Tammy M. Owings

Variability of step kinematics in young and older adults

Fall-related injuries are the most common and serious medical problems facing older adults. Recent studies of older adults have focused on the variability of step kinematics and the relationship to falling. The accuracy of step variability estimates is proportional to the number of steps that are collected. The use of an instrumented treadmill allows simultaneous collection of spatial and temporal step kinematics for a large number of continuous steps. The current study was conducted to determine the influence of age, walking velocity and handrail use on the variability of step kinematics using a treadmill protocol. Eighteen young adults (average age: 27.7 +/- 3.3 years) and 12 healthy older adults (average age: 73.4 +/- 2.3 years) were recruited from the community. Temporal and spatial gait parameters were quantified using custom designed software from measurements collected during treadmill walking. The primary independent variables were the variability of step length, step width, and step time. Step width variability of older adults was significantly larger than that of young adults. Walking velocity did not influence step kinematic variability. Handrail usage influenced the variability of step length and step width, but not of step time. The present results, and those of previous studies, point to a consistent relationship between age and step width variability. Since step width variability has been implicated in falls, further research is warranted.

Foot displacement but not velocity predicts the outcome of a slip induced in young subjects while walking

The purpose of the present study was to induce slips in healthy subjects as a means to determine if recovery from an induced slip is possible under conditions in which the displacements and velocities of the slipping foot exceed the generally accepted limits of 10cm and 50cm/s, respectively, and to determine if there are gait-related variables that predispose an individual to falling after a slip. Thirty-three young and barefoot adults, protected by an instrumented safety harness, were subjected to a single slipping trial following a series of unperturbed walking trials. The slip was induced when the bare foot contacted a vinyl sheet coated with mineral oil. Lower extremity kinematics were acquired using a video-based motion capture system. Fourteen and 12 subjects could be unambiguously categorized as having fallen or recovered, respectively. Four variables demonstrated significant between-group differences and two were used to compute the probability of the slip outcome using logistic regression. The variables were the displacement of the foot during the slip and the angle of the shank relative to the ground at the instant of ground contact just prior to the slip. Separate univariate logistic regressions using each variable were significant and correctly classified about 70% of the slip outcomes. The results demonstrated that previously published values for the displacement and velocity of the slipping foot, 10cm and 50cm/s, respectively, may not accurately represent the upper limits beyond which recovery is not possible. The results also demonstrated that heel-strike angle, reflective of stride length, exerts a significant influence on the outcome of a slip.

Mechanisms of failed recovery following postural perturbations on a motorized treadmill mimic those associated with an actual forward trip.

OBJECTIVE To examine the recovery strategies employed during a treadmill acceleration task, to determine if mechanisms that contributed to failed recoveries on a motorized treadmill are the same general biomechanical mechanisms that contributed to falls from a trip, and to determine if failed recovery responses could be modified to allow for successful recoveries on subsequent trials. DESIGN A motorized treadmill was used to induce postural perturbations in healthy older adults. BACKGROUND Previously, we induced trips in older adults to identify the mechanisms of failed recovery. However, inducing trips is not a clinically practical test for identifying older adults who are predisposed to falling. METHODS Safety-harnessed older adults stood on a treadmill that was accelerated from 0 to 0.89 m/s to impose a postural perturbation. Recoveries were classified as successful (n=42) or failed (n=23). Selected biomechanical variables were calculated using motion analysis methods. RESULTS Initial failed recoveries had slower reaction times, shorter step lengths, and greater trunk flexion angles and velocities. Subjects who failed on the initial attempt modified their recovery strategy to successfully recover. The biomechanics of these recoveries resembled those used by subjects who successfully recovered on their initial attempt. CONCLUSIONS The biomechanical mechanisms involved with a failed treadmill recovery mimic those responsible for failed recoveries from an induced trip. Subjects who failed on their initial recovery response made modifications allowing successful recoveries on subsequent attempts. RELEVANCE This protocol may be useful as a testing and rehabilitation tool for fall recovery.

Measures of Postural Stability Are Not Predictors of Recovery from Large Postural Disturbances in Healthy Older Adults

OBJECTIVES: To determine, in healthy older adults, the relationship between postural steadiness, stability limits, and the ability to recover balance from three postural disturbances requiring anteriorly directed stepping responses.

Influence of lower extremity strength of healthy older adults on the outcome of an induced trip

OBJECTIVES: To determine whether decreased lower extremity strength contributes to trip‐related falls in older adults.

Body segment inertial parameter estimation for the general population of older adults

The practical determination of accurate body segment inertial parameters for the general older adult population remains a problem, especially in estimating these parameters for women and accounting for variations in body type. A method is presented for determining the mass and center of mass location of the body segments of individuals within the general population of older adults. Effects of sex and body type on older adult mass distribution are accounted for using 32 easily obtainable body measurements. The method is based on existing results from different data sources and employs a combination of validated estimation approaches, including: body mass and segment length proportions, linear and nonlinear regression equations, and a mathematical model of the trunk. The method was applied to a validation sample of healthy, community-dwelling older adults (29 men, 50 women). Predicted body mass was 96.7+/-4.8% and 95.7+/-3.7% of measured body mass in the men and women, respectively. The estimates of body segment mass and trunk center of mass location for the sample population approximate those reported in the literature, supporting the validity of the described method. By producing practical, subject-specific estimates of body segment inertial parameters, the method should allow more accurate biomechanical analyses of the older adult population.

Motor Control of the Vastus Medialis Oblique and Vastus Lateralis Muscles Is Disrupted During Eccentric Contractions in Subjects with Patellofemoral Pain

Background Inappropriate control of the vastus medialis oblique and vastus lateralis muscles by the central nervous system can contribute to maltracking of the patella. Hypothesis The activation timing and amplitude of the vastus medialis oblique and vastus lateralis muscles will be different between normal subjects and patients with patellofemoral pain. Study Design Controlled laboratory study. Methods Subjects with patellofemoral pain and asymptomatic control subjects performed maximum voluntary knee extension contractions initiated from a flexed and an extended position. The activation timing and amplitude of the vastus lateralis and vastus medialis oblique muscles were quantified from the recorded electromyographic signals. Results There were no between-group differences in activation timing. The activation amplitude of the vastus medialis oblique and vastus lateralis muscles of the patellofemoral pain subjects was altered to the greatest extent during eccentric contractions and differed significantly from that of control subjects. Conclusions The activation amplitudes of the vastus medialis oblique and vastus lateralis muscles of subjects with patellofemoral pain are consistent with a laterally tracking patella during eccentric contractions. Clinical Relevance The findings suggest the clinical importance of determining whether altered activation patterns are sensitive to rehabilitation, and, if so, if subjective reports of knee joint pain and function parallel changes in the activation patterns as a result of rehabilitation.

The efficacy and safety of Grafix® for the treatment of chronic diabetic foot ulcers: results of a multi‐centre, controlled, randomised, blinded, clinical trial

In a randomised, controlled study, we compared the efficacy of Grafix®, a human viable wound matrix (hVWM) (N = 50), to standard wound care (n = 47) to heal diabetic foot ulcers (DFUs). The primary endpoint was the proportion of patients with complete wound closure by 12 weeks. Secondary endpoints included the time to wound closure, adverse events and wound closure in the crossover phase. The proportion of patients who achieved complete wound closure was significantly higher in patients who received Grafix (62%) compared with controls (21%, P = 0·0001). The median time to healing was 42 days in Grafix patients compared with 69·5 days in controls (P = 0·019). There were fewer Grafix patients with adverse events (44% versus 66%, P = 0·031) and fewer Grafix patients with wound‐related infections (18% versus 36·2%, P = 0·044). Among the study subjects that healed, ulcers remained closed in 82·1% of patients (23 of 28 patients) in the Grafix group versus 70% (7 of 10 patients) in the control group (P = 0·419). Treatment with Grafix significantly improved DFU healing compared with standard wound therapy. Importantly, Grafix also reduced DFU‐related complications. The results of this well‐controlled study showed that Grafix is a safe and more effective therapy for treating DFUs than standard wound therapy.

The efficacy and safety of Grafix ® for the treatment of chronic diabetic foot ulcers

In a randomised, controlled study, we compared the efficacy of Grafix®, a human viable wound matrix (hVWM) (N = 50), to standard wound care (n = 47) to heal diabetic foot ulcers (DFUs). The primary endpoint was the proportion of patients with complete wound closure by 12 weeks. Secondary endpoints included the time to wound closure, adverse events and wound closure in the crossover phase. The proportion of patients who achieved complete wound closure was significantly higher in patients who received Grafix (62%) compared with controls (21%, P = 0·0001). The median time to healing was 42 days in Grafix patients compared with 69·5 days in controls (P = 0·019). There were fewer Grafix patients with adverse events (44% versus 66%, P = 0·031) and fewer Grafix patients with wound‐related infections (18% versus 36·2%, P = 0·044). Among the study subjects that healed, ulcers remained closed in 82·1% of patients (23 of 28 patients) in the Grafix group versus 70% (7 of 10 patients) in the control group (P = 0·419). Treatment with Grafix significantly improved DFU healing compared with standard wound therapy. Importantly, Grafix also reduced DFU‐related complications. The results of this well‐controlled study showed that Grafix is a safe and more effective therapy for treating DFUs than standard wound therapy.

Effects of eccentrically and concentrically induced unilateral fatigue on the involved and uninvolved limbs

This study extended findings of others related to the fatigue resistance of maximum voluntary knee extension contractions performed eccentrically on an isokinetic dynamometer. Twelve subjects performed either 75 unilateral isokinetic concentric MVCs or 75 unilateral isokinetic eccentric MVCs at 30 degrees s(-1). A uniquely-configured dynamometer provided the opportunity to describe the effect of the concentric or eccentric fatigue protocol on the concentric or eccentric MVC force of the contralateral limb, which was not involved in the fatigue protocol, immediately following the conclusion of the fatigue protocol. Eccentric MVC of the eccentrically fatigued group decreased significantly (13%, p = 0.001) although the decrease was significantly smaller than that of the concentric MVC of the concentrically fatigued group (39%). Concentric MVC of the contralateral limb was unaffected following the concentric fatigue protocol but the eccentric MVC of the contralateral limb increased 11% (p = 0.028) following the eccentric fatigue protocol. These results suggest that eccentric MVCs are not resistant to fatigue but do follow a different time course than fatigue induced with concentric contractions. The extent to which eccentrically performed MVCs fatigue may reflect the influence of protocol parameters such as the isokinetic speed, the number of repetitions, the criteria by which the protocol is terminated and the subject selection. However, the explanations for why eccentric MVCs fatigue to such a smaller extent necessitate further systematic investigation including electrophysiologic methods, as do the results relative to the contralateral leg. Both results can be considered within the framework of current thought about the disparate nature of nervous system control of eccentric contractions.