The relationship between single muscle fibre and voluntary rate of force development in young and old males.

Purpose: It is suggested that the early phase (< 50 ms) of force development during a muscle contraction is associated with intrinsic contractile properties, while the late phase (> 50 ms) is associated with maximal force. There are no direct investigations of single muscle fibre rate of force development (RFD) as related to joint-level RFD METHODS: Sixteen healthy, young (n = 8; 26.4 ± 1.

Influence of Spine-Focused Verbal Instruction on Spine Flexion During Lifting.

Lifting with a flexed spine, especially near the end range of motion, has been identified as a potential risk factor for low back injury/pain. Therefore, individuals who develop discomfort from repetitive, prolonged and/or loaded flexed or slouched postures may benefit from a greater awareness of how to control and/or modify their spinal posture to avoid irritating their backs in these situations. This study was therefore designed to test the ability of spine-oriented verbal instructions to reduce intersegmental spine flexion during three lifting tasks.

Rate of force development is Ca-dependent and influenced by Ca-sensitivity in human single muscle fibres from older adults.

Natural adult aging is associated with declines in skeletal muscle performance, including impaired Ca sensitivity and a slowing of rapid force production (rate of force redevelopment; k). The purpose of this study was to investigate the relationship between impaired Ca sensitivity and k of single muscle fibres from young and older adults. Participants included 8 young (22-35 yrs) and 8 older (60-81 yrs) males who were living independently.

Unloaded Organ Culturing Has a Detrimental Effect on the Axial Mechanical Properties of the Intervertebral Disc.

Healthy function of intervertebral discs (IVDs) depends on their tissue mechanical properties. Native cells embedded within IVD tissues are responsible for building, maintaining, and repairing IVD structures in response to genetic, biochemical, and mechanical signals. Organ culturing provides a method for investigating how cells respond to these stimuli in their natural architectural environment.

Mechanical Consequence of Induced Intervertebral Disc Degeneration in the SPARC-Null Mouse.

Intervertebral disc (IVD) degeneration is associated with low back pain (LBP) and accompanied by mechanical changes to the spine. Secreted protein acidic and rich in cysteine (SPARC) is a protein that contributes to the functioning and maintenance of the extracellular matrix. SPARC-null mice display accelerated IVD degeneration and pain-associated behaviors.

Rapid increase in intradiscal pressure in porcine cervical spine units negatively impacts annulus fibrosus strength.

Vertebral endplate fracture is generally accepted to occur as a result of excessive, typically rapid, pressure developed within the intervertebral disc. Clinical evidence of disc disorders later in life following endplate fracture suggests that the disc is also impacted by the fracture event. There is an abundance of evidence to indicate that loss of disc pressure at the time of fracture alters annulus fibrosus loading which could impact disc health long-term.

Fiber Type and Size as Sources of Variation in Human Single Muscle Fiber Passive Elasticity.

Studies on single muscle fiber passive material properties often report relatively large variation in elastic modulus (or normalized stiffness), and it is not clear where this variation arises. This study was designed to determine if the stiffness, normalized to both fiber cross-sectional area and length, is inherently different between types 1 and 2 muscle fibers. Vastus lateralis fibers (n = 93), from ten young men, were mechanically tested using a cumulative stretch-relaxation protocol.

Immuno-stimulatory capacity of decorin in the rat tail intervertebral disc and the mechanical consequence of resultant inflammation.

Purpose: Determine whether decorin is immuno-stimulatory to rat tail IVD cells and to characterize the mechanical consequence of inflammation at the whole rat tail IVD level.

Methods: Cultured rat tail annulus fibrosus (AF) cells were exposed to decorin, a resident IVD small leucine-rich proteoglycan (SLRP), with and without the presence of a toll-like receptor (TLR) 4 inhibitor, TAK-242. Resultant expression of pro-inflammatory cytokine and chemokines (MCP-1; MIP-2; RANTES; IL-6; TNFα) were quantified over 24 h.

Age-related changes in human single muscle fibre passive elastic properties are sarcomere length dependent.

Purpose: Studies have revealed an age-related decrease in the ability to produce force as well as an increase in the contractile stiffness and passive stress of single muscle fibres. However, further insight into age-related changes to the passive properties of human skeletal muscles is needed. The aim of this study was to characterize single muscle fibre passive properties from young and old males across a physiologic range of sarcomere lengths (SLs).

Experimental validation of a novel spine model demonstrates the large contribution of passive muscle to the flexion relaxation phenomenon.

When an individual enters a maximally flexed spine position, their largest extensor muscles become electrically inactive despite a substantial extensor moment demand being placed on the low back; this is termed flexion relaxation. Stresses within intervertebral discs, ligaments, and passive muscles are thought to support this moment thereby allowing the extensor muscles to 'turn off'. While the mechanical behaviour of the intervertebral disc and ligaments have been studied extensively, less is known regarding the moment supported by passive muscle tissue during spine flexion.

Characterizing Local Dynamic Stability of Lumbar Spine Sub-regions During Repetitive Trunk Flexion-Extension Movements.

Using a technique of tracking intersegmental spine kinematics via skin surface markers, this study aimed to estimate local dynamic spine stability across smaller sub-regions (or segments) of the lumbar spine while also considering the impact of an external pelvic constraint during repetitive movements. Sixteen participants (10 males) performed two trials [Free Motion (FM), Pelvis Constrained (PC)] each consisting of 65 repetitive trunk flexion-extension movements to assess dynamic spine stability using maximum Lyapunov exponents (LyE). First, results indicated that LyE obtained from analysis of 30 repetitive flexion-extension movements did not differ from those obtained from analysis of greater numbers of repetitive movements, which aligns with results from a previous study for the whole lumbar spine.

Characterization of the passive mechanical properties of spine muscles across species.

Passive mechanical properties differ between muscle groups within a species. Altered functional demands can also shift the passive force-length relationship. The extent that passive mechanical properties differ within a muscle group (e.

Discriminating spatiotemporal movement strategies during spine flexion-extension in healthy individuals.

Background Context: The spine is an anatomically complex system with numerous degrees of freedom. Due to this anatomical complexity, it is likely that multiple motor control options exist to complete a given task.

Purpose: To identify if distinct spine spatiotemporal movement strategies are utilized in a homogenous sample of young healthy participants.

Distinguishing between typical and atypical motion patterns amongst healthy individuals during a constrained spine flexion task.

Despite 'abnormal' motion being considered a risk factor for low back injury, the current understanding of 'normal' spine motion is limited. Identifying normal motion within an individual is complicated by the considerable variation in movement patterns amongst healthy individuals. Therefore, the purpose of this study was to characterize sources of variation in spine motion among a sample of healthy participants.

Increased Substance P Immunoreactivity in Ipsilateral Knee Cartilage of Rats Exposed to Lumbar Spine Injury.

Objective: The present study aimed to investigate whether experimentally induced lumbar facet-joint OA lead to degenerative changes and enhanced SP expression within the ipsilateral neurosegmentally linked tibiofemoral cartilage.

Methods: Adult male Sprague-Dawley rats were assigned to left side L5-L6 facet mechanical compression injury (surgery) ( = 6), L5-L6 facet exposure with no compression (sham) ( = 5), or naïve (no surgery) ( = 4) groups. The morphology of the tibiofemoral articular cartilage was assessed using a modified Mankin scoring system.

Development of a Novel Technique to Record 3D Intersegmental Angular Kinematics During Dynamic Spine Movements.

A novel method of recording intersegmental spine kinematics was developed. The method was required to: (1) have similar accuracy and precision as current methods that record gross spine kinematics; (2) be reasonably insensitive to errors associated with marker detection or misplacement; and (3) be reasonably insensitive to skin movement artefacts. Four healthy participants performed trunk flexion, lateral bending, and axial twist movements; data were collected using the intersegmental method as well as electromagnetic sensors.

Investigation of the passive mechanical properties of spine muscles following disruption of the thoracolumbar fascia and erector spinae aponeurosis, as well as facet injury in a rat.

Background Context: Muscle tissue is known to remodel in response to changes to its mechanical environment. Alterations in passive mechanical properties of muscles can influence spine stiffness and stability.

Purpose: This study aimed to determine whether passive muscle elastic moduli and passive muscle stresses increased 28 days following mechanical disruption of the thoracolumbar fascia and erector spinae aponeurosis, and injury induced by facet joint compression.

Paraspinal Muscle Passive Stiffness Remodels in Direct Response to Spine Stiffness: A Study Using the ENT1-Deficient Mouse.

Study Design: Basic science study of the relationship between the structural properties of the spine and its surrounding musculature.

Objective: To determine whether an increase in spine stiffness causes an inverse compensatory change in the passive stiffness of the adjacent paraspinal muscles.

Summary Of Background Data: Intervertebral disc degeneration causes an increase in multifidus passive stiffness; this was hypothesized to compensate for a decrease in spine stiffness associated with disc degeneration.

Spine postural change elicits localized skin structural deformation of the trunk dorsum in vivo.

As the most superficial organ, the skin is the most accessible sensory system interfacing one's body and environment. With changes in posture, it is possible that the skin may undergo large deformations resulting in changes in its structural properties. The purpose of the current work was to determine the influence of spine posture on measures of trunk dorsum skin deformation, thickness and hardness in vivo.

Decreasing the required lumbar extensor moment induces earlier onset of flexion relaxation.

Flexion relaxation (FR) is characterized by the lumbar erector spinae (LES) becoming myoelectrically silent near full trunk flexion. This study was designed to: (1) determine if decreasing the lumbar moment during flexion would induce FR to occur earlier; (2) characterize thoracic and abdominal muscle activity during FR. Ten male participants performed four trunk flexion/extension movement conditions; lumbar moment was altered by attaching 0, 5, 10, or 15lb counterweights to the torso.

Factors to consider in identifying critical points in lumbar spine flexion relaxation.

Flexion relaxation (FR), a myoelectric silence of extensor muscles near end range of lumbar flexion, is commonly reported as the lumbar flexion angle at the instant the extensor muscles become silent. However, lumbar flexion angle alone is insufficient to characterize mechanisms that modulate FR. As FR requires the moment generated by passive lumbar extensor tissues to equilibrate the moment due to gravity, the inter-relationships between lumbar moment, flexion angle, and myoelectrical silence will provide added information in the understanding of FR.

The effect of contralateral submaximal contraction on the development of biceps brachii muscle fatigue.

Objective: The aim of this study was to determine if a submaximal contraction in the contralateral limb affected the fatigability of the dominant limb.

Background: Muscle fatigue is a known risk factor for musculoskeletal injury; however, it is unknown whether a submaximal contraction in the nondominant limb, such as for stabilizing a tool or load, affects the rate of development of fatigue, potentially increasing risk of injury. Current ergonomic assessments of injury risk do not involve consideration of submaximal contralateral demands.

The effect of elbow flexor fatigue on spine kinematics and muscle activation in response to sudden loading at the hands.

Sudden loads, originating at either the hands or the feet, can cause injury to spine structures. As muscles are primarily responsible for stabilization following a perturbation, the effect of spine muscle fatigue in this context has been well investigated. However, the effect of fatigue of arm muscles, which can help control perturbations originating at the hands, on the spine is unknown.

Sarcomere length organization as a design for cooperative function amongst all lumbar spine muscles.

The functional design of spine muscles in part dictates their role in moving, loading, and stabilizing the lumbar spine. There have been numerous studies that have examined the isolated properties of these individual muscles. Understanding how these muscles interact and work together, necessary for the prediction of muscle function, spine loading, and stability, is lacking.