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Clinical Rehabilitation Technologies for Force-Control–Based Exoskeleton Robot
Published in Yuehong Yin, Biomechanical Principles on Force Generation and Control of Skeletal Muscle and their Applications in Robotic Exoskeleton, 2020
Isometric contraction training: While doing isometric contraction training, the exoskeleton’s joint angle is fixed. The gasbag is bound with human leg, and human joints are fixed. When the training starts, set the hip joint and knee joint of exoskeleton as 30° and 45° so that human legs are fixed. Then, the gasbag is charged, and F/E of calf is repeated to train the thigh muscles. In this process, the gasbag pressure and the EMG signal of each muscle are recorded, as illustrated in Figure 5.24. Referring to the figure, a group of antagonistic muscles, including the quadriceps femoris, biceps femoris, semitendinosus, and semimembranosus, are responsible for the extension and flexion of knee joint, respectively. When human calf extends forward, the EMG signal of quadriceps femoris is stronger. When calf flexes backward, the EMG signals of biceps femoris, semitendinosus, and semimembranosus are stronger. The muscle force can be calculated by force models to represent the training efficacy, as illustrated in Figure 5.25.
Lower extremity injuries
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
William C. Whiting, Ronald F. Zernicke
Certain muscles are more prone to strain injury than others. The hamstrings, for example, are particularly susceptible to muscle strain. In a study of strain injuries in Australian football, 69 per cent involved the hamstring group (Orchard, 2001). Why? The hamstring group muscles (with the exception of the short head of the biceps femoris) are biarticular. This structural arrangement results in muscle length being determined by the combined action of the knee and hip joints. Knee extension and hip flexion both act to lengthen the semitendinosus, semimembranosus, and biceps femoris (long head). Simultaneous knee extension and hip flexion lengthen the hamstrings and contribute to the muscles’ risk of injury.
Skeletal Muscle
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Muscles can play the following roles: Agonist, or prime mover, is a muscle that is the main muscle, or member of a group of muscles, responsible for a particular movement. For example, the quadriceps femoris muscle of the thigh is a prime mover in extension at the knee joint.Antagonist is a muscle that opposes the movement of an agonist. Since muscles can only pull when they contract, and not push, agonists and antagonists have to act at any joint to move it in opposite directions. Thus, in the flexion at a joint, the agonists are the flexors and the antagonists are the extensors. On the other hand, in the extension of a joint, the agonists are the extensors and the antagonists are the flexors. Moreover, in the movement of a limb, whether in flexion or extension, sets of muscles at different joints have to act together so as to move the whole limb in the same direction. The sets of muscles that act together in a given movement are called synergists. For example, the biceps femoris, the semitendinosus, and the semimembranosus muscles are synergists in knee flexion. In any movement, the nervous system has to not only excite the synergist muscles, but it also must relax the antagonist muscles at the same time.Fixator is a muscle that stabilizes one part of the body during movement of another part so as to prevent any unnecessary movement. Fixators are usually required because when a muscle contracts it contracts at both ends. Hence, a desired movement at only one end of a muscle requires stabilization at the other end. For example, during elbow flexion, fixator muscles prevent unwanted movement of the shoulder and wrist.
Statistical shape modelling reveals differences in hamstring morphology between professional rugby players and sprinters
Published in Journal of Sports Sciences, 2023
Ashlee M.T. Sutherland, Joseph T. Lynch, Benjamin G. Serpell, Mark R. Pickering, Phil Newman, Diana M. Perriman, Claire Kenneally-Dabrowski
Bilateral hamstring images were acquired using a Skyra 3-Tesla MRI scanner (Siemens Healthcare, Erlangen, Germany) using a T1 Dixon Vibe sequence (TE 2.46, TR 5.73, FOV 500 × 500, slice thickness 1.6 mm, gap 0.32 mm). Participants lay supine within the scanner with their feet taped together and a small pillow under their knees. A tourniquet secured the ankles to reduce the likelihood of motion induced artefact. The images were transformed from coronal to axial slices with the voxel dimensions: 1.6 mm antero-posterior; 1.5625 mm supero-inferior; and 1.5625 mm medio-lateral. The images of the left legs were mirrored to match the right legs. Each hamstring muscle (biceps femoris long head, BFLH; biceps femoris short head, BFSH; semitendinosus, ST; semimembranosus, SM) was manually segmented by a participant-blinded examiner using LegAnnotate© software written in MATLAB® (MathWorks Inc Massachusetts, USA) (Figure 1). Proximal- and distal-bony landmarks were identified as cut-off points to standardize shape measurements. The proximal landmark was identified from the axial slice which included the most inferior point of the ischial tuberosity and distally the axial slice which included the adductor tubercle of the femur.
Comparison of force-velocity profiles of the leg-extensors for elite athletes in the throwing events relating to gender, age and event
Published in Sports Biomechanics, 2021
Axel Schleichardt, Marko Badura, Frank Lehmann, Olaf Ueberschär
As shown by Bobbert (2012), all leg extending muscles contribute positive mechanical work in a leg press task, as their transfer to the external work is permanently positive. Hence, all the mechanical work done by the propulsive force FH, representing the sum of all leg extending muscle contributions, can be assigned to the knee joint and can be thought of as the work done by a single monoarticular acting muscle force. As a consequence, and according to the principle of virtual work, the line of the acting external force has to be aligned vertically with the ankle and hip (Figure 2), which both then contribute no more. Even though this simplification cannot account for the differing transfer functions of all real muscles involved, assigning all mechanical leg extending work to the knee joint is still plausible because of the joint-linking biarticular muscles (i.e. rectus femoris, the hamstring muscles biceps femoris, semitendinosus, semimembranosus and gastrocnemii). The model is depicted in Figure 2.
Effects of knee flexion angles in supine bridge exercise on trunk and pelvic muscle activity
Published in Research in Sports Medicine, 2020
Indy Man Kit Ho, Lai Ping Cindy Ng, Kin on Leonardo Lee, Tze Chung Jim Luk
To maximize the activation and strengthening effects of gluteus maximus, biomechanical factors such as external moment arm length and patient positions should be considered (Youdas et al., 2017). One simple modification in SBE to potentially alter the hip and trunk muscle activity is through changing knee flexion angle. By moving the feet towards the hip, the moment arm length between the knee joint and foot placement in SBE is reduced. Theoretically, this may potentially decrease the demand of muscles at knee joint such as hamstring. Moreover, with the increase of knee flexion angle, the biarticular muscles of the hamstring including the long head of biceps femoris (BF), semimembranosus and semitendinosus are placed in a shortened position. This will subsequently lead to the active insufficiency and in turn decrease the force production due to the muscle length–tension relationship (Baechle & Earle, 2008; Sakamoto et al., 2009). In other words, it is speculated that activation of gluteus maximus is more desirable in SBEs with larger knee flexion angle when the hamstring is placed in the position shorter than that for optimum force production.