Onset Of Muscle Activity Research Articles

Time Course of Changes in Novice Jumpers' Countermovement Vertical Jump Performance

Time course of changes in jump height was examined to assess whether it was related to changes in the underlying mechanics or muscle activity. In Phase I, 11 novice female students performed 10 maximal jumps for eight consecutive days from two force plates. Jump height, impulse duration (t(IMP)), and mean vertical ground reaction force (VGRF) were compared using repeated-measures analysis of variance. Jump height was significantly higher (7.7%) on Days 3-8 when compared to Days 1 and 2; t(IMP) and VGRF were unchanged across days. In a followup study (Phase II), 14 novice female students performed 10 maximal jumps for five consecutive days. Electromyographic activity of five leg muscles was recorded to identify the relative onset of each muscle's activity. Using repeated-measures analysis of variance, jump height was significantly higher (4.2%) on Days 2 to 5 compared to Day 1; however, no significant changes were found across Days, for t(IMP), VGRF, or the onset of muscle activity. The findings indicate that jump performance can improve rapidly in novice jumpers but the underlying muscle activation remained unchanged.

The influence of a balance training program on the electromyographic latency of the ankle musculature in subjects with no history of ankle injury

Background Balance training is often employed for the prevention of ankle injuries. However, until now, most of the studies have focused on the prevention of a recurrent injury. The objective of this study was to look into the effects of balance training on the onset of peroneal muscle activity in healthy subjects. Methods 34 participants (mean age = 19.5 years ± 1.5; height = 1.70 m ± 0.12; weight = 62.06 kg ± 11.24), physically active, with no history of injuries took part in this study. The participants underwent a 4-week balance training program using an ankle disk. Onset of peroneal muscles activation was measured using surface electromyography and a trap-door. Findings Parametric and non-parametric tests showed no significant differences between the control group and the experimental group ( P > 0.05). Interpretation The results indicate that the use of balance training, for a 4-week period with two training sessions per week, on physically active subjects with no history of injuries in the ankle joint, does not cause noteworthy changes on the onset of peroneal muscles activity.

Changes in Excitability of the Motor Cortex Associated with Internal Model Formation during Intrinsic Visuomotor Learning in the Upper Arm

Previous studies have shown that the primary motor cortex (M1) may drive part of the feed forward control of well learnt simple movements by specifying patterns of muscle activation. This study explored the role of the M1 in the feed forward control of newly formed movement patterns after motor adaptation. Ten healthy right-handed subjects performed planar, centre-out arm reaching movement trials with a robotic manipulandum in three phases: a null force field (baseline), a velocity-dependent force field (adaptation; 25 Nsm-1) and again in a null force field (deadaptation). Reaching error and voluntary EMG were recorded from the biceps and triceps before, during and after motor adaptation. We also explored the effects of motor adaptation on evoked responses to single and paired pulse Transcranial Magnetic Stimulation from the same muscles at different delays after a visual go command, but before the onset of voluntary muscle activity. After the force field was removed, subjects produced reaching overshoot characteristic of adaptive internal model formation. Following motor adaptation, there was a significant increase in corticospinal excitability, reduction in short interval intracortical inhibition and increase in short interval intracortical facilitation that was associated with a sustained increase in voluntary muscle activity in the biceps. The adaptation-driven increase in reaching overshoot coupled with the increase in voluntary activity, corticospinal and intracortical excitability in the biceps suggests that the M1 may specify some of the feed forward components of newly learnt internal models through the control of specific muscles.

Whole body lexical decision

When a person standing upright raises an arm on cue, muscles of the left and right sides of the body exhibit changes prior to and specific to the responding arm. We had standing participants perform a visual lexical decision task (“is this letter string a word?”), responding yes by raising one arm and no by raising the other arm. We recorded onset of the arm movement and onset of electromyographic activity in thigh, trunk, and shoulder muscles. We observed the expected responding arm specificity and found that the onset difference favoring word decisions was evident in similar magnitude at all measurement sites, with the difference at the levels of thigh, trunk and shoulder muscles available 225, 189, and 120 ms, respectively, prior to its manifestation at the level of arm movement. We discuss including (a) whole body reaction time along with event-related potentials in determining the decision-response, brain–body temporal relation and (b) response execution along with response initiation in investigating mental chronometry.

Surface muscle pressure as a measure of active and passive behavior of muscles during gait

While surface electromyography (SEMG) can accurately register electrical activity of muscles during gait, there are no methods to estimate muscular force non-invasively. To better understand the mechanical behavior of muscle, we evaluated surface muscle pressure (SMP) in conjunction with SEMG. Changes in anterior thigh radial pressure during isometric contractions and gait were registered by pressure sensors on the limb. During isometric knee extensions by a single subject, SMP waveforms correlated well with SEMG ( r = 0.97), and SEMG onsets preceded those of SMP by 35–40 ms. SMP and SEMG signals were simultaneously recorded from the quadriceps of 10 healthy subjects during gait at speeds of 0.4, 0.8, 1.1, 1.4 and 2.2 m/s. Muscle activity onset and cessation times were objectively determined for both modalities, and results showed high intra-class correlations. SMP waveforms were highly consistent from stride to stride, while SEMG waveforms varied widely. SEMG waveforms were typically brief, while SMP waveforms tended to be biphasic and outlasted the SEMG by approximately 40% of gait cycle at all speeds. These results are consistent with mechanical models of muscle, and demonstrate the use of SMP to estimate the timing of knee extensor muscle stiffness during gait.

Changes in stepping response to lateral perturbations immediately following a single bout of physical activity

Fatiguing exercise can adversely alter postural stability and therefore may contribute to falling. However, older adults rarely perform exercise to fatigue. This study aimed to determine whether undertaking a single bout of moderate-intensity physical activity, similar to that experienced during daily activity or rehabilitation, altered the ability to recover balance with an outward step response to a lateral perturbation. Thirty-four healthy older adults (mean: 76±5 years) and 31 healthy young adults (29±6 years) underwent a 14-minute, self-paced, moderate-intensity physical activity protocol. Before and immediately after the protocol, their responses to lateral waist-pull perturbations were recorded. For participants who used a single outward step response before and after the perturbation, the changes to the timing of the step phases and the hip abductor muscle activity onsets were compared. Young adults responded with an outward step in 55% of trials before and 70% after activity, whereas this frequency was 35% before and 36% after among older adults. When performed, the timing of steps and muscle activity onsets were not adversely altered following the physical activity in either group, apart from a slightly later stance limb gluteus medius onset after activity, found in both groups. Before and after activity, older adults responded with a single outward step to arrest a fall less frequently than young adults. This may place older adults at risk of overbalancing. However, when responding with this strategy, both young and older adults demonstrated few changes immediately following moderate-intensity physical activity compared with before. They appear to be not adversely affected by moderate physical activity.

Dynamic postural stability is not impaired by moderate-intensity physical activity in healthy or balance-impaired older people

Older people are increasingly being encouraged to be more physically active but this may lead to physiological fatigue, tiredness and other effects, which, at high levels, can adversely alter postural stability. However, older adults rarely perform physical activity at high intensities. This study aimed to determine whether a single bout of moderate-intensity physical activity, similar to that experienced during daily living, alters dynamic postural stability, particularly among those at risk of falling. Thirty-one healthy young, 33 healthy older and 21 balance-impaired older, adults performed a rapid, voluntary step-up task before and immediately after a 14min, self-paced, moderate-intensity physical activity protocol. Timing of step components from vertical ground reaction forces, mediolateral displacement of center of pressure, and onset and amplitude of hip abductor muscle activity were recorded during the step task. All groups demonstrated the same changes after the activity, with slightly shorter weight-shift phase duration, smaller displacement of the center of pressure towards the stance leg during weight shifting, and earlier onset of stance leg gluteus medius activity. These changes indicate improved coordination of the step task after activity. Thus this study showed that dynamic postural stability is not adversely affected immediately following moderate-intensity physical activity, even among balance-impaired elderly.

Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: The effects of Latent Myofascial Trigger Points

Background Latent Myofascial Trigger Points are pain-free neuromuscular lesions that have been found to affect muscle activation patterns in the unloaded state. The aim was to extend these observations to loaded motion by investigating muscle activation patterns in upward scapular rotator muscles (upper and lower trapezius and serratus anterior) hosting Latent Myofascial Trigger Points simultaneously with lesion-free synergists for shoulder abduction (infraspinatus and middle deltoid). This approach allowed examination of the effects of these lesions on both their hosts and their lesion-free synergists in order to understand their effects on the performance of shoulder abduction. Methods Surface electromyography was employed to measure the timing of onset of muscle activation of the upper and lower trapezius and serratus anterior (upward scapular rotators), infraspinatus (rotator cuff) and middle deltoid (abductor of the arm) initially without load and then with light (1–4 kg) dumbbells. Comparisons were made between control (no Latent Trigger Points; n = 14) and Latent Trigger Point ( n = 28) groups. Findings The control group displayed a relatively stable sequence of muscle activation that was significantly different in timing and variability to that of the Latent Trigger Point group in all muscles except middle deltoid (all P < 0.05). The Latent Trigger Point group muscle activation pattern under load was inconsistent, with the only common feature being the early activation of the infraspinatus. Interpretation The presence of Latent Trigger Points in upward scapular rotators alters the muscle activation pattern during scapular plane elevation, potentially predisposing to overuse conditions including impingement syndrome, rotator cuff pathology and myofascial pain.

Ultrasound Tissue Doppler Imaging Reveals No Delay in Abdominal Muscle Feed-Forward Activity During Rapid Arm Movements in Patients With Chronic Low Back Pain

Cross-sectional study. Comparison of the timing of onset of lateral abdominal muscle activity during rapid arm movements in patients with nonspecific chronic low back pain (cLBP) and back-pain-free controls. Rapid movements of the arm are normally associated with prior activation of trunk-stabilizing muscles in readiness for the impending postural perturbation. Using invasive intramuscular electromyography techniques, studies have shown that this feed-forward function is delayed in some patients with low back pain (LBP). Ultrasound tissue Doppler imaging (TDI) provides an ultrasound method for quantifying muscle activation in a noninvasive manner, allowing investigation of larger groups of patients and controls. Ninety-six individuals participated (48 patients with cLBP and 48 matched LBP-free controls). During rapid shoulder flexion, abduction, and extension, surface electromyographic signals from the deltoid and motion-mode TDI images from the contralateral lateral abdominal muscles were recorded simultaneously. The onset of muscle activity was given by changes in the tissue velocity of the abdominal muscles, as measured with TDI. Pain and disability in the patients were assessed using standardized questionnaires. Data were analyzed using repeated measures analysis of variance. In both groups, feed-forward activity of the lateral abdominal muscles was recorded during arm movements in all directions. The main effect of "group membership" revealed no significant difference between the groups for the earliest onset of abdominal muscle activity (P = 0.398). However, a significant "group x body side" interaction (P = 0.015) was observed, and this was the result of earlier onsets in the cLBP group than controls for the abdominal muscles on the right (but not left) body side. No relationship was found between the time of onset of the earliest abdominal muscle activity and pain intensity, pain frequency, pain medication usage, or Roland Morris disability scores. Patients with cLBP did not show a delayed onset of feed-forward activation of the lateral abdominal muscles during rapid arm movements. Earlier activation was observed for one body side compared with the controls. However, the clinical relevance of this finding remains obscure, especially because there was no relationship between the onset of activation and any clinical parameters.

Innovative gait robot for the repetitive practice of floor walking and stair climbing up and down in stroke patients

BackgroundStair climbing up and down is an essential part of everyday's mobility. To enable wheelchair-dependent patients the repetitive practice of this task, a novel gait robot, G-EO-Systems (EO, Lat: I walk), based on the end-effector principle, has been designed. The trajectories of the foot plates are freely programmable enabling not only the practice of simulated floor walking but also stair climbing up and down. The article intended to compare lower limb muscle activation patterns of hemiparetic subjects during real floor walking and stairs climbing up, and during the corresponding simulated conditions on the machine, and secondly to demonstrate gait improvement on single case after training on the machine.MethodsThe muscle activation pattern of seven lower limb muscles of six hemiparetic patients during free and simulated walking on the floor and stair climbing was measured via dynamic electromyography. A non-ambulatory, sub-acute stroke patient additionally trained on the G-EO-Systems every workday for five weeks.ResultsThe muscle activation patterns were comparable during the real and simulated conditions, both on the floor and during stair climbing up. Minor differences, concerning the real and simulated floor walking conditions, were a delayed (prolonged) onset (duration) of the thigh muscle activation on the machine across all subjects. Concerning stair climbing conditions, the shank muscle activation was more phasic and timely correct in selected patients on the device. The severely affected subject regained walking and stair climbing ability.ConclusionsThe G-EO-Systems is an interesting new option in gait rehabilitation after stroke. The lower limb muscle activation patterns were comparable, a training thus feasible, and the positive case report warrants further clinical studies.

Teager–Kaiser energy operator signal conditioning improves EMG onset detection

Accurate identification of the onset of muscle activity is an important element in the biomechanical analysis of human movement. The purpose of this study was to determine if inclusion of the Teager–Kaiser energy operator (TKEO) in signal conditioning would increase the accuracy of popular electromyography (EMG) onset detection methods. Three methods, visual determination, threshold-based method, and approximated generalized likelihood ratio were used to estimate the onset of EMG burst with and without TKEO conditioning. Reference signals, with known onset times, were constructed from EMG signals collected during isometric contraction of the vastus lateralis (n = 17). Additionally, vastus lateralis EMG signals (n = 255) recorded during gait were used to evaluate a clinical application of the TKEO conditioning. Inclusion of TKEO in signal conditioning significantly reduced mean detection error of all three methods compared with signal conditioning without TKEO, using artificially generated reference data (13 vs. 98 ms, p < 0.001) and also compared with experimental data collected during gait (55 vs. 124 ms, p < 0.001). In conclusion, addition of TKEO as a step in conditioning surface EMG signals increases the detection accuracy of EMG burst boundaries.

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

Evidence of Neuromuscular Adaptation According to Motor Sequential Learning in the Serial Reaction Time Task

[Purpose] The aim of the current study was to investigate whether or not motor sequential learning leads a reduction in the temporal processing in terms of the onset of muscle activation and movement initiation as well as final motor response in a serial reaction time (SRT) task. [Subjects] We recruited 24 healthy subjects with no history of neurological or orthopedic problems. The subjects were randomly divided into a training group and a control group. [Methods] In response to five visual stimuli, subjects were instructed to move or press a moveable arm/button, and to return it toward the central position as quickly as possible, according to the corresponding stimuli. Kinetic parameters (i.e. onset of muscle activation and movement initiation, reaction time) were analyzed before and after training/controlled sessions over two consecutive days for each group. [Results] Following motor sequential learning, the temporal processing between the visual stimuli and each of three predetermined onsets were significantly declined. There were no significant changes in the control group. [Conclusion] The reduction in the total process to final motor response resulting from motor sequential learning may be attributed to rapid onset of muscle activation and movement initiation. Furthermore, neuromuscular adaptation played an important role in accomplishing rapid temporal processing after motor sequential learning.

Neuromuscular Adaptation Induced by Motor Imagery Training in the Serial Reaction Time Task

[Purpose] This study examined whether motor imagery leads to a decrease in the temporal process in terms of the onset of muscle activation and reaction time according to acquisition of motor skills in a serial reaction time (SRT) task. [Subjects] Forty one healthy, right-handed subjects with no history of neurological, orthopedic, or psychiatric disorders were enrolled in this study. The subjects were assigned randomly to the motor training group (n=13), motor imagery group (n=14), and control group (n=11). [Methods] After six visual stimuli, the subjects were instructed to move or press a moveable arm/button according to the corresponding stimuli. However, the motor imagery group performed the task without actual movement in the same task paradigm. The kinetic parameters (i.e. muscle activation and movement initiation) were analyzed before and after the training/controlled session over three consecutive days with two repetitions per day for each group. [Results] After motor skill acquisition, the motor training group and motor imagery group showed a significant decrease in processing times between the visual stimuli and two predetermined onsets, which consisted of the onset of muscular activation and reaction time. However, there were no significant changes in the control group. [Conclusion] The decrease in processing time through motor imagery can be attributed to the rapid onset of muscle activation and movement initiation, which might be induced by neuromuscular adaptation in the motor performance phase. Furthermore, we assumed that imagining the performance of a motor task could contributes to improving the motor performance in motor sequential learning.

Auto-PEEP to Treat Obstructive Sleep Apnea

In this issue of the Journal of Clinical Sleep Medicine, Rosenthal et al.1 describe the results of a study assessing the ability of nasal expiratory resistors (PROVENT™) to reduce sleep disordered breathing in a group of OSA patients with a relatively wide range of apnea severity. A study such as this raises a number of fundamental questions:

Efecto del Kinesio taping sobre la respuesta refleja de los músculos bíceps femoral y gemelo externo

Objective To analyze the immediate effect of the application of Kinesio Tape (KT) on reflex response of biceps femoris and gastrocnemius lateralis subject to a sudden and unexpected perturbation applied to the knee by means of a technique known as quick release. Methods Eleven healthy individuals volunteered to take part in this study (23.6±3.0 years; 171.8±6.8 cm; and 63.3±9.7 kg). An electrogoniometer was used to determine the onset of the perturbation and superficial electromyography was recorded to compare the intensity and the latency of the reflex response of biceps and grastrocnemius under two different conditions: without bandage (control) and with bandage (KT). In order to assess the inter-experimenter reliability, two groups of researchers independently calculated the response intensity (peak of the normalized electromyography) and latency (the time it takes between the start of the perturbation and the onset of muscle activation). Results The data obtained by both groups were similar (t-test: p≥0.04). In addiction, with the exception of the activation peak of grastrocnemius in the KT condition (ICC=0.363), high correlations between groups were found for most of the variables (0.741≤ICC≤0.996). With regard to the effect of the bandage, significant differences between the control and the KT conditions were not found (t-test: p≥0.123). However, the observed trend was a muscular response of lower intensity and larger latency when the KT was used. Conclusions Our results suggest the application of KT does not have an immediate effect on the reflex response of the analyzed muscles.

Effect of axial load on anterior tibial translation when transitioning from non-weight bearing to weight bearing

Background While the application of compressive joint loads and thigh muscle activity are associated with anterior tibial translation in vitro, less is known during early load acceptance in vivo. We investigated the effects of increasing axial loads on anterior tibial translation and thigh muscle activity in healthy knees during transition from non-weight bearing to early weight bearing. Methods Participants (11 males, 11 females) underwent 20%, 40%, and 60% body weight acceptance trials at 20° knee flexion while electromagnetic sensors measured anterior tibial translation (mm), and surface electromyography recorded quadriceps and hamstring muscle onset times (ms) and amplitudes (% maximal voluntary isometric contraction). Repeated measures ANOVA compared values across loads. Pearson correlations examined relationships between anterior tibial translation and muscle onset times and amplitudes within each load. Findings As load increased, anterior tibial translation (Mean (standard deviation)) (20% = 4.7 (1.7) mm < 40% = 7.1 (1.9) mm < 60% = 8.8 (2.1) mm), and quadriceps (20% = 23.6 (14.9)% maximal voluntary isometric contraction <40% = 32.7 (11.8)% maximal voluntary isometric contraction <60% = 41.1 (13.5)% maximal voluntary isometric contraction) and hamstring (20% = 15.5 (15.7)% maximal voluntary isometric contraction <40% = 23.0 (16.4)% maximal voluntary isometric contraction <60% = 27.6 (19.1)% maximal voluntary isometric contraction) activation increased, while quadriceps (20% = 96.7 (28.4) ms > 60% 80.2 (21.8) ms) and hamstring (20% = 141.5 (65.0) ms and 40% = 126.3 (68.8) > 60% 107.6 (28.4) ms) onset times decreased ( P ⩽ 0.05). There were no relationships between anterior tibial translation and muscle activation amplitudes ( R = 0.033–0.294) or onset times ( R = −0.031–0.374) ( P > 0.09). Interpretation Greater axial loads near full knee extension during early weight acceptance result in greater anterior tibial translation, regardless of faster and stronger activation amplitudes. These findings support injury prevention programs aimed to reduce impact forces as they may in turn reduce anterior tibial translation and corresponding ligamentous strain during dynamic activity.

Contingent negative variations associated with command swallowing in humans

To clarify the role of the cerebral cortex in the swallowing movement, the difference between the waveforms of contingent negative variation (CNV) for the command swallowing and movement-related cortical potential (MRCP) obtained during the volitional swallowing task in humans was investigated. Subjects were instructed to swallow their saliva as quickly as possible in response to a sound signal 4s after the onset of a self-paced breath holding in the command swallowing task or to swallow it while holding their breath for 4s in the volitional swallowing task. CNV and MRCP appeared at five recording areas 1.5 and 2.0s before the onset of the suprahyoid muscle activation determined by the electromyography (EMG) during the command swallowing and volitional swallowing tasks, respectively. The CNV amplitude during the command swallowing task was significantly higher than the MRCP amplitude during the volitional swallowing task (p<0.01). However, the suprahyoid muscle activities during both tasks were not significantly different (p>0.05). These results indicated that CNV may reflect the activities of the prefrontal cortex, in addition to the supplementary motor area, suggesting that the processing of the cue to swallow activates brain areas more widely than the volitional swallowing itself. It is possible to clarify the cognitive functions associated with command swallowing by analyzing CNV.

Prolonged Alterations In Hindlimb Emg Following Acl Transection In An Experimental Model Of Osteoarthritis

Alterations in knee joint loading and hind limb kinematics following anterior cruciate ligament transection (ACLT) have been associated with the onset of osteoarthritis (OA) through a reduction in joint loads. Knee joint loads have been directly measured nine days following ACLT, and subsequent changes in joint kinematics have been documented over the span of one year. However, the magnitude and duration of muscle activation adaptations in the hindlimb remain unknown following ACLT. PURPOSE: To quantify long-term changes in cat hindlimb muscle activation patterns following ACLT. METHODS: In this pilot study, indwelling bipolar electromyographic (EMG) electrodes were surgically implanted in four synergist muscle pairs on the cat hindlimb: rectus femoris (RF) and vastus lateralis (VL); semitendonosis (ST) and semimembranosus (SM); extensor digitorum longus (EDL) and tibialis anterior (TA); and medial gastrocnemius (MG) and soleus (SOL). EMG and high speed video data were recorded during level treadmill walking before ACLT and at 1, 2, 3, 4, and 6 weeks, and at 2, 6, 8, and 9 months following ACLT. RESULTS: Following ACLT, there was a reduction in mean EMG activation of the VL during stance, with an immediate increase in mean EMG amplitude in the RF during swing phase only. Both the SM and ST increased activity during stance phase for nine months after ACLT. Following ACLT, the EDL exhibited an extra burst of activity just prior to, or at paw strike in addition to the increased activity at paw off. Activity in the MG also increased during stance up to nine months, and the onset of muscle activation occurred earlier following ACLT for the SOL and MG. CONCLUSION: Following ACLT the knee flexor and extensor muscles demonstrate compensatory activation patterns that may stiffen the hindlimb, and predispose the knee joint to increased loads. The two-joint EDL muscle is recruited at paw strike following ACLT, suggesting that this muscle may function to assist in stabilizing the ACL deficient joint as a knee extensor in co-contraction with the hamstring muscles. Furthermore, long term increases in activation of the dorsiflexor and plantarflexor muscles during stance may further contribute to increasing joint loads leading to OA.

Application of Autocorrelation and Cross-correlation Analyses in Human Movement and Rehabilitation Research

Technical note. To provide background theory and information and to describe relevant applications of autocorrelation and cross-correlation methodology as they apply to the field of motor control in human movement and rehabilitation research. Commonly used methodologies for pattern and event recognition, determination of muscle activation timing for investigation of movement coordination, and motor control are generally difficult to implement, particularly with large datasets. A brief description of the underlying mathematical theory of correlation analyses is given, followed by 4 different examples of how this methodology is useful for research in the movement sciences. Examples demonstrating the utility of correlation analyses are presented from several different studies conducted at the University of Waterloo. Autocorrelation was used to demonstrate the presence of 60-Hz noise in an electromyography signal that was not visible in the raw data. A "top-down" paraspinal muscle activation pattern was demonstrated for healthy adults during gait, with the use of cross-correlation. Cross-correlation was also used to quantify coactivation of bilateral gluteus medius muscles during standing in individuals who developed low-back pain. Gender differences in gluteus medius control of mediolateral center of pressure were seen with the use of cross-correlation. Autocorrelation and crosscorrelation have been shown to be an effective tool for several different applications in the movement sciences. Examples of the method's utility include noise detection within a signal, determination of relative muscle activation onsets for postural control, objective quantification of muscle coactivation, and relating muscle activations with mechanical events.