Effects of age, speed, and step length on lower extremity net joint moments and powers during walking.

During walking older adults' gait is slower, they take shorter steps, and rely less on ankle and more on knee and hip joint moments and powers compared to young adults. Previous studies have suggested that walking speed and step length are confounds that affect joint moments and powers. Our purpose was to examine the effects of walking speed and step length manipulation on net joint moments and powers in young and older adults. Sixteen young and 18 older adults completed walking trials at three speeds under three step length conditions as marker position and force platform data were captured synchronously. Net joint moments were quantified using inverse dynamics and were subsequently used to compute net joint powers. Average extensor moments at each joint during the stance phase were then computed. Older adults displayed greater knee extensor moment compared to young adults. Older adults showed trends (p < .10) of having lower ankle and higher hip moments, but these differences were not statistically significant. Average ankle, knee, and hip extensor moments increased with speed and step length. At the fast speed, older compared to young adults generated lower average ankle power (p = .003) and showed a trend (p = .056) of exerting less average moment at the ankle joint. Age-associated distal-to-proximal redistribution of net joint moments was diminished and not statistically significant when the confounding effects of walking speed and relative step length were controlled. These findings imply that age-related distal-to-proximal redistribution of joint moments may influence the different speeds and step lengths chosen by young and older adults.

Effects of Age, Power Output, and Cadence on Energy Expenditure and Lower Limb Antagonist Muscle Coactivation During Cycling.

It is unknown if higher antagonist muscle coactivation is a factor contributing to greater energy expenditure of cycling in older adults. We determined how age, power output, and cadence affect energy expenditure and lower limb antagonist muscle coactivation during submaximal cycling. Thirteen younger and 12 older male participants completed 6-min trials at four power output-cadence conditions (75 W-60 rpm, 75 W-90 rpm, 125 W-60 rpm, and 125 W-90 rpm) while electromyographic and metabolic energy consumption data were collected. Knee and ankle coactivation indices were calculated using vastus lateralis, biceps femoris, gastrocnemius, and tibialis anterior electromyography data. Energy expenditure of cycling was greater in older compared with younger participants at 125 W (p = .002) and at 90 rpm (p = .026). No age-related differences were observed in the magnitude or duration of coactivation about the knee or ankle (p > .05). Our results indicated that the knee and ankle coactivation is not a substantive factor contributing to greater energy expenditure of cycling in older adults.

A general model for estimating lower extremity inertial properties of individuals with transtibial amputation.

Lower extremity joint moment magnitudes during swing are dependent on the inertial properties of the prosthesis and residual limb of individuals with transtibial amputation (TTA). Often, intact limb inertial properties (INTACT) are used for prosthetic limb values in an inverse dynamics model even though these values overestimate the amputated limb's inertial properties. The purpose of this study was to use subject-specific (SPECIFIC) measures of prosthesis inertial properties to generate a general model (GENERAL) for estimating TTA prosthesis inertial properties. Subject-specific mass, center of mass, and moment of inertia were determined for the shank and foot segments of the prosthesis (n=11) using an oscillation technique and reaction board. The GENERAL model was derived from the means of the SPECIFIC model. Mass and segment lengths are required GENERAL model inputs. Comparisons of segment inertial properties and joint moments during walking were made using three inertial models (unique sample; n=9): (1) SPECIFIC, (2) GENERAL, and (3) INTACT. Prosthetic shank inertial properties were significantly smaller with the SPECIFIC and GENERAL model than the INTACT model, but the SPECIFIC and GENERAL model did not statistically differ. Peak knee and hip joint moments during swing were significantly smaller for the SPECIFIC and GENERAL model compared with the INTACT model and were not significantly different between SPECIFIC and GENERAL models. When subject-specific measures are unavailable, using the GENERAL model produces a better estimate of prosthetic side inertial properties resulting in more accurate joint moment measurements for individuals with TTA than the INTACT model.

Effects of age and physical activity status on redistribution of joint work during walking.

During walking older adults rely less on ankle and more on hip work than young adults. Disproportionate declines in plantarflexor strength may be a mechanism underlying this proximal work redistribution. We tested the hypothesis that proximal redistribution is more apparent in older compared to young adults and in sedentary compared to active individuals over multiple walking speeds. We recruited 18 young (18-35 yrs) and 17 older (65-80 yrs) physically active and sedentary adults. Participants completed five trials at four walking speeds as marker positions and ground reaction forces were collected. Sagittal plane net joint moments were computed using inverse dynamics. Instantaneous joint powers for the ankle, knee, and hip were computed as products of net joint moments and joint angular velocities. Positive joint work was computed by integrating hip, knee, and ankle joint powers over time in early, mid, and late stance, respectively. Relative joint work was expressed as a percentage of total work. Isokinetic strength of lower limb flexor and extensor muscles was measured. Older adults had lower relative ankle (p=0.005) and higher relative hip (p=0.007) work than young adults for multiple speeds. Non-significant trends (p<0.10) indicating sedentary participants had lower relative ankle (p=0.068) and higher relative hip work (p=0.087) than active adults were observed. Age-related differences in plantarflexor strength were not disproportionate compared to strength differences in knee and hip musculature. Age influenced proximal work redistribution over multiple walking speeds. Physical activity status showed a similar trend for proximal work redistribution, but failed to reach statistical significance.

Asymmetrical pedaling patterns in Parkinson's disease patients.

BACKGROUND: Approximately 1.5 million Americans are affected by Parkinson's disease (Deponti et al., 2013) which includes the symptoms of postural instability and gait dysfunction. Currently, clinical evaluations of postural instability and gait dysfunction consist of a subjective rater assessment of gait patterns using items from the Unified Parkinson's Disease Rating Scale, and assessments can be insensitive to the effectiveness of medical interventions. Current research suggests the importance of cycling for Parkinson's disease patients, and while Parkinson's gait has been evaluated in previous studies, little is known about lower extremity control during cycling. The purpose of this study is to examine the lower extremity coordination patterns of Parkinson's patients during cycling. METHODS: Twenty five participants, ages 44-72, with a clinical diagnosis of idiopathic Parkinson's disease participated in an exercise test on a cycle ergometer that was equipped with pedal force measurements. Crank torque, crank angle and power produced by right and left leg were measured throughout the test to calculate Symmetry Index at three stages of exercise (20 W, 60 W, maximum performance). FINDINGS: Decreases in Symmetry Index were observed for average power output in Parkinson's patients as workload increased. Maximum power Symmetry Index showed a significant difference in symmetry between performance at both the 20 W and 60 W stage and the maximal resistance stage. Minimum power Symmetry Index did not show significant differences across the stages of the test. While lower extremity asymmetries were present in Parkinson's patients during pedaling, these asymmetries did not correlate to postural instability and gait dysfunction Unified Parkinson's Disease Rating Scale scores. INTERPRETATION: This pedaling analysis allows for a more sensitive measure of lower extremity function than the Unified Parkinson's Disease Rating Scale and may help to provide unique insight into current and future lower extremity function.

Oscillation and reaction board techniques for estimating inertial properties of a below-knee prosthesis.

The purpose of this study was two-fold: (1) demonstrate a technique that can be used to directly estimate the inertial properties of a below-knee prosthesis, and (2) contrast the effects of the proposed technique and that of using intact limb inertial properties on joint kinetic estimates during walking in unilateral, transtibial amputees. An oscillation and reaction board system was validated and shown to be reliable when measuring inertial properties of known geometrical solids. When direct measurements of inertial properties of the prosthesis were used in inverse dynamics modeling of the lower extremity compared with inertial estimates based on an intact shank and foot, joint kinetics at the hip and knee were significantly lower during the swing phase of walking. Differences in joint kinetics during stance, however, were smaller than those observed during swing. Therefore, researchers focusing on the swing phase of walking should consider the impact of prosthesis inertia property estimates on study outcomes. For stance, either one of the two inertial models investigated in our study would likely lead to similar outcomes with an inverse dynamics assessment.

Asymmetrical loading affects intersegmental dynamics during the swing phase of walking.

Much of the work related to lower extremity inertia manipulations has focused on temporal, kinematic and traditional inverse dynamics assessments during locomotion. Intersegmental dynamics is an analytical technique that provides further insights into mechanisms underlying linked-segment motion. The purpose of this study was to determine how intersegmental dynamics during the swing phase of walking are altered during asymmetrical lower extremity loading. Participants walked overground at a speed of 1.57 ms(-1) with 0, 0.5, 1.0, and 2.0 kg attached to one foot. Net, interaction, gravitational, and muscle moments were computed. Moment magnitudes at joints of the loaded leg increased systematically with increasing load, whereas unloaded leg moments were unaffected by loading. With increasing load, relative contributions of interaction moments about the knee and hip and gravitational moment about the ankle increased (i.e., 21%, 8%, and 44% increases, respectively), whereas the relative contributions of muscle moments about all three joints declined (i.e., -4%, -13%, and -8% decreases for the ankle, knee, and hip, respectively for unloaded vs. 2.0 kg). These results suggest that altered inertia properties of the limb not only affected the amount of muscular effort required to swing the leg, but also changed the nature of the interaction between segments.

Effects of prosthetic mass distribution on metabolic costs and walking symmetry.

Unilateral, transtibial amputees exhibit walking asymmetries and higher metabolic costs of walking than nonamputees walking at similar speeds. Using lightweight prostheses has previously been suggested as a contributing factor to walking asymmetries. The purpose was to investigate the effects of prosthesis mass and mass distribution on metabolic costs and walking asymmetries among six unilateral, transtibial amputees. Kinematic and temporal symmetry did not improve when mass was added at different locations on the limb. Stance and swing time asymmetries increased by 3.4% and 7.2%, respectively, with loads positioned distally on the limb. Maximum knee angular velocity asymmetries increased by 6% with mass added to the thigh, whereas maximum thigh angular velocity asymmetries increased by approximately 10% with mass positioned near the prosthetic ankle. Adding 100% of the estimated mass difference between intact and prosthetic legs to the ankle of the prosthesis increased energy costs of walking by 12%; adding the same mass to the prosthesis center of mass or thigh center of mass increased metabolic cost by approximately 7% and 5%, respectively. Unless other benefits are gained by increasing prosthesis mass, this should not be considered as a possible alternative to current lightweight prosthesis designs currently being prescribed to unilateral amputees.

Heel height affects lower extremity frontal plane joint moments during walking.

Wearing high heels alters walking kinematics and kinetics and can create potentially adverse effects on the body. Our purpose was to determine how heel height affects frontal plane joint moments at the hip, knee, and ankle, with a specific focus on the knee moment due to its importance in joint loading and knee osteoarthritis. 15 women completed overground walking using three different heel heights (1, 5, and 9 cm) for fixed speed (1.3 ms(-1)) and preferred speed conditions while kinematic and force platform data were collected concurrently. For both fixed and preferred speeds, peak internal knee abduction moment increased systematically as heel height increased (fixed: 0.46, 0.48, 0.55 N m kg(-1); preferred: 0.47, 0.49, 0.53 N m kg(-1)). Heel height effects on net frontal plane moments of the hip and ankle were similar to those for the knee; peak joint moments increased as heel height increased. The higher peak internal knee abduction moment with increasing heel height suggests greater medial loading at the knee. Kinetic changes at the ankle with increasing heel height may also contribute to larger medial loads at the knee. Overall, wearing high heels, particularly those with higher heel heights, may put individuals at greater risk for joint degeneration and developing medial compartment knee osteoarthritis.

Lower extremity mechanical work during stance phase of running partially explains interindividual variability of metabolic power.

Recent attention given to the mechanical work of the lower extremity joints, the emerging importance of the stance phase of running, and the lack of consensus regarding the biomechanical correlates to economical running were primary justifications for this study. The purpose of this experiment was to identify the correlations between metabolic power and the positive and negative mechanical work at lower extremity joints during stance. Recreational runners (n = 16) ran on a treadmill at 3.35 m s(-1) for physiological measures and overground for biomechanical measures. Inverse dynamics were used to calculate net joint moments and powers at the ankle, knee, and hip. Joint powers were then integrated over the stance phase so that positive and negative joint mechanical work were correlated with metabolic power (r = 0.60-0.69). Positive work at the hip and ankle during stance was positively correlated to metabolic power. In addition to these results, more economical runners (lower metabolic power) exhibited greater negative work at the hip, greater positive work at the knee, and less negative work at the ankle. Between the most and least economical runners, different mechanical strategies were present at the hip and knee, whereas the kinetics of the ankle joint differed only in magnitude.

Effects of age and walking speed on coactivation and cost of walking in healthy adults.

Our goal was to determine how age and walking speed affect metabolic cost of walking (C(w)), lower, extremity antagonist coactivation, and relationships between coactivation and C(w) in healthy, active, individuals. Fourteen young (25+/-3 years) and 14 older (71+/-4 years) participants walked on a treadmill at, four speeds (0.89, 1.12, 1.34, and 1.57 m s(-1)) while electromyography (EMG) and oxygen consumption, were measured. Coactivation indices were calculated for musculature about the thigh and shank. C(w), was higher in older adults across all speeds (p<0.001). Coactivation about the thigh was also higher in, older adults (p<0.001), whereas coactivation about the shank was not different between age groups (p=0.60). Total coactivation (thigh coactivation plus shank coactivation) showed significant positive, relationships to C(w) at all walking speeds (r=0.46-0.57). Higher C(w) and coactivation in older adults, along with the positive relationship between C(w) and coactivation implies coactivation contributes to, higher C(w) of older adults.

Mechanical power and efficiency of level walking with different stride rates.

Walking humans prefer to use the stride rate that results in the lowest rate of metabolic energy expenditure. Mechanical power requirements have been suggested to underlie the metabolic response, but mechanical power is consistently reported to be minimal at stride rates 20-30% lower than preferred. This may be due to limitations in how total mechanical power has been computed, as well as a failure to account for the efficiency with which muscular work is done. We investigated how mechanical power and efficiency depend on stride rate in walking, with both quantities computed from the work done by the hip, knee and ankle joint moments. Our hypotheses were that mechanical power and efficiency are both optimized at the preferred stride rate, which would explain why metabolic energy expenditure is minimized at this rate. Contrary to our hypotheses, mechanical power curves exhibited plateaus that spanned stride rates lower than preferred (predicted optima: 11-12% below preferred), while net mechanical efficiency exhibited a plateau that spanned stride rates higher than preferred (predicted optimum: 8% above preferred). As expected, preferred stride rate (54.3 strides min(-1)) was not different from the stride rate that minimized net metabolic energy expenditure (predicted optimum: 0.2% above preferred). Given that mechanical power and mechanical efficiency exhibited plateaus on opposite sides of the preferred stride rate, the preferred rate in walking likely represents a compromise between these two factors. This may also explain the relative flatness of the curve for metabolic rate in the vicinity of the preferred stride rate.

Walking patterns change rapidly following asymmetrical lower extremity loading.

The purpose of this study was to determine the amount of time needed for individuals to become well accommodated to asymmetrical changes in lower extremity inertial properties. Participants walked at 1.57 m s(-1) during four separate data collection sessions over the period of eight days. On days 1 and 7, participants completed a 60 min treadmill protocol consisting of both overground (motion and ground reaction force recorded) and treadmill (vertical ground reaction force recorded) walking. On day 1, 1.95 kg was attached distally to one shank prior to the start of the 60 min treadmill protocol and was not removed until day 7. On day 7, the load was permanently removed prior to the 60 min treadmill protocol. On days 2 and 8 participants completed three overground walking trials and walked on the treadmill for approximately 5 min. Stance and swing time asymmetries appeared immediately and were complete following initial assessment after the load was attached. Net joint moments at the knee and hip were altered and continued to change beyond initial exposure to the load, but these changes were complete within 5 min. Overall, results suggest that changes in walking symmetry due to asymmetrical lower extremity loading are immediate and complete within 5 min of exposure to the load. We recommend that at least 5 min of walking or other normal activity be used to accommodate individuals to novel asymmetrical lower extremity loading.

Muscle fiber type effects on energetically optimal cadences in cycling.

Fast-twitch (FT) and slow-twitch (ST) muscle fibers vary in their mechanical and energetic properties, and it has been suggested that muscle fiber type distribution influences energy expenditure and the energetically optimal cadence during pedaling. However, it is challenging to experimentally isolate the effects of muscle fiber type on pedaling energetics. In the present study, a modeling and computer simulation approach was used to test the dependence of muscle energy expenditure on pedaling rate during submaximal cycling. Simulations were generated using a musculoskeletal model at cadences from 40 to 120 rev min(-1), and the dynamic and energetic properties of the model muscles were scaled to represent a range of muscle fiber types. Energy expenditure and the energetically optimal cadence were found to be higher in a model with more FT fibers than a model with more ST fibers, consistent with predictions from the experimental literature. At the muscle level, mechanical efficiency was lower in the model with a greater proportion of FT fibers, but peaked at a higher cadence than in the ST model. Regardless of fiber type distribution, mechanical efficiency was low at 40 rev min(-1), increased to a broad plateau between 60 and 100 rev min(-1) , and decreased substantially at 120 rev min(-1). In conclusion, muscle fiber type distribution was confirmed as an important determinant of the energetics of pedaling.

Manipulations of leg mass and moment of inertia: effects on energy cost of walking.

PURPOSE: To investigate effects that independent alterations in limb mass and moment of inertia about a transverse axis through the hip have on metabolic and mechanical power of walking and peak electromyography (EMG) amplitude. It was hypothesized that increases in metabolic cost would parallel increases in mechanical power, and that EMG amplitude would increase with greater limb mass or limb moment of inertia. METHODS: Metabolic and mechanical power and lower-extremity EMG were measured on 14 healthy adults walking at 1.5 m.s. Four leg-loading conditions were employed: 1) no load (NL) on the legs; 2) a baseline load (BSLN) condition, with a mean of 2.0 kg per leg distributed on the proximal and distal shank; 3) a load condition with a mean of 2.0 kg per leg distributed on the proximal and distal shank, such that lower-extremity moment of inertia was increased 5% about the hip (MOI5) from the BSLN, but having the same lower-extremity mass as BSLN; and 4) a load condition with a mean of 2.8 kg per leg, concentrated proximally on the shank to increase total lower-extremity mass by 5% (Mass5) from BSLN, but having the same moment of inertia as BSLN. Total subject mass was constant between conditions, as unused leg loads were carried in a waist belt. RESULTS: Changes in mechanical power paralleled changes in metabolic cost as hypothesized. Energy cost increased significantly (4.2%) from NL to BSLN, and from BSLN to MOI5 and Mass5 (3.4 and 4.0%, respectively). EMG did not effectively explain changes in metabolic cost. CONCLUSION: Independent alterations in limb mass and moment of inertia about the hip joint influence energy cost similarly.

Longitudinal stratification of gait economy in young boys and girls: the locomotion energy and growth study.

The purpose of this study was to determine if the relative ordering of locomotor oxygen consumption ( VO(2)) values remains stable as healthy children age. Beginning at age 6 and ending at age 10, VO(2) during level treadmill walking and running was quantified in 15 boys and 18 girls who were tested on an annual basis. Following 30 min of treadmill accommodation to each exercise mode, subjects walked and ran for 5 min at 1.34 m s(-1) and 2.23 m s(-1), respectively. During the last 2 min of each 5-min stage, expired gas samples were collected and analyzed to quantify VO(2). For both walking (W) and running (R), 27% of subjects showed an average yearly change in VO(2) rank order of

Gait transitions are not dependent on changes in intralimb coordination variability.

The HKB model (H. Haken, J. A. S. Kelso, & H. Bunz, 1985) of coordination has been predominantly applied to upper extremity stationary movements. It predicts increased variability of relative phase before a transition and a decrease after a transition. The authors of the present study extended the intralimb lower extremity locomotive research of F. J. Diedrich and W. H. Warren (1995) by conducting continuous treadmill walk-to-run and run-to-walk trials with 10 participants. Standard deviation of knee-ankle and hip-ankle relative phase did not increase before walk-to-run and run-to-walk transitions, and there was no decrease in knee-ankle relative phase variability after either transition. The results of this study did not provide strong support for application of the variability predictions of the HKB model of coordination to lower extremity intralimb coordination during gait transitions.

A model of human muscle energy expenditure.

A model of muscle energy expenditure was developed for predicting thermal, as well as mechanical energy liberation during simulated muscle contractions. The model was designed to yield energy (heat and work) rate predictions appropriate for human skeletal muscle contracting at normal body temperature. The basic form of the present model is similar to many previous models of muscle energy expenditure, but parameter values were based almost entirely on mammalian muscle data, with preference given to human data where possible. Nonlinear phenomena associated with submaximal activation were also incorporated. The muscle energy model was evaluated at varying levels of complexity, ranging from simulated contractions of isolated muscle, to simulations of whole body locomotion. In all cases, acceptable agreement was found between simulated and experimental energy liberation. The present model should be useful in future studies of the energetics of human movement using forward dynamic computer simulation.

Prediction of the aerobic demand of walking in children.

PURPOSE: The purpose of this study was to develop a generalized equation to predict VO2 during level treadmill walking in young boys and girls. METHODS: On an annual basis from ages 6 to 10, 23 able-bodied children (14 girls, 9 boys) completed six 5-min walking bouts at speeds ranging from 40.2 to 107.2 m x min(-1). Before testing, each child received 60 min of treadmill walking practice. During the last 2 min of each walking trial, a 2-min sample of expired gas was collected in a meteorological balloon and analyzed to determine VO2. RESULTS: Stepwise regression analyses indicated that the following equation was best suited to predict walking VO2: VO2 = 24.852 + 0.003214 (walking speed in m x min(-1))2 - 0.995 (age in yr) - 0.263 (walking speed); R = 0.95; SEE = 1.74 mL x kg(-1) x min(-1). Bland-Altman analysis revealed that 95% of the differences between actual and predicted VO2 values fell within a range of 3.39 to -3.43 mL x kg(-1) x min(-1). CONCLUSION: We conclude that VO2 during level treadmill walking can be predicted accurately in healthy young children.

Longitudinal profiles of oxygen uptake during treadmill walking in able-bodied children: the locomotion energy and growth study.

The purpose of this study was to document age-related changes in walking V(O(2)) in able-bodied boys and girls. Beginning at age 6 and ending at age 10, 23 children (14 girls, 9 boys) performed six 5-min bouts of level treadmill walking at 0.67, 0.89, 1.12, 1.34, 1.56, and 1.79 m s(-1) on an annual basis. Prior to data collection, subjects received 60 min of treadmill walking practice. During the last 2 min of each walking bout, a 2-min sample of expired air was collected in a meteorological balloon and analyzed to determine V(O(2)). Averaged across age, interindividual variation in V(O(2)) ranged from 32 to 41%. Repeated-measures analysis of variance demonstrated a speed by age interaction for V(O(2)), such that mean V(O(2)) rose (P< or = 0.05) across the five fastest speeds for 6-, 7-, 8-, and 10-year olds and increased over the entire speed range for 9-year olds. For all speeds, V(O(2)) decreased yearly from the ages of 6 to 8. When averaged across speeds, V(O(2)) was 27% higher for 6-year olds compared with 10-year olds. From a clinical perspective, access to longitudinal measurements of walking V(O(2)) in able-bodied children should be helpful in interpreting gait energy use in children with movement disorders and evaluating treatment strategies designed to reduce the aerobic demand of locomotion in youth with impaired mobility.