Trail runners: Neuromuscular and biomechanical insights

Running is a popular recreational and competitive sport worldwide. Despite numerous proven health benefits associated with road running, the risk of sustaining a running-related injury (RRI) is extremely high. The cause of RRI is multifactorial and the result of running many kilometres on monotonous and mechanically stiff road surfaces has been suggested to increase the risk of sustaining an injury. Interestingly, this notion may be a key driving factor for the emergence and growing interest in, trail or 'off-road’ running. Research investigating road running has been well-described, whereas the impact of regular running on natural, dynamic trail surfaces on the musculoskeletal system has yet to be fully considered. Thus, this thesis sought to understand the trail running athlete, with particular focus on elucidating the clinical, biomechanical and neuromuscular consequences of habitual running training on off-road terrain. The present thesis begins with a comprehensive review of the literature. The aim of this chapter was to briefly describe the origins of trail running, explore the theoretical driving factors behind interest in trail running, and detail the current scientific understanding of trail running and the purported implications and benefits thereof. Gaps in the existing body of knowledge were highlighted, with recommendations for necessary future research. The first study aimed to describe clinical measures of dynamic stability in well-trained trail runners and contrast this group with age- and performance-matched road runners. All runners performed three clinical assessments: the Star Excursion Balance Test (SEBT), Unilateral Bridge Hold (UBH) and Single Leg Squat (SLS). No differences were found in UBH and SEBT assessments. During the SLS task, trail runners exhibited less ankle varus and less ankle external rotation at peak knee flexion in comparison to road runners. These findings suggest that trail runners’ performance in the SLS test may represent a kinematic adaptation to habitual terrain targeted at minimising ankle joint movement during weight-bearing. Subsequently, we aimed to determine whether running biomechanics would differ between 20 habitually shod trail runners and 20 road running counterparts due to their preferred training terrain. A special focus of this chapter was to determine whether the groups of runners presented with disparate risk of sustaining a running-related injury (RRI). To evaluate this hypothesis, all runners performed barefoot and shod overground running trials on a synthetic track. Regardless of footwear condition, trail runners presented with greater step frequency, shorter ground contact time and shorter step duration. Further group differences were observed, with trail contact time and shorter step duration. Further group differences were observed, with trail runners exhibiting notably advantageous kinematics at the level of the ankle and the foot, presenting with: smaller foot strike angle, lower pronation magnitude and velocity, and lower ankle stiffness. Considering these biomechanical parameters, it was unexpected to find that trail runners experienced similar initial loading rates (ILRs) and higher ground reaction forces to road runners in response to the synthetic track. The final experimental chapter explored the notion that preferred running terrain has an influence on neuromuscular regulation of running biomechanics. To examine this, electromyography and biomechanical variables were determined using previously described protocols. Regardless of footwear condition, trail runners exhibited greater gluteus maximus, biceps femoris and peroneus longus muscle activation during terminal swing in comparison to road runners. In addition, trail runners exhibited greater tibialis anterior activation during early swing. With regards to discrete biomechanics, trail runners presented with greater lower extremity joint stability in the sagittal plane, demonstrating lower pelvic, hip and knee flexion at initial ground contact. Interestingly, similar ground reaction forces were experienced by trail and road runners on the synthetic track, suggesting that the observed muscle 'tuning’ responses to these impact forces may be managed by the differing neuromuscular responses. The outcomes of this thesis suggest that there are numerous clinical, mechanical and neuromuscular implications of habitual running training on the trail and road. Although the present thesis is the first step to understanding the demands of regular trail running on the human body, future studies using portable motion capture and inertial systems are necessary to determine the precise influence of real-time trail running on the neuromuscular system and running biomechanics. Interestingly, trail runners demonstrated several purported 'advantageous’ kinematic and spatiotemporal parameters, and exhibited differing muscle activity patterns in comparison to road runners in a controlled laboratory setting. However, trail and road runners experienced similar ILRs in response to the synthetic track. Considering the high incidence of road RRI, and that higher vertical load has been associated with chronic RRI, this finding suggests that trail and road runners could be at similar risk of developing a RRI. However, due to the disparate nature of trail and road running terrains and the multifactorial nature of RRIs, further clarity on 1) the acute and long-term effects of off-road running and 2) the injury risk profile of a trail runner, is imperative for a holistic understanding of the risks and benefits associated with participation in this sport. We recommend that the influence of trail running on the musculoskeletal system presented in this thesis be considered as a foundation for future large-scale epidemiological and prospective injury research

SmartStim: A Recurrent Neural Network Assisted Adaptive Functional Electrical Stimulation for Walking

According to the Neuro Patience report of the Neurological Alliance, 1 in 6 people in the UK has a neurological condition. With the growth in technology, rehabilitation for neurological problems is one of the fastgrowing fields. Functional Electrical Stimulation (FES) is one of those neuro-rehabilitation methods that uses electrical nerve stimulation to restore functional muscle movements that are lost due to neurological problems such as stroke and multiple sclerosis. This neuroprosthetic device is frequently used to assist walking by treating a condition called Drop Foot, a result of paralysis of the pretibial muscles. This study proposes a two-channel FES device called the SmartStim, which has the ability to modulate its stimulation levels according to various obstacles such as stairs and ramps. This system employs a sensor-based module with a Recurrent Neural Network to classify these different walking scenarios. The module is built with Inertial Measurement sensors embedded in a pair of shoes, and the Recurrent Neural Network uses data from these sensors to predict various obstacles as the user is walking. These predictions are then used by a Fuzzy Logic Controller to control and regulate the stimulation current in two channels of the SmartStim system. In the two channels of the system, one channel will help aid with drop foot, while the other will be used to stimulate another muscle group to help access stairs and ramps by the user. The Recurrent Neural Network module in this system has been trained and tested using the k-fold cross-validation. The evaluation of this trained model shows that it can predict obstacles from sensor data at 97 percent accuracy. Currently, further testing is being performed to assess the workings of the fuzzy logic controller in combination with the Recurrent Neural Network in healthy individuals. It is expected that the SmartStim system may aid users in accessing various walking scenarios more efficiently

Anticipatory Muscle Responses for Transitioning Between Rigid Surface and Surfaces of Different Compliance: Towards Smart Ankle-foot Prostheses

abstract: Locomotion is of prime importance in enabling human beings to effectively respond in space and time to meet different needs. Approximately 2 million Americans live with an amputation with most of those amputations being of the lower limbs. To advance current state-of-the-art lower limb prosthetic devices, it is necessary to adapt performance at a level of intelligence seen in human walking. As such, this thesis focuses on the mechanisms involved during human walking, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human walking, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to different compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on a compliant surface. There is also an indication of varying responses for different surface stiffness levels. This response is observed across subjects. Results obtained are novel and useful in establishing a framework for implementing control algorithm parameters to improve powered ankle prosthesis. With this, it is possible for the prosthesis to adapt to a new surface and therefore resulting in a more robust smart powered lower limb prosthesis.Dissertation/ThesisMasters Thesis Biomedical Engineering 201

Biomechanics and Energetics of Bipedal Locomotion on Uneven Terrain.

Humans navigate uneven terrain in their everyday lives. From trails, grass, and uneven sidewalks, we constantly adapt to various surfaces in our environment. Past research has shown that walking on natural terrain, compared to walking on smooth flat surfaces, results in increased energy expenditure during locomotion. However, the biomechanical adaptations responsible for this energetic increase are unclear, since locomotion research is often conducted either on short walkways or in an outdoor setting, thus limiting data collections. To further our understanding of human locomotion on uneven terrain, I focused on quantifying the biomechanical and energetic changes due to increased terrain variability during walking and running. First, this thesis presents modifications to a regular exercise treadmill to allow for attachment of a separate uneven surface. Using this treadmill, I collected kinetic, kinematic, electromyographic, and energy expenditure data during continuous human walking and running. I showed that humans walking at 1.0m/s on an uneven surface, with a 2.5cm height variability, increased energy expenditure by 0.73W/kg (approx. 28%) compared to walking on smooth terrain. Greater energy expenditure was primarily caused by increased positive work at the hip and knee, with minor contributions from increased muscle activity and step parameter adaptations. I then showed that running at 2.3m/s on the same surface resulted in an energetic increase of 0.48W/kg (approx. 5%) compared to running on even terrain. In contrast to walking, humans compensated for uneven terrain during running by reducing positive work produced by the ankle and adapting a more crouched leg posture. The similar absolute increases in energetic cost between walking and running implied that much of this increase is likely due to surface height variability and changes in mechanical work. Finally, this work presents analytical and simulated analyses for the rimless wheel and simplest walker models. These analyses explored the relationship between gait dynamics, energy input strategies, surface unevenness and the energetic cost of walking. Together, these studies advance our understanding of the relationship between mechanics and energetics of human walking on uneven surfaces and could potentially lead to more robust and energetically efficient legged robots, prostheses and more effective clinical rehabilitation interventions.PhDKinesiology and Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111616/1/voloshis_1.pd

Gait analysis in neurological populations: Progression in the use of wearables

Gait assessment is an essential tool for clinical applications not only to diagnose different neurological conditions but also to monitor disease progression as it contributes to the understanding of underlying deficits. There are established methods and models for data collection and interpretation of gait assessment within different pathologies. This narrative review aims to depict the evolution of gait assessment from observation and rating scales to wearable sensors and laboratory technologies, and provide possible future directions. In this context, we first present an extensive review of current clinical outcomes and gait models. Then, we demonstrate commercially available wearable technologies with their technical capabilities along with their use in gait assessment studies for various neurological conditions. In the next sections, a descriptive knowledge for existing inertial based algorithms and a sign based guide that shows the outcomes of previous neurological gait assessment studies are presented. Finally, we state a discussion for the use of wearables in gait assessment and speculate the possible research directions by revealing the limitations and knowledge gaps in the literature

An investigation into perception of change in the foot-floor interface during repeated stretch-shortening cycles

Proprioceptive input is critical for normal and safe movement. There exists a gap in the literature regarding the assessment of proprioceptive function during dynamic tasks of the lower limb. To fill this gap, the present thesis has investigated perception of change in the foot-floor interface during repeated stretch-shortening cycles. This doctoral research serves as a foundation for considering proprioception as it pertains to dynamic function at the ankle

Applications of EMG in Clinical and Sports Medicine

This second of two volumes on EMG (Electromyography) covers a wide range of clinical applications, as a complement to the methods discussed in volume 1. Topics range from gait and vibration analysis, through posture and falls prevention, to biofeedback in the treatment of neurologic swallowing impairment. The volume includes sections on back care, sports and performance medicine, gynecology/urology and orofacial function. Authors describe the procedures for their experimental studies with detailed and clear illustrations and references to the literature. The limitations of SEMG measures and methods for careful analysis are discussed. This broad compilation of articles discussing the use of EMG in both clinical and research applications demonstrates the utility of the method as a tool in a wide variety of disciplines and clinical fields

Locomotor patterns in cerebellar ataxia

Several studies demonstrated how cerebellar ataxia (CA) affects gait, resulting in deficits in multi-joint coordination and stability. Nevertheless, how lesions of cerebellum influence the locomotor muscle pattern generation is still unclear. To better understand the effects of CA on locomotor output, here we investigated the idiosyncratic features of the spatiotemporal structure of leg muscle activity and impairments in the biomechanics of CA gait. To this end, we recorded the electromyographic (EMG) activity of 12 unilateral lower limb muscles and analyzed kinematic and kinetic parameters of 19 ataxic patients and 20 age-matched healthy subjects during overground walking. Neuromuscular control of gait in CA was characterized by a considerable widening of EMG bursts and significant temporal shifts in the center of activity due to overall enhanced muscle activation between late swing and mid-stance. Patients also demonstrated significant changes in the intersegmental coordination, an abnormal transient in the vertical ground reaction force and instability of limb loading at heel strike. The observed abnormalities in EMG patterns and foot loading correlated with the severity of pathology (clinical ataxia scale, ICARS) and the changes in the biomechanical output. The findings provide new insights into the physiological role of cerebellum in optimizing the duration of muscle activity bursts and the control of appropriate foot loading during locomotion

Central Nervous System Control of Dynamic Stability during Locomotion in Complex Environments

A major function of the central nervous system (CNS) during locomotion is the ability to maintain dynamic stability during threats to balance. The CNS uses reactive, predictive, and anticipatory mechanisms in order to accomplish this. Previously, stability has been estimated using single measures. Since the entire body works as a system, dynamic stability should be examined by integrating kinematic, kinetic, and electromyographical measures of the whole body. This thesis examines three threats to stability (recovery from a frontal plane surface translation, stepping onto and walking on a compliant surface, and obstacle clearance on a compliant surface). These threats to stability would enable a full body stability analysis for reactive, predictive, and anticipatory CNS control mechanisms. From the results in this study, observing various biomechanical variables provides a more precise evaluation of dynamic stability and how it is achieved. Observations showed that different methods of increasing stability (eg. Lowering full body COM, increasing step width) were controlled by differing CNS mechanisms during a task. This provides evidence that a single measure cannot determine dynamic stability during a locomotion task and the body must be observed entirely to determine methods used in the maintenance of dynamic stability

Flat versus simulated mountain trail running: a multidisciplinary comparison in well-trained runners

1This paper compares cardiopulmonary and neuromuscular parameters across three running aerobic speeds in two conditions that differed from a treadmill's movement: flat condition (FC) and unpredictable roll variations similar to mountain trail running (URV). Twenty well-trained male runners (age 33 ± 8 years, body mass 70.3 ± 6.4 kg, height 1.77 ± 0.06 m, V˙O2max 63.8 ± 7.2 mL·kg-1·min-1) voluntarily participated in the study. Laboratory sessions consisted of a cardiopulmonary incremental ramp test (IRT) and two experimental protocols. Cardiopulmonary parameters, plasma lactate (BLa-), cadence, ground contact time (GT) and RPE values were assessed. We also recorded surface electromyographic (sEMG) signals from eight lower limb muscles, and we calculated, from the sEMG envelope, the amplitude and width of peak muscle activation for each step. Cardiopulmonary parameters were not significantly different between conditions (V˙O2: p = 0.104; BLa-: p = 0.214; HR: p = 0.788). The amplitude (p = 0.271) and width (p = 0.057) of sEMG activation peaks did not change between conditions. The variability of sEMG was significantly affected by conditions; indeed, the coefficient of variation in peak amplitude (p = 0.003) and peak width (p < 0.001) was higher in URV than in FC. Since the specific physical demands of running can differ between surfaces, coaches should resort to the use of non-traditional surfaces, emphasizing specific surface-related motor tasks that are normally observed in natural running environments. Seeing that the variability of muscle activations was affected, further studies are required to better understand the physiological effects induced by systematic surface-specific training and to define how variable-surface activities help injury prevention