Women have higher rates of noncontact musculoskeletal injuries compared to men, as well as at certain times in their menstrual cycles compared to others. The purpose of this study was two-fold: i) to examine the neuromuscular activation patterns of trunk musculature between men and women and ii) within women at different times in their menstrual cycle, during the trunk stability test (TST). The TST is a dynamic lower limb exercise that challenged the trunk musculature to maintain lumbopelvic stability. Surface electromyograms for 24 muscle sites and three-dimensional pelvic motion data were collected during the TST for 18 male and 19 female subjects, as well as for nine female subjects at different times in their menstrual cycles. Through analysis of amplitude and temporal characteristics of the EMG waveforms it was determined that women respond to the TST task with a less coordinated response than men, mainly relying on more co-activation. It was further determined that women have differences in their neuromuscular control patterns during the TST at different points in their menstrual cycle.

Low back pain (LBP) is associated with altered neuromuscular control of the trunk, as well as impaired performance during functional tasks highly dependent upon trunk neuromuscular control. Comparing measurements between individuals with and without LBP does not distinguish whether the LBP individual exhibits altered neuromuscular control only while experiencing LBP versus at all times. Additional insight was gained on the relationship between trunk neuromuscular control and LBP by investigating individuals who experience recurrent exercise-induced LBP (eiLBP). To differentiate the effects of LBP from individual differences, comparisons were made between episodes of pain and no pain within eiLBP individuals, and between eiLBP individuals while pain free and a group of healthy controls. Three studies were completed based on repeated measurements from both eiLBP and healthy individuals. Study 1 investigated effects of eiLBP on fundamental measures of neuromuscular control, including intrinsic trunk stiffness and the paraspinal reflex delay using a series of pseudo-random position perturbations. eiLBP individuals exhibited increased stiffness compared to healthy controls unaffected by the presence of pain, and increased reflex delays concurrent only with pain. Study 2 investigated effects of eiLBP on seated sway during a functional task involving maintaining balance. Seat and trunk kinematics were obtained while participants balanced on a wobble chair at two difficulty levels. eiLBP individuals exhibited impaired seat measures at all times, with altered trunk measures only while in pain and when the task was not challenging. Study 3 investigated effects of eiLBP on the underlying control of seated sway using a model of wobble chair balance. Quantified neuromuscular control indicated increases in proportional and noise gains for a challenging level compared to an easy level, more so for eiLBP individuals compared to controls and while experiencing pain compared to pain free. Overall, fundamental measures, seated sway measures, and identified control parameters using a model of wobble chair balance were all affected by the presence of pain within the eiLBP individuals and/or the eiLBP individuals compared to healthy controls. Therefore, this study shows that some characteristics appear to be inherent to the LBP individual, while others are only concurrent with pain. / Ph. D.

Context: Despite an association between foot structure and the incidence of lower limb injury in sport, few studies have measured the effects of neutral, pronated and supinated foot structures during dynamic activity. Furthermore, despite its widespread use as an injury prevention method, the effects of athletic taping on individuals with pronated and supinated foot structures are unclear. Objectives: To explore whether individuals with pronated and supinated foot structures have poorer lower limb neuromuscular control as measured by postural stability and muscle reaction time in comparison to those with neutral feet. Additionally, the effects of athletic taping on individuals with neutral, pronated and supinated foot structures on aspects of lower limb neuromuscular control are also examined. Subjects: All subjects used in this thesis were aged from 18 – 30 years and took part in at least two hours of exercise each week. Subjects were categorised in to groups according to navicular drop height measures; neutral 5 – 9 mm; pronated ≥ 10 mm; supinated ≤ 4 mm. Methods: Neuromuscular control was analysed in subjects with neutral, pronated and supinated feet using dynamic postural stability and muscular reaction time measures. These measures were then repeated with four athletic taping conditions (arch tape, ankle tape, proprioceptive tape and no-tape) both before and after a period of exercise. Results: Individuals with pronated and supinated foot structures were shown to have reduced postural stability in comparison to those with neutral foot structures during some dynamic tasks. Pronated and supinated foot structures also resulted in slower muscle reaction times in comparison to those with neutral feet during a tilt platform perturbation. No differences were identified between dominant and non-dominant limbs on subjects with neutral, pronated or supinated foot structures; however the high incidence of foot structure asymmetry did appear to result in differences between contralateral limbs in both postural stability and reaction time parameters. Arch and ankle taping resulted in increased neuromuscular control after application, yet these effects diminished after a period of exercise. Conclusions: The results of this thesis provide evidence to suggest that foot structure does affect lower limb neuromuscular control as measured by postural stability and muscle reaction time. In addition athletic taping has been shown to affect neuromuscular control on subjects with neutral, pronated and supinated foot structures both before and after exercise. These findings may have wide implications in sport where individuals with pronated and supinated feet may be more susceptible to injury in comparison to those with neutral feet.

We present work to transfer decentralized neuromuscular control strategies of human locomotion to powered segmented robotic legs. State-of-the-art robotic locomotion control approaches, like centralized planning and tracking in fully robotic systems and predefined motion pattern replay in prosthetic systems, do not enable the dynamism and reactiveness of able-bodied humans. Animals largely realize dexterous segmented leg performance with leg-encoded biomechanics and local feedback controls that bypass central processing. A decentralized neuromuscular controller was recently developed that enables robust locomotion for a simulated multi-segmented planar humanoid. A portion of this controller was used in an active ankle-foot prosthesis to modulate ankle torque during stance, enabling level and inclined ground walking. While these results suggest that the neuromuscular controller is a promising alternative control method for both fully robotic systems and powered prostheses, it is unclear if the controller can be transferred to multi-segmented robotic legs. The goal of this thesis is to investigate the feasibility of controlling a multi-segmented robotic leg with the proposed neuromuscular control approach, which may enable robots and powered prostheses to react to locomotion disturbances dynamically and in a human-like way. Specifically, work in this thesis investigates two hypotheses. Hypothesis one posits that the proposed decentralized swing-leg controllers enable more robust foot placements into ground targets than state-of-the-art impedance controls. Hypothesis two posits that neuromuscular swing-leg control enables more human-like motion than state-of-the-art impedance control. To transfer neuromuscular controls to powered segmented robotic legs, we use a model-based design approach. The initial transfer is focused on neuromuscular swing-leg controls, important for maintaining dynamic stability of both fully robotic systems and powered prostheses in the presence of unexpected locomotion disturbances, such as trips and pushes. We first present the design of RNL, a three segment, cable-driven, antagonistically actuated robotic leg with joint compliance. The robot’s size, weight, and actuation capabilities correspond to dynamically scaled human values. Next, a highfidelity simulation of the robot is created to investigate the feasibility of transferring neuromuscular controls, pre-tune hardware gains via optimization, and serve as a benchmark for hardware experiments. An idealized version of the swing-leg controller with mono-articular actuation, as well as the neuromuscular interpretation of this controller with multi-articular actuation is then transferred to RNL and evaluated with foot placement experiments. The results suggest that the proposed swing-leg controllers can accurately regulate foot placement of robotic legs during undisturbed and disturbed motions. Compared to impedance control, the proposed controls achieve foot placements over a range of ground targets with a single set of gains, which make them attractive candidates for regulating the motion of legged robots and prostheses in the real-world. Furthermore, the ankle trajectory traced out by the robot under neuromuscular control is more human-like than the trajectories traced out under the proposed idealized control and impedance control. In parallel to this control transfer, a synthesis method for creating compact nonlinear springs with user-defined torque-deflection profiles is presented to explore methods for improving RNL’s series elastic actuators. The springs use rubber as their elastic element, which, while enabling a compact spring design, introduce viscoelastic behavior in the spring that needs to be accounted for with additional control. To accurately estimate force developed in the rubber, an empirically characterized constitutive rubber model is developed and integrated into the series elastic actuator controller used by the RNL test platforms. Benchtop experiments show that in conjunction with an observer, the nonlinear spring prototype achieves desired behavior at actuation frequencies up to 2 Hz, after which spring behavior degrades due to rubber hysteresis. These results show that while the presented methodology is capable of realizing compact nonlinear springs, careful rubber selection that mitigates viscoelastic behavior is necessary during the spring design process.

The objective of this work was threefold: 1) to assess how local dynamic spinal stability is affected by various factors including: the personal lift-assist device (PLAD), different loads when lifting, and prolonged repetitive work; 2) to establish the between-day reproducibility of local dynamic stability and kinematic variability measures; and 3) to directly compare local dynamic spinal stability to quasi-static mechanical spinal stability. The first study was an investigation into the effects of the PLAD on local dynamic spinal stability during repetitive lifting. Short- (λmax-s) and long-term (λmax-l) maximum finite-time Lyapunov exponents were calculated from measured trunk kinematics to assess stability. PLAD use did not change λmax-s, but significantly reduced λmax-l; indicating increased local dynamic spinal stability when lifting with the device. The second study was a report on the effects of lifting two different loads (0% and 10% maximum back strength) on local dynamic spinal stability and kinematic variability, expressed as the mean standard deviation (MeanSD) across cycles. It was determined that increasing the load that was lifted significantly reduced λmax-s, but not λmax-l or MeanSD. Thus, as muscular and moment demands increased with load so did subjects’ spinal stability. The third study was designed to look at changes in local dynamic spinal stability and kinematic variability resulting from 1.5 hours of repetitive automotive manufacturing work, as well as the between-day reproducibility of the measures. Operators performed a repetitive dynamic trunk flexion task immediately pre- and post-shift, as well as at the same pre-shift time on the following day. Despite significant increases in back pain scores, operators were able to maintain their stability and variability post-shift. Moreover, λmax-s was the most reproducible measure. The final study was structured to directly compare lumbar spine rotational stiffness (quasi-static mechanical spinal stability), calculated with an EMG-driven biomechanical model, to local dynamic spine stability, during a series of dynamic lifting challenges. Results suggest that spine rotational stiffness and local dynamic stability are positively associated, as they provided similar information when lifting rate was controlled. However, both models provide unique information and future research is required to fully understand their relationship. In general, the results of these studies illustrate the potential for Lyapunov analyses of kinematic data to be used to assess local dynamic spinal stability in a variety of situations. / Thesis (Ph.D, Kinesiology & Health Studies) -- Queen's University, 2012-07-31 15:34:01.804

Muscular stabilisation strategies during activities of daily living alter in the presence of knee osteoarthritis (OA). By examining neuromuscular adaptations using our weight-bearing target match protocol, the main objective of this research is to establish sex differences in adaptations of neuromuscular control that are associated with older males and females with and without OA. 66 participants completed the protocol while EMG, ground reaction forces (GRF), and kinematics were recorded. Muscle activation patterns were presented in polar plots with an EMG vector representing normalised muscle activation in twelve directions, each representing a GRF vector scaled to 30% maximal effort. Asymmetry about the polar plot (activation occurring in one direction more than another) was determined and specificity index (SI) and mean direction of activation were calculated when appropriate. Healthy females demonstrated greater rectus femoris (RF) mean muscle magnitude (XEMG) (p=0.067) and less biceps femoris (BF) XEMG than healthy males (p=0.084) and females with OA (p=0.041), and males and females with OA demonstrated greater RF XEMG than healthy controls of the same sex (p=0.016, 0.072, respectively). Females with OA had significantly greater medial gastrocnemius XEMG than healthy females (p=0.031) and males with OA (p=0.020). Females with OA have less specificity in all muscles compared to males with OA and OA participants generally had less specificity compared to healthy controls of the same sex. Healthy males had the largest SI for lateral gastrocnemius with an asymmetrical activation pattern contrasting the more symmetrical activation pattern of all other groups. In conclusion, we suggest OA-affected adults and healthy females use a quadriceps dominant strategy to stabilise the joint, and that this strategy may be a compensatory mechanism for reduced quadriceps function. We suggest RF, BF, MG, and LG should be targeted for prophylactic intervention as they displayed altered activation strategies in participants with OA and healthy females.

The anterior cruciate ligament (ACL) plays an important role in knee joint stability, and unfortunately is one of the most commonly injured knee joint structures. The muscles surrounding the knee are also critical for stabilising the knee joint and their activations are altered following ACL injury. Despite the fact that ACL injuries are up to 8 times more likely to occur in females compared to males, there is limited research evaluating the effects of sex on how ACL-deficient individuals adjust neuromuscular control strategies during varying loading conditions. In order to have clinicians implement optimal rehabilitation strategies for ACL-deficient males and females, it is crucial to understand the adaptive functional strategies that are taking place once an ACL injury has occurred. The purpose of this thesis was therefore to provide objective and quantitative measurements describing the functional roles of muscles surrounding the knee. This was accomplished and outlined in this thesis through two chapters in manuscript format and summarised below. i) Sex and ACL-deficiency influence functional muscle roles during an isometric, weight-bearing, force-generation task First, the functional roles of muscles were quantified through the assessment of muscle activations during a series of multi-directional force-production tasks in ACL-deficient males and females while weight bearing. A highly controlled, isometric, force-matching task, whereby participants modulated ground reaction forces in various combinations of sagittal and frontal plane loads was used to quantify force-generation strategies (muscle activations and functional role) of the knee joint. Mean activation magnitudes and profile patterns from 10 muscles in the lower extremity (rectus femoris, vastus lateralis, vastus medialis, biceps femoris, semitendinosus, lateral gastrocnemius, medial gastrocnemius, tensor fascia latae, adductor muscle group, and gluteus medius) were recorded using wireless electromyography (EMG) sensors. Their activations were quantified with an orientation analysis to determine if differences in functional muscle roles existed between four groups; healthy female controls, healthy male controls, ACL-deficient females, and ACL-deficient males. Overall, different functional muscle roles were found between groups. Healthy male controls activated their muscles the most specifically; females with ACL-deficiency activated their muscles the least specifically, while healthy female controls and males with ACL-deficiency shared similar functional muscle roles. This suggests that there was a specificity hierarchy in the ability, or efficiency, to modulate the activation of muscles about the knee joint when exposed to various directional loading conditions. ii) Associations between subjective measures of knee dysfunction and measures of ground reaction forces in ACL-deficient males and females Correlational relationships were evaluated between perceived knee joint function and functional capacity of the knee joint. These relationships were calculated between patient reported outcome measures (PROM) from commonly used knee assessment scoring scales maximal generated forces in the sagittal and frontal planes. Both ACL-deficient groups had significantly lower perceived knee joint function compared to healthy controls. A trend towards significance was observed in the ability to generate maximum forces in the sagittal and frontal planes, with ACL-deficient females generating smaller maximal posterior GRFs compared to healthy females. Only two statistically significant correlations (both for ACL-deficient females) were found between maximal medial GRFs and patient reported outcome measures from the Lysholm and Tegner scoring scales. This indicates that there may be a discrepancy in the sensitivity of subjective outcome measures between sexes and their corresponding ability to generate maximum GRFs. In conclusion, sex differences exist in subjective outcome measures and the functional strategy of neuromuscular control of the knee joint both before and after ACL-injury. The results of this thesis indicate the need for sex-specific tailoring of rehabilitation programs, thus providing an opportunity to improve the success rate of rehabilitation following ACL-injury. Moreover, sensitivity of subjective outcome measures and their relation to simple, practical, functional tasks between sexes warrants further investigations.

Purpose: The purpose of this study was to investigate the relationship between anthropometric measurements, proximal and distal lower extremity muscle performance, core muscle endurance, lower extremity flexibility, and neuromuscular control with the incidence of injury in recreational runners over one season. Also, when a relationship was established, we sought to evaluate the predictive validity for any of the variables being investigated for risk of injury in this population. Study Design: Prospective cohort Methods: Anthropometric measurements, proximal and distal isometric lower extremity muscle performance, isometric core muscle endurance, lower extremity flexibility and neuromuscular control were measured in 75 recreational runners prior to the start of a graded marathon training program. Incidence of injury was tracked over the course of 18 weeks, May 2014 – October 2014. Data was analyzed comparing the differences between injured and non-injured groups. Results: There were 33 repetitive stress injuries yielding a gross injury rate of 46% (male n=13, female n=20). Of all the variables analyzed, 5 variables emerged as possible a predictors including age, dominant limb rear foot posture, non dominant limb ankle DF ROM (extended), limb difference of Y balance scale composite scores and limb difference in the 6 M hop test. These variables were entered into a binary logistic regression analysis. Results of the regression indicated only the composite Y balance score difference variable as yielding a significant contribution (p = 0.01), with and predictive validity, (OR = 1.46, 95% CI =1.127 – 1.892). The model predicted 69.2% of the injuries with a specificity of 82% and sensitivity of 54.5%. A cutoff point of 3.6% was determined using a receiver operating characteristic curve. Runners were 3 times more likely to get injured with an asymmetry ≥ 3.6%. Conclusions: An asymmetry of lower extremity neuromuscular control ≥ 3.6% measured by the Y balance scale has been identified as a potential risk factor for injury in recreational runners. Clinical Relevance: This test can be performed as part of a pre-training screening or physical and may be helpful in identifying recreational runners at risk for injury.

<p>The purpose of the thesis was to evaluate the neuromuscular control of shoulder muscles when performing concurrent shoulder and hand or elbow efforts in healthy and injured individuals. Of particular interest was the response of the supraspinatus and infraspinatus muscles to performing an additional hand task, such as gripping, while also performing different shoulder actions. Two studies were undertaken to provide the necessary groundwork for the subsequent two studies of this thesis. The first study investigated whether changes to shoulder muscle activity previously seen with gripping where the result of the novelty of using feedback to regulate grip force. This study found that changes in shoulder muscle activity with gripping are not diminished with repetition. The second study provided an improved method of normalizing electromyograms from dynamic contractions and was used in the subsequent studies of this thesis. Studies 3 and 4 of this thesis examined the response of shoulder muscles in healthy individuals during static sub-maximal efforts and maximal dynamic efforts in flexion and scapular planes with neutral and supinated forearm postures. Three conditions were tested in both studies: (i) no additional load, (ii) gripping to 30% of maximum and (iii) contracting the biceps to 30% of maximum. A prevailing theme found during sub-maximal contractions was individuality in neuromuscular recruitment strategies and precluded any significant effects of gripping or biceps contractions. During dynamic contractions, concurrent shoulder efforts with gripping and biceps contractions was found to significantly decrease deltoid, supraspinatus and infraspinatus muscle forces during flexion with supinated forearm posture. This thesis provided a thorough examination of shoulder electromyography in healthy individuals, improving our understanding of the neuromuscular control of the shoulder musculature. A common theme of this thesis was the individuality of neuromuscular strategies of the shoulder.</p> / Doctor of Science (PhD)

Women are more likely to sustain knee injuries (e.g., ACL tears) than their male counterparts. The mechanisms responsible for this disparity are unclear. However fluctuating hormones during the menstrual cycle may be an influencing factor since more ACL injuries have been observed preceding ovulation when estrogen levels increase. Previous research shows females to have increased muscle strength and altered neuromuscular activation prior to ovulation. These findings have not been replicated in females using oral contraceptives (OC). To date, no study has examined all of these factors simultaneously. The purpose of this study was to determine the effect of sex, hormones, and contraceptive use on neuromuscular function at 3 points during a menstrual cycle. A prospective cohort design with independent variables of group [male (n=10), female no-OC (n=10), female OC (n=10)], and testing session (1,2,3) was used to assess knee function (i.e., tibial translation, isometric strength, vertical leg stiffness, and neuromuscular activation) on physically active college-aged participants. Three testing sessions were scheduled throughout a typical menstrual cycle. Tibial translation was measured at the start of each testing session to assess ACL laxity, for handgrip, knee extensors and knee flexors strength. Area EMG activity of the rectus femoris (representing quadriceps) and biceps femoris (representing hamstrings) was recorded over 3 46cm drop jumps, and vertical leg stiffness was calculated based on measurements obtained by a force plate. A 3 (group) x 3 (testing session) MANOVA (p ≤ 0.05) was used to assess knee function, as defined by tibial translation, strength, EMG activation and vertical leg stiffness. A significant difference was found with respect to strength, as males overall displayed greater strength than both female groups. No other significant differences were found. Although this study attempted to explain the effect of estrogen on strength and neuromuscular function with an improved design, no conclusive evidence was found to further explain this relationship. Future studies should use more sensitive and objective measures to explore this dynamic on a greater sample size over multiple menstrual cycle phases. / Kinesiology