Identifying the neural correlates of anticipatory postural control: A novel fMRI paradigm.

Altered postural control in the trunk/hip musculature is a characteristic of multiple neurological and musculoskeletal conditions. Previously it was not possible to determine if altered cortical and subcortical sensorimotor brain activation underlies impairments in postural control. This study used a novel fMRI-compatible paradigm to identify the brain activation associated with postural control in the trunk and hip musculature. BOLD fMRI imaging was conducted as participants performed two versions of a lower limb task involving lifting the left leg to touch the foot to a target. For the supported leg raise (SLR) the leg is raised from the knee while the thigh remains supported. For the unsupported leg raise (ULR) the leg is raised from the hip, requiring postural muscle activation in the abdominal/hip extensor musculature. Significant brain activation during the SLR task occurred predominantly in the right primary and secondary sensorimotor cortical regions. Brain activation during the ULR task occurred bilaterally in the primary and secondary sensorimotor cortical regions, as well as cerebellum and putamen. In comparison with the SLR, the ULR was associated with significantly greater activation in the right premotor/SMA, left primary motor and cingulate cortices, primary somatosensory cortex, supramarginal gyrus/parietal operculum, superior parietal lobule, cerebellar vermis, and cerebellar hemispheres. Cortical and subcortical regions activated during the ULR, but not during the SLR, were consistent with the planning, and execution of a task involving multisegmental, bilateral postural control. Future studies using this paradigm will determine mechanisms underlying impaired postural control in patients with neurological and musculoskeletal dysfunction.

Classifying Unstable and Stable Walking Patterns Using Electroencephalography Signals and Machine Learning Algorithms.

Analyzing unstable gait patterns from Electroencephalography (EEG) signals is vital to develop real-time brain-computer interface (BCI) systems to prevent falls and associated injuries. This study investigates the feasibility of classification algorithms to detect walking instability utilizing EEG signals. A 64-channel Brain Vision EEG system was used to acquire EEG signals from 13 healthy adults. Participants performed walking trials for four different stable and unstable conditions: (i) normal walking, (ii) normal walking with medial-lateral perturbation (MLP), (iii) normal walking with dual-tasking (Stroop), (iv) normal walking with center of mass visual feedback. Digital biomarkers were extracted using wavelet energy and entropies from the EEG signals. Algorithms like the ChronoNet, SVM, Random Forest, gradient boosting and recurrent neural networks (LSTM) could classify with 67 to 82% accuracy. The classification results show that it is possible to accurately classify different gait patterns (from stable to unstable) using EEG-based digital biomarkers. This study develops various machine-learning-based classification models using EEG datasets with potential applications in detecting unsteady gait neural signals and intervening by preventing falls and injuries.

Anticipatory postural adjustments and spatial organization of motor cortex: evidence of adaptive compensations in healthy older adults.

During anticipated postural perturbations induced by limb movement, the central nervous system generates anticipatory postural adjustments (APAs) in the trunk and hip musculature to minimize disturbances to equilibrium. Age-related changes in functional organization of the nervous system may contribute to changes in APAs in healthy older adults. Here we examined if altered APAs of trunk/hip musculature in older adults are accompanied by changes in the representation of these muscles in motor cortex. Twelve healthy older adults, 5 with a history of falls and 7 nonfallers, were compared with 13 young adults. APAs were assessed during a mediolateral arm raise task in standing. Temporal organization of postural adjustments was quantified as latency of APAs in the contralateral external oblique, lumbar paraspinals, and gluteus medius relative to activation of the deltoid. Spatial organization was quantified as extent of synergistic coactivation between muscles. Volume and location of the muscle representations in motor cortex were mapped using transcranial magnetic stimulation. We found that older adults demonstrated significantly delayed APAs in the gluteus medius muscle. Spatial organization of the three muscles in motor cortex differed between groups, with the older adults demonstrating more lateral external oblique representation than the other two muscles. Separate comparisons of the faller and nonfaller subgroups with young adults indicated that nonfallers had the greatest delay in gluteus medius APAs and a reduced distance between the representational areas of the lumbar paraspinals and gluteus medius. This study indicates that altered spatial organization of motor cortex accompanies altered temporal organization of APA synergies in older adults. NEW & NOTEWORTHY Anticipatory postural adjustments are a critical component of postural control. Here we demonstrate that, in healthy older adults with and without a history of falls, delayed anticipatory postural adjustments in the hip musculature during mediolateral perturbations are accompanied by altered organization of trunk/hip muscle representation in motor cortex. The largest adaptations are evident in older adults with no history of falls.

The motor cortical representation of a muscle is not homogeneous in brain connectivity.

Functional connectivity patterns of the motor cortical representational area of single muscles have not been extensively mapped in humans, particularly for the axial musculature. Functional connectivity may provide a neural substrate for adaptation of muscle activity in axial muscles that have both voluntary and postural functions. The purpose of this study was to combine brain stimulation and neuroimaging to both map the cortical representation of the external oblique (EO) in primary motor cortex (M1) and supplementary motor area (SMA), and to establish the resting-state functional connectivity associated with this representation. Motor-evoked potentials were elicited from the EO muscle in stimulation locations encompassing M1 and SMA. The coordinates of locations with the largest motor-evoked potentials were confirmed with task-based fMRI imaging during EO activation. The M1 and SMA components of the EO representation demonstrated significantly different resting-state functional connectivity with other brain regions: the SMA representation of the EO muscle was significantly more connected to the putamen and cerebellum, and the M1 representation of the EO muscle was significantly more connected to somatosensory cortex and the superior parietal lobule. This study confirms the representation of a human axial muscle in M1 and SMA, and demonstrates for the first time that different parts of the cortical representation of a human axial muscle have resting-state functional connectivity with distinct brain regions. Future studies can use the brain regions of interest we have identified here to test the association between resting-state functional connectivity and control of the axial muscles.

Trunk coordination in dancers and nondancers.

Variability, or how a task changes across trials, may reveal differences between athletes of differing skill levels. The purpose of this study was to examine trunk and lower extremity (LE) single joint kinematic variability and intersegmental coordination variability in dancers and nondancers during bipedal vertical dance jumps (sautés). Twenty healthy females, 10 with no formal dance training and 10 professional dancers, performed 20 consecutive sautés. Single joint kinematic variability was assessed using mean standard deviation of angular displacement, and intersegmental coordination variability was assessed using angular deviation of the coupling angle between segments. Within the context of the standard error of measure, there was no difference in single joint kinematic variability between dancers and nondancers. Intersegmental coordination variability in the trunk was higher than variability in LE couplings for both groups. Dancers had lower intersegmental coordination variability than nondancers for LE sagittal, frontal, and transverse plane couplings, and sagittal plane trunk couplings. Trunk adjustments may be important for successful performance, but lower intersegmental coordination variability in expert dancers indicates a higher level of control. Trunk coordination and postural control may be important factors to investigate in skilled athletes.

Combining Static and Dynamic Myofascial Dry Cupping Therapy to Improve Local and Regional Symptoms in Individuals with Low Back Pain: A Case Series.

Introduction: Chronic low back pain is a common musculoskeletal healthcare presentation with an expense of over $100 billion annually. The clinical effect of myofascial cupping on pain and function is not clear, especially when different cupping techniques are combined. The purpose of this case series was to explore changes in pain and function following local static and distal dynamic myofascial dry cupping treatments in patients with chronic low back pain. Case Descriptions: Three adults from the general population received three ten-minute treatment sessions, 48 hours between each session, of static dry cupping to the low back followed by dynamic myofascial cupping of the quadriceps and hamstring musculature. Outcome measures were taken at two different time points within one-week per participant. Subjective measures included the numeric pain rating scale and the Oswestry Disability Index, objective measures included passive straight leg raise measurements, and pressure pain threshold. Results and Discussion: Local static combined with distal dynamic myofascial cupping reduced pain, pain sensitivity and perceived disability, and improved hamstring muscle extensibility in all three participants. These encouraging results support the initiation of a larger controlled trial aimed at investigating the efficacy of combined dry cupping interventions to treat musculoskeletal dysfunction and pain. Level of Evidence: 4 (case series).

Understanding the Biering-Sørensen test: Contributors to extensor endurance in young adults with and without a history of low back pain.

The Biering-Sørensen test is commonly used to assess paraspinal muscle endurance. Research using a single repetition of the test has provided conflicting evidence for the contribution of impaired paraspinal muscle endurance to low back pain (LBP). This study investigated how Sørensen test duration, muscle activation, and muscle fatigability are affected by multiple repetitions of the test and determined predictors of Sørensen test duration in young adults with and without a history of LBP. Sixty-four young individuals performed three repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and hamstrings. Duration of the test was significantly less for the 3rd repetition in individuals with LBP. In individuals without LBP, test duration was predicted by fatigability of the lumbar paraspinals. In individuals with LBP, Sørensen test duration was predicted by fatigability of the hamstrings and amplitude of activation of the thoracic and lumbar paraspinals. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to reveal impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance should monitor performance of other synergist muscles during endurance exercise.

Running biomechanics differ during and after pregnancy compared to females who have never been pregnant.

BACKGROUND: Perinatal running participation has increased recently; however, pregnancy related symptoms can limit activity. Perinatal running biomechanics could inform interventions to help perinatal individuals maintain an active lifestyle. RESEARCH QUESTION: Are perinatal running biomaechanics and muscle activation different compared to nulligravida females? METHODS: Sixteen pregnant participants completed self-selected velocity running during second trimester (2 T), third trimester (3 T), and postpartum (PP) and 16 matched controls completed these procedures once in this case control study. Kinematic, kinetic, and electromyography (EMG) data were collected using a motion capture system, force plates, and EMG electrodes. Peak trunk, pelvis, hip, knee, and ankle kinematics and hip, knee, and ankle moments during stance phase, and average and peak erector spinae (ES), gluteus maximus (GMax), and gluteus medius (GMed) EMG amplitude and duration of activation during stance and swing phases were calculated. Independent t-tests were used to compare 2 T, 3 T, and PP to control participants (α < 0.05). RESULTS: Running velocity was slower during 3 T compared to control participants. At all pregnancy timepoints compared to the control group, peak trunk contralateral rotation was smaller. During 2 T and 3 T peak hip flexor moments were smaller. At 3 T pelvis contralateral rotation was smaller, ES average amplitude was greater during swing, GMax percent duration during stance and GMed percent duration during swing were smaller. At PP trunk flexion was smaller and knee abduction was greater (all p < 0.05). CONCLUSIONS: Decreased running velocity may help offset increased demand during pregnancy. During 3 T, greater ES activation, smaller trunk and pelvis motion, and altered gluteal activation could indicate trunk rigidity combined with modified hip stabilizer muscle utilization. During PP, the rigid trunk combined with greater knee abduction may indicate hip and trunk strength deficits. Altered trunk and hip motion and activation could be relevant to pathologies such as perinatal low back, pelvic girdle, or knee pain.

The Effect of Spinal Muscle Fatigue and Psychosocial Factors on Pressure-Pain Threshold in Healthy Adults.

Objective: Pain sensitivity decreases following isometric exercise. It is not clear whether this exercise-induced hypoalgesia (EIH) occurs to the same extent in men and women. It is also unclear if the effect is systemic or local to the exercised musculature. The aim of our study was to investigate whether fatiguing isometric exercise of the spinal and hip extensors would result in increased pressure pain threshold (PPT) at sites local to and remote from the exercised muscles in healthy men and women and whether there is a relationship between central sensitization, psychosocial factors, and PPT. Subjects: 35 healthy adults (age 27.1 ± 4.5 years, 22 women). Methods: This was a within-subjects cohort study. Participants completed questionnaires quantifying central sensitization, pain catastrophizing, sleepiness/insomnia, anxiety, and depression. PPT was assessed at the lumbar and thoracic paraspinals, hamstrings, gastrocnemius, wrist, and third digit before and immediately after participants performed the Biering-Sorensen test to failure. Results: PPT increased postexercise in the thoracic paraspinals, hamstrings, and gastrocnemius in men and women and in the lumbar paraspinals in men only but did not change at the wrist and digit sites. A lower average PPT at baseline was associated with a higher central sensitization scores. A greater increase in average PPT postfatigue was significantly associated with higher average PPT at baseline. Conclusions: Exercise-induced hypoalgesia occurs at sites overlying the muscles involved in fatiguing exercise, but not at remote sites, and is more evident in males than females. The magnitude of EIH depends upon baseline PPT. Even in healthy individuals, greater central sensitization is associated with lower baseline PPT.

Comparison of clinical and biomechanical characteristics between individuals with lower limb amputation with and without lower back pain: A systematic review and meta-analysis.

BACKGROUND: Lower back pain is a debilitating condition common to individuals with lower limb amputation. It is unclear what risk factors contribute to the development of back pain. This study systematically reviewed and analyzed the available evidence regarding the clinical and biomechanical differences between individuals with amputation, with and without lower back pain. METHODS: A literature search was conducted in PubMed, Web of Science, Scopus, and CINAHL databases in November 2020 and repeated in June 2021 and June 2022. Studies were included if they reported comparisons of demographic, anthropometric, biomechanical, and other clinical variables between participants with and without LBP. Study quality and potential for reporting bias were assessed. Meta-analyses were conducted to compare the two groups. FINDINGS: Thirteen studies were included, with aggregated data from 436 participants (239 with LBP; 197 pain free). The median reporting quality score was 37.5%. The included studies enrolled participants who were predominantly male (mean = 91.4%, range = 77.8-100%) and with trauma-related amputation. Meta-analyses showed that individuals with LBP exhibited moderate (3.4 out of 10) but significantly greater pain than those without LBP. We found no between-group differences in age, height, weight, BMI, and time since amputation (p = 0.121-0.682). No significant differences in trunk/pelvic kinematics during gait were detected (p = 0.07-0.446) between the groups. INTERPRETATION: Demographic, anthropometric, biomechanical, and simple clinical outcome variables may be insufficient for differentiating the risk of developing back pain after amputation. Investigators should be aware of the existing gender bias in sampling and methodological limitations, as well as to consider incorporating psychosocial measures when studying LBP in this clinical population.

Understanding the Biering-Sørensen test: contributors to extensor endurance in young adults with and without low back pain.

Impaired paraspinal muscle endurance may contribute to persistent low back pain (LBP) and is frequently assessed using a single repetition of the Biering-Sørensen test. This study investigated how Sørensen test duration, muscle activation, and muscle fatigability are affected by multiple repetitions of the test, and determined predictors of Sørensen test duration in young, active adults with and without a history of LBP. Sixty-four individuals with and without persistent LBP performed 3 repetitions of the Sørensen test. Amplitude of activation and median frequency slope (fatigability) were calculated for the lumbar and thoracic paraspinals and the hamstrings. Duration of the test was significantly less for the 2nd and 3rd repetitions in individuals with LBP. In individuals without LBP, fatigability of the lumbar paraspinals was the best predictor of test duration. In individuals with LBP, Sørensen test duration was predicted by fatigability of the hamstrings and amplitude of activation of the thoracic and lumbar paraspinals. Our findings demonstrate that it is necessary to amplify the difficulty of the Sørensen test to elucidate impairments in young, active adults with LBP. Training programs aiming to improve lumbar paraspinal performance in individuals with LBP should monitor performance of other synergist muscles during endurance exercise.

Intra-task variability of trunk coordination during a rate-controlled bipedal dance jump.

In this study, we investigated trunk coordination during rate-controlled bipedal vertical dance jumps. The aims of the study were to investigate the pattern of coordination and the magnitude of coordination variability within jump phases and relative to phase-defining events during the jump. Lumbar and thoracic kinematics were collected from seven dancers during a series of jumps at 95 beats per minute. The vector coding technique was used to quantify the pattern and variability of trunk coordination. Coordination was predominantly anti-phase during propulsion and landing. Mean coordination variability peaked just before the landing phase and at the transition from landing to propulsion phases, and was lowest during the propulsion phase just before toe-off. The results indicate that peaks in variability could be explained by task and phase-specific biomechanical demands.

Self-paced treadmills do not allow for valid observation of linear and nonlinear gait variability outcomes in patients with Parkinson's disease.

BACKGROUND: Due to the imposed constant belt speed, motorized treadmills are known to affect linear and nonlinear gait variability outcomes. This is particularly true of patients with Parkinson's Disease where the treadmill can act as an external pacemaker. Self-paced treadmills update the belt speed in response to the subject's walking speed and might, therefore, be a useful tool for measurement of gait variability in this patient population. This study aimed to compare gait variability during walking at self-paced and constant treadmill speeds with overground walking in individuals with PD and individuals with unimpaired gait. METHODS: Thirteen patients with Parkinson's Disease and thirteen healthy controls walked under three conditions: overground, on a treadmill at a constant speed, and using three self-paced treadmill modes. Gait variability was assessed with coefficient of variation (CV), sample entropy (SampEn), and detrended fluctuation analysis (DFA) of stride time and length. Systematic and random error between the conditions was quantified. RESULTS: For individuals with PD, error in variability measurement was less during self-paced modes compared with constant treadmill speed for stride time but not for stride length. However, there was substantial error for stride time and length variability for all treadmill conditions. For healthy controls the error in measurement associated with treadmill walking was substantially less. SIGNIFICANCE: The large systematic and random errors between overground and treadmill walking prohibit meaningful gait variability observations in patients with Parkinson's Disease using self-paced or constant-speed treadmills.

Do people with low back pain walk differently? A systematic review and meta-analysis.

BACKGROUND: The biomechanics of the trunk and lower limbs during walking and running gait are frequently assessed in individuals with low back pain (LBP). Despite substantial research, it is still unclear whether consistent and generalizable changes in walking or running gait occur in association with LBP. The purpose of this systematic review was to identify whether there are differences in biomechanics during walking and running gait in individuals with acute and persistent LBP compared with back-healthy controls. METHODS: A search was conducted in PubMed, CINAHL, SPORTDiscus, and PsycINFO in June 2019 and was repeated in December 2020. Studies were included if they reported biomechanical characteristics of individuals with and without LBP during steady-state or perturbed walking and running. Biomechanical data included spatiotemporal, kinematic, kinetic, and electromyography variables. The reporting quality and potential for bias of each study was assessed. Data were pooled where possible to compare the standardized mean differences (SMD) between back pain and back-healthy control groups. RESULTS: Ninety-seven studies were included and reviewed. Two studies investigated acute pain and the rest investigated persistent pain. Nine studies investigated running gait. Of the studies, 20% had high reporting quality/low risk of bias. In comparison with back-healthy controls, individuals with persistent LBP walked slower (SMD = -0.59, 95% confidence interval (95%CI): -0.77 to -0.42)) and with shorter stride length (SMD = -0.38, 95%CI: -0.60 to -0.16). There were no differences in the amplitude of motion in the thoracic or lumbar spine, pelvis, or hips in individuals with LBP. During walking, coordination of motion between the thorax and the lumbar spine/pelvis was significantly more in-phase in the persistent LBP groups (SMD = -0.60, 95%CI: -0.90 to -0.30), and individuals with persistent LBP exhibited greater amplitude of activation in the paraspinal muscles (SMD = 0.52, 95%CI: 0.23-0.80). There were no consistent differences in running biomechanics between groups. CONCLUSION: There is moderate-to-strong evidence that individuals with persistent LBP demonstrate differences in walking gait compared to back-healthy controls.

An exploratory analysis of gait biomechanics and muscle activation in pregnant females with high and low scores for low back or pelvic girdle pain during and after pregnancy.

BACKGROUND: The purpose of this study was to compare gait kinematics, kinetics, and muscle activation between pregnant females with high and low scores for low back and/or pelvic girdle pain during and after pregnancy. METHODS: Twenty participants tested during second trimester, third trimester, and again post-partum. At each session, motion capture, force plates, and surface electromyography data were captured during self-selected velocity over-ground walking. Participants completed the Quebec Back Pain Disability Scale (QBPDS) and were assigned to high (QBPDS ≥15) or low pain groups (QBPDS <15) based on third trimester scores. Two-way mixed model ANOVAs were used to compare high and low pain groups over time. FINDINGS: Nine participants met the high pain group criteria and 11 were low pain. During second trimester the high pain group compared to the low pain group demonstrated smaller peak hip flexor moments, total hip work, percent hip contribution to work, and larger percent ankle contribution to work. Pregnant females demonstrated greater hip, knee, and ankle moments, ankle work, and gluteus maximus muscle activation third trimester than second trimester. INTERPRETATION: Reduced hip and greater ankle contribution to work in the high pain group during second trimester could indicate decreased hip utilization early in pregnancy and may contribute to disability as pregnancy progresses. It is also possible kinetic differences during second trimester reflect an early strategy to reduce pain by avoiding hip joint loading. Increased moments and work during third trimester indicate a clinical imperative to better prepare pregnant females to accommodate increased joint loading and muscular demand.

Fear Avoidance Predicts Persistent Pain in Young Adults With Low Back Pain: A Prospective Study.

OBJECTIVES: To (1) quantify relationships between low back pain (LBP) symptoms, physical activity, and psychosocial characteristics in young adults and (2) identify subclasses of young adults with distinct pain trajectories. DESIGN: Prospective cohort study with 12-month follow-up. METHODS: One hundred twenty adults (mean ± SD age, 20.8 ± 2.6 years; 99 women) participated. Participants completed a baseline survey that measured anxiety, depression, fear avoidance, quality of life, and history and impact of any LBP. Participants completed follow-up surveys every 3 months for 1 year. Subclasses based on pain trajectories over time were identified using latent class analysis, and predictors of class membership at baseline were assessed. RESULTS: Individuals with LBP at baseline had lower physical quality-of-life scores than back-healthy participants (P = .01). Subclass 1 (25% of individuals with LBP) had persistent moderate-to-high pain intensity over the 1-year study period. Subclass 2 (75% of individuals with LBP) had significantly improving pain over the 1-year study period. Higher fear avoidance (physical activity subscale) and pain interference at baseline were associated with greater odds of membership in subclass 1 (odds ratio = 1.2; 95% confidence interval: 1.0, 1.3 and odds ratio = 1.4; 95% confidence interval: 1.1, 1.6, respectively). CONCLUSION: Most young adults with LBP had symptoms that improved over time. Levels of fear avoidance and pain interference may help to identify individuals at risk of persistent pain early in the lifespan. J Orthop Sports Phys Ther 2021;51(8):383-391. Epub 15 May 2021. doi:10.2519/jospt.2021.9828.

Corticomotor Excitability of Gluteus Maximus Is Associated with Hip Biomechanics During a Single-Leg Drop-Jump.

The purpose of this study was to determine the association between corticomotor excitability (CME) of gluteus maximus (GM) and hip biomechanics during a single-leg drop-jump task. Thirty-two healthy individuals participated. The slope of the input-output curve (IOC) obtained from transcranial magnetic stimulation was used to assess CME of GM. The average hip extensor moment and peak hip flexion angle during the stance phase of the drop jump task was calculated. The slope of the IOC of GM was found to be a predictor of the average hip extensor moment (r2 = 0.18, p = 0.016) and peak hip flexion angle (r2 = 0.20, p = 0.01). Our results demonstrate that greater functional use of the hip was associated with enhanced descending neural drive of GM.

Adaptations in trunk-pelvis coordination variability in response to fatiguing exercise.

BACKGROUND: During walking, variability in how movement is coordinated between body segments from stride to stride facilitates adaptation to changing environmental or task constraints. Magnitude of this inter-segmental coordination variability is reduced in patient populations and may also decrease in response to muscle fatigue. Previously, stride-to-stride variability has been quantified with the Vector Coding (VC) method, however recent research introduced a new Ellipse Area Method (EAM) to avoid statistical artifacts associated with VC. RESEARCH QUESTION: Determine changes in trunk-pelvis coordination variability during walking turns in response to fatiguing exercise and to compare coordination variability quantified with VC to the EAM method. METHODS: 15 young adults (mean age: 23.7 (±3.2) years) performed 15 trials of a 90-degree walking turn before and after fatiguing paraspinal muscle exercise. Angular kinematics of the trunk and pelvis segments in the axial plane were quantified using three-dimensional motion capture. Stride to stride variability of axial coordination between the trunk and pelvis pre- and post-fatigue was calculated using both VC and EAM methods. Magnitudes of pre- and post-fatigue variability for VC and EAM were compared with paired t-tests and relationship between the magnitude of variability for the two methods was calculated using Pearson correlation coefficients. RESULTS: Using both analytical approaches, trunk-pelvis coordination variability decreased significantly post-fatiguing exercise across the stride cycle and within the stance phase of the turn (p < 0.034 for all comparisons). Average magnitudes of variability calculated with VC and EAM were highly correlated. Time series cross correlations pre-post fatigue ranged from 0.81 to 0.98. SIGNIFICANCE: In healthy individuals, magnitude of trunk-pelvis stride-to-stride coordination variability is reduced following fatiguing exercise but the temporal distribution of variability across the stride cycle is maintained. This finding is robust to the method used to quantify coordination variability.

Task-invariance and reliability of anticipatory postural adjustments in healthy young adults.

BACKGROUND: Anticipatory postural adjustments (APAs) occur in the trunk during tasks such as rapid limb movement and are impaired in individuals with musculoskeletal and neurological dysfunction. To understand APA impairment, it is important to first determine if APAs can be measured reliably and which characteristics of APAs are task-invariant. RESEARCH QUESTION: What is the test-retest reliability of latency, amplitude and muscle activation patterns (synergies) of trunk APAs during arm-raise and leg-raise tasks, and to what extent are these APA characteristics invariant across tasks at the individual and group levels? METHODS: 15 young adults (mean age: 23.7 (±3.2) years) performed six trials of a rapid arm raise task in standing and a leg raise task in supine on two occasions. Latency, amplitude and coactivation of APAs in the erector spinae and external/internal oblique musculature were measured, and APA synergies were identified with principle components analysis. Test-retest reliability across the two sessions was calculated with intraclass correlation coefficients. Task-invariance was assessed at the individual level with correlation and at the group level with tests of equivalence. RESULTS: Most variables demonstrated acceptable test-retest reliability. Synergies and many features of APA activation varied across tasks, although at the individual level, motor performance time and amplitude of lumbar erector spinae activation were significantly correlated across tasks. Average pre-motor reaction time, external oblique latency, contralateral oblique amplitude and internal oblique coactivation were equivalent across tasks. SIGNIFICANCE: Characteristics of trunk muscle APAs quantified during a single task may not be representative of an anticipatory postural control strategy that generalizes across tasks. Therefore, APAs must be assessed during multiple tasks with varying biomechanical demands to adequately investigate mechanisms contributing to movement dysfunction. The reliability analysis in this study facilitates interpretation of group differences or changes in APA behavior in response to intervention for the selected tasks.

Biomechanical characteristics of lumbar manipulation performed by expert, resident, and student physical therapists.

BACKGROUND: Lumbar manipulation is a commonly used treatment for low back pain, but little research evidence exists regarding practitioner biomechanics during manipulation. Most existing evidence describes rate of force production through the hands into instrumented manikins and it is unclear how the practitioner moves their body and legs to generate this force. OBJECTIVES: To identify and characterize important kinetic and kinematic factors in practitioners of varying experience performing lumbar manipulation in order to identify which factors distinguish experts from less experienced practitioners. STUDY DESIGN: This was a cohort observational laboratory study. METHODS: 43 male physical therapists (PT) and PT students (4 experts, 11 residents, 13 third year, and 15 first year students) performed 4 manipulations each on asymptomatic patient models. Angular and linear kinematics of the pelvis were measured using motion capture, and ground reaction forces were measured with force plates under the practitioner's feet. RESULTS: Peak pelvic angular velocity was greater and in the opposite direction in experts compared to other groups in the frontal plane (p = 0.020) and transverse plane (p = 0.000). Experts had greater downward pelvic linear velocity than third year students and first year students (p = 0.000). Experts also demonstrated faster rate of vertical ground reaction force unloading during the manipulation (p = 0.002). CONCLUSIONS: Expert performance of manipulation was characterized by increased speed of linear and angular pelvic motion, and increased modulation of vertical ground reaction force. These results help to inform educators and practitioners that teach and use this complex manual skill.