Forces in Motion and Resistance

Forces in Biomechanics

• Normal force is perpendicular to the surface and is usually measured by a force platform.
• Fluid resistance affects both human and projectile motion, and can be split into lift and drag components.
• It is an important factor to consider in sports such as swimming, cycling, and sprinting.

Internal Forces

• Joint reaction force is the net force generated by bone on bone contact between adjacent segments when loaded.
• It is calculated as it is difficult to measure, and often acts solely on a joint center, contributing little to joint torque.
• Muscle force, specifically intra-abdominal pressure (IAP), transmits forces from the muscles encasing the IA cavity to the supporting structures of the trunk.
• IAP is generated by muscles such as the transverse abdominis, rectus abdominis, obliques, diaphragm, and pelvic floor muscles.

Inverse Dynamics Modelling

• It is a modelling technique that uses external forces to estimate internal ones.
• It involves kinematic data, kinematic model, dynamic model, kinetic data, anthropometric data, and anthropometric model.

Advanced Techniques

• Skin pin markers are a more invasive technique that uses high-tensile strength markers surgically placed into the underlying bone.

Tendon to Bone Attachment

• The collagen fibres in the tendon intermesh with the fibrocartilage, which gradually becomes mineralized fibrocartilage and merges into cortical bone.

Lower Limb Strain Injury

• It is a common injury in many sports, particularly in running and sprinting based sports.
• It is thought to be caused by acceleration and rapid braking.

Mechanical Problem Solving Methods

• The sequential approach involves breaking down the movement into phases.
• The mechanical approach involves using a deterministic model and a concept map to identify the primary performance factor and its subcategories.
• The free body diagram (FBD) is a technique used to reduce the complexity of a mechanical analysis and identify the significant forces involved.

Free Body Diagram (FBD)

• It is a method used to analyze the movement of a system.
• It involves creating a stick figure along a set of coordinates, with the forces added as arrows.
• The forces are described by their magnitude, direction, line of action, and point of application.

Types of Forces on the FBD

• External forces include weight (the combination of mass and gravity) and ground reaction force (the reaction force from interaction with the ground).
• Weight is always directed downwards, originates from the body's center of gravity, and is determined through an analysis of body segments.

Musculoskeletal Mechanics

• Tendons and ligaments are dense connective tissue containing 70% water, 25% collagen fibers, and 5% elastin.
• Tendons have a parallel collagen fiber arrangement, are stiff, and carry high tensile loads, but have minimal resistance to compression and shear loads.
• Ligaments have a nearly parallel collagen fiber arrangement, can carry high tensile loads, and are less stiff and slightly weaker than tendons.

Ligaments

• Their role is to provide connection from bone to bone, and transmit energy from the muscle to the bone.
• Ligaments can stretch about 8-10% before failure, while bone can only stretch up to 1%.
• They provide mechanical stability to joints, guide joint motion, and prevent excessive motion.
• Ligaments have viscoelastic behavior and control the dissipation of energy.