Plantar Kinetics During Wheeled Knee Walker Use Compared to Different Assistive Walking Devices in Persons With Type 2 Diabetes Mellitus.

Background: Diabetic patients with foot ulcers are commonly prescribed assistive walking devices to unload the affected foot and promote tissue healing. However, the effect on shear loads to the contralateral foot is unknown. This study investigated the effect of a wheeled knee walker (WKW), compared to common devices, on compressive and shear plantar forces carried by the propulsive foot during walking in patients with type 2 diabetes mellitus. A secondary objective investigated plantar forces' correlations with body weight unloaded (BWU). Methods: Participants walked a maximum of 200 m per condition during normal walking or when using crutches, a standard walker, and a WKW in randomized order. Plantar forces were measured with force plates, and wireless force-sensitive pads measured BWU through the hands. The WKW was instrumented to measure BWU onto the seat and handlebars. Three-dimensional motion capture confirmed gait events. Results: The WKW produced the lowest vertical, braking, propulsive, and medial shear forces but the highest lateral shear force among all conditions. Using crutches or a walker had negligible medial and lateral shear (mean = -6.69 N and -7.80 N), with normal walking producing the highest medial shear. There was a poor relationship between BWU and assistive walking devices and shear force values. Conclusion: A WKW could be the preferred assistive device for unloading a diabetic foot ulcer. The magnitude of lateral force would need further investigation to determine ulceration risk, given patient susceptibility and neuropathy. Clinical Relevance: Understanding shear forces on the propulsive foot is important for minimizing contralateral limb tissue damage risk while treating an ulcer. Different assistive walking devices change walking patterns and affect shear forces on the plantar surface of the foot. Although the WKW minimizes several loading metrics, a clinical trial investigating assistive walking device compliance and wound healing in diabetic foot ulcer patients across devices is needed.

Hand loading, rates of perceived exertion, and usability during assisted walking in patients with type 2 diabetes mellitus.

BACKGROUND: Patients suffering from a diabetic foot ulcer often receive a non-weight bearing prescription of the affected limb to promote healing. Total unilalteral offloading of the affected foot necessitates walking aids that require loading at the hands during ambulation. Excessive loading at the hands can increase of the risk of crutch palsy. In addition, certain walking aids can also be more strenuous and less comfortable to use than others, resulting in lower prescription compliance. This study aimed to investigate hand loading, rates of perceived exertion, and usability of typically prescribed walking aids in patients with Type 2 Diabetes. METHODS: Twenty patients (12 F | 8 M, 61.0 ± 10.36 yrs., 90.54 ± 13.34 kg, 1.71 ± 0.08 m) walked as much as 200 m without assistance and with crutches, walkers, and a wheeled knee walker instrumented with flexible force-sensing pads on walking aid handles. Patients rated exertion using a Modified Borg Scale and completed a System Usability Scale questionnaire after each walking condition with or without walking aids. FINDINGS: Results show that using a wheeled knee walker required 94% less hand loading than crutches and walkers. Patients reported 45% lower exertion with the WKW compared to crutches and walkers, and scored the usability of the wheeled knee walker 106% higher than crutches and walkers. INTERPRETATION: The wheeled knee walker could be the preferred walking aid for total unilateral offloading because of the reduced loading demand at the hands, lower exertion during use, and greater usability compared to crutches and walkers.

Comparison of markerless and marker-based motion capture of gait kinematics in individuals with cerebral palsy and chronic stroke: A case study series.

Background: Three-dimensional (3D) motion analysis is an advanced tool used to quantify movement patterns in adults with chronic stroke and children with cerebral palsy. However, gold-standard marker-based systems have limitations for implementation in clinical settings. Markerless motion capture using Theia3D may provide a more accessible and clinically feasible alternative, but its accuracy is unknown in clinical populations. The purpose of this study was to quantify kinematic differences between marker-based and markerless motion capture systems in individuals with gait impairments. Methods: Three adults with chronic stroke and three children with cerebral palsy completed overground walking trials while marker-based and markerless motion capture data were synchronously recorded. Time-series waveforms of 3D ankle, knee, hip, and trunk angles were stride normalized and compared. Root mean squared error, maximum peak, minimum peak, and range of motion were used to assess discrete point differences. Pearson's correlation and coefficient of multiple correlation were computed to assess similarity between the time series joint angle waveforms from both systems. Results: This study demonstrates that markerless motion capture using Theia3D produces good agreement with marker-based in the measurement of gait kinematics at most joints and anatomical planes in individuals with chronic stroke and cerebral palsy. Conclusions: This is the first investigation to study the feasibility of Theia3D markerless motion capture for use in chronic stroke and cerebral palsy gait analysis. Our results indicate that markerless motion capture may be an acceptable tool to measure gait kinematics in clinical populations to provide clinicians with objective movement assessment data.

Muscle activation and rating of perceived exertion of typically developing children during DRY and aquatic treadmill walking.

Aquatic treadmill gait training is a poorly understood rehabilitation method that alters bodyweight support, increases lower limb resistance, and assists with postural stability. This training could be an attractive tool for clinical populations with balance control issues or limited weight-bearing prescriptions for the lower limb. As a first step, the purpose of this study was to quantify differences in mean muscle activity of the tibialis anterior, rectus femoris, medial gastrocnemius, and semitendinosus, and perceived exertion (RPE) in typically developing children (7:8 M:F, age = 11.3 ± 4.1 years, 1.46 ± 0.18 m, and 44.2 ± 16.8 kg) during dry and aquatic treadmill walking at 75 %, 100 %, and 125 % self-selected speed. We hypothesized that the greatest mean muscle activity, normalized to percent maximum voluntary contraction and averaged across all strides, would be observed during 125 % dry treadmill walking and that aquatic treadmill walking would produce lower RPE. Overall, aquatic treadmill walking reduced mean medial gastrocnemius activity by 50.2 % (padj < 0.001), increased mean rectus femoris activity at least 32.8 % (padj < 0.006), and produced 78.0 % (padj = 0.007) greater RPE compared to dry treadmill walking. This study provides normative pediatric data for future aquatic treadmill walking studies in clinical populations to help inform gait rehabilitation protocols.

Alterations to plantar loading and ankle range of motion of the contralateral foot during assisted walking in patients with Type 2 Diabetes Mellitus.

AIMS: Patients with diabetic foot ulcers are instructed to be non-weight bearing on the affected limb to promote healing. Therefore, the aim of this study was to investigate the effect of different assistive devices on whole foot plantar loading, peak forefoot force, ankle range of motion, and locomotion speed during gait in patients with Type 2 Diabetes Mellitus. METHODS: Participants walked normally, with crutches, a walker, and a wheeled knee walker (WKW) in randomized order. Force sensitive insoles and 3D motion capture were used to record plantar normal force and ankle kinematics. Force sensitive pads were wrapped around handles of the crutches and walker to measure bodyweight offloaded onto the assistive device. An instrumented WKW was used to measure bodyweight offloaded onto the handlebars and knee cushion. RESULTS: Locomotion with the WKW produced the lowest whole foot plantar loading and peak forefoot force in the propulsive limb, while also producing the greatest ankle range of motion and locomotion speed amongst assistive devices. CONCLUSIONS: This pre-clinical study found that the WKW could be the preferred assistive device for total unilateral offloading of diabetic foot ulcers as it reduced propulsive limb whole foot and forefoot plantar loading while retaining ankle range of motion and locomotion speed.

Lower Limb Movement Pattern Differences Between Males and Females in Squatting and Kneeling.

Movement pattern differences may contribute to differential injury or disease prevalence between individuals. The purpose of this study was to identify lower limb movement patterns in high knee flexion, a risk factor for knee osteoarthritis, and to investigate kinematic differences between males and females, as females typically develop knee osteoarthritis more commonly and severely than males. Lower extremity kinematic data were recorded from 110 participants completing 4 variations of squatting and kneeling. Principal component analysis was used to identify principal movements associated with the largest variability in the sample. Across the tasks, similar principal movements emerged at maximal flexion and during transitions. At maximal flexion, females achieved greater knee flexion, facilitated by a wider base of support, which may alter posterior and lateral tibiofemoral stress. Principal movements also detected differences in movement temporality between males and females. When these temporal differences occur due to alterations in movement velocity and/or acceleration, they may elicit changes in muscle activation and knee joint stress. Movement variability identified in the current study provides a framework for potential modifiable factors in high knee flexion, such as foot position, and suggests that kinematic differences between the sexes may contribute to differences in knee osteoarthritis progression.

Implications of Walking Aid Selection for Nonweightbearing Ambulation on Stance Limb Plantar Force, Walking Speed, Perceived Exertion, and Device Preference in Healthy Adults 50 Years of Age and Older.

BACKGROUND: Young adults often tolerate the increased energy expenditure, coordination, and stance limb discomfort associated with walking aids for nonweightbearing ambulation. Adults aged ≥50 years may not have the same tolerance. Therefore, the objective of this study was to determine how walking aid selection affects stance limb plantar force, walking speed, perceived exertion, and device preference in adults aged ≥50 years. METHODS: A prospective randomized crossover study was performed using healthy adults, aged ≥50 years, with no use of walking aids within 5 years. Participants walked 200 m in 4 randomized conditions: single nonweightbearing ambulation using crutches, a walker, a wheeled knee walker, and unaided walking. An in-shoe sensor measured stance limb plantar force, a stopwatch timed each walk, perceived exertion was reported using the BORG CR-10 scale, and device preference was identified. RESULTS: Twenty-one participants (7 male; age: 56 ± 5 years; BMI: 26.6 ±1.9) showed stance limb plantar force was lowest when using a wheeled knee walker (P < .001). Walking speed was similar in unaided and wheeled knee walker conditions (1.41 and 1.31 m/s), but slower with crutches or a walker (42%-68%, P < .001). Perceived exertion was similar in unaided and wheeled knee walker conditions (1.6 and 2.8), but higher with crutches or a walker (5.7 and 6.1, P < .001). Most (20/21) participants preferred the wheeled knee walker. CONCLUSIONS: Using a wheeled knee walker for nonweightbearing ambulation reduced stance limb plantar force, maintained unaided walking speed and perceived exertion, and was preferred to crutches or a walker. LEVEL OF EVIDENCE: Level II, comparative study.

Analysis of invoked slips while wearing flip-flops in wet and dry conditions: Does alternative footwear alter slip kinematics?

Minimal footwear has become more ubiquitous; however, it may increase slip severity. This study specifically examined the slipping kinematics of flip-flop sandals. Invoked slips from standing were evaluated in dry and wet tile, and a unique wet footbed + wet tile condition, with 40, 50, and 60% bodyweight (BW) committed to the slipping foot. Water did not alter peak slip velocity (PV) at 40% BW, but PV increased with greater slip-foot force on wet tile by ~1 m/s. Interestingly, when floor-contact was lost during the slip, the flip-flops could come off the heel. This decoupling occurred most often when both the tile and footbed were either dry or wet. Given that both decoupling and greater PV were observed on wet tile, slipping in flip-flops under wet conditions may have more serious consequences. The results highlight that slips may occur at both the foot-flip-flop, and flip-flop-tile interfaces.

Development of a Full Flexion 3D Musculoskeletal Model of the Knee Considering Intersegmental Contact During High Knee Flexion Movements.

A musculoskeletal model of the right lower limb was developed to estimate 3D tibial contact forces in high knee flexion postures. This model determined the effect of intersegmental contact between thigh-calf and heel-gluteal structures on tibial contact forces. This model includes direct tracking and 3D orientation of intersegmental contact force, femoral translations from in vivo studies, wrapping of knee extensor musculature, and a novel optimization constraint for multielement muscle groups. Model verification consisted of calculating the error between estimated tibial compressive forces and direct measurements from the Grand Knee Challenge during movements to ∼120° of knee flexion as no high knee flexion data are available. Tibial compression estimates strongly fit implant data during walking (R2 = .83) and squatting (R2 = .93) with a root mean squared difference of .47 and .16 body weight, respectively. Incorporating intersegmental contact significantly reduced model estimates of peak tibial anterior-posterior shear and increased peak medial-lateral shear during the static phase of high knee flexion movements by an average of .33 and .07 body weight, respectively. This model supports prior work in that intersegmental contact is a critical parameter when estimating tibial contact forces in high knee flexion movements across a range of culturally and occupationally relevant postures.

Changes to stance limb peak, cumulative, and regional plantar foot forces among normal walking and three mobility aids in healthy older adults.

BACKGROUND: Mobility aids are commonly prescribed to offload an injured lower extremity. Device selection may impact stance foot loading patterns and foot health in clinical populations at risk of foot ulceration. RESEARCH QUESTIONS: Two questions motivated this study: How does device selection influence peak plantar and regional (rearfoot, mid foot and forefoot) foot forces on the stance foot? Does device selection influence peak, cumulative, and regional plantar forces within a 200 m walking trial? METHODS: Twenty-one older adults walked 200 m at self-selected pace in four randomized conditions for this prospective crossover study. Participants used a walker, crutches, wheeled knee walker (WKW), and no assistive device (control condition). Plantar forces were measured using a wireless in-shoe system (Loadsol, Novel Inc., St. Paul, MN). Repeated measures analyses of variance were used to determine differences in peak and cumulative total and regional forces among walking conditions. Paired sample t-tests compared forces during first and last 30 s epochs of each condition to determine device influence over time. RESULTS: The WKW reduced peak net forces by 0.29 and 0.35 bodyweight (BW) when compared to the walker or control condition with similar trends in all foot regions. Crutch use had similar peak forces as control. There were no differences in the number of steps taken within devices comparing first and last epochs. Crutches had a 0.04 and 0.07 BW increase in peak net and forefoot forces during the last epoch. Walker use had 66.44 BW lower cumulative forefoot forces in the last epoch. SIGNIFICANCE: Crutches had similar stance foot loading as normal walking while a walker lowered forefoot forces at the expense of increased steps. A WKW may be the best choice to 'protect' tissues in the stance foot from exposure to peak and cumulative forces in the forefoot region.

Haemodynamic and cerebrovascular effects of intermittent lower-leg compression as countermeasure to orthostatic stress.

NEW FINDINGS: What is the central question of this study? Does smartly timed intermittent compression of the lower legs alter cerebral blood velocity and oxygenation during acute orthostatic challenges? What is the main finding and its importance? Intermittent compression timed to the local diastolic phase increased the blood flux through the legs and heart after two different orthostatic stress tests. Cerebral blood velocity improved during the first minute of recovery, and indices of cerebral tissue oxygenation remained elevated for 2 min. These results provide promise for the use of lower-leg active compression as a therapeutic tool for individuals vulnerable to initial orthostatic hypotension and orthostatic stress. ABSTRACT: Intermittent compression of the lower legs provides the possibility of improving orthostatic tolerance by actively promoting venous return and improving central haemodynamics. We tested the hypothesis that intermittent compression of 65 mmHg timed to occur only within the local diastolic phase of each cardiac cycle would attenuate the decrease in blood pressure and improve cerebral haemodynamics during the first minute of recovery from two different orthostatic stress tests. Fourteen subjects (seven female) performed four squat-to-stand transitions and four repeats of standing bilateral thigh-cuff occlusion and release (TCR), with intermittent compression of the lower legs applied in half of the trials. Blood flow in the superficial femoral artery, mean arterial pressure, Doppler ultrasound cardiac output, total peripheral resistance, middle cerebral artery blood velocity (MCAv) and cerebral tissue saturation index (TSI%) were monitored. With both orthostatic stress tests, there was a significant compression × time interaction for superficial femoral artery flow (P < 0.001). The hypotensive state was attenuated with intermittent compression despite decreased total peripheral resistance (squat-to-stand, compression × time interaction, P < 0.001; TCR, compression × time interaction, P = 0.002) as a consequence of elevated cardiac output in both tests (P < 0.001). Intermittent compression also increased MCAv (P = 0.001) and TSI% (P < 0.001) during the squat-to-stand transition and during TCR (MCAv and TSI%, compression × time interaction, P < 0.001). Intermittent compression of the lower legs during quiet standing after an active orthostatic challenge augmented local, central and cerebral haemodynamics, providing potential as a therapeutic tool for individuals vulnerable to orthostatic stress.

Prediction of thigh-calf contact parameters from anthropometric regression.

High knee flexion postures are common in industry and cultural practices, but the mechanical effect of intersegmental force, particularly thigh-calf contact force, on knee joint compressive force is poorly understood. Although some studies have measured thigh-calf contact parameters occurring in a number of high flexion postures, joint contact modeling would benefit from efforts to predict thigh-calf contact force for use in computational models. Therefore, this study assessed the strength of correlations and linear multiple regression models on the following five high flexion thigh-calf contact parameters in a young, healthy population: the onset angle of thigh-calf contact, maximum flexion angle, total thigh-calf contact force, center of force, and contact area at maximum flexion. Regressions used anthropometric values (and in some cases, maximum flexion angle). Overall, maximum flexion angle and center of force location had the most significant correlates and strong linear fits with regressive models. Thigh-calf contact onset, total force magnitude, and contact area had only moderate to weak relationships. An exploratory attempt at regression using grouped movements into gross patterns (e.g. two types of squatting were grouped into a general squatting category) using maximum flexion angle and center of force location as dependent variables resulted in similar model fitting. These findings suggest that a causal relationship between select anthropometrics and lower limb range of motion may exist, but further exploration is necessary to determine clinically reliable predictive models.

Representing fine-wire EMG with surface EMG in three thigh muscles during high knee flexion movements.

Activation waveforms of vastus intermedius, adductor magnus, and semimembranosus have not been reported for high knee flexion activities such as kneeling or squatting, likely due to the invasive procedures required for their measurement. Their relatively large physiological cross sectional areas would suggest their contributions to knee joint loading could be considerable. Therefore, the purpose of this study was to quantify the activities of these muscles using fine-wire EMG and to assess easy to measure surface sites (vastus lateralis, rectus femoris, vastus medialis, semitendinosus, and biceps femoris) for their potential as proxy measures using <10 %MVC RMS and >0.85 R2 as criteria for successful representation of deep muscle activity by that measured at a surface site. Overall, no surface and fine-wire site pair met both criteria for these movements. When fine-wire measurement of muscle activity is infeasible or impractical, the waveforms presented in supplementary material could be used as a guide for the activity of these deep muscles. Although select muscles for some participants satisfied our criteria, inter-participant variability was considerable. Therefore, future muscle models may benefit from fine-wire measurement of these muscles, but researchers should be cautious of electrode site specificity.

Thigh-calf contact parameters for six high knee flexion postures: Onset, maximum angle, total force, contact area, and center of force.

In high knee flexion, contact between the posterior thigh and calf is expected to decrease forces on tibiofemoral contact surfaces, therefore, thigh-calf contact needs to be thoroughly characterized to model its effect. This study measured knee angles and intersegmental contact parameters in fifty-eight young healthy participants for six common high flexion postures using motion tracking and a pressure sensor attached to the right thigh. Additionally, we introduced and assessed the reliability of a method for reducing noise in pressure sensor output. Five repetitions of two squatting, two kneeling, and two unilateral kneeling movements were completed. Interactions of posture by sex occurred for thigh-calf and heel-gluteal center of force, and thigh-calf contact area. Center of force in thigh-calf regions was farther from the knee joint center in females, compared to males, during unilateral kneeling (82 and 67 mm respectively) with an inverted relationship in the heel-gluteal region (331 and 345 mm respectively), although caution is advised when generalizing these findings from a young, relatively fit sample to a population level. Contact area was larger in females when compared to males (mean of 155.61 and 137.33 cm2 across postures). A posture main effect was observed in contact force and sex main effects were present in onset and max angle. Males had earlier onset (121.0°) and lower max angle (147.4°) with onset and max angles having a range between movements of 8° and 3° respectively. There was a substantial total force difference of 139 N between the largest and smallest activity means. Force parameters measured in this study suggest that knee joint contact models need to incorporate activity-specific parameters when estimating loading.

Knee joint moments during high flexion movements: Timing of peak moments and the effect of safety footwear.

AIM: (1) Characterize knee joint moments and peak knee flexion moment timing during kneeling transitions, with the intent of identifying high-risk postures. (2) Determine whether safety footwear worn by kneeling workers (construction workers, tile setters, masons, roofers) alters high flexion kneeling mechanics. METHODS: Fifteen males performed high flexion kneeling transitions. Kinetics and kinematics were analyzed for differences in ascent and descent in the lead and trail legs. RESULTS: Mean±standard deviation peak external knee adduction and flexion moments during transitions ranged from 1.01±0.31 to 2.04±0.66% body weight times height (BW∗Ht) and from 3.33 to 12.6% BW∗Ht respectively. The lead leg experienced significantly higher adduction moments compared to the trail leg during descent, when work boots were worn (interaction, p=0.005). There was a main effect of leg (higher lead vs. trail) on the internal rotation moment in both descent (p=0.0119) and ascent (p=0.0129) phases. CONCLUSION: Peak external knee adduction moments during transitions did not exceed those exhibited during level walking, thus increased knee adduction moment magnitude is likely not a main factor in the development of knee OA in occupational kneelers. Additionally, work boots only significantly increased the adduction moment in the lead leg during descent. In cases where one knee is painful, diseased, or injured, the unaffected knee should be used as the lead leg during asymmetric bilateral kneeling. Peak flexion moments occurred at flexion angles above the maximum flexion angle exhibited during walking (approximately 60°), supporting the theory that the loading of atypical surfaces may aid disease development or progression.

Peak activation of lower limb musculature during high flexion kneeling and transitional movements.

Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions. Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.

Influence of Input Hardware and Work Surface Angle on Upper Limb Posture in a Hybrid Computer Workstation.

OBJECTIVE: We evaluated the effect of work surface angle and input hardware on upper-limb posture when using a hybrid computer workstation. BACKGROUND: Offices use sit-stand and/or tablet workstations to increase worker mobility. These workstations may have negative effects on upper-limb joints by increasing time spent in non-neutral postures, but a hybrid standing workstation may improve working postures. METHOD: Fourteen participants completed office tasks in four workstation configurations: a horizontal or sloped 15° working surface with computer or tablet hardware. Three-dimensional right upper-limb postures were recorded during three tasks: reading, form filling, and writing e-mails. Amplitude probability distribution functions determined the median and range of upper-limb postures. RESULTS: The sloped-surface tablet workstation decreased wrist ulnar deviation by 5° when compared to the horizontal-surface computer when reading. When using computer input devices (keyboard and mouse), the shoulder, elbow, and wrist were closest to neutral joint postures when working on a horizontal work surface. The elbow was 23° and 15° more extended, whereas the wrist was 6° less ulnar deviated, when reading compared to typing forms or e-mails. CONCLUSION: We recommend that the horizontal-surface computer configuration be used for typing and the sloped-surface tablet configuration be used for intermittent reading tasks in this hybrid workstation. APPLICATION: Offices with mobile employees could use this workstation for alternating their upper-extremity postures; however, other aspects of the device need further investigation.

Viscoelastic creep induced by repetitive spine flexion and its relationship to dynamic spine stability.

Repetitive trunk flexion elicits passive tissue creep, which has been hypothesized to compromise spine stability. The current investigation determined if increased spine flexion angle at the onset of flexion relaxation (FR) in the lumbar extensor musculature was associated with altered dynamic stability of spine kinematics. Twelve male participants performed 125 consecutive cycles of full forward trunk flexion. Spine kinematics and lumbar erector spinae (LES) electromyographic (EMG) activity were obtained throughout the repetitive trunk flexion trial. Dynamic stability was evaluated with maximum finite-time Lyapunov exponents over five sequential blocks of 25cycles. Spine flexion angle at FR onset, and peak LES EMG activity were determined at baseline and every 25th cycle. Spine flexion angle at FR increased on average by 1.7° after baseline with significant increases of 1.7° and 2.4° at the 50th and 100th cycles. Maximum finite-time Lyapunov exponents demonstrated a transient, non-statistically significant, increase between cycles 26 and 50 followed by a recovery to baseline over the remainder of the repetitive trunk flexion cycles. Recovery of dynamic stability may be the consequence of increased active spine stiffness demonstrated by the non-significant increase in peak LES EMG that occurred as the repetitive trunk flexion progressed.