Crouch gait can be an effective form of forced-use/no constraint exercise for the paretic lower limb in stroke

Muscle activity during crouched walking

OBJECTIVES

Muscle activity during crouched walking has been previously studied in the context of the evolution of hominin bipedalism and human movement disorders. However, crouched walking could also be used in approach hunting where postural height (actual height of the body from the ground to the top of the head during locomotion) is the limiting factor. Here, we aim to analyze the relationship between relative postural height (%stature), kinematics, and muscle activity during crouched walking.

MATERIALS AND METHODS

Adult males (n = 19) walked with extended limbs and at three degrees of crouch while their 3D motion capture kinematics and lower limb muscle electromyography were recorded. We measured activation of tibialis anterior, soleus, gastrocnemius medialis, gastrocnemius lateralis, vastus lateralis, rectus femoris, biceps femoris, and gluteus maximus. We analyzed the effects of postural height on kinematics and muscle activation using linear mixed effects model.

RESULTS

Flexion angles, individual muscle activation (except for medial gastrocnemius), and total muscle activation were negatively related to relative postural height, that is, were greater at more crouched postures. Relative postural height had a stronger effect on the activation of the thigh and gluteal muscles compared to shank muscles.

DISCUSSION

General increase in lower limb muscle activation at lower postural heights suggests a negative relationship between relative postural height and fatigue, and may indicate a possible mechanism by which short stature could benefit the hunter in approach hunting. Greater activation of thigh and gluteal muscles relative to shank muscles may help to identify crouched walking in past human populations.

Reversed Mirror Therapy (REMIT) after Stroke-A Proof-of-Concept Study

In mirror training (MIT), stroke patients strive to move their hands while looking at the reflected image of the unaffected one. The recruitment of the mirror neurons and visual-proprioceptive conflict are expected to facilitate the paretic voluntary movement. Here, a reversed MIT (REMIT) is presented, which requires moving hands while looking at the reflected image of the paretic one, giving the illusion of being unable to move the unimpaired hand. This study compares MIT and REMIT on post-stroke upper-limb recovery to gain clues on the mechanism of action of mirror therapies. Eight chronic stroke patients underwent two weeks of MIT and REMIT (five sessions each) in a crossover design. Upper-limb Fugl-Meyer, Box and Block and handgrip strength tests were administered at baseline and treatments end. The strength of the mirror illusion was evaluated after each session. MIT induced a larger illusory effect. The Fugl-Meyer score improved to the same extent after both treatments. No changes occurred in the Box and Block and the handgrip tests. REMIT and MIT were equally effective on upper-limb dexterity, challenging the exclusive role of mirror neurons. Contrasting learned nonuse through an intersensory conflict might provide the rationale for both forms of mirror-based rehabilitation after stroke.

Determinants of age-related decline in walking speed in older women

Background

Walking speed is reduced with aging. However, it is not certain whether the reduced walking speed is associated with physical and coordination fitness. This study explores the physical and coordination determinants of the walking speed decline in older women.

Methods

One-hundred-eighty-seven active older women (72.2 ± 6.8 years) were asked to perform a 10-m walk test (self-selected and maximal walking speed) and a battery of the Senior fitness test: lower body strength, lower body flexibility, agility/dynamic balance, and aerobic endurance. Two parameters characterized the walking performance: closeness to the modeled speed minimizing the energetic cost per unit distance (locomotor rehabilitation index, LRI), and the ratio of step length to step cadence (walk ratio, WR). For dependent variables (self-selected and maximal walking speeds), a recursive partitioning algorithm (classification and regression tree) was adopted, highlighting interactions across all the independent variables.

Results

Participants were aged from 60 to 88 years, and their self-selected and maximal speeds declined by 22% and 26% (p < 0.05), respectively. Similarly, all physical fitness variables worsened with aging (muscle strength: 33%; flexibility: 0 to -8 cm; balance: 22%; aerobic endurance: 12%; all p < 0.050). The predictors of maximal walking speed were only WR and balance. No meaningful predictions could be made using LRI and WR as dependent variables.

Discussion

The results suggest that at self-selected speed, the decrease in speed itself is sufficient to compensate for the age-related decline in the motor functions tested; by contrast, lowering the WR is required at maximal speed, presumably to prevent imbalance. Therefore, any excessive lowering of LRI and WR indicates loss of homeostasis of walking mechanics and invites diagnostic investigation.

Kinematic patterns during walking in children: Application of principal component analysis

The relative displacements of body segments during walking can be reduced to a small number of multi-joint kinematic patterns, pm_k, through Principal Component Analysis (PCA). These patterns were extracted from two groups of children (n = 8, aged 6-9 years, 4 males, and n = 8, aged 10-13 years, 4 males) and 7 adults (21-29 years, 1 male), walking on a treadmill at various velocities, normalized to body stature (adimensional Froude number, Fr). The three-dimensional coordinates of body markers were captured by an optoelectronic system. Five components (pm₁ to pm₅) explained 99.1% of the original dataset variance. The relationship between the variance explained ("size") of each pm_k and the Fr velocity varied across movement components and age groups. Only pm₁ and pm₂, which described kinematic patterns in the sagittal plane, showed significant differences (at p < 0.05) across pairs of age groups. The time course of the size of all the five components matched various mechanical events of the step cycle at the level of both body system and lower limb joints. Such movement components appeared clinically interpretable and lend themselves as potential markers of neural development of walking.

Dynamic Asymmetries Do Not Match Spatiotemporal Step Asymmetries during Split-Belt Walking

While walking on split-belt treadmills (two belts running at different speeds), the slower limb shows longer anterior steps than the limb dragged by the faster belt. After returning to basal conditions, the step length asymmetry is transiently reversed (after-effect). The lower limb joint dynamics, however, were not thoroughly investigated. In this study, 12 healthy adults walked on a force-sensorised split-belt treadmill for 15 min. Belts rotated at 0.4 m s−1 on both sides, or 0.4 and 1.2 m s−1 under the non-dominant and dominant legs, respectively. Spatiotemporal step parameters, ankle power and work, and the actual mean velocity of the body’s centre of mass (CoM) were computed. On the faster side, ankle power and work increased, while step length and stance time decreased. The mean velocity of the CoM slightly decreased. As an after-effect, modest converse asymmetries developed, fading within 2–5 min. These results may help to decide which belt should be assigned to the paretic and the unaffected lower limb when split-belt walking is applied for rehabilitation research in hemiparesis.

The curvature peaks of the trajectory of the body centre of mass during walking: A new index of dynamic balance

During walking, falling is most likely to occur towards the side of the supporting lower limb during the single stance. Timely lateral redirection of the centre of mass (CoM) preceding the no-return position is necessary for balance. We analysed the curvature peaks (the inverse of the radius of curvature) of the three-dimensional path of the CoM during the entire stride. Twelve healthy adults walked on a force-sensorized treadmill at constant velocities from 0.4 to 1.2 m s^-1, in 0.2 m s^-1 increments. The three-dimensional displacements of the CoM, the muscular power sustaining the CoM motion with respect to the ground, and the efficiency of the pendulum-like transfer of the CoM were computed via the double integration of the ground reaction forces. The curvatures of the CoM trajectory were measured (Frenet-Serret formula). During the single stance, the curvature showed a bell-shaped increment, lasting a few tenths of a millisecond, and peaking at 365-683 m^-1 (radius of 2.7-1.4 mm, respectively), the higher the walking velocity. The CoM was redirected towards the swinging lower limb. The curvature increment was sustained by muscle-driven braking of the CoM. Smoother increments of curvature (peaking at approximately 37-150 m^-1), further orienting the CoM towards the leading lower limb, were observed during the double stance. The peaks of the curvatures were symmetric between the two sides. The high curvature peaks during the single stance may represent an index of dynamic balance during walking. This index might be useful for both rehabilitation and sports training purposes.

The Motion of Body Center of Mass During Walking: A Review Oriented to Clinical Applications

Human walking is usually conceived as the cyclic rotation of the limbs. The goal of lower-limb movements, however, is the forward translation of the body system, which can be mechanically represented by its center of mass (CoM). Lower limbs act as struts of an inverted pendulum, allowing minimization of muscle work, from infancy to old age. The plantar flexors of the trailing limbs have been identified as the main engines of CoM propulsion. Motion of the CoM can be investigated through refined techniques, but research has been focused on the fields of human and animal physiology rather than clinical medicine. Alterations in CoM motion could reveal motor impairments that are not detectable by clinical observation. The study of the three-dimensional trajectory of the CoM motion represents a clinical frontier. After adjusting for displacement due to the average forward speed, the trajectory assumes a figure-eight shape (dubbed the “bow-tie”) with a perimeter about 18 cm long. Its lateral size decreases with walking velocity, thus ensuring dynamic stability. Lateral redirection appears as a critical phase of the step, requiring precise muscle sequencing. The shape and size of the “bow-tie” as functions of dynamically equivalent velocities do not change from child to adulthood, despite anatomical growth. The trajectory of the CoM thus appears to be a promising summary index of both balance and the neural maturation of walking. In asymmetric gaits, the affected lower limb avoids muscle work by pivoting almost passively, but extra work is required from the unaffected side during the next step, in order to keep the body system in motion. Generally, the average work to transport the CoM across a stride remains normal. In more demanding conditions, such as walking faster or uphill, the affected limb can actually provide more work; however, the unaffected limb also provides more work and asymmetry between the steps persists. This learned or acquired asymmetry is a formerly unsuspected challenge to rehabilitation attempts to restore symmetry. Techniques of selective loading of the affected side, which include constraining the motion of the unaffected limb or forcing the use of the affected limb on split-belt treadmills which impose a different velocity and power to either limb, are now under scrutiny.

Limping on split-belt treadmills implies opposite kinematic and dynamic lower limb asymmetries

Walking on a split-belt treadmill (each of the two belts running at a different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise. However, the scarcity of dynamic investigations challenges the validity of the available findings. The aim of the present study was to investigate the dynamic asymmetries of lower limbs of healthy adults during adaptation to gait on a split-belt treadmill. Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('tied' condition) or at different speeds ('split' condition, 0.4 vs. 0.8 or 0.8 vs. 1.2 m/s). The sagittal power and work provided by ankle, knee and hip joints, joint rotations, muscle lengthening, and surface electromyography were recorded simultaneously. Various tied/split walking sequences were requested. In the split condition a marked asymmetry between the parameters recorded from each of the two lower limbs, in particular from the ankle joint, was recorded. The work provided by the ankle (the main engine of body propulsion) was 4.8 and 2.2 times higher (in the 0.4 vs. 0.8, and 0.8 vs. 1.2 m/s conditions, respectively) compared with the slower side, and 1.2 and 1.1 times higher compared with the same speed in the tied condition. Compared with overground gait in hemiplegia, split gait entails an opposite spatial and dynamic asymmetry. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view. These differences challenge the proposed protocols of split gait as forms of therapeutic exercise.

Gait analysis on force treadmill in children: comparison with results from ground-based force platforms

Gait analysis (GA) typically includes surface electromyographic (sEMG) recording from several lower limb muscles, optoelectronic measurement of joint rotations, and force recordings from ground-based platforms. From the latter two variables, the muscle power acting on the lower limb joints can be estimated. Recently, gait analysis on a split-belt force treadmill (GAFT) was validated for the study of adult walking. It showed high reliability of spatiotemporal, kinematic, dynamic, and sEMG parameters, matching those obtainable with GA on the basis of ground walking. GAFT, however, still needs validation in children. Potential differences with respect to adult GAFT relate to (a) possible high signal-to-noise ratio, given the lower forces applied; (b) higher differences between treadmill and over-ground walking; and (c) limited compliance with the experimental setup. This study aims at investigating whether GAFT provides results comparable with those obtainable from ground walking in children and consistent with results from GAFT in adults. GAFT was applied to three groups of healthy children aged 5-6 years (n=6), 7-8 years (n=6), and 9-13 years (n=8) walking at the same average speed spontaneously adopted overground. The results were compared with those obtained from another study applying GA to an age-matched and speed-matched sample of 47 children, and with those obtained from GAFT in adults. The reliability (as indicated by the SD) of both spatiotemporal and dynamic parameters was higher in GAFT compared with GA. In the 5-6-, 7-8-, and 9-13-year-old groups, at average speeds of 0.83, 1.08, and 1.08 m/s, step length was shorter by 9.19, 3.57, and 2.30% compared with GA in controls at comparable speeds, respectively. For the youngest group, a lower power generation from the plantar flexors (peak power: 1.35±0.32 vs. 2.11±1.02 W/kg) and a slightly more flexed posture of the hip, knee, and ankle joints were observed during GAFT compared with GA in controls. The other gait parameters were very similar between the GAFT and the GA groups. The shortening of step length during GAFT, relative to GA at superimposable speed, was on average of all children 6.8%, in line with the 8% decrease found in adults. The profiles of sEMG and joint rotations, and all of the weight-standardized joint power parameters, matched those recorded in adults. The entire experimental session lasted about 1 h. All children complied with the experimental setting and easily completed the requested tests. In conclusion, GAFT seems to be a promising alternative to conventional GA in children.