Amir A. Mohagheghi

The effects of distant and on-line visual information on the control of approach phase and step over an obstacle during locomotion

Abstract.One of the goals of this study was to examine the nature and role of distant visual information sampled during locomotion in the feedforward control of leading and trailing limb while an individual is required to step over an obstacle in the travel path. In addition we were interested in whether or not on-line visual information available while the limb (lead or trail) is stepping over the obstacle influences limb trajectory control and whether the information provided during lead limb cross would be used to calibrate movement of the trail limb. Towards this end, we manipulated availability of vision following an initial dynamic sampling period during the approach phase in proximity to the obstacle and during the lead and trail limb stepping over the obstacle. Ten participants completed 40 trials of obstacle crossing in 8 testing conditions. Initial dynamic visual sampling was sufficient to ensure successful task performance in the absence of vision in the approach phase and during both lead and trail limb stepping over the obstacle. Despite successful task performance, foot placement of the lead and trail limb before obstacle crossing and limb elevation over the obstacle were increased after withdrawal of vision in the approach area. Furthermore, the correlation between toe clearance and foot placement was diminished. While both limbs require feedforward visual information to control the step over the obstacle, only lead limb elevation was influenced by availability of on-line visual information during obstacle crossing. Results were in agreement with the notion of primacy of information inherent in the optic array over those from static samples of the environment in guiding locomotion. It is suggested that the expected proprioceptive feedback information associated with the limb posture before the obstacle, reconstructed using visual memory from dynamic sampling of the environment, mismatched with those from the actual limb position. Accordingly, participants adopted a different strategy that enabled them to clear the obstacle with a higher safety margin.

In vivo gastrocnemius muscle fascicle length in children with and without diplegic cerebral palsy

The effect of spastic cerebral palsy on in vivo gastrocnemius muscle fascicle length is not clear. Similarity of fascicle lengths in children with diplegia and typically developing children, but shortening of fascicle lengths in the paretic legs of children with hemiplegia compared with the non‐paretic legs, are both reported. In the former case, comparisons were made between fascicle lengths normalized to leg length, whereas in the latter case, absolute fascicle lengths were compared. The inherent assumptions when normalizing fascicle length (measured via ultrasonography) were not validated, raising the possibility that inappropriate normalization contributed to the controversy. We used statistical methods to control the potential confounding effect of leg length on fascicle length, and tested the feasibility of the normalization method for a group of 18 children with diplegia (nine males, nine females; mean age 8y 7mo [SD 3y 11mo], range 2‐15y; Gross Motor Function Classification System levels II and III) and 50 typically developing children (20 males, 30 females; mean age 9y 1mo [SD 2y 4mo], range 4‐14y). Children with diplegia, as a group, had shorter absolute and normalized fascicle lengths (p<0.05) but we could not refute the appropriateness of the normalization method. Other methodological issues (such as sample characteristics) might have contributed to the apparent controversy between the stdies.

Influence of light handrail use on the biomechanics of stair negotiation in old age

The high incidence of falls in older adults during stair negotiation suggests that this task is physically challenging and potentially dangerous. The present study aimed to examine the influence of light handrail use on the biomechanics of stair negotiation in old age. Thirteen older adults ascended and descended a purpose-built staircase at their self-selected speed: (i) unaided and (ii) with light use of the handrails. Ground reaction forces (GRFs) were measured from force platforms mounted into each step and motion capture was used to collect kinematic data. Knee and ankle joint moments were calculated using the kinetic and kinematic data. The horizontal separation between the centre of mass (COM) and the centre of pressure (COP) was assessed in the sagittal and frontal planes. During stair ascent, handrail use caused a different strategy to be employed compared to unaided ascent with a redistribution of joint moments. Specifically, the ankle joint moment (of the trailing leg) was reduced with handrail use, which has previously been shown to approach its limits during unaided stair ascent, but the knee joint moment (of the leading leg) increased. Previous research has shown that a larger joint moment reserve is available at the knee during unaided stair ascent. During stair descent, the ankle joint moment increased with handrail use, this was associated, however, with a more effective control of balance as shown by a reduced COM-COP separation in the direction of progression compared to unaided descent. These results indicate that although the biomechanical mechanisms are different for stair ascent and descent, the safety of stair negotiation is improved for older adults with light use of the handrails.

Does acute passive stretching increase muscle length in children with cerebral palsy

BACKGROUND Children with spastic cerebral palsy experience increased muscle stiffness and reduced muscle length, which may prevent elongation of the muscle during stretch. Stretching performed either by the clinician, or children themselves is used as a treatment modality to increase/maintain joint range of motion. It is not clear whether the associated increases in muscle-tendon unit length are due to increases in muscle or tendon length. The purpose was to determine whether alterations in ankle range of motion in response to acute stretching were accompanied by increases in muscle length, and whether any effects would be dependent upon stretch technique. METHODS Eight children (6-14 y) with cerebral palsy received a passive dorsiflexion stretch for 5 × 20 s to each leg, which was applied by a physiotherapist or the children themselves. Maximum dorsiflexion angle, medial gastrocnemius muscle and fascicle lengths, and Achilles tendon length were calculated at a reference angle of 10 ° plantarflexion, and at maximum dorsiflexion in the pre- and post-stretch trials. FINDINGS All variables were significantly greater during pre- and post-stretch trials compared to the resting angle, and were independent of stretch technique. There was an approximate 10 ° increase in maximum dorsiflexion post-stretch, and this was accounted for by elongation of both muscle (0.8 cm) and tendon (1.0 cm). Muscle fascicle length increased significantly (0.6 cm) from pre- to post-stretch. INTERPRETATION The results provide evidence that commonly used stretching techniques can increase overall muscle, and fascicle lengths immediately post-stretch in children with cerebral palsy.

Does long-term passive stretching alter muscle–tendon unit mechanics in children with spastic cerebral palsy?

BACKGROUND Cerebral palsy causes motor impairments during development and many children may experience excessive neural and mechanical muscle stiffness. The clinical assumption is that excessive stiffness is thought to be one of the main reasons for functional impairments in cerebral palsy. As such, passive stretching is widely used to reduce stiffness, with a view to improving function. However, current research evidence on passive stretching in cerebral palsy is not adequate to support or refute the effectiveness of stretching as a management strategy to reduce stiffness and/or improve function. The purpose was to identify the effect of six weeks passive ankle stretching on muscle-tendon unit parameters in children with spastic cerebral palsy. METHODS Thirteen children (8-14 y) with quadriplegic/diplegic cerebral palsy were randomly assigned to either an experimental group (n=7) or a control group (n=6). The experimental group underwent an additional six weeks of passive ankle dorsiflexion stretching for 15 min (per leg), four days per week, whilst the control group continued with their normal routine, which was similar for the two groups. Measures of muscle and tendon stiffness, strain and resting length were acquired pre- and post-intervention. FINDINGS The experimental group demonstrated a 3° increase in maximum ankle dorsiflexion. This was accompanied by a 13% reduction in triceps surae muscle stiffness, with no change in tendon stiffness. Additionally, there was an increase in fascicle strain with no changes in resting length, suggesting muscle stiffness reductions were a result of alterations in intra/extra-muscular connective tissue. INTERPRETATION The results demonstrate that stretching can reduce muscle stiffness by altering fascicle strain but not resting fascicle length.

Mechanical and material properties of the plantarflexor muscles and Achilles tendon in children with spastic cerebral palsy and typically developing children

BACKGROUND Children with spastic cerebral palsy (CP) experience secondary musculoskeletal adaptations, affecting the mechanical and material properties of muscles and tendons. CP-related changes in the spastic muscle are well documented whilst less is known about the tendon. From a clinical perspective, it is important to understand alterations in tendon properties in order to tailor interventions or interpret clinical tests more appropriately. The main purpose of this study was to compare the mechanical and material properties of the Achilles tendon in children with cerebral palsy to those of typically developing children. METHODS Using a combination of ultrasonography and motion analysis, we determined tendon mechanical properties in ten children with spastic cerebral palsy and ten aged-matched typically developing children. Specifically, we quantified muscle and tendon stiffness, tendon slack length, tendon strain, cross-sectional area, Young׳s Modulus and the strain rate dependence of tendon stiffness. FINDINGS Children with CP had a greater muscle to tendon stiffness ratio compared to typically developing children. Despite a smaller tendon cross-sectional area and greater tendon slack length, no group differences were observed in tendon stiffness or Young׳s Modulus. The slope describing the stiffness strain-rate response was steeper in children with cerebral palsy. INTERPRETATION These results provide us with a more differentiated understanding of the muscle and tendon mechanical properties, which would be relevant for future research and paediatric clinicians.

Interactions among end-effectors and movement parameters influence reaction time in discrete, rapid aimed movements.

Two reliable findings in discrete, rapid aimed movements are that reaction time increases with decrease in target diameter (for the short-length movements), and reaction time is not affected by movement length [Journal of Experimental Psychology, Human Perception and Performance 104 (2) (1975) 147]. Participants normally use a short stylus (SS) to tap targets located on either side of a central (aligned with body midline) start-point with no restrictions imposed on the initial posture of the limb or segmental recruitment except as determined by movement conditions. Thus, the effects of movement parameters on reaction time in previous work are potentially confounded with the effect of initial posture of the limb at the start-point, along with order and amount of the contribution of segments recruited in response execution. Two experiments were performed to resolve the confounding between initial posture and recruitment of limb segments. In the first experiment a conventional stylus (pen-like) was employed and the starting position of the limb was aligned either with the body midline or with the participants right shoulder. The effect of starting position on reaction time was not significant. In the second experiment the starting position was in line with the right shoulder. Two groups participated. One group used a conventional stylus. For the second group a modified (lengthened) stylus was used that permitted initial limb posture and number of limb segments recruited to be held constant across an extended range of movement lengths. When similar sets of limb segments were used, reaction time increased with decreasing movement length and diminishing target diameter. These findings suggest that uncontrolled initial limb posture, uncontrolled order of joint(s) recruitment, and the subsequent inclusion of reaction time values from incompatible sources may, in the final analysis, have confounded previous work investigating movement amplitude and target diameter effects on reaction time.

Dynamic stretching is not detrimental to neuromechanical and sensorimotor performance of ankle plantarflexors

The acute effects of two dynamic stretching (DS) protocols on changes in the ankle range of motion (RoM), neuromechanical, and sensorimotor properties of the plantarflexor muscle group were examined. Eighteen participants received slow (SDS) or fast dynamic stretching (FDS) on two separate days. Outcome measures were assessed pre‐ and 2 minutes post‐interventions, and included maximum dorsiflexion angle, maximum isometric torque at neutral ankle position, maximum concentric and eccentric torques, force matching capacity, joint position sense and medial gastrocnemius muscle and tendon strain. Possibly and likely small increases in dorsiflexion RoM were observed after SDS (mean ± 90% confidence intervals; 1.8 ± 1.2°) and FDS (2.1 ± 1.2°), respectively. Very likely moderate decreases in muscle strain after SDS (−38.0 ± 20.6%) and possibly small decrease after FDS (−13.6 ± 21.2%) were observed. SDS resulted in a likely beneficial small increase in tendon strain (25.3 ± 29.7%) and a likely beneficial moderate increase after FDS (41.4 ± 44.9%). Effects on strength were inconsistent. Possibly small effect on positional error after SDS (−27.1 ± 37.5%), but no clear effect after FDS was observed. Both DS protocols increased RoM, and this was more due to an increase in tendon elongation rather than the muscle. However, SDS showed greater improvement than FDS in both neuromechanical and sensorimotor performance, and hence, SDS can be recommended as part of warm‐up in sporting contexts.

Effects of an acute bout of dynamic stretching on biomechanical properties of the gastrocnemius muscle determined by shear wave elastography

Aims The aim of this study was to examine the acute effects of dynamic stretching (DS) exercise on passive ankle range of motion (RoM), resting localized muscle stiffness, as measured by shear wave speed (SWS) of medial gastrocnemius muscle, fascicle strain, and thickness. Methods/Results Twenty-three participants performed a DS protocol. Before and after stretching, SWS was measured in the belly of the resting medial gastrocnemius muscle (MGM) using shear wave elastography. DS produced small improvements in maximum dorsiflexion (+1.5° ±1.5; mean difference ±90% confidence limits) and maximum plantarflexion (+2.3° ±1.8), a small decrease in fascicle strain (-2.6% ±4.4) and a small increase in SWS at neutral resting angle (+11.4% ±1.5). There was also a small increase in muscle thickness (+4.1mm ±2.0). Conclusions Through the use of elastography, this is the first study to suggest that DS increases muscle stiffness, decreases fascicle strain and increases muscle thickness as a result of improved RoM. These results can be beneficial to coaches, exercise and clinical scientists when choosing DS as a muscle conditioning or rehabilitation intervention.

A Mechatronic Solution for Stroke Rehabilitation in a Reaching Task

This paper describes a mechanically simple, tactile sensing solution as a mechatronic system for discriminating human motion in the process of stroke recovery in reaching task. Three seated healthy volunteers and five stroke survivors were included in trials and demonstrated that the system can discriminate motion of arm and trunk of the body. The results show robustness with respect to variations in volunteers with a accuracy above 90% for both types of participants.