Dynamic balance during running using running-specific prostheses

Patients with multiple sclerosis and low disability display cautious rotational behavior during gait initiation

BACKGROUND

Multiple sclerosis induces locomotor impairments. The objective was to characterize the effects of Multiple Sclerosis on whole-body angular momentum control during gait initiation.

METHODS

Fifteen patients with Multiple Sclerosis with Expanded Disability status scale of 2.5 and 16 healthy participants were instructed to perform gait initiation. Spatiotemporal parameters, whole-body angular momentum, net external moment about the body's center of mass and its components were calculated by using a 3D motion capture system and two force plates.

FINDINGS

Patients with Multiple Sclerosis had a significantly smaller whole-body angular momentum range during the double support phase of gait initiation in the transversal plane (p = 0.011), and smaller net external moment at the transition between the initial double support phase and the execution phase in the sagittal plane (p = 0.013). In the transversal plane, patients with Multiple Sclerosis had a smaller net external moment during the double support phase (p = 0.024) and between the double support phase and the execution phase (p < 0.001).

INTERPRETATION

Despite preserved spatiotemporal parameters during gait initiation, patients with Multiple Sclerosis with low disability had reduced net external moments in the transversal and sagittal planes during the critical transitional period of this functional task, which appeared as a compensatory modality to preserve global postural stability. This finding highlights the cautious rotational behaviors in these planes to prevent the risk of falling and preserve dynamic stability. Whole-body angular momentum and net external moment are relevant parameters for functional and disease progression follow-up of the disease.

Development and Preliminary Evaluation of a Bimodal Foot Prosthesis for Walking and Running

People often alternate between bouts of walking and running, for instance, when adults participate in recreational activities. Transitioning between activities can be challenging for prosthesis users because existing prosthetic feet are not well-suited for both tasks. Meanwhile, switching between prostheses for different tasks is often impractical. Collectively, these challenges can present barriers to physical activity participation for people with limb loss, which can negatively impact social or physical health. This work describes the development and evaluation of a passive bimodal prosthetic foot prototype with different configurations and stiffnesses for walking and running. Users rated the bimodal prosthesis higher for standing and walking compared to a running prosthesis (+2.3 for both tasks on a seven-point Likert scale). Users rated the bimodal prosthesis higher for running compared to a walking prosthesis (+1.7 and +0.5 for 2.0 and 2.5 m/s running, respectively). Changing from walking to running mode increased the device's stiffness by 23-84%, depending on the user's preference. Users could switch between bimodal prosthesis walking and running modes quickly (21.3 ± 12.0 s). Overall, the preliminary results were encouraging in terms of user satisfaction, stiffness change between modes, and mode-switching speed. These findings motivate future exploration of this bimodal prosthesis concept.

Mediation of the mediolateral ground reaction force profile to maintain straight running among unilateral transfemoral amputees

The mediolateral ground reaction force (M-L GRF) profile that realizes a symmetrical mediolateral ground reaction impulse (M-L GRI) between both limbs is essential for maintaining a straight movement path. We aimed to examine the M-L GRF production across different running speeds in unilateral transfemoral amputees (TFA) to identify strategies for maintaining straight running. The average medial and lateral GRF, contact time (t_c), M-L GRI, step width, and center of pressure angle (COPANG) were analyzed. Nine TFAs performed running trials at 100% speed on an instrumented treadmill. Trials were set at 30-80% speed with an increment of 10%. Seven steps from the unaffected and affected limbs were analyzed. Overall, the unaffected limbs exhibited a higher average medial GRF than the affected limbs. The M-L GRI were similar between both limbs at all speeds, implying that the participants were able to maintain a straight running path. The affected limb exhibited a longer t_c and a lower M-L GRF profile than the unaffected limb. The results showed that unilateral TFAs adopted limb-specific strategies to maintain a straight running path, and that these limb-specific strategies were consistent across different running speeds.

'It's more than just a running leg': a qualitative study of running-specific prosthesis use by children and youth with lower limb absence

PURPOSE

The purpose of this study was to investigate the use of running-specific prostheses (RSPs) by children with lower limb absence (LLA) along with the benefits and challenges of RSPs.

MATERIALS AND METHODS

In this descriptive qualitative study, eight children (ages 8-20 years) and their parents participated in semi-structured interviews. The interviews were audio-recorded and transcribed. Coded data were the foundation for central theme development.

RESULTS

Three main themes were generated. "Run faster, jump higher, do more" (the benefits of RSP use), "Every leg serves its purpose" (comparing functionality between daily use prostheses and RSPs), and "A lot more to think about" (additional considerations with RSP use).

CONCLUSIONS

RSPs have a positive impact in promoting children's engagement in sports and physical activities. While some children used their RSP primarily for running, others wore it for a broader range of physical activities. Issues with balance and discomfort caused by leg length discrepancies and/or ill-fitting sockets limited daily wear time. Limitations related to current RSP designs and clinical implementation should be addressed to optimize the functional potential of children with unilateral or bilateral LLA.Implications for rehabilitationRunning-specific prostheses (RSPs) positively impacted children's ability to participate in some sports with peers promoting their physical and social well-being.The main issues that children faced were discomfort, difficulty balancing, and inability to use RSPs for certain sports, while parents' issues focused on supporting prosthesis use and transport, and adjustments of different prostheses to keep up with their child's growth.Clinicians should be aware of the challenges of RSP use to best support children and their families.Designers should focus on addressing limitations with current RSPs to facilitate the diverse needs of pediatric users.

Spring-mass behavioural adaptations to acute changes in prosthetic blade stiffness during submaximal running in unilateral transtibial prosthesis users

BACKGROUND

Individuals with lower-limb amputation can use running specific prostheses (RSP) that store and then return elastic energy during stance. However, it is unclear whether varying the stiffness category of the same RSP affects spring-mass behaviour during self-selected, submaximal speed running in individuals with unilateral transtibial amputation.

RESEARCH QUESTION

The current study investigates how varying RSP stiffness affects limb stiffness, running performance, and associated joint kinetics in individuals with a unilateral transtibial amputation.

METHODS

Kinematic and ground reaction force data were collected from eight males with unilateral transtibial amputation who ran at self-selected submaximal speeds along a 15 m runway in three RSP stiffness conditions; recommended habitual stiffness (HAB) and, following 10-minutes of familiarisation, stiffness categories above (+1) and below (-1) the HAB. Stance-phase centre of mass velocity, contact time, limb stiffness' and joint/RSP work were computed for each limb across RSP stiffness conditions.

RESULTS

With increased RSP stiffness, prosthetic limb stiffness increased, whilst intact limb stiffness decreased slightly (p<0.03). Centre of mass forward velocity during stance-phase (p<0.02) and contact time (p<0.04) were higher in the intact limb and lower in the prosthetic limb but were unaffected by RSP stiffness. Intact limb hip joint positive work increased for both the +1 and -1 conditions but remained unchanged across conditions in the prosthetic limb (p<0.02).

SIGNIFICANCE

In response to changes in RSP stiffness, there were acute increased mechanical demands on the intact limb, reflecting a reliance on the intact limb during running. However, overall running speed was unaffected, suggesting participants acutely adapted to an RSP of a non-prescribed stiffness.

Running-specific prosthesis model, stiffness and height affect biomechanics and asymmetry of athletes with unilateral leg amputations across speeds

Athletes with transtibial amputation (TTA) use running-specific prostheses (RSPs) to run. RSP configuration likely affects the biomechanics of such athletes across speeds. We determined how the use of three RSP models (Catapult, Sprinter and Xtend) with three stiffness categories (recommended, ±1), and three heights (recommended, ±2 cm) affected contact length (L_c ), stance average vertical ground reaction force (F _avg), step frequency (f _step) and asymmetry between legs for 10 athletes with unilateral TTA at 3-7 m s^-1. The use of the Xtend versus Catapult RSP decreased L_c (p = 2.69 × 10^-7) and F _avg asymmetry (p = 0.032); the effect on L_c asymmetry diminished with faster speeds (p = 0.0020). The use of the Sprinter versus Catapult RSP decreased F _avg asymmetry (p = 7.00 × 10^-5); this effect was independent of speed (p = 0.90). The use of a stiffer RSP decreased L_c asymmetry (p ≤ 0.00033); this effect was independent of speed (p ≥ 0.071). The use of a shorter RSP decreased L_c (p = 5.86 × 10^-6), F _avg (p = 8.58 × 10^-6) and f _step asymmetry (p = 0.0011); each effect was independent of speed (p ≥ 0.15). To minimize asymmetry, athletes with unilateral TTA should use an Xtend or Sprinter RSP with 2 cm shorter than recommended height and stiffness based on intended speed.

Back squat mechanics in persons with a unilateral transtibial amputation: A case study

CASE DESCRIPTION

A 30-year-old person with a unilateral transtibial amputation (TTAmp) was assessed performing an Olympic-style back squat with an energy storage and return prosthetic foot.

OBJECTIVE

Determine joint-level movement strategies of an individual with TTAmp while performing an Olympic-style back squat.

STUDY DESIGN

Case study design.

TREATMENT

Back squat mechanics are evaluated in an individual with TTAmp by comparing the contribution of the ankle, knee, and hip joint to total positive and negative amputated and sound limb work.

OUTCOMES

The hip joint was the greatest contributor to total positive limb work compared with the knee and ankle, respectively, in the amputated (55.0% hip vs. 30.8% knee, P < 0.001; vs. 14.2% ankle, P = 0.001) and sound limbs (52.2% hip vs. 38.9% knee, P < 0.001; vs. 8.9% ankle, P < 0.001). The hip joint was the greatest contributor to total negative limb work compared with the ankle in both the amputated (51.0% hip vs. 15.9% ankle, P < 0.001) and sound limbs (47.3% hip vs. 10.0% ankle, P < 0.001) and the knee in the amputated limb (51.0% hip vs. 32.5% knee, P < 0.001). Ankle joint power demonstrated an atypical bimodal negative/positive/negative/positive pattern.

CONCLUSION

The individual with TTAmp used a hip-dominant joint strategy in both the amputated and sound limbs while demonstrating more potential to optimize the prosthetic foot's energy storage and return capabilities when performing a back squat.

Biomechanical factors affecting individuals with lower limb amputations running using running-specific prostheses: A systematic review

BACKGROUND

Running-specific prostheses (RSPs) are biomechanically designed to enable individuals with lower limb amputations to engage in high level sports.

RESEARCH QUESTION

What is the influence of RSP use on the running biomechanics of individuals with lower limb amputations?

METHODS

An article search was conducted in six databases since their inception to July 2021. Two independent reviewers assessed the title, abstract and full texts in the review process. The quality of the papers was appraised. The review included a total of 35 articles.

RESULTS

Main findings indicate force production is a limitation of RSPs. Individuals with lower limb absence employ a variety of compensatory strategies such as adjusting their step frequency, contact length and joint kinetics to improve their running performance. Leg stiffness modulation and external factors relating to the RSP design and fitting play important roles in RSP biomechanics. For individuals with unilateral amputations, the increased loading of the intact limb could increase the risk of acute injury or chronic joint degradation.

SIGNIFICANCE

To improve their running performance, runners with lower limb amputations employ various compensatory strategies, such as altering the spatiotemporal and kinetic parameters. Factors relating to RSP height, stiffness, shape, and alignment also play an important role in terms of running biomechanics and should be considered in RSP design and fitting. Future studies should focus on the use of RSPs for recreation, in pediatric populations, with certain amputation levels, as well as the impact of training and running techniques.

Human balance control in 3D running based on virtual pivot point concept

Balance control is one of the crucial challenges in bipedal locomotion. Humans need to maintain their trunk upright while the body behaves like an inverted pendulum which is inherently unstable. Instead, the virtual pivot point (VPP) concept introduced a new virtual pendulum model to the human balance control paradigm by analyzing the ground reaction forces (GRF) in the body coordinate frame. This paper presents novel VPP-based analyses of the postural stability of human running in a 3D space. We demonstrate the relation between the VPP position and the gait speed. The experimental results suggest different control strategies in frontal and sagittal planes. The ground reaction forces intersect below the center of mass in the sagittal plane and above the center of mass in the frontal plane. These VPP locations are found for the sagittal and frontal planes at all running speeds, respectively. We introduced a 3D VPP-based model which can replicate the kinematic and kinetic behavior of human running. The similarity between the experimental and simulation results indicates the ability of the VPP concept in predicting human balance control in running and can support its applicability for gait assistance.

Segmental contribution to whole-body angular momentum during stepping in healthy young and old adults

Recent evidence suggests that during volitional stepping older adults control whole-body angular momentum (H) less effectively than younger adults, which may impose a greater challenge for balance control during this task in the elderly. This study investigated the influence of aging on the segment angular momenta and their contributions to H during stepping. Eighteen old and 15 young healthy adults were instructed to perform a series of stepping at two speed conditions: preferred and as fast as possible. Full-body kinematics were recorded to compute angular momenta of the trunk, arms and legs and their contributions to total absolute H on the entire stepping movement. Results indicated that older adults exhibited larger angular momenta of the trunk and legs in the sagittal plane, which contributed to a higher sagittal plane H range during stepping compared to young adults. Results also revealed that older adults had a greater trunk contribution and lower leg contribution to total absolute H in the sagittal plane compared to young adults, even though there was no difference in the other two planes. These results stress that age-related changes in H control during stepping arise as a result of changes in trunk and leg rotational dynamics.

Effect of increasing speed on whole-body angular momentum during stepping in the elderly

Recent evidence suggests that older adults may have difficulty controlling whole-body angular momentum (H) during volitional stepping, which could impose a major challenge for balance control and result in potential falls. However, it is not known if and how H is influenced by speed when stepping. This study aimed to investigate the effect on H of increasing speed during step initiation in older adults. Twenty-seven healthy individuals over 60 were enrolled in the current study and were instructed to perform a series of step initiations with their dominant leg under two speed conditions: at preferred speed and as fast as possible. Two force plates and a motion-capture system were used to record H and the components of the net external moment (moment arms and ground reaction forces) during the double support and step execution phases of stepping. Results revealed that increasing speed of stepping affected H differently in both stepping phases and in the different planes. H ranges in all three planes increased with speed during the double support phase. During the step execution phase, while H ranges in frontal and transversal planes decreased, sagittal plane H range significantly increased with speed. This increased H range in the sagittal plane, which may result from the task demands, could impose a greater challenge for balance control in the elderly.

Muscle Contributions to Balance Control During Amputee and Nonamputee Stair Ascent

Dynamic balance is controlled by lower-limb muscles and is more difficult to maintain during stair ascent compared to level walking. As a result, individuals with lower-limb amputations often have difficulty ascending stairs and are more susceptible to falls. The purpose of this study was to identify the biomechanical mechanisms used by individuals with and without amputation to control dynamic balance during stair ascent. Three-dimensional muscle-actuated forward dynamics simulations of amputee and nonamputee stair ascent were developed and contributions of individual muscles, the passive prosthesis, and gravity to the time rate of change of angular momentum were determined. The prosthesis replicated the role of nonamputee plantarflexors in the sagittal plane by contributing to forward angular momentum. The prosthesis largely replicated the role of nonamputee plantarflexors in the transverse plane but resulted in a greater change of angular momentum. In the frontal plane, the prosthesis and nonamputee plantarflexors contributed oppositely during the first half of stance while during the second half of stance, the prosthesis contributed to a much smaller extent. This resulted in altered contributions from the intact leg plantarflexors, vastii and hamstrings, and the intact and residual leg hip abductors. Therefore, prosthetic devices with altered contributions to frontal-plane angular momentum could improve balance control during amputee stair ascent and minimize necessary muscle compensations. In addition, targeted training could improve the force production magnitude and timing of muscles that regulate angular momentum to improve balance control.

Joint work and ground reaction forces during running with daily-use and running-specific prostheses

Some individuals with a transtibial amputation (TTA) may not have access to running-specific prostheses and therefore choose to run using their daily-use prosthesis. Unlike running-specific prostheses, daily-use prostheses are not designed for running and may result in biomechanical differences that influence injury risk. To investigate these potential differences, we assessed the effect of amputation, prosthesis type, and running speed on joint work and ground reaction forces. 13 people with and without a unilateral TTA ran at speeds ranging from 2.5 m/s to 5.0 m/s. People with TTA ran using their own daily-use and running-specific prostheses. Body kinematics and ground reaction forces were collected and used to compute joint work. People with TTA had smaller peak braking, propulsive and medial/lateral ground reaction forces from the amputated leg compared to people without TTA. People wearing running-specific prostheses had smaller peak amputated leg vertical ground reaction forces compared to daily-use prostheses at speeds above 3.5 m/s. Medial/lateral forces were also smaller in running-specific prostheses, which may present balance challenges when running on varied terrain. Running-specific prostheses stored and returned more energy and provided greater propulsion, resulting in more similar positive hip work between legs compared to daily-use prostheses. Increases in positive hip work, but not device work, highlight the importance of the hip in increasing running speed. Running-specific devices may be beneficial for joint health at running-speeds above 3.5 m/s and provide advantages in propulsion and energy return at all speeds compared to daily-use prostheses, helping people with TTA achieve faster running speeds.

Age-related changes in the control of whole-body angular momentum during stepping

BACKGROUND

Appropriate control of whole-body angular momentum (H) is crucial to maintain dynamic balance and thus avoid falling during daily activities. Poor H control ability during locomotion has been found in people with an increased risk of falling, such as post-stroke patients and amputees. In contrast, little is known about the control of H during locomotion in the elderly. The aim of this study was to investigate whether and how aging influences three-dimensional H control during initiation of stepping.

METHODS

Twenty-two healthy old and 22 healthy young individuals were instructed to perform a series of initiation of stepping with their dominant leg and at their self-selected preferred pace. Two force plates and a motion capture system were used to record H, the net external moment about the body's center of mass and components of this net external moment (moment arms and ground reaction forces) during the double support and step execution phases of stepping.

RESULTS

In the double support phase, older participants exhibited smaller peak-to-peak ranges of H in the sagittal and transversal planes compared to their younger counterparts. These results were explained by decreased net external moments in both planes in the older participants. Conversely, during the step execution phase, older adults had higher peak-to-peak ranges of H in the frontal and sagittal planes compared to the younger adults. These higher ranges of H were associated with a longer duration of the step execution phase. Furthermore, in the sagittal plane, a higher external moment also contributed to increasing peak-to-peak ranges of H in older adults.

CONCLUSION

The current study revealed that older and younger adults exhibit different control strategies of H during initiation of stepping. The age-related changes, which may emphasize a higher difficulty to control H in the older adults, could impose a higher challenge for balance control and a potentially higher risk of falling during the step execution phase in this population.