Biomedical subjects

P O Riley

Publications and source records attributed to P O Riley.

At least 19 recordsLinked to original sources

PubMed2001

Propulsive adaptation to changing gait speed.

Understanding propulsion and adaptation to speed requirements is important in determining appropriate therapies for gait disorders. We hypothesize that adaptations for changing speed requirements occur primarily at the hip. The slow, normal and fast gait of 24 healthy young subjects was analyzed. The linear power was analyzed at the hip joint. The anterior-posterior and vertical induced accelerations of the hip were also determined. Linear power and anterior-posterior-induced acceleration (IA) analyses of the hip reveal that the lower limb joint's moments contribute to body forward propulsion primarily during late swing and early stance. Propulsive adaptations to speed changes occur primarily at the hip and secondarily at the ankle. These analyses show that hip muscles, particularly the hip extensors, are critical to propulsion. They also show that ankle function is primarily for support, but is important to propulsion, especially at slow speeds.

Adolescent↗

PubMed2001

The effect of voluntary toe-walking on body propulsion.

OBJECTIVE: We studied the kinetics of toe-walking by comparing the linear power flow from the leg to the upper-body. Our hypothesis was that toe-walking has no inherent biomechanical disadvantage with regard to upper-body propulsion and support. DESIGN: We studied healthy subjects capable of both heel-toe gait and voluntary toe-walking so that the two forms of gait could be directly compared. BACKGROUND: Ankle joint power at terminal stance is significantly reduced in toe-walking, which has been presumed to imply impaired propulsion and support. However, linear power analysis may be more appropriate for assessing this aspect of gait. METHODS: We compared the normal heel-toe gait of 10 healthy young adult subjects to their voluntary toe-walking gait using gait laboratory kinematic and kinetic data. Inverse dynamic analysis was performed to determine the net joint moments and joint linear powers. The contribution of each joint moment to the total hip linear power was also determined. RESULTS: Hip linear power for toe-walking was similar to that of heel-toe gait with no significant differences in the linear power peaks. The stance phase contributions of the knee and ankle moments were significantly altered in toe-walking only in early stance. CONCLUSIONS: Toe-walking does not inherently impair propulsion and support. RELEVANCE: Linear power analysis is a useful adjunct to clinical gait analysis, complementing joint power analysis. Understanding the inherent kinetics of toe-walking will enhance our analysis of pathological toe-walking and improve treatment design.

Adult↗

PubMed2001

A refined view of the determinants of gait.

We evaluated the effect of reducing the vertical displacement of the centre of mass (COM) on the six determinants of gait proposed by Saunders, Inman and Eberhart in 30 healthy adults. We compared the estimated reduction in COM vertical displacement due to the determinants in their compass model with the actual reduction of vertical displacement. The maximum height of the COM for the compass gait model occurred earlier than the actual COM maximum height. Different gait functions were determinant in reducing COM vertical displacement. In both cases heel rise was the main determinant (up to 2/3 of total reduction). Pelvic obliquity and single stance knee flexion contributions were more important when compass gait COM maximum was used while they were barely detectable at the actual COM maximum. Ipsi- and contra-lateral knee flexion were detrimental to the reduction of COM vertical displacements, while pelvic rotation contribution was beneficial and accounted for up to 10% of the overall COM vertical displacement reduction. Although a reduction of COM vertical displacement may have important energy implications, determining the specific gait parameters associated with this function is fundamental in understanding gait disability.

Adult↗

PubMed2001

Effect of age on lower extremity joint moment contributions to gait speed.

We investigated the relationship of hip, knee and ankle function to gait speed in healthy elderly subjects. We hypothesized that the hip extension moment would make a significantly smaller contribution to propulsion power in the elderly than in healthy young subjects even when the elders were ambulating at speeds comparable to those of the young subjects. We analyzed the free speed gait of 16 young and 14 elderly subjects, and the fast gait of the elder subjects. In elderly subjects free speed gait linear power transfer from the leg to the upper body due to the hip and knee moments was decreased compared with young subjects walking at their normal gait speed. However, when asked to walk fast, elders significantly increase knee and hip moment contributions to hip linear power to levels comparable to those of young subjects at a similar speed. These results refute our hypothesis and support our earlier findings indicating that kinematic alterations at the hip are a cause of reduced gait speed in the elderly.

Adolescent↗

PubMed2001

Quantification of pelvic rotation as a determinant of gait.

OBJECTIVE: To evaluate the effect of pelvic rotation, originally described as the first determinant of gait, on reducing the vertical displacement of the center of mass (COM) during comfortable speed walking. DESIGN: Pelvic and lower extremity kinematic data during walking were collected. A modified compass gait model incorporating measured inputs was used to estimate the effect of pelvic rotation on reducing the vertical displacement of the COM. The actual reduction in vertical displacement was also calculated. SETTING: A gait laboratory. PARTICIPANTS: Thirty able-bodied subjects. MAIN OUTCOME MEASURE: The estimated reduction in COM vertical displacement caused by pelvic rotation was compared with the actual reduction in COM displacement. RESULTS: The estimated effect of pelvic rotation in reducing COM displacement was 2.5 +/- 1.1mm, accounting for only 12% of the actual reduction. CONCLUSION: During normal comfortable speed walking by able-bodied subjects, pelvic rotation contributes only a small portion of the actual reduction in the vertical displacement of the COM compared with a compass gait model. Other primary gait factors or determinants are needed to explain the actual reduction in vertical displacement of the COM.

Adult↗

PubMed2001

Reduced hip extension during walking: healthy elderly and fallers versus young adults.

OBJECTIVES: To test the hypothesis that reduced hip extension range during walking, representing a limiting impairment of hip tightness, is a consistent dynamic finding that (1) occurs with increased age and (2) is exaggerated in elderly people who fall. DESIGN: Using a 3-dimensional optoelectronic motion analysis system, we compared full sagittal plane kinematic (lower extremity joint motion, pelvic motion) data during walking between elderly and young adults and between elderly fallers and nonfallers. Comparisons were also performed between comfortable and fast walking speeds within each elderly group. SETTING: A gait laboratory. PARTICIPANTS: Twenty-three healthy elderly subjects, 16 elderly fallers (otherwise healthy elderly subjects with a history of recurrent falls), and 30 healthy young adult subjects. MAIN OUTCOME MEASURES: All major peak joint angle and pelvic position values. RESULTS: Peak hip extension was the only leg joint parameter measured during walking that was both significantly lower in elderly nonfallers and fallers than in young adult subjects and was even lower in elderly fallers compared with nonfallers (all p <.05). Peak hip extension +/- standard deviation during comfortable walking speed averaged 20.4 degrees +/- 4.0 degrees for young adults, 14.3 degrees +/- 4.4 degrees for elderly nonfallers, and 11.1 degrees +/- 4.8 degrees for elderly fallers. Peak hip extension did not significantly improve when elderly subjects walked fast. CONCLUSION: An isolated and consistent reduction in hip extension during walking in the elderly, which is exaggerated in fallers, implies the presence of functionally significant hip tightness, which may limit walking performance. Overcoming hip tightness with specific stretching exercises is worthy of investigation as a simple intervention to improve walking performance and to prevent falls in the elderly.

Accidental Falls↗

PubMed2001

Can toe-walking contribute to stiff-legged gait?

OBJECTIVE: Spastic paretic stiff-legged gait, defined as reduced knee flexion in swing, has previously been attributed solely to spastic quadriceps activity. In earlier work, the authors suggested that reduced knee flexion in swing can be attributed to other indirect factors, such as poor hip flexion and abnormal foot-ankle function during gait. The present study was undertaken to determine whether toe-walking, which often occurs in conjunction with stiff-legged gait, in and of itself, might explain some of the reduced knee flexion in swing. DESIGN: An analysis was performed of three-dimensional kinematic data collected from able-bodied subjects while walking on their toes vs. normal heel-toe walking. RESULTS: Peak knee flexion was reduced significantly compared with normal heel-toe walking (42.2+/-8.9 degrees toe-walking vs. 59.2+/-5.7 degrees heel-toe walking; P < 0.00001). CONCLUSIONS: This finding, which occurred when controlling for walking speed, may be clinically relevant for patients who have both a toe-walking and a stiff-legged gait pattern. Some of the reduced knee flexion in swing may be merely a consequence of toe-walking, rather than a result of other causes, such as intrinsic spasticity or abnormal muscle firing about the knee.

Adult↗

PubMed2001

Spastic paretic stiff-legged gait: joint kinetics.

OBJECTIVE: The authors previously suggested that spastic paretic stiff-legged gait, defined as reduced knee flexion in swing associated with upper-motor neuron injury, can be attributed to multiple impairments besides spastic quadriceps activity. This study hypothesizes that subjects with spastic paretic stiff-legged gait have altered kinetics not only about the knee but also about the hip and ankle. DESIGN: Joint kinetic data of 20 subjects with spastic paretic stiff-legged gait caused by stroke were compared with data obtained from 20 able-bodied subjects. RESULTS: Significant reductions in the subject group were found in both peak knee-joint power absorption (0.42+/-0.34 vs. 0.99+/-0.27 W/(kg x m x m/sec)) and peak ankle-joint power generation (0.74+/-0.42 vs. 1.51+/-0.17 W/(kg x m x m/sec); both P < 0.0001). The authors observed increases in peak external-hip flexion torque in stance, hip-power generation in loading response, knee-extension torque in midstance, ankle-dorsiflexion torque, and ankle-power absorption in stance. There was substantial variability in most torque and power values among subjects, which was significantly greater than that observed in the control subjects. CONCLUSIONS: These findings, in conjunction with previous studies, support the likelihood of multiple mechanisms for reduced knee flexion in swing. Alternatively, some of the joint kinetic differences could be compensations for or associated with reduced knee flexion in swing. The substantial variability among subjects implies that despite a similar visual appearance of reduced knee flexion among subjects with a spastic paretic stiff-legged gait pattern, each individual has unique mechanisms associated with this observed gait pattern.

Ankle Joint↗

PubMed2000

Kinetic alterations independent of walking speed in elderly fallers.

OBJECTIVES: To determine if joint kinetic gait alterations in fallers persist when they attempt to walk at a faster speed that is more comparable with nonfallers' comfortable walking speed. DESIGN: Retrospective, case-control study. Stereophotogrammetric and force platform data were collected. SETTING: A gait laboratory. PARTICIPANTS: Sixteen elderly subjects who had at least 2 falls in the last 6 months from an unclear cause and 23 elderly subjects with no history of repeated falls. MAIN OUTCOME MEASURES: Differences in all major peak joint kinetic (moment and power) values during the gait cycle between elderly nonfallers walking at comfortable speed and elderly fallers walking at (1) comfortable and (2) fast speed. RESULTS: Statistically significant differences present at both comfortable and fast walking speeds were present in 4 sagittal plane parameters. There was an increase in peak external hip flexion moment in stance, a reduction in peak hip extension moment, a reduction in knee flexion moment in preswing, and a reduction in knee power absorption in preswing. CONCLUSION: The presence and persistence of 4 specific alterations in sagittal plane joint kinetics at both comfortable and fast walking speeds imply specific intrinsic pattern differences and allow for new insights into the mechanics of gait in elderly people who fall. The presence of these alterations also suggests they may serve as potential identifiable markers to detect those who may be at risk for falls.

Accidental Falls↗

PubMed2000

A refined view of the determinants of gait: significance of heel rise.

OBJECTIVES: Although the major determinants of gait described by Saunders and colleagues have been accepted for more than 40 years, recent investigations raise the question of whether the reduction in center of mass (COM) displacement compared with a compass gait model indeed results from the factors originally described. We tested the hypothesis that heel rise at the end of stance is a true determinant that can explain a considerable portion of the reduction in COM vertical displacement during walking. DESIGN: Stereophotogrammetric data during walking were collected. A modified compass gait model incorporating the effect of heel rise, as compared with predictions based on a standard compass model, were used to estimate the isolated effect of heel rise on reducing the vertical displacement of COM. SETTING: A gait laboratory. PARTICIPANTS: Thirty able-bodied subjects. MAIN OUTCOME MEASURE: The estimated reduction in COM displacement due to heel rise was compared with the actual reduction in displacement. RESULTS: The estimated effect of heel rise on reduction in COM displacement was 23.4+/-7.6mm, whereas the actual reduction in COM displacement was 21.2+/-6.5mm (difference not significant, paired p = .185). CONCLUSION: During normal walking, heel rise from foot flat has a considerable role in raising the height of the COM when it is at its lowest, thus reducing its overall displacement. Insofar as reduction of COM vertical displacement may have important energy implications, appreciating the specific gait parameter of heel rise is key in rehabilitative approaches to improve gait disability.

Adult↗

PubMed2000

Knee joint torques: a comparison between women and men during barefoot walking.

OBJECTIVE: To determine if knee joint torques, which are likely relevant to the development and, possibly, progression of knee osteoarthritis, are equivalent between genders during natural, barefoot walking. DESIGN: Collected stereophotogrammetric and force platform data during comfortable, barefoot walking. Knee joint torques were plotted and statistically compared between genders using both an unpaired t test (p < .05) and an equivalence test (20% delta). SETTING: A gait laboratory. PARTICIPANTS: One hundred ten healthy, nondisabled young women and men. MAIN OUTCOME MEASURES: Four knee joint torque parameters normalized for height and weight: (1) peak and (2) duration of sagittal flexor joint torque from early to midstance, and (3) first and (4) second peak coronal (frontal) varus torque values during the stance period. RESULTS: No statistically significant differences between genders were found, and the values were equivalent between genders for each of the 4 knee joint torque parameters. CONCLUSION: These findings support the hypothesis that under similar barefoot conditions women and men have a similar intrinsic biomechanic risk for knee osteoarthritis. Future research to assess the effects of other potential biomechanic factors, such as shoe-wear and activity type, may assist not only in preventing knee joint osteoarthritis, but also in developing new rehabilitative strategies to treat osteoarthritis of the knee.

Adult↗

PubMed2000

Compensatory advantages of toe walking.

OBJECTIVES: The study's hypothesis is that toe walking requires less peak muscle strength distally about the ankle and knee compared with normal heel-toe walking and thus may have compensatory advantages for patients with upper motor neuron injury and distal muscle weakness. DESIGN: Motion analysis and force platform data were collected in able-bodied subjects during toe walking and normal walking. Sagittal plane joint torques reflecting muscle force requirements and joint powers reflecting nonisometric muscle contraction were compared between the two conditions using paired t tests, applying a Bonferroni correction for multiple comparisons. SETTING: A gait laboratory. SUBJECTS: Seventeen able-bodied adults, 9 of whom were ballet dancers. MAIN OUTCOME MEASURES: Peak hip, knee, and ankle joint torque and power variables during walking. RESULTS: Peak ankle plantarflexor torque and ankle power generation during terminal stance and preswing were reduced (p<.001), as compared with normal heel-toe walking. The normal ankle dorsiflexor torque at initial contact-and the knee extensor torque and knee power generation during loading response were all essentially absent during toe walking. Hip extensor torque and hip power generation during the loading response phase were greater for toe walking (p<.001). CONCLUSION: Toe walking may require less ankle plantarflexor, ankle dorsiflexor, and knee extensor strength than normal heel-toe walking and thus may have compensatory advantages for patients with upper motor neuron injury and distal lower extremity weakness.

Adult↗

PubMed1999

Kinetics of stiff-legged gait: induced acceleration analysis.

Treating spastic paretic stiff-legged gait, defined as reduced knee flexion in swing, holds a high priority in the rehabilitation of patients with upper motor neuron lesions. We propose a method to determine the relative contributions of hip, knee, and ankle impairments to this disability. We analyzed the gait of ten patients with stiff-legged gait (SLG) due to a single stroke and ten healthy, able-bodied controls. Using subject specific models, we analyzed the induced accelerations (IA's) at the knee. Knee IA's throughout the gait cycle were calculated and the sum of the IA's was compared to the knee joint angular acceleration estimated from kinematic data. The preswing and early swing IA's were the focus of our examination as these largely determine knee kinematics in swing. Knee angular accelerations estimated from IA's and kinematic data agreed for both controls and patients. Gait cycle IA analysis of individual patients identified highly variable causes of SLG including ankle and hip joint impairments. Induced acceleration analysis (IAA) suggested that multiple impairments, not just about the knee, but also about the hip and ankle, lead to this disability. Individual subjects are likely to have individual reasons for their stiff-legged gait. Defining the link between the patients specific impairments and their gait disability should be a goal of clinical gait analysis. IAA is a useful tool for this purpose with a strong potential for clinical application.

Acceleration↗

PubMed1998

Knee osteoarthritis and high-heeled shoes.

BACKGROUND: Little is known about the effects of walking in high heels on joints in the legs. Since osteoarthritis of the knee is twice as common in women as in men, we investigated torques (forces applied about the leg joints) of women who wore high-heeled shoes. METHODS: We studied 20 healthy women who were comfortable wearing high-heeled shoes. The women walked with their own high-heeled shoes and barefoot. Data were plotted and qualitatively compared; major peak values for high-heeled and barefoot walking were statistically compared. Bonferroni adjustment was made for multiple comparisons. FINDINGS: Measurement showed increased force across the patellofemoral joint and a greater compressive force on the medial compartment of the knee (average 23% greater forces) during walking in high heels than barefoot. INTERPRETATION: The altered forces at the knee caused by walking in high heels may predispose to degenerative changes in the joint.

Adult↗

PubMed1998

Torque action of two-joint muscles in the swing period of stiff-legged gait: a forward dynamic model analysis.

Stiff-legged gait, characterized by limited knee flexion during the swing period, is a common consequence of upper motor neuron injury. The purpose of this investigation was to determine whether the rectus femoris and hamstrings muscles (which act at both the hip and knee) contribute to stiff-legged gait if active during the swing period of the gait cycle. Ten subjects with unilateral stiff-legged gait due to stroke were evaluated. Swing period free gait data were obtained. A biomechanical model of the affected limb was developed for each subject. Muscle and tendon lengths were scaled to individual subjects while constant nominal values for maximum muscle forces were used for all subjects. Torque driven forward dynamic simulations were employed to determine the sensitivity of swing period maximum knee flexion angle to changes in hip and knee torques. Combined torque and muscle driven simulations were used to access the action of specific two-joint muscles. Both hip flexion torque and knee extension torque were found to influence knee angle, but knee angle was more sensitive to changes in torque at the knee joint. The actions of the rectus femoris and long hamstrings are most marked at the knee, although their action at the hip opposes their action at the knee. Rectus femoris activity during early swing acts to limit knee flexion and contributes to stiff-legged gait. Long hamstring activity in early swing contributes to knee flexion.

Adult↗

PubMed1998

Dynamic stability in elders: momentum control in locomotor ADL.

BACKGROUND: Momentum must be controlled in stable locomotor activities, including sit-to-stand and gait. The relationship of momentum control and balance maintenance in elders or in a balance-impaired population has not been studied. Although decreased locomotor speed has long been reported among elders, the literature is lacunar concerning the mechanical mechanisms underlying this slowing. The purpose of this study was to describe the whole body and upper body linear and angular momentum for healthy elders during sit-to-stand and gait and compare them to a group of balance-impaired elders who have bilateral vestibular hypofunction (BVH). METHODS: Ten elders with BVH were matched to 10 healthy elders aged 67-90. Linear and angular momentum were calculated for sit-to-stand and for free speed and paced gait. Means and 95% confidence intervals were used to compare groups. RESULTS: Elders with BVH used significantly less linear and angular momentum to rise from a chair than healthy elders and showed excessive lateral momentum during gait, despite walking at a slower velocity. CONCLUSIONS: Healthy elders limit momentum generation by decreasing gait velocity, apparently because they lack sufficient strength or balance control to safely dissipate the momentum that a faster, less controlled gait engenders. Elders with BVH further limit momentum in locomotor activities to decrease their risk of falling, but are apparently unable to control lateral momentum during gait. Excessive lateral momentum in gait among balance-impaired elders leads to loss of balance, a frequent occurrence in this patient population.

Activities of Daily Living↗

PubMed1997

Comparison of hip center estimation using in-vivo and ex-vivo measurements from the same subject.

OBJECTIVE: To evaluate the accuracy of locating the hip center (HIPC) by comparing in-vivo estimations to posthumous HIPC measurement in the same subject. BACKGROUND: Numerous techniques have been used to locate the HIPC in living subjects and in cadavers. There are no published reports, however, which have compared measurements of the HIPC obtained in-vivo and ex-vivo for the same subject. DESIGN AND METHODS: Bilateral hip centers (HIPC) were estimated for an elderly male patient seven times over 32 months in a gait laboratory using a technique which combines kinematic data and static pointing. The patient's pelvis was recovered posthumously and analytical photogrammetry used to estimate the HIPC locations. Published methods which scale anatomical measurements to locate the HIPC were compared to our ex-vivo and in-vivo measurements. RESULTS: HIPC precision was 0.94 cm for the in-vivo measurements (N = 7 trial days) and 0.15 cm for the ex-vivo measurements (N = 6 photogrammetry trials). The resultant error between ex-vivo and in-vivo estimates of HIPC position was 1.17 cm. Resultant errors in locating the HIPC using published anatomical scaling factors ranged between 1.48 cm and 5.37 cm. CONCLUSIONS: Although we have been unable to compare in-vivo and ex-vivo HIPC measurements for more than one subject, results of our analysis suggest that using anatomical scaling to locate the HIPC may result in unsatisfactory subject-specific estimates of the HIPC.

Journal Article↗

PubMed1997

Biomechanical analysis of failed sit-to-stand.

Background sit-to-stand (STS) failure is a transient loss of balance that can engender falls among elders. The purpose of this paper is to describe the mechanisms whereby failed STS differs from successful STS. The authors compared successful STS from 11 normal elders to 20 "sitback" and 20 "step" type failed STS's in 13 subjects. Kinematic and kinetic data were incorporated into our 11-segment whole body model to estimate the net joint forces and torques and body segment momenta. Significant between group differences in the magnitude and timing of momentum generation and dissipation, knee extensor torques and the magnitude of the vertical ground reaction force were identified. Both types of failed sit-to-stand maneuvers are less energetic than successful rises. STS failures might result from either weakness or balance control and coordination impairment, or both, resulting in an insufficiently energetic effort. Further research is required to differentiate between these two possible sources of impairment. Determining the root cause of functional limitations is necessary to develop effective interventions.

Aged↗