-
[show abstract]
[hide abstract]
ABSTRACT: OBJECTIVE: To prospectively and longitudinally examine how concussion affects gait balance control in adolescents during single and dual-task walking. DESIGN: Cohort, prospective, repeated-measures design. SETTING: Motion analysis laboratory. PARTICIPANTS: Twenty adolescents identified as suffering a concussion were matched with twenty healthy control subjects and tested five times across a two month period following injury. INTERVENTIONS: Not applicable MAIN OUTCOME MEASURES: Gait temporal-distance parameters included average walking speed, step length, step width; whole body center of mass (COM) parameters included medial/lateral displacement, and peak COM medial/lateral and anterior velocities; dual-task cost was defined as percent change from single to dual-task conditions; and Stroop test accuracy. RESULTS: No between-group differences were observed for step length and step width. The dual-task cost for average walking speed for concussed subjects was greater than control subjects across the two month testing period (main effect of group p = .019), as were the dual-task costs for peak anterior COM velocity (main effect of group p = .017) and total COM medial/lateral displacement (main effect of group p = .013). The total COM medial/lateral displacement (group x task interaction p = .006) and peak COM medial/lateral velocity (main effect of group p = .027; main effect of task p = .010) were significantly greater in concussed subjects compared with control subjects during dual-task walking. Concussed subjects were significantly less accurate than controls on the Stroop test (main effect of group p = .004). CONCLUSIONS: The findings suggest that concussion affects the ability of adolescents to control body posture during gait up to two months following injury. Furthermore, dual-task paradigms may provide additional useful information in the clinical assessment and recovery of concussion.
Archives of physical medicine and rehabilitation 04/2013; · 2.18 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The consequences of lower limb torsion deformity on knee loading in knee osteoarthritis are poorly understood. The purpose of this study was to quantify the associations between the mechanical axis, tibial torsion and knee loading in subjects with medial knee OA and in controls.
Twenty-four subjects: end-staged medial knee osteoarthritis (OA) with apparent torsion deformity (TKO, n=6) and without torsion deformity (KOA, n=8) and controls (CON, n=10) were imaged using long standing lower extremity (LSLE) radiographs and computed tomography (CT). Medial knee loading was assessed using the internal knee varus moment determined by gait analysis. The LSLE mechanical axis, CT tibial torsion and the foot progression angle were used to predict medial knee loading.
The TKOs had significantly greater mechanical axis varus and knee varus moment compared to KOAs and CONs. The regression model predicting medial knee loading using the mechanical axis (β=0.898), tibial torsion (β=0.264) and foot progression angle (β=-0.369) showed a goodness of fit of 0.774.
Medial knee loading was predicted by the mechanical axis and the foot progression angle. Future longitudinal studies are needed to assess the role of tibial intorsion during disease progression and following total knee replacement surgery.
Gait & posture 03/2011; 33(4):625-9. · 2.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this study was to assess the use of a multivariate statistical method to rank clinical and gait variables, thus describing a ranking of patient dysfunction prior to and following total knee replacement (TKR) surgery. Twenty end-stage knee osteoarthritis (KOA) subjects scheduled for TKR and 20 healthy controls performed level walking and stair ascent twice: pre- (P1) and 6 months post-surgery (P2). Clinical and gait measures were entered into a principle component analysis (PCA) to determine orthogonal principle components (PCs). The PCs were entered into a discriminant function analysis to determine the best predictors of group membership. The PCA extracted three PCs for both the P1 and P2 data sets. Three orthogonal dimensions were formed: "knee dysfunction", "gait dysfunction", and "stair ascent dysfunction". For P1 the "knee dysfunction" dimension composed of both subjective and objective measures, best discriminated between end-stage knee osteoarthritis patients and controls. For P2, the "stair ascent dysfunction" dimension best discriminated between 6 months post-TKR patients and controls. The results of this study suggest that a multivariate statistical method provides a clinically relevant ranking of patient dysfunction prior to and following TKR. This ranking of dysfunction could serve to identify rehabilitation priorities.
Gait & posture 06/2009; 30(2):197-200. · 2.58 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study examined the effect of total knee replacement surgery on the frontal plane knee varus angle and moment. Secondarily, the relationships between knee varus angle and moment to a clinical outcome measure were assessed.
Twenty-one patients with total knee replacement and 21 controls performed level walking and stair ascent at two testing periods, pre- and 6-months post-surgery. The dependent variables included frontal plane knee angle and moment, and Western Ontario and McMaster Universities Osteoarthritis Index scores.
During level walking the mean knee varus moment of the patient group was significantly greater than controls at pre-surgery but was restored to control level post-operatively. During stair ascent the patient group produced a significantly smaller knee varus moment post-surgically. The mean frontal knee valgus angle of total knee replacement patients increased significantly from pre- to post-surgery during level walking. The Western Ontario and McMaster Universities Osteoarthritis Index score was not significantly correlated to the knee variables. However, the knee angle and moment were significantly correlated during level walking pre- and post-operatively and stair ascent post-operatively.
The decreased frontal plane knee moment in total knee replacement patients during level walking appeared to be affected by surgical realignment of the tibio-femoral joint, as the frontal knee angle and varus moment were strongly correlated. The subjective Western Ontario and McMaster Universities Osteoarthritis Index and the objective gait measures appeared to capture different dimensions of knee osteoarthritis.
Clinical Biomechanics 07/2008; 23(8):1053-8. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this study was to investigate the effect of knee pain and total knee replacement (TKR) surgery on the gait stability of knee osteoarthritis (OA) patients compared to controls. Gait spatio-temporal measures, center of mass kinematics and pain levels of 21 TKR subjects and 21 controls (CON) were assessed during level walking and obstacle crossing at two testing periods, pre-surgery (P1) and 6 months post-surgery (P2). The TKR patients reported greater pain and disability than CONs at P1 and P2, walked and negotiated the obstacle more slowly and had a shorter stride length than CONs. After surgery, the TKR center of mass-center of pressure (COM-COP) separation distance and the peak anterior inclination angle were significantly smaller than CONs. Pain was found to be significantly related to sagittal plane measures, but not to similar measures in the frontal plane. The data suggest that total knee replacement surgery and pain affect gait stability predominantly in sagittal plane variables. The TKR subjects used a conservative strategy to manage the COM and COP in the sagittal plane, possibly to reduce the kinetic demands on the involved limb.
Gait & Posture 02/2008; 27(1):103-9. · 2.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Current literature provides only limited information regarding performance on dynamic motor tasks following concussion. However, recent investigations have suggested that participation in contact sports may have a negative effect on cognitive function without the existence of a medically diagnosed concussion. The purpose of this study was to examine balance control during gait in concussed and uninjured athletes and non-athletes. Twenty-eight Grade 2 concussed individuals (14 athletes and 14 non-athletes) and 28 uninjured matched controls (14 athletes and 14 non-athletes) were assessed for their gait performance within 48 h, 5, 14, and 28 days post-injury under conditions of divided and undivided attention. Athletes, whether concussed or not, walked slower and swayed more and faster than non-athletes. Athletes consistently demonstrated gait imbalance even in the absence of concussion. The findings of this study support the supposition that participation in high-impact sports has a measurable and possibly detrimental effect on balance control in the absence of a medically diagnosed concussion.
Medical Engineering & Physics 02/2008; 30(8):959-67. · 1.62 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Neuropsychological testing has been advocated as an important tool of proper post-concussion management. Although these measures provide information that can be used in the decision of when to return an individual to previous levels of physical activity, they provide little data on motor performance following injury. The purpose of this investigation was to examine the relationship between measures of dynamic motor performance and neuropsychological function following concussion over the course of 28 days.
Participants completed two experimental protocols: gait stability and neuropsychological testing. The gait stability protocol measured whole-body centre of mass motion as subjects walked under conditions of divided and undivided attention. Neuropsychological testing consisted of a computerised battery of tests designed to assess memory, reaction time, processing speed and concussion symptoms. Correlation coefficients were computed between all neuropsychological and gait variables and comparisons of neuropsychological and gait stability post-concussion recovery curves were assessed.
Dynamic motor tasks, such as walking under varying conditions of attention, are complex and demanding undertakings, which require a longer recovery time following a concussion than cognitive measures. Little statistical relationship was found between the neuropsychological and gait variables, and the recovery curves of neuropsychological and gait domains were observed to be independent.
In order to fully examine the effects of concussion and determine the optimal time for a safe return to activity, a multi-factorial approach, including both cognitive and motor tasks, should be employed.
British journal of sports medicine 01/2008; 41(12):868-73; discussion 873. · 2.55 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Joint position sense (JPS) is important in the maintenance of optimal movement coordination of limb segments in functional activities. Researchers have shown that the sensitivity of musculotendinous mechanoreceptors increases as muscle activation levels increase. In the present study, when 25 participants tried to replicate the same presented position, both vector and elevation angle repositioning errors decreased linearly as the external load increased up to 40% above unloaded shoulder torque. However, external load had no effect on plane repositioning error. The results indicated that JPS increased under conditions of increasing external load but only in the direction of the applied load. That finding indicates that JPS acuity improves as muscle activation levels increase.
Journal of Motor Behavior 12/2007; 39(6):517-25. · 1.64 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Little is known about the effects of total knee replacement surgery on the contributions of individual joint moments to the total support moment. A better understanding of these effects may enhance rehabilitation protocols and determine factors related to long-term surgical outcome.
Twenty-one subjects with total knee replacement and 21 controls performed level walking and stair ascent at two testing periods, pre- and 6 months post-surgery. Variables studied included gait velocity, stride length, knee flexion angle, net joint moments of the hip, knee and ankle, and total support moment. Data were analyzed at the first peak vertical ground reaction force.
For level walking, the total support moment, knee extensor moment, and knee flexion angle of total knee replacement patients were less than controls at post-surgery. For stair ascent, the patient group total support moment, ankle plantarflexor moment, and knee flexion angle were less than controls at both testing periods, while knee extensor moment was less than controls at post-surgery. Extensor synergies of the total knee replacement patients revealed less knee and more hip contributions during level walking and larger hip contributions during stair ascent to the total support moment than controls at both testing periods.
A feature of total knee replacement gait, pre- and post-surgery, is a stiff knee attitude which may serve to protect the quadriceps. The larger hip extensor contribution to the total support moment observed in the patients may compensate for the diminished knee extensor contribution during level walking and stair ascent.
Clinical Biomechanics 09/2007; 22(7):787-94. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Concussion, or mild traumatic brain injury (mTBI), leads to a number of cognitive, attentional, and sensorimotor deficits that can last a surprisingly long time after the initial injury. We have previously shown that the ability to orient visuospatial attention is deficient in participants with mTBI within 2 days of their injury, but then recovers to normal levels within a week. Orienting attention requires disengagement from the point of fixation, movement of attention to the location of interest, and re-engagement at that location. Deficits in any or all of these processes could lead to the difficulties with orienting attention that we have observed in mTBI. To address this issue, we tested participants with mTBI using a gap saccade task. Because this task manipulates the temporal gap between the offset of the fixation target and the appearance of the peripheral saccade target, it isolates the contribution of the disengagement process to saccadic reaction time. We found that participants with mTBI had significantly longer saccadic reaction times than controls when the temporal gap was short but not when it was long. This gap-dependent difference in saccadic reaction time was present within 2 days of the injury and resolved within 1 week. This pattern of results suggests that as the contribution of the disengagement process is reduced, so too is the extent of the reaction time deficit in the participants with mTBI. Taken together, this is consistent with the idea that the deficits in orienting visuospatial attention in participants with mTBI are fully accounted for by difficulties with the initial disengagement process.
Neuroscience Letters 05/2007; 417(1):61-5. · 2.11 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Mild traumatic brain injury (mTBI) leads to a variety of attentional, cognitive, and sensorimotor deficits. An important aspect of behavior that intersects each of these functions is the ability to cancel a planned action. Thus, the purpose of this study was to determine the effects of mTBI on the ability to perform a countermanding saccade task. In this task, participants were asked to generate a saccade to a target appearing in peripheral vision, but to inhibit saccade execution if an auditory stop signal was presented. The delay between the appearance of the peripheral target and the presentation of the auditory stop signal was varied between 0 and 125ms. We found that the change in the probability of cancelling the saccade as a function of this delay was no different between participants with mTBI tested within 2 days of their injury and matched controls. However, saccadic reaction times and the stop signal reaction time were unexpectedly faster in the participants with mTBI and, furthermore, they inaccurately inhibited saccades during 15% of the trials with no stop signal. Taken together, this data suggests that the ability to cancel planned actions is subtly yet adversely affected by mTBI.
Neuropsychologia 02/2007; 45(2):406-11. · 3.64 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The need to identify functional impairment following a brain injury is critical to prevent reinjury during the period of recovery. However, little is known about the effect of concussion on dynamic motor function.
The purpose of this study was to examine the effect of concussion on a dynamic motor task under conditions of divided and undivided attention over the course of 28 d.
Fifteen subjects with concussions (CONC) and 15 uninjured controls (NORM) were observed while walking with undivided attention and while concurrently completing simple mental tasks. The CONC were assessed within 48 h of injury and again at 5, 14, and 28 d postinjury. The NORM were evaluated at the same time intervals. Whole-body motion data were collected to examine displacement and velocity of the center of mass (COM) and the maximum separation between the COM and center of pressure (COP). Three-way repeated-measures mixed-design ANOVA and Tukey post hoc tests were completed to determine differences between group, task, and testing day (P<0.05).
Several aspects of gait stability were compromised in the CONC group for up to 4 wk after injury. CONC were found to walk significantly slower during dual tasks on all testing days when compared with the uninjured controls. The injured subjects were also found to have greater sway and sway velocity than controls when attention was divided for up to 28 d postinjury.
The findings of this study suggest that concussion may have long-term observable and measurable effects on the control of gait stability.
Medicine & Science in Sports & Exercise 06/2006; 38(6):1032-40. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The goal of the current investigation was to probe the deficits in the alerting, orienting and executive components of visuospatial attention in individuals who have recently suffered a mild traumatic brain injury (mTBI) and to assess the rate and degree of recovery for each of these components over a month post-injury. A group design was employed to assess and compare the performance of participants (12 males, 8 females; mean age: 21 +/- 1.74 years) identified with mTBI relative to control subjects matched for gender, age, height, weight and activity level. Participants performed the attentional network test, designed to isolate the constituents of attention into alerting, orienting and executive components. Reaction times (RTs) and response accuracy were the main dependent variables. The results showed that the orienting and executive components were significantly affected by mTBI immediately after the injury, whereas the alerting component was not. Furthermore, participants with mTBI recovered from the deficits in the orienting component of attention within a week of their injury, whereas the deficits in the executive component remained throughout the month post-injury. In addition, the RT cost to generate accurate compared with inaccurate responses was significantly larger in participants with mTBI than in controls, and this difference was maintained throughout the 1 month testing period. These findings indicate that the regions of the brain associated with the orienting and executive components of visuospatial attention may be most susceptible to neural damage resulting from mTBI. Moreover, the lack of recovery in the executive component indicates that the degree and time course for recovery may be regionally specific.
Brain 04/2006; 129(Pt 3):747-53. · 9.46 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Proprioception, encompassing the submodalities of kinesthesia and joint position sense, is important in the maintenance of joint stability, especially in the shoulder. The purpose of this study was to examine the effects of plane and elevation angle on unconstrained shoulder joint position sense. Twenty-two subjects (12 male, 10 female) without a history of shoulder pathology were recruited from a university campus. Subjects attempted to replicate, with respect to plane and elevation angles, various target positions. Target positions consisted of five plane angles at 90 degrees of arm elevation and five arm elevation angles in the scapular plane. All target positions were tested twice to assess the reliability of the measurement. Intraclass correlation coefficients were generally low across target positions, possibly owing to the novelty and demanding nature of the task. No differences in repositioning errors were observed between plane angles (p = 0.255). Repositioning errors decreased linearly as the elevation angle increased from 30 degrees to 90 degrees (p = 0.007) and increased again from 90 degrees to 110 degrees of elevation (p = 0.029). Our results suggest that unconstrained joint position sense may be enhanced with increased muscular activation levels. Further, afferent feedback from musculotendinous mechanoreceptors may dominate over that from capsuloligamentous sources in unconstrained movements.
Journal of Orthopaedic Research 04/2006; 24(3):559-68. · 2.81 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The need to identify functional impairment following a brain injury is critical to prevent re-injury during the period of recovery. While many neuropsychological tests have been developed to assess cognitive performance, relatively little information on gait and dynamic stability is available on motor task performance for young adults following concussion. This study was performed to investigate the effect of divided attention following concussion on various gait variables. It was hypothesized that, when compared to uninjured controls, concussed subjects would demonstrate deficits in maintenance of dynamic stability.
Ten subjects with Grade 2 concussion completed testing within 48 h of injury as well as 10 age-, height-, weight-, and activity-matched controls. The gait protocol consisted of level walking under two conditions: (1) undivided attention (single-task) and (2) while simultaneously completing simple mental tasks (dual-task). Whole-body motion data were collected using a six-camera motion analysis system. A 13-segment biomechanical model was used to compute whole body center of mass motion and velocity.
Walking with a concurrent cognitive task resulted in significant changes in gait and center of mass measurements for both groups. Concussed subjects were found to be able to conservatively adjust their whole body center of mass motion to maintain dynamic stability while walking without divided attention. However, while walking with divided attention, subjects with concussion demonstrated a significantly greater medio-lateral center of mass sway.
These data suggest that the ability to control and maintain stability in the frontal plane during walking is diminished under divided attention in individuals following a concussion.
Clinical Biomechanics 06/2005; 20(4):389-95. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: OBJECTIVE To determine bilateral lower extremity joint accommodations during gait in anterior cruciate ligament deficient subjects and uninjured controls.
Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and 3 months following reconstructive surgery, and 10 uninjured controls.
It is possible that bilateral joint accommodations could occur as a result of anterior cruciate ligament injury and in response to surgical repair. Few studies have investigated bilateral joint accommodations to anterior cruciate ligament injury and there is little consistency in the reported results.
Bilateral lower extremity kinematic and kinetic data were collected from 12 walking trials and inverse dynamics calculations were made to estimate bilateral knee and hip joint angle, moment, and power patterns during the stance phase of gait.
Control subjects exhibited asymmetrical hip but symmetrical knee joint moment and power patterns. In contrast, the anterior cruciate ligament deficient subjects exhibited symmetrical hip and asymmetrical knee joint moment and power patterns prior to and following reconstructive surgery.
Gait asymmetry in healthy subjects should not be considered pathological. In addition, chronic anterior cruciate ligament injury results in joint specific, bilateral lower extremity accommodations in gait mechanics. These accommodations persist 3 months following surgical repair.
Clinical Biomechanics 03/2004; 19(2):136-44. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine how chronic anterior cruciate ligament deficient and surgically repaired subjects react to unexpected forward perturbations during gait as compared to healthy controls.
Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and three months following reconstructive surgery, and 10 uninjured controls.
The ability of an anterior cruciate ligament injured individual to react and maintain equilibrium during gait perturbations is critical for the prevention of reinjury. No studies have investigated how these individuals respond to unexpected perturbations during normal gait.
An unexpected forward perturbation was induced upon heel strike using a force plate capable of translational movement.
Prior to surgery, the anterior cruciate ligament subjects exhibited a greater knee extensor moment in response to the perturbation compared to healthy controls. Following surgery, the anterior cruciate ligament injured subjects exhibited a static knee position and a sustained knee extensor moment throughout stance in response to the perturbation as compared to controls.
These data suggest that chronic anterior cruciate ligament deficient subjects rely heavily on knee extensor musculature to prevent collapse in response to an unexpected perturbation. This same reactive response was more pronounced 3 months following surgery.
The results suggest that, prior to and following surgery, chronic anterior cruciate ligament injured subjects respond differently than healthy controls to an unexpected perturbation during gait. Anterior cruciate ligament injured or repaired subjects do not reduce or avoid vigorous contraction of the quadriceps muscles when responding to gait perturbations.
Clinical Biomechanics 03/2003; 18(2):132-41. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The purpose of this investigation was to determine the effect of unexpected forward perturbations (FP) during gait on lower extremity joint mechanics and muscle Electromyographic (EMG) patterns in healthy adults. The muscles surrounding the hip were found to be most important in maintaining control of the trunk and preventing collapse in response to the FP. Distinct lower extremity joint moment and power patterns were observed in response to the FP but an overall positive moment of support (M(s)) was maintained. Therefore, reactive balance control was a synchronized effort of the lower extremity joints to prevent collapse during the FP.
Gait & Posture 01/2003; 16(3):238-48. · 2.12 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: To determine how normal gait patterns may change as a result of chronic anterior cruciate ligament deficiency and subsequent reconstructive surgery.
Gait testing of 10 chronic anterior cruciate ligament deficient subjects prior to and 3 months following reconstructive surgery, and 10 uninjured controls.
There is controversy whether persons with chronic anterior cruciate ligament deficiency develop a "quadriceps avoidance" pattern and how anterior cruciate ligament reconstructive surgery influences gait mechanics in these same individuals.
Gait analysis was employed to determine kinematic, kinetic, and muscle Electromyographic data.
Prior to surgery, no anterior cruciate ligament deficient subject exhibited a quadriceps avoidance pattern. Following surgery, the subjects exhibited a significantly greater knee extensor moment during early stance as compared to the control group. Prior to and following surgery, anterior cruciate ligament deficient subjects demonstrated a significantly greater hip extensor moment possibly to reduce anterior tibial translation. CONCLUSIONS; These data suggest that (1) development of a quadriceps avoidance pattern is less common than previously reported, (2) anterior cruciate ligament deficient subjects accommodate through alterations of hip joint mechanics, (3) surgical repair significantly alters lower extremity gait patterns, and (4) re-establishment of pre-injury gait patterns takes longer than 3 months to occur.
The results suggest that chronic anterior cruciate ligament deficient subjects do not exhibit a quadriceps avoidance gait pattern. Surgical intervention significantly alters lower extremity gait mechanics in a population that has accommodated to anterior cruciate ligament deficiency.
Clinical Biomechanics 06/2002; 17(4):274-85. · 2.07 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: INTRODUCTION According to Kahnemn's [2] model of information processing, processing capacity in humans is limited. When two tasks are presented to an individual, the desired outcome(s) will occur so long as the capacity of the system has not been exceeded. Once the capacity has been reached, there will be a decline in performance in one or all tasks. It has been estimated that, between the ages of 15-24 years, 133 people out of 100,000 will receive a traumatic brain injury (TBI) each year [3]. This accounts for 31.7% of all concussions. The maintenance of dynamic stability while perturbed by different secondary tasks is crucial day by day. Motor perturbations have been previously described to have significant detrimental effects on a TBI population [1]. To date, there have been no studies measuring a simple reaction time, a cognitive, and a motor dual-task with level walking, specifically in a concussed population. Our study looked to determine how different secondary tasks affect dynamic stability of patients with concussion and how balance is maintained during each task. METHODS Subjects (Conc), n=11, were identified as suffering a grade II concussion within 48 hours of collection. Controls (Norm), n=8, were matched by gender, age, and stature. The whole body motion data were collected with an 8-camera motion analysis system (Motion Analysis Corp., Santa Rosa, CA) during gait. Twenty-nine reflective markers were placed on bony landmarks. A thirteen-link model was created, each with the segmental center of mass (CoM) defined according to Winter [4]. The whole -body CoM was calculated using the weighted sum of each segment [1]. Center of pressure (CoP) location was found with two force plates (AMTI, Watertown, MA). The collection was divided into three parts. The single task session (level) was walking without a concurrent task. The first dual task session (OB) required crossing an obstacle at 10% of body height midway down the walkway. The second dual task session (COG) added in a cognitive task (e.g. backward digit span, spelling backwards) to level walking. Then the 3rd dual task session added a simple reaction time test (RT on) that was imposed with random catch trials (RT off) while walking. During RT trials, the subject responds to an audio perturbation by pressing a button on a wireless remote. Gait temporal-distance parameters as well as the maximum CoM-CoP separation distances and the time -corresponding CoM linear velocities in the anterior-posterior (A/P) and medio-lateral (M/L) directions were examined [1]. 2x5 ANOVA's with repeated measures were used to assess the differences between tasks and groups. If there was a significant difference (p<.05), a post-hoc pairwise comparison was completed to find between which specific tasks there was significance.
