Neurological issues
Andrea Utley in Motor Control, Learning and Development, 2018
In a polysynaptic reflex, sensory and motor neurons do not synapse directly, but the impulses there are involved within the reflex arc. The longer the reflex loop time, or the time taken from the presentation of the external stimuli to the time a response is recorded in the muscle fibers. The simplest example of a polysynaptic reflex or a flexion reflex is the withdrawal of a limb from painful stimulus via a process called reciprocal inhibition. The pain receptor causes the sensory neuron to fire; this then proceeds via the dorsal root to synapse with the interneuron(s) in the spinal cord. The excitatory interneuron then synapses with a motor neuron, causing the motor neuron in the ventral root to fire. This excitation causes subsequent contraction of the flexor muscle. At the same time, and just as important, the extensor muscle is stretched and inhibitor interneurons prevent the extensor muscle from firing, to allow the limb to move away from the stimulus.
Biomechanical simulation models of sports activities
Youlian Hong, Roger Bartlett in Routledge Handbook of Biomechanics and Human Movement Science, 2008
All simulation models that include individual muscle models have the disadvantage that it is very difficult to determine individual parameters for each element of each muscle, as it is impossible to measure all the parameters required non-invasively. As a consequence, researchers rely on data from the literature for their muscle models and so the models are not specific to an individual. An alternative approach is to use torque generators to represent the net effect of all the muscles crossing a joint (e.g. King and Yeadon, 2002) as the net torque produced by a group of muscles can be measured on a constant velocity dynamometer. More recently the extensor and flexor muscle groups around a joint have been represented using separate torque generators (King et al., 2006). In both cases each torque generator consists of rotational elastic and contractile elements. Using torque generators instead of individual muscles gives similar mathematical relationships, with the maximum voluntary torque produced by the contractile element being expressed as a function of the muscle angle and muscle angular velocity (Yeadon et al., 2006a).
Weight Lifting and Training
Christopher L. Vaughan in Biomechanics of Sport, 2020
Movement speed (1-, 2-, or 3-sec concentric and 2-sec eccentric phases) and equipment type, had considerable effect on the elbow-torque curves. Barbell curls required an elbow- extensor torque in the region of maximal elbow flexion (60 to 120 N·m) and required the greatest flexor torque (100 to 140 N·m) in the region of maximal elbow extension. The fastest speed of execution required greater torques at the extremes of movement range, but similar torques compared with slow and medium speeds in the mid-range of motion. DVR machine curls resulted in an almost constant elbow-flexor torque (80 N·m) for slow and medium execution speeds, but oscillating values (0 to 100 N·m) for the fast speed. Extensor torque did not develop with the DVR machine. Since skeletal muscle can produce lower maximal forces at higher contraction rates, it was argued that the fast curling speed provided greater overload (absolute and relative to maximal capability). This is true, but injury potential is also increased with speed, especially at the extremes of motion when elbow-torque values were greatest. This is especially true with “preacher bench” curls since the upper arms are in a fixed position. A standing barbell curl may be safer for fast curling speeds since the torso and upper arms can move to absorb kinetic energy at the extremes of motion. Such “body swing”, however, is often used to initiate the curl motion and thus reduces flexor muscle range of involvement.
Comparison of transcutaneous electrical nerve stimulation (TENS) and functional electrical stimulation (FES) for spasticity in spinal cord injury - A pilot randomized cross-over trial
Published in The Journal of Spinal Cord Medicine, 2018
Anjali Sivaramakrishnan, John M. Solomon, Natarajan Manikandan
Effects of FES on spastic reflexes (SCATS) lasted for four hours unlike TENS. Most of the participants had non-traumatic myelopathies and in addition to tonal changes in spasticity, they presented with spasmodic behavior such as clonus, flexor, and extensor spasms. We observed that SCATS values at baseline were relatively higher (around 5–9) compared to MAS. Flexor spasms in SCI are associated with the flexion withdrawal reflex7 and extensor spasms can be triggered by a change in hip joint position, particularly extension.45 The threshold for flexor muscle activation has shown to be reduced in SCI.7 Electrical stimulation with FES may increase the threshold of spastic reflexes via a muscle contraction which may account for the observed findings. FES may be more effective than TENS for reducing spasmodic behavior and improving functional activities, as both flexor and extensor spasms can interfere with ambulation and transfers.1,37,45
Reliability and validity of a dual-probe personal computer-based muscle viewer for measuring the pennation angle of the medial gastrocnemius muscle in patients who have had a stroke
Published in Topics in Stroke Rehabilitation, 2018
Ji-Eun Cho, Ki Hun Cho, Jun sang Yoo, Su Jin Lee, Wan-Hee Lee
The architecture of the skeletal muscle, defined as the geometric arrangement of the muscle fibers, is a primary determinant of muscle function. Therefore, assessment of the morphological changes in muscle architecture (e.g. muscle thickness, fascicle length, and pennation angle) provides an alternative measurement of muscle activity related to muscle function.28 One of the most important impairments after the development of central nervous system lesions, even in individuals who have had a stroke, is the inability to generate normal muscle activation and normal muscle force levels.29 The phenomenon of degenerating normal muscle force of the lower limb affects the abnormal gait pattern and gait speed of post-stroke patients. Clinically, the foot drop phenomenon, which is a significant problem in gait speed, is associated with an increased muscle tone in the calf muscle.30 Although muscle tone is usually associated with both reflex and increased passive joint/muscle stiffness,31–33 how hypertonia in the ankle joints is associated with changes in the biomechanical properties of the plantar flexors is unclear. A better understanding of the changes in the plantar flexor muscle architecture and its association with joint biomechanical properties could provide insight into the gait mechanisms in post-stroke patients. Therefore, a reliable method to measure the MG muscle, which is a major ankle plantar flexor, is required.
Effect of hand postures and object properties on forearm muscle activities using surface electromyography
Published in International Journal of Occupational Safety and Ergonomics, 2020
Kyung-Sun Lee, Myung-Chul Jung
The contributions of individual forearm muscles to the muscle activity varied. The EPL and FPL muscles, which are involved with thumb functions, had the largest muscle activities, followed by the extension of the metacarpophalangeal joint, which is related to the ED for all four fingers, and the extension of the wrist in the ulnar direction, which is related to the ECU. In addition, the extensor muscle group showed higher muscle activity than the flexor muscle group. Similar to the study by Ayoub and Presti [15], this study found that the extensor muscles were activated to a greater extent than the flexor muscles when participants held an object weighing less than 2000 g. All of the extensor and flexor muscles must be activated to hold an object. In particular, the wrist extensors have to be activated to counteract the wrist flexor torque caused by the finger flexor tendons [40].
Related Knowledge Centers
- Anatomy
- Standard Anatomical Position
- Carpal Bones
- Joint
- Intervertebral Disc
- Limb
- Anatomical Plane
- Shoulder
- Wrist
- Metacarpal Bones