Biomechanics Week 6.docx

Biomechanics Week 6 Lecture 1: Neuromuscular Control Neuromuscular control: the control of human movement is controlled by a complex interaction between the neural and muscle systems Motor learning: is the adaptation of control of movement that occurs with task rehearsal Motor control: execution of...

Biomechanics Week 6 Lecture 1: Neuromuscular Control Neuromuscular control: the control of human movement is controlled by a complex interaction between the neural and muscle systems Motor learning: is the adaptation of control of movement that occurs with task rehearsal Motor control: execution of learnt patterns of movement and motor control Neuromuscular adaptations is a develop of a pattern of repeated movements resulting in more skilled movement. This leads to decreased amplitude and duration of muscle activity, decreased muscle co-activation and less variability of movement and muscle activation patterns. High variability during movement is at the beginning of learning new tasks and results in increases in errors executing movements. As movements are practiced, this variability decreases and the movement becomes more accurate and 'patterned'. Eg: in highly trained cyclists, they had lower muscle activation and contraction during cycling output compared to non trained cyclists. Some variability in movement is a good thing, as it can help reduce the risk of injury due to repetitive loading patterns. Cross training: short term motor learning studies provide strong evidence that there's interference in acquisition of a skill when another task is practiced in sequence within short interim periods (< 6hrs). If you practice one task immediately after the other or a very small break, it takes away some of the learning and retention of the initial task. Initial performance gains in strength training are initially due to neuromuscular adaptations before hypertrophy occurs. Neuromuscular control and pain: those with pain have exhibited altered neuromuscular control in comparison to healthy individuals Lower back pain is now as common as getting the cold. There is research looking into how to reduce it across the population. Experimental pain induces changes in neuromuscular control EMG can look at the relationship between different muscles as a phase diagram. This is frequently used in gait analysis   Lecture 2: Musculoskeletal Biomechanics (Muscle) Muscles are a major contributor to human movement Muscle acts in a pulling force and creates motion cause it crosses one or two joints Tension developed by muscles applies compression to joints and enhances their stability. However if there's too muscle tension, it may decrease stability and result in dislocation Force is generated in the muscle along the line of action of the force and applied to a bone. This causes a rotation about the joint The functional effect produced by a pulling muscle force is called a torque. T = force x perpendicular distance Moment arms change during movements. It's affected by the distance of the muscle insertion from the axis of rotation and the angle of pull of the muscle. This may vary anatomically between people Skeletal muscle does: production of voluntary movement, maintain posture and enhance joint stability. Muscles may produce very small and fine or very large and powerful movement. Groups of muscles are within compartments that are then surrounded by fascia. Anterior compartment syndrome: this is when there is too much within the compartment and may compress on nerves, blood vessels, etc. Can be due to overdevelopment of muscles in the given area. Sometimes these compartments are not big enough to hold all the muscles Force generation: tendons and muscles work together to absorb or generate force. The exact mechanical interaction depends on the force that is being applied or generated, the speed of the muscle action and the slack in the tendon. Hill's Muscle Model: Contractile component: muscle Parallel elastic component: surrounding connective tissue Series elastic component: tendon Factors Influencing Force Generation Muscle morphology Length tension relationship Force velocity relationship Uni or bi articular muscle Muscle fibre differentiation Recruitment of motor units Muscle cross sectional area Temperature   Length Tenson Relationship Represents the static capability of a muscle and indicates the force that muscle can exert at different lengths Muscle force varies in proportion to the amount of overlap between actin and myosin filaments. Translating to an angle torque relationship is confounded by three factors: Movement of most body segments is controlled by groups of muscles rather than a single muscle Bi-articular muscles have length tension relationships different to uni-articular muscles Change in instantaneous axis of rotation at a given joint Shape of the angle torque relationship varies amongst muscles   Sport Performance Implications By applying a quick stretch to muscle while it's contracting an additional force can be generated. This the stretch shortening cycle Negative work: while being stretched, the muscle is lengthening and therefore, negative work Is being performed and energy is being absorbed. Tendon compliance and muscle flexibility affects this. Aging increases muscular stiffness and increases risk of injury.   Effects of stretching Increases flexibility Maintains and augments ROM Increases the elasticity and length of the musculotendinous units Increases ability to store energy.   Force Velocity Relationship Ability to produce max tension in a muscle is affected by the velocity of the contraction The faster the movement is, the harder it is to produced max force More stretched and slower movements allows for a better max force production Therefore, greatest tensions are achieved when being actively stretched under load.   Reasons for Force Velocity Relationship Resistance due to viscous damping (drag within a muscle) Resistive force increases with increasing shortening velocity, thus, in concentric contraction, the viscous damping decreases the net force output by muscle In negative shortening velocities (ie: lengthening velocities during eccentric contraction) the viscous damping force increases the force required to stretch the muscle. During changes in length of the muscle the cross bridges are periodically detached and reformed Cross bridge recycling occurs with greater frequency with increasing speed of concentric or eccentric contraction In the case of concentric contraction, this results in a smaller force with increasing velocity of shortening In the case of eccentric contraction, greater force is required to stretch and break the cross bridge bonds with increasing lengthening velocity   Muscle power output Power = force x velocity Power is the rate that work can be performed, important in high performance sport. Force decreases with increasing velocity and vice versa There is an optimum shortening velocity that maximises power output   Uni and Bi Articular Muscles One can't determine the function or contribution of a muscle to a joint movement by looking at the attachment points A muscle can move a segment at one end of its attachment or two segments at both ends of its attachment Most muscles on cross one joint. (mono articular) Bi articular muscles convert rotational to translational movement They're efficient cause the produce motion in two joints with one contraction Disadvantage is that they're incapable of shortening to extent required to produce full ROM at all joints simultaneously. Bi articular muscles have an important role in refining coordination and re-distributing mechanical movemen