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Biomechanical Analysis of Long Bones Provides the Crucial Break in Decedent Identification
Published in Heather M. Garvin, Natalie R. Langley, Case Studies in Forensic Anthropology, 2019
Although people often think of bone as static or unchanging, bone responds to mechanical stimuli caused by dynamic loading during normal activities such as walking, running, and jumping throughout life. Forces created by muscles and forces exerted by the ground on the body (ground reaction force) during normal activities can cause physical deformation or strain on the bones (Wallace, 2014). Under sufficient compression, a long bone deforms by shortening and slightly bulging. Under tension, it lengthens and narrows slightly. Shear forces cause angular deformation. Bone cells known as osteocytes detect strain, and bone responds by adding bone to specific locations to reduce future strain or by removing bone in areas where strain is low (Robling et al., 2014; Wallace, 2014). In other words, bone responds to mechanical forces by forming bone in areas that receive a signal that increased strength is necessary and removing bone where strength is less important. As a result, bone size and shape changes throughout life to reduce mechanical strain caused by the stress of daily activities. Activities such as jumping create greater strain than walking, and therefore evoke greater change.
Impulse and momentum
Published in Paul Grimshaw, Michael Cole, Adrian Burden, Neil Fowler, Instant Notes in Sport and Exercise Biomechanics, 2019
In order to have achieved this action and jump into the air you will have applied a force to the ground for a period of time (contact with the ground). The ground reaction force (i.e. from the ground and acting on the person) would be the force that is used to determine the amount of impulse that is acting on the body (impulse = force × time). This impulse would provide a change in momentum (because the two are related by Ft = mv2 – mv1). Now, since your mass is constant throughout this activity, this change in momentum will result in a change in velocity. The greater the impulse (the more positive the net result) the greater will be the change in velocity. Since at the beginning of the jump you are not moving (zero velocity – stationary) the more net vertical impulse you can generate the greater will be the take-off velocity in a vertical direction (important since we are considering the vertical impulse generated). The more vertical take-off velocity you have, the higher you will jump, although, as we know, gravity, which is acting throughout this whole activity, will begin to slow you down at a constant rate as soon as you take off. However, if you have more vertical velocity to begin with, it will take longer for gravity to slow you down at this constant rate and hence you will jump higher.
Gait
Published in Manoj Ramachandran, Tom Nunn, Basic Orthopaedic Sciences, 2018
Pramod Achan, Mark Paterson, Fergal Monsell
Certain concepts need to be understood before the events of the gait cycle can be fully appreciated: Muscle contraction may be concentric, eccentric or isometric. When a muscle contracts concentrically, the muscle–tendon unit shortens and kinetic energy is released. When contracting eccentrically the overall unit lengthens and energy is stored.The moment about a joint is a measure of the turning effect produced by a force about the joint. The magnitude of the moment is the product of the force and the perpendicular distance from the centre of rotation of the joint axis to the line of action of the force.The ground reaction force (GRF) is defined as the reaction to the force that the body exerts on the ground. It combines gravity’s effect on the body and the effects of the body’s movement and acceleration (Figure 26.2a). The position of the GRF in relation to each lower limb joint at any point in the gait cycle determines whether the overall moment at that joint is a flexion or extension moment, and this in turn will dictate which muscles will need to act, and in what manner, to maintain stability. The GRF is key to determining the forces required to make forward progress whilst at the same time maintaining stability.
Reduced joint reaction and muscle forces with barefoot running
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Hyun Kyung Kim, Qichang Mei, Yaodong Gu, Ali Mirjalili, Justin Fernandez
Prior to and approximately 5–10 min following 5 km running, participants performed a gait assessment in a motion analysis laboratory. During the gait assessment, the researcher verbally instructed runners to run with the same constant speed as their 5 km intervention speed. Three gait cycles of the right leg were accepted if an entire foot stepped into a single force plate for data processing. An 8-camera VICON motion capture system (Oxford Metrics Ltd, Oxford, UK) was used for capturing three-dimensional marker trajectories at 200 Hz. Three force plates, which were embedded into a 20 m walkway, were simultaneously used for measuring ground reaction force at 1000 Hz (Bertec Corporation, Ohio, USA). Markers trajectories and ground reaction force data were filtered with zero-lag 4th-order Butterworth filter at a cut-off frequency of 6 Hz. The best cut-off frequencies were determined from a recent OpenSim running study (Mei et al. 2019).
What are the effects of simulated muscle weakness on the sit-to-stand transfer?
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Elena J. Caruthers, Grant Schneider, Laura C. Schmitt, Ajit M. W. Chaudhari, Robert A. Siston
Six young, healthy participants (4 males and 2 females, age: 23.0 ± 3.0 years, mass: 78.6 ± 11.9 kg, height: 1.77 ± 0.07 m) who provided written consent for our previous STS transfer investigation (Caruthers et al. 2016), were further analyzed in this study. Participants performed three STS transfer trials on a hard-backed, armless chair with a seat 55.2 cm from the ground. Participants sat at the edge of the chair with their arms crossed over their chest and their feet on two force plates. They were instructed to rise from the chair at a self-selected speed without moving their feet, rest for two seconds, and return to sitting. No other specific directions were given with regard to the participant’s chair rise strategy. An optical motion analysis system (8 Vicon MX-F40, Centennial, CO) captured (150 Hz) reflective markers that were placed on the participant’s body, with the lower extremity marker set arranged according to the Point-Cluster technique and the upper extremity and torso marker set arranged on bony landmarks (Jamison et al. 2013). Ground reaction force (GRF) data were collected (600 Hz) from force plates below the participant’s feet (Bertec 406010, Columbus, OH). Surface electromyography (EMG) data were collected (1500 Hz) bilaterally from the gluteus maximus, gluteus medius, rectus femoris, vastus lateralis, biceps femoris, tibialis anterior, medial gastrocnemius, and soleus (Telemyo DTS, Noraxon USA, Inc., Scottsdale, AZ). A description of electrode preparation can be found in Jamison et al. (2013). The EMG data were high-pass filtered at 10 Hz, rectified, and smoothed with a 20 ms window RMS filter.
Individual muscle contributions to hip joint-contact forces during walking in unilateral transfemoral amputees with osseointegrated prostheses
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Vahidreza Jafari Harandi, David Charles Ackland, Raneem Haddara, L. Eduardo Cofré Lizama, Mark Graf, Mary Pauline Galea, Peter Vee Sin Lee
All subjects performed three complete trials of over-ground walking in an 8-m walkway. They were given a 30-s rest between each trial. The three-dimensional positions of retro-reflective markers placed on each subject were recorded using an eight-camera motion capture system (Vicon, Oxford Metrics) sampling at 200 Hz while subjects walked at their preferred speed. Markers were placed using a modified marker set previously published (Dorn 2011). During testing, three AMTI force platforms embedded in the floor (Watertown MA, USA) were used to measure ground reaction force at a sample rate of 1000 Hz. Surface electromyography (EMG) was simultaneously recorded at a sample rate of 1000 Hz (Cometa, Milan, Italy) on intact limb muscles that included gluteus maximus (GMAX), gluteus medius (GMED), soleus (SOL), gastrocnemius (GAS) and vasti (VAS) and residual leg muscles GMAX and GMED following a previously published procedure (Hermens et al. 1999, 2000; Wentink et al. 2013) (see Supporting Information). Marker trajectories and ground reaction force data were low-pass filtered using a fourth-order Butterworth filter with a cut-off frequency of 4 Hz and 60 Hz, respectively. EMG offset signals were removed, rectified and low-pass filtered at 10 Hz using a second-order Butterworth filter to create linear envelopes (Schache et al. 2018; Harandi et al. 2020).