Muscle Onset Times Research Articles

Comparing Muscle Activity and Onset Time of Cervical and Thoracoscapular Muscles during Shoulder Flexion and Abduction in Individuals with and without Forward Head Posture

Comparing Muscle Activity and Onset Time of Cervical and Thoracoscapular Muscles during Shoulder Flexion and Abduction in Individuals with and without Forward Head Posture

Postural Control During Single-Leg Landing in Female Athletes After Anterior Cruciate Ligament Reconstruction.

Secondary anterior cruciate ligament (ACL) injury is a complication of ACL reconstruction (ACLR), which may result from altered neuromuscular control affecting anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs) required for maintaining balance during movement. However, it remains unclear how APAs and CPAs differ in single-leg landings post-ACLR compared to healthy subjects. The purpose of this study was to clarify the differences in muscle activities of APAs and CPAs, lower limb kinematics, and kinetics between athletes with a history of ACLR and healthy athletes during single-leg landing. Cross-sectional study. Eighteen female athletes were recruited and divided into ACLR (n = 9) and control groups (n = 9). The experimental task involved a single-leg landing from a 30 cm box. Joint angles and moments were determined using a 3-dimensional motion analysis system, while muscle activity was assessed using surface electromyography. Analysis intervals were divided into two phases: the APA phase (-150 ms to 50 ms) and the CPA phase (50 ms to 250 ms), with initial contact (0 ms) as the reference point. Muscle activity onset time was defined as the time when the baseline exceeded by the sum of mean values and 2 standard deviations. No significant differences were observed in muscle activity or onset time between the ACLR and control groups. However, an increased hip external rotation moment was observed during the CPA phase in the ACLR group. These findings suggest that APAs and CPAs of athletes who returned to sports more than 1 year post-ACLR may be similar. The increased hip external rotation moment in the ACLR group during the CPA phase could represent a specific compensatory strategy to decrease the hip internal rotation angle post-ACLR. III.

거북목을 가진 젊은 남성의 팔의 굽힘과 벌림 운동 시 목과 등어깨 근육의 근 활성도에 대한 머리자세 교정의 영향 : 단일그룹 반복측정 연구

거북목을 가진 젊은 남성의 팔의 굽힘과 벌림 운동 시 목과 등어깨 근육의 근 활성도에 대한 머리자세 교정의 영향 : 단일그룹 반복측정 연구

Cortical Changes of Dual Cognitive-Task Balance Training in Patients with Chronic Ankle Instability: A Randomized Trial.

Researchers have shown that patients with chronic ankle instability (CAI) have deficits in memory and attention allocation. This functional deficit affects the lower extremity performance. Motor-cognitive dual-task training may improve lower limb dysfunction caused by central nervous system injury. Whether dual-task training is more favorable than single-task training for neuromuscular control in patients with single-task training still needs to be further proven. To determine whether balance-cognitive dual-task training can influence cortical activity and has more effective treatment effects than balance single-task training. Randomized controlled clinical trial (Clinical Trials: XXX). Rehabilitation training room. After recruitment, twenty-four patients with CAI (age=22.33±2.43 years, height=175.62±7.7 cm, mass=70.63±14.59 kg) were block randomized into two groups. Protocols were performed three times per week for six weeks. The single-task group underwent one-leg static balance training with and without vision and hopping balance training. The dual-task group underwent balance and cognitive training (backward counting task). The follow variables were assessed before and after the interventions: cortical activity, proprioception, muscle onset time, and dynamic balance. We performed MANOVAs to compare changes of main effects and interactions across groups and time. A post-hoc Bonferroni test was performed for pairwise comparisons when there were significant interactions with the MANOVAs. Twenty-four participants successfully completed the six-week interventions. Proprioception, peroneus longus muscle onset time, and dynamic postural control improved significantly after the interventions in both groups (P<0.05). Dual-task training was superior to single-task training in improving JPS plantarflexion, shortening peroneus longus muscle onset time, and altering cortical activity(P<0.05). A six-week balance training program or balance combined with cognitive training could improve the functional deficits associated with CAI. Meanwhile, the dual-task training could improve cortical activity and lower extremity function.

Passenger muscle responses in emergency braking events with reclined seating

Emergency braking can generate forward displacement that may influence the effectiveness of protection in collisions, especially for passengers. The development of automated vehicles has enabled the diversification and rationalization of sitting positions, including reclined seating. However, the passenger response in pre-crash scenarios in reclined seating differs from that in standard seating, which poses different requirements for biofidelic human body models (HBMs) to evaluate passenger injuries in collisions. This study conducted emergency braking trials in vehicles at an initial velocity of 80 km/h. Five volunteers were exposed to approximately 1 g manual emergency braking (MEB), and the muscle responses at the front passenger seat with backrest angles of 25°, 45°, and 65° were recorded. The electromyography obtained from 14 muscles of the neck, torso, and lower extremity were normalized using maximum voluntary contractions (MVCs). In the quiet sitting phase, the activity levels were low (< 5% MVC) in all muscles for the three sitting positions. During emergency braking, the muscles are activated to restrict the body motion. There were differences in muscle amplitude and onset time in different backrest angles, with higher muscle activity levels in most muscles in a reclined sitting position. In particular, the sternocleidomastoid, rectus abdominis, and vastus medialis showed different patterns in the peak and steady-state phases. We found that the tibialis anterior was consistently activated at a lower level in all sitting postures (< 8% MVC), which indicates limited support of the shank for the body. The data provided in the paper are presented in corridors and intended for use in the development and validation of HBMs with active muscle models to simulate evasive maneuvers that potentially occur before a crash in the reclined sitting position.

Functional relationship between the foot intrinsic and extrinsic muscles in walking.

The intrinsic and extrinsic muscles are considered to stabilize the foot and contribute to propulsion during walking. This study aimed to clarify the functional relationship between intrinsic and extrinsic muscles during walking. Thirteen healthy men participated in this study. The muscle activities of the intrinsic muscles (quadratus plantae and abductor hallucis), and the extrinsic muscles (flexor hallucis longus, flexor digitorum longus, and tibialis posterior) were measured using fine-wire and surface electromyography during walking. The muscle onset timing after foot contact was calculated and compared among muscles using the one-way ANOVA. The stance phase was divided into early and late braking, and early and late propulsion phases. Muscle activity among phases was compared using repeated-measures ANOVA. The onset time of the abductor hallucis was significantly earlier than those of the flexor digitorum longus and tibialis posterior. The quadratus plantae demonstrated significantly earlier onset than that of the tibialis posterior. In the late propulsion phase, the activity of extrinsic muscles decreased, whereas intrinsic muscles were continuously active. Early activation of the intrinsic muscles may stabilize the foot for efficient torque production by the extrinsic muscles. Furthermore, the intrinsic muscles may contribute to the final push-off after the deactivation of extrinsic muscles.

Effect of speed and leading or trailing limbs on surface muscle activities during canter in Thoroughbred horses.

Given that Thoroughbred horses' canter is an asymmetric gait, not only speed but also leading or trailing limbs could affect muscle activities. However, the muscle activity during a canter remains poorly understood. Hence, we aimed to investigate speed and lead-side (leading or trailing) effects on surface electromyography (sEMG) during a canter. The sEMG data were recorded from left Musculus brachiocephalicus (Br), M. infraspinatus (Inf), long head of M. triceps brachii (TB), M. gluteus medius (GM), M. semitendinosus (ST), and M. flexor digitorum longus of seven Thoroughbreds with hoof-strain gauges at the left hooves. Horses cantered on a flat treadmill at 7, 10, and 13 m/s for 25 s each without lead change. Subsequently, the horses trotted for 3 min and cantered at the same speed and duration in the opposite lead side ("leading" at the left lead and "trailing" at the right lead). The order of the lead side and speed was randomized. The mean of 10 consecutive stride durations, duty factors, integrated-EMG values (iEMG) for a stride, and muscle onset and offset timing were compared using a generalized mixed model (P < 0.05). Stride durations and duty factors significantly decreased with speed regardless of the lead side. In all muscles, iEMG at 13 m/s significantly increased compared with 7 m/s (ranging from +15% to +134%). The lead-side effect was noted in the iEMG of Br (leading > trailing, +47%), Inf (leading > trailing, +19%), GM (leading < trailing, +20%), and ST (leading < trailing, +19%). In TB, GM, and ST, muscle onset in trailing was earlier than the leading, while offset in the leading was earlier in Br. In conclusion, different muscles have different responses to speed and lead side; thus, both the lead side and running speed should be considered during training and/or rehabilitation including canter or gallop.

Role of Rotated Head Postures on Volunteer Kinematics and Muscle Activity in Braking Scenarios Performed on a Driving Simulator

Occupants exposed to low or moderate crash events can already suffer from whiplash-associated disorders leading to severe and long-lasting symptoms. However, the underlying injury mechanisms and the role of muscle activity are not fully clear. Potential increases in injury risk of non-nominal postures, i.e., rotated head, cannot be evaluated in detail due to the lack of experimental data. Examining changes in neck muscle activity to hold and stabilize the head in a rotated position during pre-crash scenarios might provide a deeper understanding of muscle reflex contributions and injury mechanisms. In this study, the influence of two different head postures (nominal vs. rotation of the head by about 63 ± 9° to the right) on neck muscle activity and head kinematics was investigated in simulated braking experiments inside a driving simulator. The braking scenario was implemented by visualization of the virtual scene using head-mounted displays and a combined translational-rotational platform motion. Kinematics of seventeen healthy subjects was tracked using 3D motion capturing. Surface electromyography were used to quantify muscle activity of left and right sternocleidomastoideus (SCM) and trapezius (TRP) muscles. The results show clear evidence that rotated head postures affect the static as well as the dynamic behavior of muscle activity during the virtual braking event. With head turned to the right, the contralateral left muscles yielded higher base activation and delayed muscle onset times. In contrast, right muscles had much lower activations and showed no relevant changes in muscle activation between nominal and rotated head position. The observed delayed muscle onset times and increased asymmetrical muscle activation patterns in the rotated head position are assumed to affect injury mechanisms. This could explain the prevalence of rotated head postures during a crash reported by patients suffering from WAD. The results can be used for validating the active behavior of human body models in braking simulations with nominal and rotated head postures, and to gain a deeper understanding of neck injury mechanisms.

Differences In Lower-extremity Muscle Activation Patterns During Anticipated Or Unanticipated Single-leg Drop Jump Tasks

PURPOSE: To examine the muscle activation patterns of the lower-extremity during an anticipated or unanticipated single-leg drop jump task. METHODS: Surface electromyography (EMG, 1,500 Hz) was collected from 17 healthy young male subjects (173 cm; 72 kg), including gluteus medius (GM), rectus femoris (RF), vastus medialis (VM), semitendinosus (ST), biceps femoris (BF), tibialis anterior (TA), and medial gastrocnemius (MG) on the dominant leg. Subjects were asked to drop down from a wooden box with a height of 40-cm with their dominant leg (landing), then immediately jump as high as possible (jumping). For the anticipated condition, subjects were informed of the drop jump task prior to the initial drop. For the unanticipated condition, the specific task was visually shown on the light-emitting diode screen (upwards or downwards arrow for jumping or landing, respectively), which triggered by the infrared sensor when a subject’s foot was sensed prior to initial contact (average time from sensor to initial contact: 48-ms). The data during unanticipated jumping were selectively compared to those during anticipated jumping. Time of muscle onset (time to reach 8% of peak amplitude) and time to peak amplitude were identified during the pre-contact phase (before initial contact: BIC) and the post-contact phase (after initial contact: AIC), and then analysed through t-tests (p < 0.05) and Cohen’s d effect size (d). RESULTS: Time of muscle onset of the BF (t = -2.21, p = 0.03) and TA (t = -2.76, p = 0.01) were different. Specifically, onset of the BF (116-ms BIC, d = 0.45) and TA (174-ms BIC, d = 0.56) was faster in the anticipated than the unanticipated condition (BF: 54-ms BIC; TA: 118-ms BIC). Time to peak amplitude of the GM (t = -2.51, p = 0.01), VM (t = -2.33, p = 0.02), ST (t = -2.01, p = 0.05), and BF (t = -2.69, p = 0.01) were different. Specifically, time to peak of the GM (350-ms AIC, d = 0.52), VM (365-ms AIC, d = 0.47), ST (374-ms AIC, d = 0.41), and BF (454-ms AIC, d = 0.54) was faster in the anticipated than unanticipated (GM: 439-ms AIC; VM: 451-ms AIC; ST: 472-ms AIC; BF: 646-ms AIC). CONCLUSIONS: When the task was unanticipated (between either landing or jumping after a drop landing from a 40-cm), the onset of the BF and TA were delayed during pre-contact while the GM, VM, ST, and BF were delayed reaching the peak amplitude during the post-contact phase.

Wavelet-Based Assessment of the Muscle-Activation Frequency Range by EMG Analysis

The assessment of muscle-recruitment timing from electromyography (EMG) signal is relevant in different fields, including clinical gait analysis and robotic systems to interpret user&#x2019;s motion intention. However, available methods typically provide only information in time domain without evaluating muscle-activation frequency content. This study aims to propose a novel adaptative algorithm for detecting muscle activation in time-frequency domain based on continuous wavelet transform (CWT) analysis. Precisely, the novel contribution of the proposed algorithm consists of evaluating the frequency range of every muscle activations detected in time domain. Performances are evaluated on a test bench of 720 simulated and 105 real surface EMG signals, stratified for signal-to-noise ratio (SNR), and then validated against different reference algorithms. Outcomes indicate that the proposed approach can provide an accurate prediction of muscle onset and offset timing in both simulated (mean absolute error, MAE <inline-formula> <tex-math notation="LaTeX">$\approx 10$ </tex-math></inline-formula> ms) and real datasets (MAE &#x003C; 30 ms), minimally affected by the SNR variability and compatible with the timing of EMG-driven assistive devices. Concomitantly, the maximum frequency of the activations is computed, ranging from around 100 Hz up to almost 500 Hz. This suggests a large within-muscle between-muscle variability of the frequency range. In conclusion, the current study introduces a novel reliable wavelet-based algorithm to detect both time and frequency content of muscle activation, suitable in different conditions of signal quality.

A Study on the Relationship between Postural Control and Pain-Related Clinical Outcomes in Patients with Chronic Nonspecific Low Back Pain.

Objectives To explore the relationship between postural control and pain-related clinical outcomes in patients with chronic nonspecific low back pain (cNLBP). Methods Participants with cNLBP and healthy individuals were recruited. Muscle activities were recorded during internal and external perturbation tasks. Postural control capacity was assessed by muscle onset time and integrals of electromyography (iEMGs) of postural muscles during the phases of anticipatory postural adjustments (APAs) and compensatory postural adjustments (CPAs). Correlation analysis was employed to investigate the relationship between postural control capacity, pain, and disability. Results Twenty-seven patients with cNLBP and 27 healthy participants were recruited. Gastrocnemius (GA) muscle onset time was earlier in the cNLBP group than in the control group in the internal perturbation task. The onset time of GA and erector spinae (ES) of the cNLBP group was later than that of the controls in the external perturbation task. Disability level moderately correlated with the iEMGs of rectus abdominis (RA), GA, and external oblique (EO) during APAs. Pain score moderately correlated with the iEMGs of RA, EO, and ES during CPAs of perturbation tasks. Conclusion cNLBP participants had altered muscle activation strategy to maintain postural stability in response to perturbation. This study further discovered that pain-related disabilities of cNLBP participants were likely related to the APAs capacity, whereas the pain intensity may relate to the CPAs capacity. Pain and disability may therefore be related to the control process of the posture-related muscles.

Physiotherapy Rehabilitation in Subjects Diagnosed with Subacromial Impingement Syndrome Does Not Normalize Periscapular and Rotator Cuff Muscle Onset Time of Activation.

Clinicians suggest that rehabilitation of Subacromial Impingement Syndrome (SIS) should target improving movement patterns to ensure better clinical outcomes. Understanding changes in onset time of activation patterns and associated changes in clinical outcomes could improve our understanding of rehabilitation strategies. In this prospective longitudinal study, we examined neuromuscular firing patterns and clinical features before and after a standardized physiotherapy program in subjects diagnosed with SIS. Electromyography (EMG) recordings of eleven shoulder muscles were taken at the initial and discharge consultation in 34 male volunteers diagnosed with SIS. EMG recording was performed during flexion, scaption, and abduction at slow, medium, and fast speeds with a loaded (3 kg) and unloaded arm, as well as rotational motion, rotational strength, pain, and shoulder function. Completion of standardized shoulder physiotherapy program for SIS resulted in improvements in clinical outcomes. Resulted showed inconsistent differences of onset time of activation mainly in some of the periscapular muscles for all movements. No differences were seen on the EMG recordings for rotator cuff muscles. Differences in range of motion, strength and function were shown. Despite some changes in onset time of activation, this study was not able to demonstrate consistent changes of onset time of activation of the periscapular and rotator cuff muscles.

Think about it: Cognitive-motor dual-tasking affects sub-regional spine responses to unexpected trunk perturbations.

Cognitive motor interference (CMI) is a psychomotor phenomenon characterized by alterations in kinematic spatial-temporal parameters during concurrent cognitive and motor tasks (i.e. dual-tasking). Previous literature has demonstrated that cognitive-motor dual-tasking induces alterations gait parameters; however, the influence of CMI on spine reflexive motion has yet to be researched. The purpose of this study was to assess the influence of cognitive-motor dual-tasking during unexpected spine loading, in particular focusing on paraspinal muscle responses and spine sub-regional kinematic responses. To do this, the spine was perturbed by unexpectedly dropping a 6.8kg mass into the participants' hands during cognitive dual-task and control conditions. Intersegmental spine angles, paraspinal muscle onset latencies, baseline activations, and response magnitudes were measured. The results demonstrated that participants experienced greater spine flexion at all intersegmental levels during the cognitive dual-task condition compared to the control condition. Additionally, muscle onset latencies were significantly delayed in three of the four paraspinal muscles studied when performing the cognitive-motor dual-task. These results demonstrate that the additional cognitive load led to delayed muscle activation responses and subsequently greater intersegmental lumbar spine flexion in response to a sudden loading perturbation. This suggests that cognitive-motor dual-tasking may increase the risk of developing an acute spine injury under similar conditions.

Neuromuscular function in anterior cruciate ligament reconstructed patients at long-term follow-up

BackgroundThe permanence of neuromuscular adaptations following anterior cruciate ligament reconstruction is not known. The aim of this study was to compare bilateral muscle co-contraction indices, time to peak ground reaction force, and timing of muscle onset between anterior cruciate ligament reconstruction subjects 10–15 years post reconstruction with those of matched uninjured controls during a one-leg hop landing. MethodsNine healthy controls and 9 reconstruction subjects were recruited. Clinical and functional knee exams were administered. Lower limb co-contraction indices, time to peak ground reaction force, and muscle onset times were measured bilaterally. Differences in clinical and functional outcomes were assessed with unpaired t-tests, and mixed model repeated measures were used to examine effects of group, limb and interaction terms in electromyography measures. Findings89% of control knees were clinically “normal”, whereas only 33% of reconstructed knees were “normal”. Anterior cruciate ligament-reconstructed subjects tended to achieve shorter functional hop distances but demonstrated symmetrical lower limb electromyography measures that were no different from those of controls' with the exception that biceps femoris activation was delayed bilaterally prior to ground contact but was greater during the injury risk phase of landing. InterpretationWith the exception of hamstring activation, lower limb electromyography measures were largely similar between ligament-reconstructed and matched control subjects, which was in contrast to the clinical findings. This result brings into question the significance of neuromuscular function at this long-term follow-up but raises new questions regarding the role of symmetry and pre-injury risk.

Effects of Posture Correction Exercise on Muscle Activity and Onset Time during Arm Elevation in Subject with Forward Head and Rounded Shoulder Posture

Effects of Posture Correction Exercise on Muscle Activity and Onset Time during Arm Elevation in Subject with Forward Head and Rounded Shoulder Posture

Effects of a 12-week home exercise therapy program on pain and neuromuscular activity in patients with patellofemoral pain syndrome.

The aim of this study is to evaluate the effects of a 12-week home exercise therapy program on pain, function and neuromuscular activity of the vastus medialis and vastus lateralis. Fifty patients with patellofemoral pain syndrome were treated with a 12-week online home exercise program. The primary outcomes of pain and function were assessed at the 12-week follow-up using the Visual Analog Scale and Kujala Score, respectively. Secondary outcomes were the muscle onset time and the ratio of vastus medialis and vastus lateralis during different daily activities. After 12weeks, patients showed significant (p < 0.05) improvements of 27 points on the Visual Analog Scale and 10 points on Kujala Score. Differences in pre-post comparison regarding both temporal and amplitude-related neurophysiological differences between the vastus medialis and lateralis were only found when the subjects were divided into groups of different electromyographic patterns. Then changes in the pre-post comparison were particularly evident in the patient group with a delayed vastus medialis onset and a lower activity of the vastus medialis compared to the VL. Pain and function improved significantly after a home exercise therapy program in patients with patellofemoral pain syndrome. In addition, patients with a delayed onset or reduced activity of the vastus medialis compared to the vastus lateralis experienced a reduction in this imbalance.

Effect of predictability of the magnitude of a perturbation on anticipatory and compensatory postural adjustments.

Balance maintenance in response to a perturbation could be affected by the predictability of the magnitude of the body disturbance. We investigated anticipatory (APAs) and compensatory (CPAs) postural adjustments in response to perturbations of predictable and unpredictable magnitudes. Twenty young adults received series of perturbations of small or large magnitudes the order of which was varied. Electromyographic activity of six leg and trunk muscles and displacements of the center-of-pressure (COP) were recorded. The muscle onset time, integrals of muscle activity, and COP displacements in the anterior-posterior direction were analyzed during the APA and CPA phases. The results indicated that when the participants were exposed to the repeated perturbation magnitude, it became predictable and they generated APAs more precisely according to the magnitudes of the perturbation. Moreover, when the magnitude of perturbation changed unpredictably, the participants overestimated or underestimated the magnitudes of the perturbation, as they generated APAs based on their prior experience of dealing with the perturbation. The optimal adjustment of APAs occurred after five trials of repeated perturbations. The findings imply that the process of APAs and CPAs generation depends on the accuracy of the predictability of perturbation magnitudes.

앉은 자세에서 일어나 걷기 훈련이 만성 뇌졸중 환자의 발목 선행적 자세 조절과 다중 과제 수행력에 미치는 효과 : 사례군 연구

Sit-to-walk (STW) movement is a complex task characterized by starting one step before reaching a full standing posture and maintaining the body moment forward until the end of the movement. The purpose of this study was to provide an efficient interventional perspective in close proximity to daily life for improving the function of patients with chronic stroke by providing information on the positive effects of sit-to-walk training. Two patients with chronic stroke volunteered for this study. The STW training fior Subject 1 and the sit-to-stand training for Subject 2 were performed an average 30 minutes per day, 3 times a week for 4 weeks (a total of 12 sessions). Measurements included electromyographic analysis (muscle activity and onset time) on vastus medialis, bicepps femoris, tibialis anterior, and soleus, and timed up and go (TUG) test. With respect to anticipatory postural adjustments before and after training, the tibialis anterior muscle onset time of Subject 1 and 2 decreased from 1.09 to .63 seconds and from 2.46 to 1.25 seconds, respectively. In relation to multi-task performance, the TUG test with a motor task decreased by 5.90 seconds for Subject 1 and 12.03 seconds for Subject, respectively. These findings suggest that the STW training might be considered as a part of functional movement re-education close to everyday life in rehabilitation programs of stroke patients and as higher difficulty training.

Subacromial Impingment Syndrome does not alter muscle onset activation patterns during shoulder cardinal movement at different speed and load

This study examines neuromuscular firing patterns in healthy and subjects diagnosed with SIS of the periscapular, prime-moving, and rotator cuff muscles during “clinical” cardinal plane physiological movements at different speeds and loads. EMG recordings were taken in 34 healthy and 34 subjects diagnosed with Subacromial Impingement Syndrome (SIS) of the prime movers, periscapular, and rotator cuff muscles during flexion, scaption, and abduction performed at fast, medium, and slow speeds with a loaded (3 kg) and unloaded arm. Differences in firing patterns between groups were analyzed by fitting mixed linear models with random intercepts per subject, and fixed factors for group, muscle, movement type, speed, and load. No difference in timing of activation was seen between the healthy and SIS. Onset timing of prime movers, periscapular, and rotator cuff muscles were prior to movement in all scenarios studied, with rotator cuff muscles firing last. Speed and load appear to independently vary muscle activation timing in a non-intuitive manner in both healthy and SIS. The lack of different firing neuromuscular patterns in subjects diagnosed with SIS and healthy subjects raises the need to consider individual assessment of motor patterns rather than generalized patterns.

Fatigue changes neck muscle control and deteriorates postural stability during arm movement perturbations in patients with chronic neck pain

BACKGROUND CONTEXTMultisensory afferent inputs to the cervical spine affect the generation of neck muscle control. Chronic neck pain (CNP) and muscle fatigue are factors that disturb somatosensory function. Whether they affect postural control under self-initiated perturbation in daily activities is still unclear. PURPOSETo investigate the effect of CNP and neck flexor muscle fatigue on muscle control strategy and postural control in young patients performing voluntary shoulder flexion movements. STUDY DESIGNCross-sectional case-control study. PATIENT SAMPLETwenty-five patients with CNP and 25 age-matched asymptomatic controls. OUTCOME MEASURESThe postural sway, muscle onset time, and activation level of the erector spinae, rectus abdominal, semispinalis capitis (SSC), and sternocleidomastoid (SCM) muscles were recorded and analyzed using two-way ANOVA to evaluate the interaction of CNP and muscle fatigue on standing balance and muscle control upon self-initiated perturbations. METHODSAll participants were instructed to perform shoulder flexion movements in the standing position before and after a neck flexor muscle fatigue exercise under either the eyes-open or eyes-closed condition. RESULTSThe CNP group exhibited significantly larger body sway, greater neck muscle activation (SCM and SSC), and longer onset time of neck flexor muscle (SCM) compared with the control group. The CNP group also demonstrated a trend of greater postural sway and shorter muscle onset under the eyes-closed condition than those under the eyes-open condition. After muscle fatigue, the CNP group further exhibited (1) greater body sway during the eyes-open condition but decreased body sway during the eyes-closed condition, (2) higher activation of the neck flexor (SCM) and lower activation of the trunk extensor (erector spinae), and (3) early onset of the neck muscles (SCM and SSC). CONCLUSIONSCNP causes poor postural control and altered neck muscle control patterns. The addition of neck flexor muscle fatigue further decreases balance stability and provokes a protective neck muscle control strategy during the shoulder flexion movement. Those findings facilitate the understanding of the strategies adopted by patients and suggest that neck endurance training programs may be beneficial to improve whole postural control in patients with CNP.