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start [2019/08/14 14:21]
Christian Schumacher [News]
start [2020/01/08 13:05] (current)
Martin Grimmer [Review of balance recovery in response to external perturbations during daily activities]
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 ====== News ====== ====== News ======
  
-  * {{::​ansymb_logo_i.png?​90 | Teaching course ANSYMB II}} **Running ​upcoming ​winter term!** [[http://​www.ansymb.tu-darmstadt.de/​| ​  ​Analysis and Synthesis of Human Movements]] +  * {{::​ansymb_logo_i.png?​90 | Teaching course ANSYMB II}} **Running ​this winter term!** [[http://​www.ansymb.tu-darmstadt.de/​| ​  ​Analysis and Synthesis of Human Movements]]
-====== Pick of the Month  ======+
  
  
-==== Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking  ​====+====== Latest Publications ======
  
 +==== Review of balance recovery in response to external perturbations during daily activities ​ ====
  
 +Balance related responses to perturbations were investigated in one of our latest studies by Dr. Dario Tokur, Dr. [[lab_members:​lab_members_martingrimmer|Martin Grimmer]] and Prof. Andre Seyfarth. The work was recently published in [[https://​doi.org/​10.1016/​j.humov.2019.102546|Human Movement Science]]. ​
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 +{{ ::​perturbation.png?​300|}}
  
-A new concept for stance and swing detection based on lower limb segments is introduced in a recently published paper by Grimmer et al. in //Frontiers in Neurorobotics//​ [[https://​www.frontiersin.org/​articles/​10.3389/​fnbot.2019.00057/​full?&​utm_source=Email_to_authors_&​utm_medium=Email&​utm_content=T1_11.5e1_author&​utm_campaign=Email_publication&​field=&​journalName=Frontiers_in_Neurorobotics&​id=459435|Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking]]. ​ 
  
-{{ :​stance_swing_concept.png?​nolink&​500|}} 
-{{ :​stance_and_swing2.png?​nolink&​108|}} 
  
 **Abstract:​** ​ **Abstract:​** ​
 +Balance is an essential capability to ensure upright standing and locomotion. Various external perturbations challenge our balance in daily life and increase the risk for falling and associated injury. Researchers try to identify the human mechanisms to maintain balance by intentional perturbations. The objectives of this work were to point out which areas of perturbation based research are well covered and not well covered and to extract which coping mechanisms humans use to respond to external perturbations. A literature review was performed to analyze mechanisms in response to external perturbations such as pushes to the body or ground level changes during standing, walking, running and hopping. To get a well-structured overview on the two dimensions, the perturbation type and the task, the Perturbation Matrix (PMA) was designed. We found that multiple studies exist for the tasks walking and standing, while hopping and running are covered less. However, all tasks still offer opportunities for both in-depth and fundamental research. Regarding the recovery mechanisms we found that humans can recover from various types of perturbations with versatile mechanisms using combinations of trunk, as well as upper and lower limb movements. The recovery movements will adapt depending on the perturbation intensity, direction and timing. Changes in joint kinetics, joint kinematics and muscle activity were identified on the joint level and leg stiffness and leg length on the global leg level. We believe that the insights from the extracted mechanisms may be applied to the hardware and control of robotic limbs or lower limb exoskeletons to improve the balance and robustness during standing or locomotion.
  
-Lower limb exoskeletons require the correct support magnitude and timing to achieve user assistance. This study evaluated whether the sign of the angular velocity of lower limb segments can be used to determine the timing of the stance and the swing phase during walking. We assumed that stance phase is characterized by a positive, swing phase by a negative angular velocity. Thus, the transitions can be used to also identify heel-strike and toe-off. Thirteen subjects without gait impairments walked on a treadmill at speeds between 0.5 and 2.1 m/s on level ground and inclinations between −10 and +10°. Kinematic and kinetic data was measured simultaneously from an optical motion capture system, force plates, and five inertial measurement units (IMUs). These recordings were used to compute the angular velocities of four lower limb segments: two biological (thigh, shank) and two virtual that were geometrical projections of the biological segments (virtual leg, virtual extended leg). We analyzed the reliability (two sign changes of the angular velocity per stride) and the accuracy (offset in timing between sign change and ground reaction force based timing) of the virtual and biological segments for detecting the gait phases stance and swing. The motion capture data revealed that virtual limb segments seem superior to the biological limb segments in the reliability of stance and swing detection. However, increased signal noise when using the IMUs required additional rule sets for reliable stance and swing detection. With IMUs, the biological shank segment had the least variability in accuracy. The IMU-based heel-strike events of the shank and both virtual segment were slightly early (3.3–4.8% of the gait cycle) compared to the ground reaction force-based timing. Toe-off event timing showed more variability (9.0% too early to 7.3% too late) between the segments and changed with walking speed. The results show that the detection of the heel-strike,​ and thus stance phase, based on IMU angular velocity is possible for different segments when additional rule sets are included. Further work is required to improve the timing accuracy for the toe-off detection (swing). ​ 
  
-For further publications of the autohr ​please check: [[https://​www.researchgate.net/​profile/​Martin_Grimmer3|ResearchGate]],​ [[https://​scholar.google.de/​citations?​hl=de&​user=gDF_uHUAAAAJ&​view_op=list_works&​sortby=pubdate|Google Scholar]], [[https://​orcid.org/​0000-0003-1921-1433|ORCID]] or [[https://​loop.frontiersin.org/​people/​390560/​overview|LOOP]]+ 
 +For further ​projects and publications of [[lab_members:​lab_members_martingrimmer|M. Grimmer]] ​please check: [[https://​www.researchgate.net/​profile/​Martin_Grimmer3|ResearchGate]],​ [[https://​scholar.google.de/​citations?​hl=de&​user=gDF_uHUAAAAJ&​view_op=list_works&​sortby=pubdate|Google Scholar]], [[https://​orcid.org/​0000-0003-1921-1433|ORCID]] or [[https://​loop.frontiersin.org/​people/​390560/​overview|LOOP]]
 \\ \\
 +
 +==== Biomechanical effects of passive hip springs during walking ​ ====
 +
 +The effects of passive springs at the hip were investigated in a collaboration project of Florian Haufe, Peter Wolf and Robert Riener from the [[https://​sms.hest.ethz.ch/​|Sensory-Motor Systems Lab]] from ETH Zurich and [[lab_members:​lab_members_martingrimmer|Martin Grimmer]] from the Lauflabor. The work was recently published in the [[https://​www.sciencedirect.com/​science/​article/​abs/​pii/​S0021929019306797|Journal of Biomechanics]]. ​
 +
 +{{ ::​passive_hip_spring.jpg?​400|}}
 +
 +
 +
 +**Abstract:​** ​
 +
 +Passive spring-like structures can store and return energy during cyclic movements and thereby reduce the energetic cost of locomotion. That makes them important components of the human body and wearable assistive devices alike. This study investigates how springs placed anteriorly across the hip joint affect leg joint angles and powers, and leg muscle activities during level walking at 0.5 to 2.1 m/s.
 +
 +We hypothesized that the anterior hip springs (I) load hip extension, (II) support hip flexion and (III) affect ankle muscle activity and dynamics during walking. Effects at the ankle were expected because hip and ankle redistribute segmental power in concert to achieve forward progression.
 +
 +We observed that the participants’ contribution to hip power did not increase during hip extension as the spring stored energy. Simultaneously,​ the activities of plantarflexor muscles that modulate energy storage in the Achilles tendon were reduced by 28% (gastrocnemius medialis) and 9% (soleus). As the spring returned energy with the onset of hip flexion, the participants’ contribution to hip power was reduced by as much as 23%. Soleus activity before push-off increased by up to 9%.
 +
 +Instead of loading hip extension, anterior hip springs seem to store and return parts of the energy normally exchanged with the Achilles tendon. Thereby, the springs support hip flexion but may reduce elastic energy storage in and hence recoil from the Achilles tendon. This interaction should be considered during the design and simulation of wearable assistive devices as it might – depending on user characteristics – enhance or diminish their overall functionality.
 +
 +
 +For further projects and publications of [[lab_members:​lab_members_martingrimmer|M. Grimmer]] please check: [[https://​www.researchgate.net/​profile/​Martin_Grimmer3|ResearchGate]],​ [[https://​scholar.google.de/​citations?​hl=de&​user=gDF_uHUAAAAJ&​view_op=list_works&​sortby=pubdate|Google Scholar]], [[https://​orcid.org/​0000-0003-1921-1433|ORCID]] or [[https://​loop.frontiersin.org/​people/​390560/​overview|LOOP]]
 +\\
 +
 +===== Biarticular muscles are most responsive to upper-body pitch perturbations in human standing =====
 +
 +Our latest publication features the results of [[http://​lauflabor.ifs-tud.de/​doku.php?​id=lab_members:​lab_members_christian_schumacher|Christian]]'​s lab visit in the [[http://​dbl.tudelft.nl/​|Delft Biorobotics Lab]]. The study investigates important muscle groups to maintain an upright body posture when being perturbed. For this purpose, he used a novel type of balance perturbation,​ a control moment gyroscope (see Figure) that exerts a torque on the subject'​s upper body. Find more information in the published paper: [[https://​www.nature.com/​articles/​s41598-019-50995-3|Link to Scientific Reports]]. ​
 +
 +{{ :​gyro.jpg?​nolink&​600|[[https://​www.nature.com/​articles/​s41598-019-50995-3|Link to Scientific Reports]] }}  ​
 +
 +**Abstract:​** ​
 +Balancing the upper body is pivotal for upright and efficient gait. While models have identified potentially useful characteristics of biarticular thigh muscles for postural control of the upper body, experimental evidence for their specific role is lacking. Based on theoretical findings, we hypothesised that biarticular muscle activity would increase strongly in response to upper-body perturbations. To test this hypothesis, we used a novel Angular Momentum Perturbator (AMP) that, in contrast to existing methods, perturbs the upper-body posture with only minimal effect on Centre of Mass (CoM) excursions. The impulse-like AMP torques applied to the trunk of subjects resulted in upper-body pitch deflections of up to 17° with only small CoM excursions below 2 cm. Biarticular thigh muscles (biceps femoris long head and rectus femoris) showed the strongest increase in muscular activity (mid- and long-latency reflexes, starting 100 ms after perturbation onset) of all eight measured leg muscles which highlights the importance of biarticular muscles for restoring upper-body balance. These insights could be used for improving technological aids like rehabilitation or assistive devices, and the effectiveness of physical training for fall prevention e.g. for elderly people.
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