Wearable technology mediated biofeedback to modulate spine motor control: a scoping review.

BACKGROUND: Lower back pain (LBP) is a disability that affects a large proportion of the population and treatment for this condition has been shifting towards a more individualized, patient-centered approach. There has been a recent uptake in the utilization and implementation of wearable sensors that can administer biofeedback in various industrial, clinical, and performance-based settings. Despite this, there is a strong need to investigate how wearable sensors can be used in a sensorimotor (re)training approach, including how sensory biofeedback from wearable sensors can be used to improve measures of spinal motor control and proprioception. RESEARCH QUESTION: The purpose of this scoping review was to examine the wide range of wearable sensor-mediated biofeedback frameworks currently being utilized to enhance spine posture and motor function. METHODS: A comprehensive scoping review was conducted in adherence with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Guidelines extension for Scoping Reviews (PRISMA-ScR) across the following databases: Embase, PubMed, Scopus, Cochrane, and IEEEXplore. Articles related to wearable biofeedback and spine movement were reviewed dated from 1980 - 2020. Extracted data was collected as per a predetermined checklist including the type, timing, trigger, location, and magnitude of sensory feedback being applied to the body. RESULTS: A total of 23 articles were reviewed and analysed. The most used wearable sensor to inform biofeedback were inertial measurement units (IMUs). Haptic (vibrotactile) feedback was the most common sensory stimulus. Most studies used an instantaneous online trigger to initiate sensory feedback derived from information pertaining to gross lumbar angles or the absolute orientations of the thorax or pelvis. CONCLUSIONS: This is the first study to review wearable sensor-derived sensory biofeedback to modulate spine motor control. Although the type of wearable sensor and feedback were common, this study highlights the lack of consensus regarding the timing and structure of sensory feedback, suggesting the need to optimize any sensory feedback to a specific use case. The findings from this study help to improve the understanding surrounding the ecological utility of wearable sensor-mediated biofeedback in industrial, clinical, and performance settings to enhance the sensorimotor control of the lumbar spine.

The role of diurnal variation in development of musculoskeletal pain during prolonged standing.

BACKGROUND: Research suggests mechanical changes occur to the body over the course of the day including shrinking of the intervertebral disc height which can increase rotational stiffness and rigidity of the spinal column. Further, pain sensitivity has been observed to fluctuate throughout the day, suggesting variations in pain sensitivity. Previous work has identified biomechanical and neuromuscular features related to the development of musculoskeletal pain during prolonged standing; however, many protocols have not controlled for time of day. RESEARCH QUESTION: Does the time of day (i.e., diurnal variation) have an effect on the common neuromuscular and biomechanical variables characterizing the development of standing musculoskeletal pain in a two-hour prolonged standing protocol? METHODS: A convenience sample of 20 healthy young adults (10 female and 10 male) completed two 2-hour prolonged standing bouts (8:00 a.m. and 8:00 p.m.) on separate days. Visual analogue scales were used to measure pain perception of the low back, legs, and feet throughout each protocol. Neuromuscular control was measured using surface EMG on muscles of the trunk and lower extremities. Postural sway was captured using measures of joint range of motion, and the analysis of center of pressure trajectory data using a force plate. RESULTS: Diurnal variation was observed to influence the development of musculoskeletal pain. Specifically, pain perception was found to be increased in the evenings as more participants were classified as pain developers in the PM sessions, and mean leg and foot pain perceptions were higher in the evening. Reduced postural sway patterns, and elevated co-contraction indices were found to be associated with the development of pain. SIGNIFICANCE: These results suggest that future research assessing standing-pain protocols should control for time of day. Additionally, further research is warranted to explore the mechanistic causes of the development of standing pain.

Assessment of the Acute Effects of Wearable Sensor Derived Auditory Biofeedback on Gross Lumbar Proprioception.

Lower back disorders (LBDs) affect a large proportion of the population, and treatment for LBDs have been shifting toward individualized, patient-centered approaches. LBDs are typically associated with poor proprioception. Therefore, there has been a recent uptake in the utilization of wearable sensors that can administer biofeedback in various industrial, clinical, and performance-based settings to improve lumbar proprioception. The aim of this study was to investigate whether wearable sensor-derived acute auditory biofeedback can be used to improve measures of gross lumbar proprioception. To assess this, healthy participants completed an active target repositioning protocol, followed by a training period where lumbar-spine posture referenced auditory feedback was provided for select targets. Target re-matching abilities were captured before and after acute auditory biofeedback training to extract measures related to accuracy and precision across spine flexion targets (i.e., 20%, 40%, 60%, 80% maximum). Results suggest a heterogenous response to proprioceptive training whereby certain individuals and spine flexion targets experienced positive effects (i.e., improved accuracy and precision). Specifically, results suggest that mid-range flexion targets (i.e., 40-60% maximum flexion) benefited most from the acute auditory feedback training. Further, individuals with poorer repositioning abilities in the pre-training assessment showed the greatest improvements from the auditory feedback training.

The effects of supplemental instruction derived from peer leaders on student outcomes in undergraduate human anatomy.

Supplemental instruction (SI) confers student success, as represented by grades, knowledge retention, and student engagement. However, studies often report professional, not undergraduate, program findings. To measure these effects, students studying human anatomy at a university in Ontario, Canada, attended structured (peer-assisted) or unstructured (nonpeer-assisted) SI sessions and completed a pre-/post-survey. Fifty-eight learners (39 systems (SYS) and 19 musculoskeletal (MSK) anatomy) completed both surveys and had responses analyzed. Both cohorts, maintained initial perceptions across pre-/post-analyses (MSK p = 0.1376 and SYS p = 0.3521). Resource usage was similar across both cohorts with discrepancies in skeletal model and textbook use. No MSK learner ranked any lab resources as "not at all useful." MSK learners felt more prepared to write a graded assessment (p = 0.0269), whereas SYS learners did not (p = 0.0680). Stratification of learners in MSK and SYS revealed learners spending between 30 and 60 min in SI sessions during the study period had the highest grades compared to students who spent less than 30 (p = 0.0286) or more than 60 (p = 0.0286) min attending SI sessions, respectively. Most learners in MSK (89.4%) and SYS (66%) concluded that they preferred structured over unstructured SI. Sentiment/thematic analysis using a generative AI-driven large language model revealed learners held positive perceptions of SI, emphasizing structured learning, resources, personalized learning, and support offered as the most prevalent themes surrounding SI. Ultimately, this study provides evidence that supports SI for improving student outcomes related to perceived preparedness for completing assessments and preferred teaching/learning styles in undergraduate human anatomy.

The Effects of Load, Crank Position, and Sex on the Biomechanics and Performance during an Upper Body Wingate Anaerobic Test.

INTRODUCTION: The upper body Wingate Anaerobic Test (WAnT) is a 30-s maximal effort sprint against a set load (percentage of body mass). However, there is no consensus on the optimal load and no differential values for males and females, even when there are well-studied anatomical and physiological differences in muscle mass for the upper body. Our goal was to describe the effects of load, sex, and crank position on the kinetics, kinematics, and performance of the upper body WAnT. METHODS: Eighteen participants (9 females) performed three WAnTs at 3%, 4%, and 5% of body mass. Arm crank forces, 2D kinematics, and performance variables were recorded during each WAnT. RESULTS: Our results showed an increase of ~49% effective force, ~36% peak power, ~5° neck flexion, and ~30° shoulder flexion from 3% to 5% load ( P < 0.05). Mean power and anaerobic capacity decreased by 15%, with no changes in fatigue index ( P < 0.05). The positions of higher force efficiency were at 12 and 6 o'clock. The least force efficiency occurred at 3 o'clock ( P < 0.05). Sex differences showed that males produced 97% more effective force and 109% greater mean power than females, with 11.7% more force efficiency ( P < 0.001). Males had 16° more head/neck flexion than females, and females had greater elbow joint variability with 17° more wrist extension at higher loads. Males cycled ~32% faster at 3% versus 5% WAnT load with a 65% higher angular velocity than females. Grip strength, maximal voluntary isometric contraction, mass, and height positively correlated with peak and mean power ( P < 0.001). CONCLUSIONS: In conclusion, load, sex, and crank position have a significant impact on performance of the WAnT. These factors should be considered when developing and implementing an upper body WAnT.

The acute effects of kinesio-taping on movement kinematics and muscle co-activation in rowing athletes.

BACKGROUND: Rowing-related low back disorders may occur from inconsistent technique, high trunk flexion and training volumes, overactivation of paraspinal muscles, and fatigue. OBJECTIVE: To examine if kinesiology tape (KT) affixed to the trunk dorsum affects muscular co-activation and neuromuscular control to limit dangerous rowing movements and associated injuries. METHODS: Participants (n= 18) completed two 2000 m rowing trials under BASELINE and KT conditions. KT was applied to the skin superficial to the paraspinals bilaterally with 60% pre-strain. Participants were instructed to minimize any sensation of tension. Whole body kinematics were obtained using inertial measurement units (IMUs), and surface electromyograms (EMGs) were recorded from trunk and lower extremity. Changes in joint range-of-motion (ROM) and co-activation indices (CAIs) were analyzed for shoulder, lumbar, hip, and knee. RESULTS: Responding participants (n= 5) were identified by reduced maximum lumbar flexion during the KT condition. As expected, significant differences occurred in maximum and minimum lumbar flexion/extension between responders and non-responders to KT. Additionally, there was significant reduction in mean trunk muscle co-activation in both those who did and did not respond to KT through reductions in maximum lumbar flexion. CONCLUSION: KT can be an effective at reducing mean trunk co-activation during a rowing trial in the flexed catch position. Variable responses suggest that further work is necessary to optimize the efficacy of sensory cues derived from KT during rowing movements.

Non-invasive assessment of sacroiliac joint and lumbar spine positioning in different unilateral sitting postures.

BACKGROUND: Sacroiliac joint (SIJ) motion has been documented using invasive and noninvasive kinematic techniques. No study has explored SIJ angular positions in functional postures using noninvasive techniques. The purpose of this study was to quantify SIJ positioning among different seated postures in a healthy population. METHODS: Twelve female and 11 male healthy young participants participated. Left and right anterior and posterior superior iliac spines were manually digitized during standing, neutral sitting and four different seated postures. Rigid bodies recorded the kinematics of the lumbar spine. Angles calculated included transverse sacroiliac angle, innominate sagittal angle, sacral tilt, lumbar flexion-extension, lumbar lateral bend and lumbar axial twist. FINDINGS: The observed range of angular positions was approximately 3 to 4 degrees across the SIJ-related angles. The main effect of seated posture was observed for all angles measured. The main effect of sex was observed for all angles except lumbar lateral bending. Females consistently experienced more posterior sacral tilt than males. Interaction effects between sex and posture were only observed at the right-transverse sacroiliac angle and sacral tilt. Previous sitting posture affected the subsequent neutral sitting posture for the right-transverse sacroiliac angle and lumbar spine angle. INTERPRETATION: SIJ angular position differences among the seated postures were similar in magnitude to motions previously reported in participants undergoing prone passive hip abduction and external rotation. Sex differences, including greater sacral posterior tilt observed in females, likely reflect underlying morphological and physiological differences. Future studies should explore SIJ positioning during functional tasks in pathological populations to help elucidate the underlying causes of SIJ pain and inform treatment strategies.

The effects of COVID-19 related shutdowns on perceived lifestyle and prevalence of musculoskeletal discomfort.

BACKGROUND: COVID-19 caused a transition to work-from-home conditions, closures of recreation facilities and cancelation of social events. OBJECTIVE: This study sought to characterize and quantify the impact COVID-19 related shutdowns had on perceptions of health and wellbeing, musculoskeletal discomfort, and physical characteristics of workstation set-up in full time workers who transitioned to working from home. METHODS: 297 participants from 8 countries completed a retrospective pre/post survey design that assessed outcomes prior to COVID-19 shutdowns and when each participant was experiencing peak pandemic-related restrictions. There were 3 categories including, health and wellbeing, musculoskeletal discomfort, and workplace ergonomics. RESULTS: General discomfort on a scale from 1 to 100 increased from 31.4 pre to 39.9 during COVID-19. Notable areas increasing in severity of discomfort from pre to during included the neck (41.8 to 47.7), upper back (36.3 to 41.3) and right wrist (38.7 to 43.5). The percentage of the population experiencing discomfort increased from pre to during in the low back (41.5% to 55.2%), upper back (28.7% to 40.9%), neck (45.5% to 60.9%) and right wrist (16.1% to 23.7%). CONCLUSION: There were three distinct groups for physical activity one group including, one maintaining and one that decreased, which did not have an impact on perceived general discomfort. There was a significant decrease in usage of a desk and adjustable chair and an increase in laptop use. Working from home in some capacity will likely be a more common occurrence which will require further ergonomic assessments and considerations to keep a healthy workforce.

The effect of vertebral body tethering on spine range of motion in adolescent idiopathic scoliosis: a pilot study.

PURPOSE: Posterior spinal fusion and instrumentation (PSF) and vertebral body tethering (VBT) are corrective surgical techniques used in treating adolescent idiopathic scoliosis (AIS). Comparing the preservation of spine range of motion (ROM) following PSF and VBT for treatment of AIS has yet to be explored. The purpose of this work was to retrospectively compare global spine ROM in adolescents (9-18 years of age) without spine deformity, adolescents with untreated AIS, adolescents having undergone PSF, and adolescents having undergone VBT to gain insight on the effect of VBT on spine motion. METHODS: Twenty participants were recruited into four groups including Control (n = 6), untreated AIS (n = 5), post-operative PSF (n = 4) and post-operative VBT (n = 5). Three-dimensional kinematics of the spine were collected and analyzed using an intersegmental spine model during constrained forward flexion, right-left lateral bending, and right-left axial twist movements. RESULTS: The PSF group displayed significantly lower spine ROM than the two non-operative groups during thoracic and total left axial twist (p ≤ 0.048), whereas thoracic and total ROM during right-left lateral bending is almost equally lower in the PSF (p ≤ 0.03) and VBT (p ≤ 0.01) groups when compared to the Control and AIS groups. CONCLUSION: These results suggest some preservation of spine motion in the transverse plane following VBT. This study provides initial evidence of some potential preservation of spine ROM following VBT; however, further prospective investigation of VBT is needed to assess and confirm these hypotheses.

Assessing Time-Varying Lumbar Flexion-Extension Kinematics Using Automated Pose Estimation.

The purpose of this research was to evaluate the algorithm DeepLabCut (DLC) against a 3D motion capture system (Vicon Motion Systems Ltd) in the analysis of lumbar and elbow flexion-extension movements. Data were acquired concurrently and tracked using DLC and Vicon. A novel DLC model was trained using video data derived from a subset of participants (training group). Accuracy and precision were assessed using data derived from the training group as well as in a new set of participants (testing group). Two-way analysis of variance were used to detect significant differences between the training and testing sets, capture methods (Vicon vs DLC), as well as potential higher order interaction effect between these independent variables in the estimation of flexion-extension angles and variability. No significant differences were observed in any planar angles, nor were any higher order interactions observed between each motion capture modality with the training versus testing data sets. Bland-Altman plots were used to depict the mean bias and level of agreement between DLC and Vicon for both training and testing data sets. This research suggests that DLC-derived planar kinematics of both the elbow and lumbar spine are of acceptable accuracy and precision when compared with conventional laboratory gold standards (Vicon).

A need for speed: Objectively identifying full-body kinematic and neuromuscular features associated with faster sprint velocities.

Sprinting is multifactorial and dependent on a variety of kinematic, kinetic, and neuromuscular features. A key objective in sprinting is covering a set amount of distance in the shortest amount of time. To achieve this, sprinters are required to coordinate their entire body to achieve a fast sprint velocity. This suggests that a whole-body kinematic and neuromuscular coordinative strategy exists which is associated with improved sprint performance. The purpose of this study was to leverage inertial measurement units (IMUs) and wireless surface electromyography (sEMG) to find coordinative strategies associated with peak over-ground sprint velocity using machine learning. We recruited 40 healthy university age sprint-based athletes from a variety of athletic backgrounds. IMU and sEMG data were used as inputs into a principal components analysis (PCA) to observe major modes of variation (i.e., PC scores). PC scores were then used as inputs into a stepwise multivariate linear regression model to derive associations of each mode of variation with peak sprint velocity. Both the kinematic (R 2 = 0.795) and sEMG data (R 2 = 0.586) produced significant multivariate linear regression models. The PCs that were selected as inputs into the multivariate linear regression model were reconstructed using multi-component reconstruction to produce a representation of the whole-body movement pattern and changes in the sEMG waveform associated with faster sprint velocities. The findings of this work suggest that distinct features are associated with faster sprint velocity. These include the timing of the contralateral arm and leg swing, stance leg kinematics, dynamic trunk extension at toe-off, asymmetry between the right and left swing side leg and a phase shift feature of the posterior chain musculature. These results demonstrate the utility of data-driven frameworks in identifying different coordinative features that are associated with a movement outcome. Using our framework, coaches and biomechanists can make decisions based on objective movement information, which can ultimately improve an athlete's performance.

Cutaneous Sensitivity Across Regions of the Foot Sole and Dorsum are Influenced by Foot Posture.

Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.

A Subject-Specific Approach to Detect Fatigue-Related Changes in Spine Motion Using Wearable Sensors.

An objective method to detect muscle fatigue-related kinematic changes may reduce workplace injuries. However, heterogeneous responses to muscle fatigue suggest that subject-specific analyses are necessary. The objectives of this study were to: (1) determine if wearable inertial measurement units (IMUs) could be used in conjunction with a spine motion composite index (SMCI) to quantify subject-specific changes in spine kinematics during a repetitive spine flexion-extension (FE) task; and (2) determine if the SMCI was correlated with measures of global trunk muscle fatigue. Spine kinematics were measured using wearable IMUs in 10 healthy adults during a baseline set followed by 10 sets of 50 spine FE repetitions. After each set, two fatigue measures were collected: perceived level of fatigue using a visual analogue scale (VAS), and maximal lift strength. SMCIs incorporating 10 kinematic variables from 2 IMUs (pelvis and T8 vertebrae) were calculated and used to quantify subject-specific changes in movement. A main effect of set was observed (F (1.7, 15.32) = 10.42, p = 0.002), where the SMCI became significantly greater than set 1 starting at set 4. Significant correlations were observed between the SMCI and both fatigue VAS and maximal lift strength at the individual and study level. These findings support the use of wearable IMUs to detect subject-specific changes in spine motion associated with muscle fatigue.

The effect of head and gaze orientation on spine kinematics during forward flexion.

Compound, or awkward, spine postures have been suggested as a biomechanical risk factor for low back injury. This experiment investigates the influence of head (i.e. head-on-torso) and gaze (i.e. eye-in-head) orientation on three-dimensional (3D) neck and spine range of motion (ROM) during forward flexion movements. To emulate previous experimental protocols and replicate real-world scenarios, a sample of ten young, healthy males (mean ± standard deviation: age: 20.8 ± 1.03 years, height: 180.2 ± 7.36 cm, and mass: 81.9 ± 6.47 kg) completed forward flexion movements with a constrained and unconstrained pelvis, respectively. Surface kinematics were gathered from the head and spine (C7-S1). Movements were completed under a baseline condition as well as upward, downward, leftward, and rightward head and gaze orientations. For each condition, mean neck angle and inter-segmental spine (C7T1 through L5S1) ROM were evaluated. The results demonstrate that directed head and gaze orientations can influence the ROM of specific spine regions during a forward flexion task. With leftward and rightward directed head and gaze orientations, the neck became increasingly twisted and superior thoracic segments (i.e. C7T1-T2T3) were significantly more twisted during the leftward head orientation condition than the baseline condition. With upward and downward directed head and gaze orientations, a similar effect was observed for neck and superior thoracic (i.e. C7T1-T4T5) flexion-extension. Interestingly, it was also demonstrated that changes in upward/downward head orientation can also change flexion-extension kinematics of the thoracolumbar region as well (i.e. T7T8-L1L2), suggesting that head postures requiring neck extension may also promote extension throughout these spine regions. These findings provide evidence for a functional link between changes in neck flexion-extension posture and flexion-extension movement of the thoracolumbar region of the spine.

Concurrent validity of a wearable IMU for objective assessments of functional movement quality and control of the lumbar spine.

Inertial measurement units (IMUs) are being recognized in clinical and rehabilitation settings for their ability to assess movement-related disorders of the spine for better guidance of treatment-planning and tracking of recovery. This study evaluated the Mbientlab MetaMotionR IMUs, relative to Vicon motion capture equipment in measuring local dynamic stability of the spine (quantified using maximum finite-time Lyapunov exponent; λmax), lumbopelvic coordination (quantified using mean absolute relative phase; MARP), and intersegmental motor variability (quantified using deviation phase; DP) of lumbopelvic segments in 10 participants during 35 cycles of repetitive spine flexion-extension (FE). Intraclass correlations were strong between systems when using both the FE angle time-series and the sum of squares (SS) time-series to measure local dynamic stability (0.807 ≤ICC2,1λmax,FE ≤ 0.919; 0.738 ≤ ICC2,1λmax,SS ≤ 0.868), sagittal-plane lumbopelvic coordination (0.961 ≤ICC2,1MARP ≤ 0.963), and sagittal-plane lumbopelvic variability (0.961 ≤ICC2,1DP ≤ 0.963). It was concluded that the MetaMotionR IMUs can be reliably used for measuring features associated with spine movement quality and motor control during a repetitive FE task. Future work will assess the reliability of sensor placement, performance during multi-directional movements, and ability to discern clinical and healthy populations based on assessment of movement quality and control.

Experimentally induced neck pain causes a decrease in thoracic but not lumbar spine stability.

Maintenance of spine stability is considered to be a critical component of spine health. Ross et al. (2015) used a topical capsaicin/heat pain sensitization model to experimentally induce lower back pain, and demonstrated that the experimental pain experience caused a decrease in the muscular contribution to lumbar spine rotational stiffness (related to mechanical stability) as well as lower back local dynamic stability (LDS). It has yet to be established if pain elsewhere in the body, specifically in other regions of the spine, can similarly affect the stability of the lower back. The purpose of this investigation was therefore to quantify thoracic and lumbar spine LDS as well as the muscular contribution to lumbar spine rotational stiffness after an experimental neck pain protocol. Results demonstrated that LDS of the thoracic spine decreased in response to the capsaicin/heat induced neck pain. Limited adaptation was required at the lumbar spine as demonstrated by the lack of statistically significant changes in lower back LDS or rotational stiffness.

Effects of foot position on skin structural deformation.

As the largest and most superficial organ, the skin is well positioned for receiving sensory information from the environment. It is conceivable that changes in posture could result in deformations of the skin and subsequent changes in skin material properties. Specifically, the ankle and metatarsophalangeal joints have the capability to undergo large postural alterations with the potential to induce large structural deformations in the skin of the foot. The purpose of this study was to determine the extent to which alterations in foot posture may influence measures of foot sole and dorsum skin stretch, hardness, and thickness in vivo. Ten young and healthy individuals were tested while three static foot postures (plantar flexion, neutral and dorsiflexion) were maintained passively. Skin stretch deformation was quantified across each posture using an 11 × 4 point matrix of 3D kinematic markers affixed to the skin of the foot sole and dorsum. Skin hardness was assessed across each posture at specific locations of the foot sole (1st metatarsal, 5th metatarsal, medial arch, lateral arch and heel) and foot dorsum (proximal, middle and distal) using a handheld Shore durometer. Skin (epidermal + dermal) thickness was measured in each posture from the same test locations using ultrasound images obtained for the foot sole and dorsum. In the plantar flexion ankle posture, the foot sole skin was observed to relax/retract on average (± standard errorr of the mean (SEM) by 9 ± 2% to become both 20 ± 6% softer and 10 ± 6% thicker. In this posture, the foot dorsum skin stretched on average by 7 ± 2% resulting in 84 ± 8% harder and 5 ± 4% thinner skin. In the dorsiflexion ankle posture, the skin of the foot sole was observed to stretch on average by 5 ± 1% to become both 20 ± 8% harder and 4 ± 7% thinner. In this posture, the skin of the foot dorsum relaxed/retracted on average by 9 ± 1% resulting in the skin becoming 27 ± 12% softer and 7 ± 5% thicker. Notably, all of the sites responded with movement in a similar direction, but each site responded to a variable extent. Importantly, it was clear that the majority of skin structural deformation of the foot sole occurred within the 1st metatarsal, 5th metatarsal, and medial arch regions, while deformation was more evenly distributed across regions of the foot dorsum. The results suggest there is location specificity in the retraction and stretch characteristics of the foot skin. While not tested directly, this may suggest that local stretch distributions could be in part due to the underlying dermal and hypodermal structures in these foot regions. With these observed changes in the mechanical structure of the foot sole and dorsum skin tissue matrix, it is possible that corresponding posture-dependent changes in cutaneous mechanoreceptor activation may be present.

Discriminating spatiotemporal movement strategies during spine flexion-extension in healthy individuals.

BACKGROUND CONTEXT: The spine is an anatomically complex system with numerous degrees of freedom. Due to this anatomical complexity, it is likely that multiple motor control options exist to complete a given task. PURPOSE: To identify if distinct spine spatiotemporal movement strategies are utilized in a homogenous sample of young healthy participants. STUDY DESIGN: Kinematic data were captured from a single cohort of male participants (N=51) during a simple, self-controlled spine flexion-extension task. METHODS: Thoracic and lumbar flexion-extension data were analyzed to extract the continuous relative phase between each spine subsection. Continuous relative phase data were evaluated using a principal component analysis to identify major sources of variation in spine movement coordination. Unsupervised machine learning (k-means clustering) was used to identify distinct clusters present within the healthy participants sampled. Once distinguished, intersegmental spine kinematics were compared amongst clusters. RESULTS: The findings of the current work suggest that there are distinct timing strategies that are utilized, within the participants sampled, to control spine flexion-extension movement. These strategies differentiate the sequencing of intersegmental movement and are not discriminable on the basis of simple participant demographic characteristics (ie, age, height, and body mass index), total movement time or range of motion. CONCLUSIONS: Spatiotemporal spine flexion-extension patterns are not uniform across a population of young healthy individuals. CLINICAL SIGNIFICANCE: Future work needs to identify whether the motor patterns characterized with this work are driven by distinct neuromuscular activation patterns, and if each given pattern has a varied risk for low back injury.

Distinguishing between typical and atypical motion patterns amongst healthy individuals during a constrained spine flexion task.

Despite 'abnormal' motion being considered a risk factor for low back injury, the current understanding of 'normal' spine motion is limited. Identifying normal motion within an individual is complicated by the considerable variation in movement patterns amongst healthy individuals. Therefore, the purpose of this study was to characterize sources of variation in spine motion among a sample of healthy participants. The second objective of this study was to develop a multivariate model capable of predicting an expected movement pattern for an individual. The kinematic shape of the lower thoracic and lumbar spine was recorded during a constrained dynamic trunk flexion movement; as this is not a normal everyday movement task, movements are considered 'typical' and 'atypical' for this task rather than 'normal' and 'abnormal'. Variations in neutral standing posture accounted for 85% of the variation in spine motion throughout the task. Differences in total spine range of flexion and a regional re-weighting of range of motion between lower thoracic and lumbar regions explained a further 9% of the variance among individuals. The analysis also highlighted a difference in temporal sequencing of motion between lower thoracic and lumbar regions which explained 2% of the total movement variation. These identified sources of variation were used to select independent variables for a multivariate linear model capable of predicting an individuals' expected movement pattern. This was done as a proof-of-concept to demonstrate how the error between predicted and observed motion patterns could be used to differentiate between 'typical' and 'atypical' movement strategies.

The effect of attentional focus on local dynamic stability during a repetitive spine flexion task.

The association between low back pain and spine movement control suggests that it is important to reliably quantify movement behavior. One method to characterize spine movement behavior is to measure the local dynamic stability (LDS) of spine movement during a repetitive flexion task in which a participant is asked to touch multiple targets repetitively. Within the literature, it has been well established that an individual's focus of attention (FOA) can modulate their neuromuscular control and affect task performance. The goal of this project was to examine the unknown effect of FOA on LDS measurements and timing error during a repetitive spine flexion task that is commonly used to assess movement control. Fourteen healthy adults (7 male) were instructed to touch two targets (shoulder height and knee height) to the beat of a metronome (4 s/cycle) for 35 consecutive cycles. They completed this task under internal (focus on trunk movement) and external (focus on targets) FOA conditions. Motion capture data of the trunk and sacrum were collected at 120 Hz. The lumbar spine angle was defined as the orientation of the trunk relative to the pelvis. The local divergence exponent (λmax) was calculated from the sum of squares of the 3-dimensional spine angle. Timing error was calculated as the time difference between target touches and metronome beats. Changing an individual's FOA had no effect on λmax calculations or timing error. Although clear task instructions are important, it is not essential to control for FOA during this movement assessment protocol.