Co-Planar Stereotaxic Atlas of the Human Brain—3-Dimensional Proportional System: An Approach to Cerebral Imaging, J. Talairach, P. Tournoux. Georg Thieme Verlag, New York (1988), 122 pp., 130 figs. DM 268

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Biomechanics And Motor Control Of Human Movement

This paper introduces a newly developed gait rehabilitation device. The device, called LOPES, combines a freely translatable and 2-D-actuated pelvis segment with a leg exoskeleton containing three actuated rotational joints: two at the hip and one at the knee. The joints are impedance controlled to allow bidirectional mechanical interaction between the robot and the training subject. Evaluation measurements show that the device allows both a "pa- tient-in-charge" and "robot-in-charge" mode, in which the robot is controlled either to follow or to guide a patient, respectively. Electromyography (EMG) measurements (one subject) on eight important leg muscles, show that free walking in the device strongly resembles free treadmill walking; an indication that the device can offer task-specific gait training. The possibilities and limitations to using the device as gait measurement tool are also shown at the moment position measurements are not accurate enough for inverse-dynamical gait analysis.

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Design and Evaluation of the LOPES Exoskeleton Robot for Interactive Gait Rehabilitation

The world population is ageing rapidly. As society ages, the incidence of physical limitations is dramatically increasing, which reduces the quality of life and increases healthcare expenditures. In western society, ~30% of the population over 55 years is confronted with moderate or severe physical limitations. These physical limitations increase the risk of falls, institutionalization, co-morbidity, and premature death. An important cause of physical limitations is the age-related loss of skeletal muscle mass, also referred to as sarcopenia. Emerging evidence, however, clearly shows that the decline in skeletal muscle mass is not the sole contributor to the decline in physical performance. For instance, the loss of muscle strength is also a strong contributor to reduced physical performance in the elderly. In addition, there is ample data to suggest that motor coordination, excitation-contraction coupling, skeletal integrity, and other factors related to the nervous, muscular, and skeletal systems are critically important for physical performance in the elderly. To better understand the loss of skeletal muscle performance with ageing, we aim to provide a broad overview on the underlying mechanisms associated with elderly skeletal muscle performance. We start with a system level discussion and continue with a discussion on the influence of lifestyle, biological, and psychosocial factors on elderly skeletal muscle performance. Developing a broad understanding of the many factors affecting elderly skeletal muscle performance has major implications for scientists, clinicians, and health professionals who are developing therapeutic interventions aiming to enhance muscle function and/or prevent mobility and physical limitations and, as such, support healthy ageing.

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Skeletal muscle performance and ageing

Learning to walk with a robotic ankle exoskeleton

To produce successful and safe walking movements, the locomotor control system must have a detailed awareness of the mechanical properties of the lower limbs. Flexibility of this control comes from an ability to identify and accommodate any changes in limb mechanics by updating its internal representation of the lower limb. To explore the ability of the locomotor control system to tune its representation of the lower limb, eight participants performed three 5 min trials (PRE, WEIGHT and POST) of treadmill walking. During the middle trial the participants wore a 2 kg mass around the leg segment of the left lower limb. Joint kinematics and kinetics were determined to assess changes in the walking movements. The modification of limb inertia by adding mass to the limbs (WEIGHT) required a substantive period of adaptation, which lasted between 45 and 50 strides, before individuals fully adjusted to their new lower limb mechanics to achieve steady-state joint kinematics. These movements were caused in part from an increase in hip flexor and knee extensor activity in early swing followed by an increase in hip extensors and knee flexor activity in late swing. Following the removal of the mass (POST), ankle, knee and hip flexion all increased above the levels that were observed in the PRE condition and returned the baseline levels within 20, 70 and 70 strides, respectively. The removal of the mass appeared to cause a greater disruption to walking than the addition of mass to the limb despite a quick return of the joint moments to the PRE condition. Both the changes following the addition of the mass and its subsequent removal may embody a recalibration of the internal limb representation. These changes were characterized by an integrated response consisting of primary recalibration to the modified mechanical parameters and secondary actions to main the integrity of locomotor objectives such as propulsion, balance, support and safe foot trajectories. These recalibration responses were similar to those demonstrated in upper limb movements in response to altered force environments. Understanding this recalibration process will have implications for the prevention of trips and falls as individuals encounter different movement environments or changes to mechanical properties of their limbs, especially for individuals with decreased proprioception or other neural challenges.

Adaptation to unilateral change in lower limb mechanical properties during human walking

Background: The timed-up-and-go test (TUG) is one of the most commonly used tests of physical function in clinical practice and for research outcomes. Inertial sensors have been used to parse the TUG test into its composite phases (rising, walking, turning, etc.), but have not validated this approach against an optoelectronic gold-standard, and to our knowledge no studies have published the minimal detectable change of these measurements. Methods: Eleven adults performed the TUG three times each under normal and slow walking conditions, and 3 m and 5 m walking distances, in a 12-camera motion analysis laboratory. An inertial measurement unit (IMU) with tri-axial accelerometers and gyroscopes was worn on the upper-torso. Motion analysis marker data and IMU signals were analyzed separately to identify the six main TUG phases: sit-to-stand, 1st walk, 1st turn, 2nd walk, 2nd turn, and stand-to-sit, and the absolute agreement between two systems analyzed using intra-class correlation (ICC, model 2) analysis. The minimal detectable change (MDC) within subjects was also calculated for each TUG phase. Results: The overall difference between TUG sub-tasks determined using 3D motion capture data and the IMU sensor data was 0.90), but less for chair activity (ICC range 0.5–0.9) and typically poor for the turn time (ICC < 0.4). MDC values for total TUG time ranged between 2–4 s or 12–22% of the TUG time measurement. MDC of the sub-task times were higher proportionally, being 20–60% of the sub-task duration. Conclusions: We conclude that a commercial IMU can be used for quantifying the TUG phases with accuracy sufficient for clinical applications; however, the MDC when using inertial sensors is not necessarily improved over less sophisticated measurement tools.

Convergent Validity of a Wearable Sensor System for Measuring Sub-Task Performance during the Timed Up-and-Go Test

The lower-limb segment elevation angles during human locomotion have been shown to co-vary in a manner such that they approximate a plane when plotted against each other over a gait cycle. This relationship has been described as the Planar Co-Variation Law and has been shown to be consistent across various modes of locomotion on level ground. The goal of this study is to determine whether the Planar Co-Variation Law will hold in situations where the orientation of the walking surface is altered and if aging will have an effect on this intersegmental coordination during these locomotor tasks. Nine healthy young females (mean age = 21.4), and nine older adult females (mean age = 73.3) were asked to complete walking trials on level ground, and walking up ramps with inclines of 3°, 6°, 9° and 12° while the kinematics of their lower limbs were measured. It was found that the Planar Co-Variation Law was held across all ramp incline conditions by both the young adult and older adult groups. It was found that the changes in intersegmental coordination required to walk up the ramp resulted in a unique orientation of the co-variation plane for both groups when walking up a particular incline. The results of this study indicate that the Planar Co-Variation Law will include situations where the walking surface is not level and provides further support to models of motor control that have been proposed where walking patterns for different modes of gait can be predicted based on the orientation of the co-variation plane.

Intersegmental coordination while walking up inclined surfaces: age and ramp angle effects.

The purpose of this study was to determine pedometer accuracy during slow overground walking in older adults (Mean age = 63.6 years). A total of 18 participants (6 males, 12 females) wore 5 different brands of pedometers over 3 pre-set cadences that elicited walking speeds between 0.3 and 0.9 m/s and one self-selected cadence over 80 meters of indoor track. Pedometer accuracy decreased with slower walking speeds with mean percent errors across all devices combined of 56%, 40%, 19% and 9% at cadences of 50, 66, and 80 steps/min, and self selected cadence, respectively. Percent error ranged from 45.3% for Omron HJ105 to 66.9% for Yamax Digiwalker 200. Due to the high level of error across the slowest cadences of all 5 devices, the use of pedometers to monitor step counts in healthy older adults with slower gait speeds is problematic. Further research is required to develop pedometer mechanisms that accurately measure steps at slower walking speeds.

Jeremy W. Noble

Papers

Adaptation to unilateral change in lower limb mechanical properties during human walking

Convergent Validity of a Wearable Sensor System for Measuring Sub-Task Performance during the Timed Up-and-Go Test

Intersegmental coordination while walking up inclined surfaces: age and ramp angle effects.

Pedometer accuracy in slow-walking older adults

Aging effects on the control of grip force magnitude: an fMRI study.