Improvement of postural stability and gait velocity after cervical decompression surgery in patients with cervical spondylotic myelopathy.

OBJECTIVE: Cervical spondylotic myelopathy (CSM) is a progressive degenerative condition that can lead to significant neurological deficits, including gait instability. Biomechanical alterations of gait and its various components are poorly understood. The goal of the current study was to determine how spatiotemporal gait parameters, as well as postural and dynamic stability, change after surgery in CSM patients. METHODS: A total of 47 subjects were included, with 23 test subjects and 24 controls. Baseline measurements were made for both cohorts. In the CSM cohort, repeat measurements were made at 3 and 6 months postoperatively. To record spatiotemporal and dynamic stability parameters, subjects performed walking trials over force plates on a 15-m runway. To assess postural stability, standing balance trials were conducted on a floor-mounted force plate. Three-dimensional motion analysis cameras and gait modeling software were used to quantify and visually represent results. Statistical analysis was completed using repeated-measures ANOVA and paired t-tests. Significance was set at p < 0.05. RESULTS: CSM patients had significantly increased gait velocity at the 6-month follow-up (mean 0.948 ± 0.248 m/sec/leg length) versus baseline (mean 0.852 ± 0.257 m/sec/leg length) (p = 0.039). The tilted ellipse area was significantly decreased at the 6-month follow-up compared with baseline (mean 979.8 ± 856.7 mm2 vs 598.0 ± 391.1 mm2, p = 0.018). Angular momentum excursion was not significantly different between baseline and the 3- and 6-month follow-ups. CONCLUSIONS: CSM patients displayed significant improvement in gait velocity and postural stability parameters after decompressive surgery. Dynamic stability parameters did not change significantly during the study period.

Comprehensive dynamic and kinematic analysis of the rodent hindlimb during over ground walking.

The rat hindlimb is a frequently utilized pre-clinical model system to evaluate injuries and pathologies impacting the hindlimbs. These studies have demonstrated the translational potential of this model but have typically focused on the force generating capacity of target muscles as the primary evaluative outcome. Historically, human studies investigating extremity injuries and pathologies have utilized biomechanical analysis to better understand the impact of injury and extent of recovery. In this study, we expand that full biomechanical workup to a rat model in order to characterize the spatiotemporal parameters, ground reaction forces, 3-D joint kinematics, 3-D joint kinetics, and energetics of gait in healthy rats. We report data on each of these metrics that meets or exceeds the standards set by the current literature and are the first to report on all these metrics in a single set of animals. The methodology and findings presented in this study have significant implications for the development and clinical application of the improved regenerative therapeutics and rehabilitative therapies required for durable and complete functional recovery from extremity traumas, as well as other musculoskeletal pathologies.

Evaluation of Gait and Functional Stability in Preoperative Cervical Spondylotic Myelopathy Patients.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: The aim of this study was to 1) determine postural stability and spatiotemporal gait parameters and 2) characterize dynamic stability and variances in angular momentum (AM) of preoperative cervical spondylotic myelopathy (CSM) patients compared with healthy controls. SUMMARY OF BACKGROUND DATA: CSM is the most common cause of spinal cord dysfunction in the world and can lead to significant functional deficits including proprioception and gait disturbances. Biomechanical feedback mechanisms compensating for these deficits, specifically AM regulation, have remained largely unexplored. METHODS: Fifty-six subjects: 32 preoperative Nurick grade 2 or 3 CSM patients and 24 controls were included. Standing balance trials were performed on a single force plate, while walking trials were conducted at self-selected pace over a 15 m runway and a series of five force plates. All trials were recorded with three-dimensional motion analysis cameras and gait modeling software was utilized to calculate stability, spatiotemporal gait parameters, and joint kinematics. RESULTS: Tilted ellipse area, a measure of center of pressure variance and postural stability, was significantly greater among CSM patients (847.54 ±â€Š764.33 mm2vs. 258.18 ±â€Š103.35 mm2, P < 0.001). These patients had two times as much variance medial-lateral (72.12 ±â€Š51.83 mm vs. 29.15 ±â€Š14.95 mm, P = 0.001) and over three times as much anterior-posterior (42.25 ±â€Š55.01 mm vs. 9.17 ±â€Š4.83 mm, P = 0.001) compared with controls. Spatiotemporal parameters indicated that the CSM patients tending to have slower, shorter, and wider gait compared with controls, while spending greater amount of time in double support. Compensatory AM among CSM patients was significantly increased in all three anatomic planes, where whole-body AM was approximately double that of controls (0.057 ±â€Š0.034 vs. 0.023 ±â€Š0.006), P < 0.001). CONCLUSION: Preoperative CSM patients showed significant alterations in spatiotemporal gait parameters and postural stability compared with controls, consistent with prior literature. Likewise, angular momentum analysis demonstrates that these patients have globally increased body excursion to maintain dynamic balance.Level of Evidence: 3.

Motion and Strength Analysis of 2-Tine Staple and K-Wire Fixation in Scapholunate Ligament Stabilization in a Cadaver Model.

Purpose: Previous studies have demonstrated the benefits of 2- and 4-tine staple fixation in scapholunate interosseous ligament (SLIL) reconstruction, including improved rotational control and avoidance of the articular surface. This study compared scaphoid and lunate kinematics after SLIL fixation with traditional Kirschner wire (K-wire) fixation or 2-tine staple fixation. Methods: Eight fresh frozen cadaver arms with normal scapholunate (SL) intervals were included. Infrared motion capture was used to assess kinematics between the scaphoid and lunate as the wrists were moved through a simulated dart-throw motion. Kinematic data were recorded for each wrist in 4 states: SLIL intact, SLIL sectioned, K-wire fixation across SL interval and scaphocapitate joint, and 2-tine Nitinol staple fixation across SL interval. Strength of the SL staple fixation was evaluated using an axial load machine to assess load to failure of the staple construct. Results: Range of motion of the scaphoid and lunate with SLIL intact and SLIL sectioned were similar. K-wire fixation across the SL interval significantly decreased the overall wrist range of motion as well as scaphoid and lunate motion in all planes except for scaphoid flexion. Conversely, scaphoid and lunate motion after staple fixation was similar to that in normal wrists, except for a significant decrease in scaphoid extension. Under axial load simulating a ground-level fall, 3 of 8 arms demonstrated no failure, and none of the failures was due to direct failure of the 2-tine staple. Conclusions: This study demonstrates 2-tine staple fixation across the SL interval is effective in providing initial stability and maintaining physiologic motion of the scaphoid and lunate compared with K-wire fixation after SLIL injury. Clinical relevance: This study demonstrates an alternate technique for the stabilization of the SL interval in repair of acute SLIL injuries using 2-tine staple fixation, which maintains near physiologic motion of the scaphoid and lunate after SLIL injury.

Visual Biofeedback and Changes in Lower Extremity Kinematics in Individuals With Medial Knee Displacement.

CONTEXT: Increased frontal-plane knee motion during functional tasks, or medial knee displacement, is a predictor of noncontact anterior cruciate ligament injury and patellofemoral pain. Intervention studies that resulted in a reduced risk of knee injury included some form of feedback to address aberrant lower extremity movement patterns. Research on integrating feedback into single-legged tasks and the ability to train 1 task and test another is limited. OBJECTIVE: To determine if adding real-time visual biofeedback to common lower extremity exercises would improve single-legged landing mechanics in females with medial knee displacement. DESIGN: Cohort study. SETTING: University laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-four recreationally active females with medial knee displacement were randomized to a visual-biofeedback group (n = 12; age = 19.75 ± 0.87 years, height = 165.32 ± 8.69 cm, mass = 62.41 ± 8.91 kg) or a control group (n = 12; age = 19.75 ± 0.97 years, height = 166.98 ± 6.89 cm, mass = 59.98 ± 6.24 kg). INTERVENTION(S): Individuals in the feedback group viewed a real-time digital model of their body segments generated by Microsoft Kinect. The skeletal model changed color according to the knee-abduction angle of the test limb during the exercise tasks. MAIN OUTCOME MEASURE(S): Participants completed 3 trials of the single-legged drop vertical jump (SL-DVJ) while triplanar kinematics at the trunk, hip, knee, and ankle were collected via 3-dimensional motion capture. The feedback and control groups completed lower extremity exercises with or without real-time visual biofeedback, respectively. After the intervention, participants completed 3 additional trials of the SL-DVJ. RESULTS: At baseline, the feedback group had 3.83° more ankle eversion than the control group after initial contact. After the intervention, the feedback group exhibited 13.03° more knee flexion during the flight phase of the SL-DVJ and 6.16° less knee abduction after initial contact than the control group. The feedback group also demonstrated a 3.02° decrease in peak knee-abduction excursion compared with the baseline values (P = .008). CONCLUSIONS: Real-time visual biofeedback immediately improved faulty lower extremity kinematics related to knee-injury risk. Individuals with medial knee displacement adjusted their movement patterns after a single training session and reduced their medial knee motion during a dynamic task.

Landing Stiffness Between Individuals With and Without a History of Low Back Pain.

CONTEXT: Reduced spinal stabilization, delayed onset of muscle activation, and increased knee joint stiffness have been reported in individuals with a history of low back pain (LBP). Biomechanical adaptations resulting from LBP may increase the risk for future injury due to suboptimal loading of the lower-extremity or lumbar spine. Assessing landing mechanics in these individuals could help identify which structures might be susceptible to future injury. OBJECTIVE: To compare vertical and joint stiffness of the lower-extremity and lumbar spine between individuals with and without a previous history of LBP. DESIGN: Cross-sectional study. SETTING: Research laboratory. PARTICIPANTS: There were 45 participants (24 without a previous history of LBP-age 23 [8] y, height 169.0 [8.5] cm, mass 69.8 [13.8] kg; 21 with a previous history of LBP-age 25[9] y, height 170.0 [8.0] cm, mass 70.2 [11.8] kg). INTERVENTIONS: Single-limb landing trials on the dominant and nondominant limb from a 30-cm box. MAIN OUTCOME MEASURES: Vertical stiffness and joint stiffness of the ankle, knee, hip, and lumbar spine. RESULTS: Individuals with a previous history of LBP had lower vertical stiffness (P = .04), but not joint stiffness measures compared with those without a previous history of LBP (P > .05). Overall females had lower vertical (P = .01), ankle (P = .02), and hip stiffness (P = .04) compared with males among all participants. Males with a previous history of LBP had lower vertical stiffness compared with males without a previous history LBP (P = .01). Among all individuals without a previous history of LBP, females had lower vertical (P < .01) and ankle stiffness measures (P = .04) compared with males. CONCLUSIONS: Landing stiffness may differ among males and females and a previous history of LBP. Comparisons between individuals with and without previous LBP should be considered when assessing landing strategies, and future research should focus on how LBP impacts landing mechanics.

Improvements in Lower-Extremity Function Following a Rehabilitation Program With Patterned Electrical Neuromuscular Stimulation in Females With Patellofemoral Pain: A Randomized Controlled Trial.

CONTEXT: Patellofemoral pain (PFP) is a challenging condition, with altered kinematics and muscle activity as 2 common impairments. Single applications of patterned electrical neuromuscular stimulation (PENS) have improved both kinematics and muscle activity in females with PFP; however, the use of PENS in conjunction with a rehabilitation program has not been evaluated. OBJECTIVE: To determine the effects of a 4-week rehabilitation program with PENS on lower-extremity biomechanics and electromyography (EMG) during a single-leg squat (SLS) and a step-down task (SDT) in individuals with PFP. STUDY DESIGN: Double-blinded randomized controlled trial. SETTING: Laboratory. Patients of Other Participants: Sixteen females with PFP (age 23.3 [4.9] y, mass 66.3 [13.5] kg, height 166.1 [5.9] cm). INTERVENTION: Patients completed a 4-week supervised rehabilitation program with or without PENS. MAIN OUTCOME MEASURES: Curve analyses for lower-extremity kinematics and EMG activity (gluteus maximus, gluteus medius, vastus medialis oblique, vastus lateralis, biceps femoris, and adductor longus) were constructed by plotting group means and 90% confidence intervals throughout 100% of each task, before and after the rehabilitation program. Mean differences (MDs) and SDs were calculated where statistical differences were identified. RESULTS: No differences at baseline in lower-extremity kinematics or EMG were found between groups. Following rehabilitation, the PENS group had significant reduction in hip adduction between 29% and 47% of the SLS (MD = 4.62° [3.85°]) and between 43% and 69% of the SDT (MD = 6.55° [0.77°]). Throughout the entire SDT, there was a decrease in trunk flexion in the PENS group (MD = 10.91° [1.73°]). A significant decrease in gluteus medius activity was seen during both the SLS (MD = 2.77 [3.58]) and SDT (MD = 4.36 [5.38]), and gluteus maximus during the SLS (MD = 1.49 [1.46]). No differences were seen in the Sham group lower-extremity kinematics for either task. CONCLUSION: Rehabilitation with PENS improved kinematics in both tasks and decreased EMG activity. This suggests that rehabilitation with PENS may improve muscle function during functional tasks.

Analysis and Modeling of Rat Gait Biomechanical Deficits in Response to Volumetric Muscle Loss Injury.

There is currently a substantial volume of research underway to develop more effective approaches for the regeneration of functional muscle tissue as treatment for volumetric muscle loss (VML) injury, but few studies have evaluated the relationship between injury and the biomechanics required for normal function. To address this knowledge gap, the goal of this study was to develop a novel method to quantify the changes in gait of rats with tibialis anterior (TA) VML injuries. This method should be sensitive enough to identify biomechanical and kinematic changes in response to injury as well as during recovery. Control rats and rats with surgically-created VML injuries were affixed with motion capture markers on the bony landmarks of the back and hindlimb and were recorded walking on a treadmill both prior to and post-surgery. Data collected from the motion capture system was exported for post-hoc analysis in OpenSim and Matlab. In vivo force testing indicated that the VML injury was associated with a significant deficit in force generation ability. Analysis of joint kinematics showed significant differences at all three post-surgical timepoints and gait cycle phase shifting, indicating augmented gait biomechanics in response to VML injury. In conclusion, this method identifies and quantifies key differences in the gait biomechanics and joint kinematics of rats with VML injuries and allows for analysis of the response to injury and recovery. The comprehensive nature of this method opens the door for future studies into dynamics and musculoskeletal control of injured gait that can inform the development of regenerative technologies focused on the functional metrics that are most relevant to recovery from VML injury.

Impairment-Based Rehabilitation With Patterned Electrical Neuromuscular Stimulation and Lower Extremity Function in Individuals With Patellofemoral Pain: A Preliminary Study.

CONTEXT: Patellofemoral pain (PFP) is a chronic condition that presents with lower extremity muscle weakness, decreased flexibility, subjective functional limitations, pain, and decreased physical activity. Patterned electrical neuromuscular stimulation (PENS) has been shown to affect muscle activation and pain after a single treatment, but its use has not been studied in a rehabilitation trial. OBJECTIVE: To determine the effects of a 4-week impairment-based rehabilitation program using PENS on subjective function, pain, strength, range of motion, and physical activity in individuals with PFP. DESIGN: Randomized controlled trial. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 21 patients with PFP (5 males, 16 females; age = 23.4 ± 7.6 years, height = 168.0 ± 7.5 cm, mass = 69.0 ± 19.5 kg). INTERVENTION(S): Participants completed a 4-week supervised rehabilitation program in conjunction with random assignment to receive PENS or sham treatments. MAIN OUTCOME MEASURE(S): Subjective function, pain, strength, range of motion, and physical activity levels were assessed prerehabilitation and postrehabilitation. Subjective function and pain were also assessed at 6 and 12 months postrehabilitation. Repeated-measures analyses of variance and Tukey post hoc testing were conducted with α ≤ .05. We calculated Cohen d effect sizes with 95% confidence intervals. RESULTS: Both groups had statistically and clinically meaningful differences in subjective function, pain, strength, range of motion, and activity level after 4 weeks of impairment-based rehabilitation. Improved subjective function was observed in both groups at 6 and 12 months after the interventions. The PENS group had improvements in current pain for all 3 postrehabilitation times compared with baseline measures. CONCLUSIONS: An impairment-based intervention effectively improved subjective function, pain, strength, range of motion, and physical activity levels in individuals with PFP. Participants who received PENS in addition to the rehabilitation program had improved current pain at 6 and 12 months postrehabilitation compared with baseline scores. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT02441712.

The effects of knee support on the sagittal lower-body joint kinematics and kinetics of deep squats.

Little work has been done to examine the deep squat position (>130° sagittal knee flexion). In baseball and softball, catchers perform this squat an average of 146 times per nine-inning game. To alleviate some of the stress on their knees caused by this repetitive loading, some catchers wear foam knee supports. OBJECTIVES: This work quantifies the effects of knee support on lower-body joint kinematics and kinetics in the deep squat position. METHODS: Subjects in this study performed the deep squat with no support, foam support, and instrumented support. In order to measure the force through the knee support, instrumented knee supports were designed and fabricated. We then developed an inverse dynamic model to incorporate the support loads. From the model, joint angles and moments were calculated for the three conditions. RESULTS: With support there is a significant reduction in the sagittal moment at the knee of 43% on the dominant side and 63% on the non-dominant side compared to without support. These reductions are a result of the foam supports carrying approximately 20% of body weight on each side. CONCLUSION: Knee support reduces the moment necessary to generate the deep squat position common to baseball catchers. Given the short moment arm of the patella femoral tendon, even small changes in moment can have a large effect in the tibial-femoral contact forces, particularly at deep squat angles. Reducing knee forces may be effective in decreasing incidence of osteochondritis dissecans.

Changes in Muscle Thickness Across Positions on Ultrasound Imaging in Participants With or Without a History of Low Back Pain.

CONTEXT: Injury-prediction models have identified trunk muscle function as an identifiable factor for future injury. A history of low back pain (HxLBP) may also place athletes at increased risk for future low back pain. Reduced muscle thickness of the lumbar multifidus (LM) and transversus abdominis (TrA) has been reported among populations with clinical low back pain via ultrasound imaging in multiple positions. However, the roles of the LM and TrA in a more functional cohort and for injury prediction are still unknown. OBJECTIVES: To (1) assess the reliability of LM and TrA ultrasound measures, (2) compare changes in muscle thickness across positions between persons reporting or not reporting HxLBP, and (3) determine the ability to distinguish between groups. DESIGN: Cross-sectional study. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Participants were 34 people who did not report HxLBP (age = 22 ± 7 years, body mass index = 23.7 ± 2.7) and 25 people who reported HxLBP (age = 25 ± 10 years, body mass index = 24.0 ± 3.2). MAIN OUTCOME MEASURE(S): Muscle thickness and changes in muscle thickness of the LM and TrA as shown on ultrasound imaging. RESULTS: Intraclass correlation coefficients ranged from 0.641 to 0.943 for all thickness measures and from 0 to 0.693 for all averaged thickness modulations bilaterally. Participants who reported HxLBP had voluntarily reduced TrA thickness modulations compared with those not reporting HxLBP ( P = .03), and the testing position influenced TrA thickness modulations ( P < .01). No differences were observed for LM thickness modulations between groups or positions ( P > .05). A tabletop cutoff value of 1.32 had a sensitivity of 0.640 and a specificity of 0.706, whereas a seated cutoff value of 1.18 had a sensitivity of 0.600 and a specificity of 0.647. CONCLUSIONS: In participants reporting HxLBP, TrA thickness modulations were lower and both tabletop and seated thickness modulations were able to distinguish reported HxLBP status. These findings suggest that TrA muscle function may be altered by HxLBP.

Full Step Cycle Kinematic and Kinetic Comparison of Barefoot Walking and a Traditional Shoe Walking in Healthy Youth: Insights for Barefoot Technology.

OBJECTIVE: Barefoot technology shoes are becoming increasingly popular, yet modifications are still needed. The present study aims to gain valuable insights by comparing barefoot walking to neutral shoe walking in a healthy youth population. METHODS: 28 healthy university students (22 females and 6 males) were recruited to walk on a 10-meter walkway both barefoot and in neutral running shoes at their comfortable walking speed. Full step cycle kinematic and kinetic data were collected using an 8-camera motion capture system. RESULTS: In the early stance phase, the knee extension moment (MK1), the first peak absorbed joint power at the knee joint (PK1), and the flexion angle of knee/dorsiflexion angle of the ankle were significantly reduced when walking in neutral running shoes. However, in the late stance, barefoot walking resulted in decreased hip joint flexion moment (MH2), second peak extension knee moment (MK3), hip flexors absorbed power (PH2), hip flexors generated power (PH3), second peak absorbed power by knee flexors (PK2), and second peak anterior-posterior component of joint force at the hip (APFH2), knee (APFK2), and ankle (APFA2). CONCLUSIONS: These results indicate that it should be cautious to discard conventional elements from future running shoe designs and rush to embrace the barefoot technology fashion.

Neuroplasticity in post-stroke gait recovery and noninvasive brain stimulation.

Gait disorders drastically affect the quality of life of stroke survivors, making post-stroke rehabilitation an important research focus. Noninvasive brain stimulation has potential in facilitating neuroplasticity and improving post-stroke gait impairment. However, a large inter-individual variability in the response to noninvasive brain stimulation interventions has been increasingly recognized. We first review the neurophysiology of human gait and post-stroke neuroplasticity for gait recovery, and then discuss how noninvasive brain stimulation techniques could be utilized to enhance gait recovery. While post-stroke neuroplasticity for gait recovery is characterized by use-dependent plasticity, it evolves over time, is idiosyncratic, and may develop maladaptive elements. Furthermore, noninvasive brain stimulation has limited reach capability and is facilitative-only in nature. Therefore, we recommend that noninvasive brain stimulation be used adjunctively with rehabilitation training and other concurrent neuroplasticity facilitation techniques. Additionally, when noninvasive brain stimulation is applied for the rehabilitation of gait impairment in stroke survivors, stimulation montages should be customized according to the specific types of neuroplasticity found in each individual. This could be done using multiple mapping techniques.

The effects of ankle foot orthoses on energy recovery and work during gait in children with cerebral palsy.

BACKGROUND: Studies suggest that 50% of children with cerebral palsy are prescribed ankle foot orthoses. One of the aims of ankle foot orthosis use is to aid in walking. This research examined the effects that ankle foot orthoses have on the energy recovery and the mechanical work performed by children with cerebral palsy during walking. METHODS: Twenty-one children with spastic diplegia walked with and without their prescribed bilateral ankle foot orthoses. Ten of the subjects wore articulated (hinged) orthoses and 11 subjects wore solid orthoses. Three dimensional kinematic data were collected and between and within group repeated measures ANOVAs were applied to the dependent measures. FINDINGS: The results were similar for both groups. There was an increase in stride length, energy recovery, and potential energy and the kinetic energy variation. There was no change in the mechanical work performed to walk or the normalized center of mass vertical excursion. Unfortunately, the increase in energy recovery did not alter the external work, as it was offset by increased variation in the potential and kinetic energies of the center of mass. There was a great deal of variability in the measured work, with both large increases and decreases in the work of individual subjects when wearing orthoses. INTERPRETATION: These results suggest that current ankle foot orthoses can reduce the work to walk, but do not do so for many children with cerebral palsy. This research suggests that ankle foot orthosis prescription could be aided by measuring the mechanical work during walking.

The gait of children with and without cerebral palsy: work, energy, and angular momentum.

This paper describes a method to characterize gait pathologies like cerebral palsy using work, energy, and angular momentum. For a group of 24 children, 16 with spastic diplegic cerebral palsy and 8 typically developed, kinematic data were collected at the subjects self selected comfortable walking speed. From the kinematics, the work-internal, external, and whole body; energy-rotational and relative linear; and the angular momentum were calculated. Our findings suggest that internal work represents 53% and 40% respectively of the whole body work in gait for typically developed children and children with cerebral palsy. Analysis of the angular momentum of the whole body, and other subgroupings of body segments, revealed a relationship between increased angular momentum and increased internal work. This relationship allows one to use angular momentum to assist in determining the kinetics and kinematics of gait which contribute to increased internal work. Thus offering insight to interventions which can be applied to increase the efficiency of bipedal locomotion, by reducing internal work which has no direct contribution to center of mass motion, in both normal and pathologic populations.

Angular momentum of walking at different speeds.

Recently, researchers in robotics have used regulation of the angular momentum of body segments about the total body center of mass (CoM) to develop control strategies for bipedal gait. This work was spurred by reports finding that for a "large class" of human movement tasks, including standing, walking, and running the angular momentum is conserved about the CoM. However, there is little data presented to justify this position. This paper describes an analysis of 11 male adults walking overground at 0.7, 1.0, and 1.3 times their comfortable walking speed (CWS). The normalized angular momenta about the body CoM of 12 body segments were computed about all three coordinate axes. The normalized angular momenta were both small (<0.03) and highly regulated for all subjects and walking speed with extrema that negatively correlated with walking speeds. It was found that the angular momentum of the body about its CoM during walking could be described by a small number of principal components. For the adult walkers the first three principal components accounted for more than 97% of the variability of the angular momentum about each of the three principal axes at all walking speeds. In addition, it was found that the orthogonal principal components at each speed and for each subject were similar, i.e., the vectors of the principal components at each speed and for each subject were co-linear.

Angular momentum synergies during walking.

We studied the coordination of body segments during treadmill walking. Specifically, we used the uncontrolled manifold hypothesis framework to quantify the segmental angular momenta (SAM) synergies that stabilize (i.e., reduce the across trials variability) the whole body angular momentum (WBAM). Seven male subjects were asked to walk over a treadmill at their comfortable walking speed. A 17-segment model, fitted to the subject's anthropometry, was used to reconstruct their kinematics and to compute the SAM and WBAM in three dimensions. A principal component analysis was used to represent the 17 SAM by the magnitudes of the first five principal components. An index of synergy (DeltaV) was used to quantify the co-variations of these principal components with respect to their effect on the WBAM. Positive values of DeltaV were observed in the sagittal plane during the swing phase. They reflected the synergies among the SAM that stabilized (i.e., made reproducible from stride to stride) the WBAM. Negative values of DeltaV were observed in both frontal and sagittal plane during the double support phase. They were interpreted as "anti-synergies", i.e., a particular organization of the SAM used to adjust the WBAM. Based on these results, we demonstrated that the WBAM is a variable whose value is regulated by the CNS during walking activities, and that the nature of the WBAM control changed between swing phase and double support phase. These results can be linked with humanoid gait controls presently employed in robotics.