Striatal dopaminergic denervation and gait in healthy adults.

Parkinsonian-like motor impairments are common in the elderly. The etiology of these symptoms in the absence of clinically diagnosable Parkinson's disease (PD) is unknown. The aim of this study was to evaluate associations between striatal dopaminergic neuron losses that occur with aging and gait in healthy adults. Forty healthy subjects aged 21-85 years old underwent [(11)C]-beta-CFT dopamine transporter (DAT) positron emission tomography (PET). Subjects were also asked to walk in a gait laboratory at their own pace. Gait variables of interest included average general spatiotemporal characteristics of walking patterns and their standard deviation reflecting gait variability. Segmented nonlinear models were used to investigate the relationship between striatal DAT activity and gait while controlling for age. Gait speed, cadence, and single and double support durations were significantly slower than age-based predictions in adults with lower striatal DAT activity (P < 0.05). After controlling for age, striatal DAT activity was not significantly associated with average step length and step width and with gait variability. We conclude that dopaminergic physiology influences certain aspects of gait independent of age-related changes. The findings of this study may augur novel therapeutic approaches to treating gait disorders in the elderly.

Effects of slip severity on muscle activation of the trailing leg during an unexpected slip.

Falls and injuries due to falls are a major health concern, and accidental slips are a leading cause of falls during gait. Understanding how the body reacts to an unexpected slip can aid in developing intervention techniques to reduce the number of injuries due to falls. In this study, muscle activation patterns, specifically those of the trailing (non-slipping) limb, were studied in unexpected slips of 24 young and 24 middle-aged adults. The typical reaction of the trailing limb is swing phase interruption in an attempt to arrest the slip. Variables examined were the reactive muscle activation onset, peak electromyography (EMG) magnitude, and time-to-peak of the vastus lateralis and medial hamstring of the trailing limb. Statistical analysis was performed to determine the effects of slip severity, quantified by peak slip velocity, and age on outcome variables. As slip severity increased, the reactive activation onset of the medial hamstring was significantly faster and there was a trend approaching significance for the onset of the vastus lateralis. Additionally, the peak magnitude and time-to-peak of the vastus lateralis increased with slip severity. No significant effects of age were found on any of the output variables. These findings may aid in development of perturbation-based paradigms, as it may be possible to "tune" the postural control system to generate an appropriate response to unexpected slips.

Lower extremity corrective reactions to slip events.

A significant number of injuries in the workplace is attributed to slips and falls. Biomechanical responses to actual slip events determine whether the outcome of a slip will be recovery or a fall. The goal of this study was to examine lower extremity joint moments and postural adjustments for experimental evidence of corrective strategies evoked during slipping in an attempt to prevent falling. Sixteen subjects walked onto a possibly oily vinyl tile floor, while ground reaction forces and body motion were recorded at 350 Hz. The onset of corrective reactions by the body in an attempt to recover from slips became evident at about 25% of stance and continued until about 45% into stance, i.e. on average between 190 and 350 ms after heel contact. These reactions included increased flexion moment at the knee and extensor activity at the hip. The ankle, on the other hand, acted as a passive joint (no net moment) during fall trials. Joint kinematics showed increased knee flexion and forward rotation of the shank in an attempt to bring the foot back towards the body. Once again, the ankle kinematics appeared to play a less dominant role (compared to the knee) in recovery attempts. This study indicates that humans generate corrective reactions to slips that are different than previously reported responses to standing perturbations translating the supporting surface.

A comparison of prediction equations for the estimation of body fat percentage in non-obese and obese older Caucasian adults in the United States.

OBJECTIVES: The predictive capabilities of skinfold regression equations are limited across populations and current equations may not be well suited for the prediction of body fat in older adults or obese Americans. The goal of this study was to compare percent body fat (%BF) predicted by several skinfold regression equations to %BF determined by Dual-Energy X-ray Absorptiometry (DXA) in obese and non-obese Caucasian men and women in the United States over the age of 65 years. DESIGN: A block design was used with two blocks: obesity (non-obese/obese) and gender (male/female). All subjects underwent the same testing procedures in one visit. SETTING: University of Pittsburgh Clinical and Translation Research Center. PARTICIPANTS: Seventy-eight older healthy adults were recruited for participation. MEASUREMENTS: Actual percent body fat was determined from a whole body DXA scan. Estimated percent body fat (%BF) was calculated using skinfold measurements and established regression equations. The predictive accuracy of the regression equations was evaluated by comparing the estimated %BF to the actual %BF measured with DXA using a within subject ANOVA (α=0.05). This was done within subgroups: obese males, obese females, non-obese males and non-obese females. RESULTS: Durnin and Womersly and Jackson and Pollock had reasonably good agreement with DXA in older Caucasian American females and males, respectively. The remaining equations significantly overestimated %BF in older Caucasian American males. Mixed results were found in females with Gause-Nilsson and Jackson and Pollock significantly underestimating %BF, while Visser and Kwok overestimated %BF. CONCLUSION: Numerous factors of a population including age, race, ethnicity, gender and obesity should be considered when selecting a skinfold regression equation to estimate %BF. While Durnin and Womersly and Jackson and Pollock are recommended for predicting %BF in older Caucasian American females and males, respectively, there exists a need to develop accurate regression models that consider obesity, gender, race or ethnicity when predicting %BF in a diverse geriatric American population.

The impact of a systematic reduction in shoe-floor friction on heel contact walking kinematics-- A gait simulation approach.

Falls initiated by slips and trips are a serious health hazard to older adults. Experimental studies have provided important descriptions of postural responses to slipping, but it is difficult to determine why some slips result in falls from experiments alone. Computational modeling and simulation techniques can complement experimental approaches by identifying causes of failed recovery attempts. The purpose of this study was to develop a method to determine the impact of a systematic reduction in the foot-floor friction coefficient (mu) on the kinematics of walking shortly after heel contact (approximately 200 s). A walking model that included foot-floor interactions was utilized to find the set of moments that best tracked the joint angles and measured ground reaction forces obtained from a non-slipping (dry) trial. A "passive" slip was simulated by driving the model with the joint-moments from the dry simulation and by reducing mu. Slip simulations with values of mu greater than the subject-specific peak required coefficient of friction (RCOF), an experimental measure of slip-resistant gait, resulted in only minor deviations in gait kinematics from the dry condition. In contrast, slip simulations run in environments characterized by mu

Biomechanics of trailing leg response to slipping - evidence of interlimb and intralimb coordination.

This gait study characterizes the trailing leg's biomechanical response to slips. Twenty-eight healthy participants divided into two age groups (20-33 years and 55-67 years) were asked to walk in two conditions: a known dry floor and a glycerol-contaminated floor expected to be dry, inducing an unexpected slip of the leading foot at heel contact. Four slip-related trailing leg response strategies were identified, ranging from a minimal disruption of the swing phase to a premature ( approximately 50 ms after toe off) interruption of the swing phase. Aging effects were minimal. The response of the leading/slipping leg preceded that of the trailing limb. The magnitude of the trailing leg's response was associated with that of the knee in the leading/slipping leg, suggesting interlimb coordination. The corrective moment at the knee of the trailing leg was also correlated with that measured at the hip in the same leg, suggesting intralimb coordination. The specific trailing leg's strategy used in a slip is partially determined by pre-slip walking patterns and early stance slip dynamics.

Impact of joint torques on heel acceleration at heel contact, a contributor to slips and falls.

Slips/falls are a health burden in the workplace. Previous research has implied a relationship between foot dynamics at heel contact and slips/falls; however, heel acceleration has received little attention. Heel acceleration as the heel contacts the ground is the result of the combined effort of the leg joint torques to control motion of the foot. This study aims to examine the association of heel acceleration with fall risk, and explore the main joint torque determinant of heel acceleration at contact. Sixteen young and eleven older adults walked on known dry floors and in slippery environments expected to be dry. Heel acceleration at heel contact in the direction of motion, i.e. anterior/posterior, was compared between slip-recovery and slip-fall outcomes. Results showed that subjects that recovered contacted the floor with a greater heel deceleration (p < 0.05) than fall subjects. Knee torque alone explained 76% of the heel acceleration variability (p < 0.01). These data suggest that walking with reduced knee flexion torque at heel contact results in a reduced heel deceleration, a potential risk factor for slip-initiated falls.

Gait parameters as predictors of slip severity in younger and older adults.

This study investigated the association between slip severity and pre-slip gait characteristics of younger and older subjects. Sixteen younger and eleven older healthy adults walked onto an unexpectedly slippery surface. Slip severity was categorized as either hazardous or non-hazardous using a 1.0 ms peak slip velocity threshold. The results showed that hazardous slips were associated with greater step lengths (normalized by leg length) (SLR), larger and more rapidly changing foot - floor angles (FFA) at heel strike, and increased cadence across the two subject groups. Older subjects were found to walk with shorter SLR and with smaller and more slowly changing FFA at heel strike compared to younger subjects. However, both younger and older subjects experienced hazardous slips at the same rate. A logistic regression model relating SLR and cadence to slip severity predicted that increased SLR and decreased cadence would result in increased probability of hazardous slip (R2 = 0.45, chi2 = 15.30, p<0.01). A second logistic regression model relating FFA with slip severity predicted that increased FFA would result in increased probability of hazardous slip (R2 = 0.53, chi2 = 16.55, p<0.01). These results suggest that gait characteristics prior to foot contact play an important role in the severity of an ensuing slip. The finding that older adults experienced hazardous slips at the same rate as young adults even though their SLR and FFA are smaller suggests that age is also playing a role in other aspects of postural control that impact slip severity.

Effect of flooring on standing comfort and fatigue.

This study investigated the influence of flooring on subjective discomfort and fatigue during standing and on potentially related objective measures. Participants stood for 4 h on each of 7 flooring conditions while performing computer tasks. During the 3rd and 4th h, floor type had a significant effect on a number of subjective ratings, including lower-leg and lower-back discomfort/fatigue and 2 of 4 objective variables (center of pressure weight shift and lower-extremity skin temperature). In addition, lower-leg volumetric measurements showed tendencies toward greater lower-extremity swelling on uncomfortable floors. The hard floor and 1 floor mat condition consistently had the worst discomfort/fatigue and objective ratings. Significant relationships were noted between the affected subjective ratings and objective variables. In general, floor mats characterized by increased elasticity, decreased energy absorption, and increased stiffness resulted in less discomfort and fatigue. Thus flooring properties do affect low-back and lower-leg discomfort/fatigue, but the result may be detectable only after 3 h of standing. Potential applications of this research include the reduction of work-related health problems associated with long-term standing.

The influence of flooring on standing comfort and fatigue.

Many occupations require standing for extended periods of time, resulting in complaints of musculoskeletal fatigue and pain. One intervention method to reduce this problem has been to alter the flooring on which workers stand by using "antifatigue" mats. This article reviews the published research on the influence of flooring on people during long-term standing. Most studies have used subjective ratings of fatigue and discomfort experienced while standing in controlled laboratory settings. Some have included objective measures, such as electromyography, leg volume changes, and postural movements. Studies in the literature report mixed and sometimes conflicting results. There are methodological differences across the studies that could have led to many of the conflicting results, with the foremost variable being duration of testing. Generally, softer floors result in reduced discomfort as compared with a hard floor, particularly for the lower extremities and the lower back. Objective measures have been less conclusive, with no consensus about the influence of flooring on any physiological or biomechanical measures. Investigations of the influence of flooring characteristics on discomfort suggest that elasticity, stiffness, and thickness play roles. Further research is needed on underlying physiological causes of standing discomfort and fatigue as well as the influence of flooring properties on subjective and objective measures.

Absorbable versus nonabsorbable suture for microneurorrhaphy.

The results of epineural microneurorrhaphy with use of 10/0 monofilament absorbable (Vicryl and Dexon) and nonabsorbable ( Dermalon , Ethilon, and Prolene) microsuture were compared in 150 isogeneic male Sprague-Dawley rats. After sciatic nerve transection and epineural repair, the animals were observed clinically and reexplored before death at intervals from 2 days to 20 weeks. Half of the animals were randomly selected for electrodiagnostic studies at 6, 12, and 20 weeks before sacrificed. We found no significant clinical, electrodiagnostic, or histologic differences affecting axonal regeneration that were attributable to any of the suture types used. All sutures incited moderate zones of localized inflammation acutely. After dissolution, the absorbable group was essentially free of inflammation, whereas the nonabsorbable sutures persisted in small local granulomas. A possible advantage may be suggested in the use of monofilament absorbable sutures for microneural repairs in certain situations.

Biomechanics of slips.

The biomechanics of slips are an important component in the prevention of fall-related injuries. The purpose of this paper is to review the available literature on the biomechanics of gait relevant to slips. This knowledge can be used to develop slip resistance testing methodologies and to determine critical differences in human behaviour between slips leading to recovery and those resulting in falls. Ground reaction forces at the shoe-floor interface have been extensively studied and are probably the most critical biomechanical factor in slips. The ratio of the shear to normal foot forces generated during gait, known as the required coefficient of friction (RCOF) during normal locomotion on dry surfaces or 'friction used/achievable' during slips, has been one biomechanical variable most closely associated with the measured frictional properties of the shoe/floor interface (usually the coefficient of friction or COF). Other biomechanical factors that also play an important role are the kinematics of the foot at heel contact and human responses to slipping perturbations, often evident in the moments generated at the lower extremity joints and postural adaptations. In addition, it must be realized that the biomechanics are dependent upon the capabilities of the postural control system, the mental set of the individual, and the perception of the environment, particularly, the danger of slipping. The focus of this paper is to review what is known regarding the kinematics and kinetics of walking on surfaces under a variety of environmental conditions. Finally, we discuss future biomechanical research needs to help to improve walkway-friction measurements and safety.