Contractile behavior of the medial gastrocnemius in children with bilateral spastic cerebral palsy during forward, uphill and backward-downhill gait

BACKGROUND

Plantarflexor tightness due to muscle degenerations has been frequently documented in children with spastic cerebral palsy but the contractile behavior of muscles during ambulation is largely unclear. Especially the adaptability of gastrocnemius muscle contraction on sloped surface could be relevant during therapy.

METHODS

Medial gastrocnemius contractions were measured during flat-forward, uphill (+12% incline) and backward-downhill (-12% decline) treadmill gait in 15 children with bilateral cerebral palsy, walking in crouch, and 17 typically developing controls (age: 7-16years) by means of ultrasound and motion analysis. Tracked fascicle and calculated series elastic element length during gait were normalized on seated rest length. Additionally electromyography of the medial gastrocnemius, soleus and tibialis anterior was collected.

FINDINGS

During forward gait spastic gastrocnemii reached 10% shorter relative fascicle length, 5% shorter series elastic element length and showed 37% less concentric fascicle excursion than controls. No difference in eccentric fascicle excursion existed. Uphill gait increased concentric fascicle excursion in children with cerebral palsy and controls (by 23% and 41%) and tibialis anterior activity during swing (by 33% and 48%). Backward downhill gait more than doubled (+112%) eccentric fascicle excursion in cerebral palsy patients.

INTERPRETATION

Apart from having innately shorter fascicles at rest, flat-forward walking showed that spastic gastrocnemius fascicles work at shorter relative length than those of controls. Uphill gait may be useful to concentrically train push-off skills and foot lift. During backward-downhill gait the gastrocnemius functions as a brake and displays more eccentric excursion which could potentially stimulate sarcomere-genesis in series with repeated training.

Footwear traction and three-dimensional kinematics of level, downhill, uphill and cross-slope walking

Outdoor activities are a popular form of recreation, with hiking being the most popular outdoor activity as well as being the most prevalent in terms of injury. Over the duration of a hike, trekkers will encounter many different sloped terrains. Not much is known about the required traction or foot-floor kinematics during locomotion on these sloped surfaces, therefore, the purpose was to determine the three-dimensional foot-floor kinematics and required traction during level, downhill, uphill and cross-slope walking. Ten participants performed level, uphill, downhill and cross-slope walking along a 19° inclined walkway. Ground reaction force data as well as 3D positions of retro reflective markers attached to the shoe were recorded using a Motion Analysis System. Peak traction coefficients and foot-floor kinematics during sloped walking were compared to level walking. When walking along different sloped surfaces, the required traction coefficients at touchdown were not different from level walking, therefore, the increased likelihood of heel slipping during hiking is potentially due to the presence of loose material (rocks, dirt) on hiking slopes, rather than the overall lack of traction. Differences in required traction were seen at takeoff, with uphill and cross-sloped walking requiring a greater amount of traction compared to level walking. Changes in sagittal plane, frontal plane and transverse plane foot-floor angles were seen while walking on the sloped surfaces. Rapid foot-floor eversion was observed during cross-slope walking which could place the hiker at risk of injury with a misstep or if there was a slight slip.

Margins of stability of persons with transtibial or transfemoral amputations walking on sloped surfaces

Gait is a complex motor skill. However, most falls in humans occur during gait, and people with lower limb amputation have an increased risk of falls. Thus, this study evaluated the stability of persons with unilateral amputation by quantifying the margin of stability (MoS) during gait, to contribute to understanding the strategies adopted by these people to reduce falls. The participants were divided into 3 groups: persons with transtibial amputations (n = 12, 32.27 ± 10.10 years, 76.9 ± 10.3 kg, 1.74 ± 0.06 m); persons with transfemoral amputations (n = 13, 32.21 ± 8.34 years, 72.55 ± 10.23 kg, 1.73 ± 0.05 m); and controls (n = 15, 32.2 ± 10.17 years, 75.4 ± 9.25 kg, 1.75 ± 0.05 m), who walked for 4 min on a level and sloped (8% down and up) treadmill. The pelvic and foot marker kinematic data were used to estimate the center of mass and base of support, and from these, the MoS was estimated. Although both groups of persons with amputations showed higher values for the ML MoS than did the control group (transtibial: 8.81 ± 1.79, 8.97 ± 1.74, 8.79 ± 1.76, transfemoral: 10.15 ± 2.03, 10.60 ± 1.98, 10.11 ± 1.75, control: 8.13 ± 1.30, 7.18 ± 1.85, 8.15 ± 1.57, level, down, and up, respectively), only the transfemoral group presented a significant higher value compared to the control group. Our findings suggest that the documented limitations in persons with amputations, especially with transfemoral amputation, are exacerbated in situations that require more skills, such as walking on sloped surfaces, triggering protective mechanisms.

Multi-joint biomechanics during sloped walking in patients with developmental dysplasia of the hip

BACKGROUND

Developmental dysplasia of the hip is characterized by abnormal acetabular and femoral geometries that alter joint loading and increase the risk of hip osteoarthritis. Current understanding of biomechanics in this population remains isolated to the hip and largely focused on level-ground walking, which may not capture the variable loading conditions that contribute to symptoms and intra-articular damage.

METHODS

Thirty young adult females (15 with dysplasia) underwent gait analysis during level, 10° incline, and 10° decline walking while whole-body kinematics, ground reaction forces, and electromyography (EMG) were recorded. Low back, hip, and knee joint kinematics and internal joint moments were calculated using a 15-segment model and integrated EMG was calculated within the functional phases of gait. Dependent variables (peak joint kinematics, moments, and integrated EMG) were compared across groups with a one-way ANOVA with multiple comparisons controlled for using the Benjamini-Hochberg method (α = 0.05).

FINDINGS

During level and incline walking, patients with developmental dysplasia of the hip had significantly lower trunk flexion angles, lumbar and knee extensor moments, and erector spinae activity than controls. Patients with developmental dysplasia of the hip also demonstrated reduced rectus femoris activity during loading of level walking and increased gluteus maximus activity during mid-stance of decline walking.

INTERPRETATION

Patients with developmental dysplasia of the hip adopt compensations both proximal and distal to the hip, which vary depending on the slope of walking. Furthering the understanding of multi-joint biomechanical compensations is important for understanding the mechanism of osteoarthritis development as well as secondary conditions.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

BACKGROUND

The ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown.

RESEARCH QUESTION

Do foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces?

METHODS

This study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests.

RESULTS

FC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses.

SIGNIFICANCE

In terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

The 6DOF knee kinematics of healthy subjects during sloped walking compared to level walking

BACKGROUND

Level Walking is a frequent functional movement during daily life. However, sloped walking is also common. Exploring 6DOF knee kinematics during sloped walking is important. It provides a reference for the rehabilitation, safety, and knee health of patients with knee diseases walking on sloped surfaces.

RESEARCH QUESTION

The study aimed to explore 6DOF knee kinematics characteristics during sloped walking compared to level walking. We hypothesized that tibial anteroposterior translation and flexion angle (the sagittal plane) were significantly different from those of level walking.

METHODS

One hundred young, healthy adults (50 males and 50 females) were recruited for this study. A three-dimensional gait analysis system was used to collect 6DOF knee kinematics during level and sloped walking. The slope was set to ± 15% when the sloped walking was performed.

RESULTS

Sloped walking mainly increased knee flexion angle (upslope, 2.5-26.2°, 1-100% gait cycle (GC), p < 0.05; downslope, 1.7-11.9°, 15-95% GC, p < 0.05) and anterior tibial translation (upslope, 0.7-4.1 mm, 3-54% GC & 0.6-2.1 mm, 80-94% GC; downslope, 1.0-2.2 mm, 21-69% GC) in the participants' knees. However, participants' other 4DOF knee kinematics during sloped walking were significantly different from those during level walking (p < 0.05). Participants had 'drastically changeable' knee kinematic alterations in the transverse and coronal plane (the other 4DOF knee kinematics) during sloped walking compared to level walking.

SIGNIFICANCE

Our results confirmed the hypothesis. Sloped walking significantly increased anterior tibial translation (in most GC) and flexion angle. These kinematic changes in healthy subjects should be evaluated and further explored for patients with knee diseases, such as anterior cruciate ligament deficiency. Our findings are meaningful for their rehabilitation or safety or knee health while walking on sloped surfaces. Our study may provide a pilot reference for the 6DOF knee kinematic exploration of sloped walking.

Concentric and eccentric hip musculotendon work depends on backpack loads and walking slopes

Hip muscle weakness is associated with low back and leg injuries. In addition, hiking with heavy loads is linked to high incidence of overuse injuries. Walking with heavy loads on slopes alters hip biomechanics compared to unloaded walking, but individual muscle mechanical work in these challenging conditions is unknown. Using movement simulations, we quantified hip muscle concentric and eccentric work during walking on 0° and ±10° slopes with, and without 40% bodyweight added loads, and with and without a hip belt. For gluteus maximus, psoas, iliacus, gluteus medius, and biceps femoris long head, both concentric and eccentric work were greatest during uphill walking. For rectus femoris and semimembranosus, concentric work was greatest during uphill and eccentric work was greatest during downhill walking. Loaded walking had greater concentric and eccentric work from rectus femoris, biceps femoris long head, and gluteus maximus. Psoas concentric work was greatest while carrying loads regardless of hip belt usage, but eccentric work was only greater than unloaded walking when using a hip belt. Loaded and uphill walking had high concentric work from gluteus maximus, and high eccentric work from gluteus medius and biceps femoris long head. Carrying heavy loads uphill may lead to excessive hip muscle fatigue and heightened injury risk. Effects of the greater eccentric work from hip flexors when wearing a hip belt on lumbar spine forces and pelvic stability should be investigated. Military and other occupational groups who carry heavy backpacks with hip belts should maintain eccentric strength of hip flexors and hamstrings.

Psoas force recruitment in full-body musculoskeletal movement simulations is restored with a geometrically informed cost function weighting

Simulations of musculoskeletal models are useful for estimating internal muscle and joint forces. However, predicted forces rely on optimization and modeling formulations. Geometric detail is important to predict muscle forces, and greater geometric complexity is required for muscles that have broad attachments or span many joints, as in the torso. However, the extent to which optimized muscle force recruitment is sensitive to these geometry choices is unclear. We developed level, uphill and downhill sloped walking simulations using a standard (uniformly weighted, "fatigue-like") cost function with lower limb and full-body musculoskeletal models to evaluate hip muscle recruitment with different geometric representations of the psoas muscle under walking conditions with varying hip moment demands. We also tested a novel cost function formulation where muscle activations were weighted according to the modeled geometric detail in the full-body model. Total psoas force was less and iliacus, rectus femoris, and other hip flexors' force was greater when psoas was modeled with greater geometric detail compared to other hip muscles for all slopes. The proposed weighting scheme restored hip muscle force recruitment without sacrificing detailed psoas geometry. In addition, we found that lumbar, but not hip, joint contact forces were influenced by psoas force recruitment. Our results demonstrate that static optimization dependent simulations using models comprised of muscles with different amounts of geometric detail bias force recruitment toward muscles with less geometric detail. Muscle activation weighting that accounts for differences in geometric complexity across muscles corrects for this recruitment bias.