT paradigms. Patients/Methods: Five subjects were requested to perform a hand pinch in response to a visual stimulus in the context of SRT/CRT paradigms. MEPs were recorded from the first dorsal interosseous. TMS was applied over the contralateral hand area at an intensity of 0.95 active motor threshold for conditioning stimuli and 1.2 resting motor threshold for test stimuli. We obtained sets of responses combining single and paired (interstimulus interval 2.5 ms) stimuli with control and movement trials. Test stimuli were applied at 100, 75, 50 and 25 ms with respect to EMGonset. We used ANOVA to determine the differences between control and test trials. Results: During SRT, significant reduction of SICI with respect to baseline values occurred at 50 ms before EMGonset, while MEP facilitation started 25 ms later. Reduction of SICI occurred significantly later during CRT than during SRT (p 0.05). Discussion: The time course of intracortical excitability changes before EMGonset is different in SRT and CRT. In SRT, with direct stimulus/response mapping, SICI reduction precedes MEP facilitation. In CRT, characterized by uncertain stimulus/response mapping, reduction of SICI and MEP facilitation occur in parallel. Conclusion: The timing of premovement modulation of SICI with respect to MEP facilitation before EMGonset depends on the behavioral context.

Initial Changes in Jump Height and Lower Extremity EMG across Five Consecutive Days in Novices

Practice is an important variable for improving motor skill performance; however, little is known about either the time course or causal mechanisms underlying changes in motor skill performance with practice. PURPOSE: The purpose was to investigate the time course of changes in vertical jump height during countermovement jumps and determine if changes in jump height were associated with alterations in either muscular activity or the mechanical parameters associated with jumping performance. METHODS: Ten novice (mean Day 1 jump height = 24.9 cm) college-age participants performed 10 jumps over five consecutive days from two Kistler force plates (1 kHz). Knowledge of results was given after each trial in an effort to evoke maximum efforts. Jump height, average vertical ground reaction force (VGRF), and duration of the takeoff phase (tTAKEOFF) were determined for the six intermediate trials daily and analyzed using separate 5x6 (days x trials) repeated measures ANO VAs. EMG data were simultaneously collected on days 1, 2 and 5 from five leg muscles (gluteus maximus, rectus femoris, vastus lateralis, biceps femoris and gastrocnemius) using a Noraxon telemetered EMG system (1 kHz) in accordance with ISEK standards. EMG onset relative to takeoff was determined for each muscle in each trial using visual estimation techniques and multiple experimenters. The EMG onset data were analyzed using separate 3x6 repeated measures ANO VAs. RESULTS: Jump height increased across days (F = 3.72, p<0.05) and post hoc analysis (pairwise t-tests) indicated that jump height on days 2 through 5 significantly (p<0.05) differed from Day 1 (average increase = 3.8%). Average VGRF and tTAKEOFF did not differ across days or trials. Vastus lateralis activity occurred earlier in the takeoff phase across days (Day 1 = 75%, Day 2 = 78% & Day 5 = 81% before takeoff, respectively); however, this change was significant only at the p<0.10 level. The onset of EMG activity did not change across days for the other muscles. Day by Trial interactions were not present for any variable. CONCLUSIONS: Significant increases in jump height occurred during the first 24 hours of the study, but no further increases in jump height occurred. As average VGRF, tTAKEOFF and the onset of muscle activity for four of the five muscles tested did not change across days, a common mechanism for increased jump height was not present. The results suggest that the subj ects adapted differently across days to improve their jump performance.

Initial Changes in Jump Height and Lower Extremity EMG across Five Consecutive Days in Novices

Practice is an important variable for improving motor skill performance; however, little is known about either the time course or causal mechanisms underlying changes in motor skill performance with practice. PURPOSE: The purpose was to investigate the time course of changes in vertical jump height during countermovement jumps and determine if changes in jump height were associated with alterations in either muscular activity or the mechanical parameters associated with jumping performance. METHODS: Ten novice (mean Day 1 jump height = 24.9 cm) college-age participants performed 10 jumps over five consecutive days from two Kistler force plates (1 kHz). Knowledge of results was given after each trial in an effort to evoke maximum efforts. Jump height, average vertical ground reaction force (VGRF), and duration of the takeoff phase (tTAKEOFF) were determined for the six intermediate trials daily and analyzed using separate 5×6 (days × trials) repeated measures ANO VAs. EMG data were simultaneously collected on days 1, 2 and 5 from five leg muscles (gluteus maximus, rectus femoris, vastus lateralis, biceps femoris and gastrocnemius) using a Noraxon telemetered EMG system (1 kHz) in accordance with ISEK standards. EMG onset relative to takeoff was determined for each muscle in each trial using visual estimation techniques and multiple experimenters. The EMG onset data were analyzed using separate 3x6 repeated measures ANO VAs. RESULTS: Jump height increased across days (F = 3.72, p<0.05) and post hoc analysis (pairwise t-tests) indicated that jump height on days 2 through 5 significantly (p<0.05) differed from Day 1 (average increase = 3.8%). Average VGRF and tTAKEOFF did not differ across days or trials. Vastus lateralis activity occurred earlier in the takeoff phase across days (Day 1 = 75%, Day 2 = 78% & Day 5 = 81% before takeoff, respectively); however, this change was significant only at the p<0.10 level. The onset of EMG activity did not change across days for the other muscles. Day by Trial interactions were not present for any variable. CONCLUSIONS: Significant increases in jump height occurred during the first 24 hours of the study, but no further increases in jump height occurred. As average VGRF, tTAKEOFF and the onset of muscle activity for four of the five muscles tested did not change across days, a common mechanism for increased jump height was not present. The results suggest that the subjects adapted differently across days to improve their jump performance.

Timing of Rotator Cuff Activation During Shoulder External Rotation in Throwers With and Without Symptoms of Pain

Fine-wire EMG rotator cuff onset time analysis in 2 matched groups of throwers with and without pain. To identify if there is a difference in the activation patterns of the rotator cuff muscles during a rapid shoulder external rotation task between throwers with and without pain. The coordinated action of the rotator cuff is recognized as essential for glenohumeral joint control in the throwing athlete. Identification of abnormalities occurring in muscle activation patterns for injured athletes is relevant when prescribing rehabilitative exercises. Twelve throwers with shoulder pain were compared to a matched group of 11 asymptomatic throwers. Participants were matched for age, height, body mass, and habitual activity. Fine-wire EMG electrodes were inserted into the subscapularis, supraspinatus, and infraspinatus. EMG activity was measured during a reaction time task of rapid shoulder external rotation in a seated position. The timing of onset of EMG activity was analyzed in relation to visualization of a light (reaction time) and to the onset of infraspinatus activity (relative latency). In the group with shoulder pain, the onset of subscapularis activity was found to be significantly delayed (reaction time, P = .0018; relative latency, P = .0005) from the onset of infraspinatus activity when compared to the control group. The presence of shoulder pain in these athletes was associated with a difference in the onset of subscapularis EMG activity during a rapid shoulder external rotation movement. This was an initial step in the understanding of the joint protection mechanisms of the glenohumeral joint and the problems that occur in throwers. This information may assist in providing future guidelines for more effective rehabilitation and prevention strategies for this condition.

19.14 Effect of lower body muscle fatigue on a whole body pointing task

Objective. The purpose of the study was to identify a sequential activation of lumbar and hip muscles in active prone hip extension from neutral position in subjects without a history of low back pain.Design. Using surface electromyography, the myoelectric activity onsets of agonistic and antagonistic hip muscles were recorded.Background. The development of low back pain is ascribed to changes of the muscle firing order in prone hip extension. There appeared to be no normative data on muscle firing order of the lumbar and hip musculature to provide a basis for recognizing variations.Methods. Fifteen healthy subjects performed standardized right hip extensions. Time-normalized onset of EMG activity in each muscle was measured for each trial.Results. A manova revealed significant (P < 0.01) differences between the activity onsets of synergistic muscles in hip extension.Conclusions. On the results it was concluded that the consistent muscle firing order of ipsilateral lumbar erector spinae, semitendinosus, contralateral lumbar erector spinae, tensor fasciae latae, and gluteus maximus demonstrate the characteristic pattern in prone hip extension. In future studies it is essential to evaluate also the hip extension pattern in functional upright conditions during gait and their relationship to spinal mechanics.