🏋🏼Sports Medicine Unit 2 – Biomechanics of human movement

Key Concepts and Terminology

• Biomechanics studies the structure, function, and motion of biological systems (muscles, bones, joints) using mechanical principles
• Kinematics describes motion without considering the forces that cause it, including linear and angular displacement, velocity, and acceleration
• Kinetics examines the forces that cause motion, such as internal (muscle contractions) and external (gravity, friction) forces
• Statics analyzes systems in equilibrium where the sum of all forces equals zero and no acceleration occurs
• Dynamics deals with systems not in equilibrium, involving the study of forces and resulting motion
  • Subdivided into kinetics (forces causing motion) and kinematics (motion itself)
• Torque represents the rotational force acting on an object, calculated as the product of force and moment arm ($\tau = F \times d$)
• Lever systems in the body (bones and joints) provide mechanical advantage by altering the magnitude or direction of forces

Anatomical Structures Involved

• Bones act as rigid levers, providing attachment points for muscles and transmitting forces
  • Classified as long (femur), short (carpals), flat (scapula), or irregular (vertebrae) based on shape and function
• Joints allow relative motion between bones, with different types enabling various degrees of freedom
  • Synovial joints (knee, hip) permit the greatest range of motion
  • Cartilaginous joints (intervertebral discs) allow limited movement
  • Fibrous joints (skull sutures) are immobile
• Muscles generate force through contraction, acting on bones via tendons to produce movement
  • Skeletal muscle fibers are organized into fascicles, innervated by motor neurons
• Ligaments connect bones to bones, providing stability and limiting excessive joint motion
• Tendons attach muscles to bones, transmitting forces generated by muscle contractions
• Fascia is a connective tissue that envelops and separates muscles, allowing smooth gliding between structures
• Neuromuscular control involves the coordination of sensory input, central processing, and motor output to produce efficient movement patterns

Principles of Motion and Force

• Newton's laws of motion describe the relationship between forces and motion
  • First law (inertia): Objects at rest stay at rest, and objects in motion stay in motion unless acted upon by an external force
  • Second law (acceleration): $F = ma$, where force equals mass times acceleration
  • Third law (action-reaction): For every action, there is an equal and opposite reaction
• Force-velocity relationship states that as the velocity of muscle contraction increases, the force output decreases
  • Muscles generate maximum force during isometric (static) contractions
• Length-tension relationship describes how muscle force output varies with sarcomere length
  • Optimal force production occurs at resting length; too short or too long reduces force
• Stretch-shortening cycle involves an eccentric contraction followed by a concentric contraction, enhancing force output (countermovement jump)
• Impulse ($F \times t$) represents the product of force and time, determining the change in momentum
• Momentum ($p = mv$) is the product of mass and velocity, conserved in the absence of external forces
• Center of mass is the point at which an object's mass is evenly distributed, affecting balance and stability

Biomechanical Analysis Techniques

• Motion capture systems use markers placed on the body to track and analyze movement in 3D space
  • Optical systems (Vicon) utilize infrared cameras to detect reflective markers
  • Inertial systems (Xsens) use accelerometers, gyroscopes, and magnetometers to measure motion
• Force plates measure ground reaction forces (GRF) in three dimensions (vertical, anterior-posterior, medial-lateral)
  • Used to calculate joint forces, moments, and power during activities like running and jumping
• Electromyography (EMG) records the electrical activity of muscles during contraction
  • Surface EMG uses electrodes placed on the skin over the muscle belly
  • Intramuscular EMG involves inserting fine wire electrodes directly into the muscle
• Isokinetic dynamometry assesses muscle strength, power, and endurance at a constant angular velocity
  • Commonly used for knee flexion/extension and shoulder internal/external rotation
• High-speed video analysis captures motion at high frame rates (120+ fps) for detailed kinematic analysis
  • Allows for frame-by-frame breakdown of technique and identification of critical events
• Pressure mapping systems measure the distribution of pressure between the body and a surface (foot-ground, athlete-equipment)
  • Used to assess footwear, insoles, and equipment design for performance and injury prevention

Movement Patterns in Sports

• Gait cycle describes the repetitive sequence of events during walking and running
  • Stance phase: Foot is in contact with the ground (initial contact, mid-stance, terminal stance)
  • Swing phase: Foot is not in contact with the ground (initial swing, mid-swing, terminal swing)
• Throwing motion involves a coordinated sequence of steps to generate and transfer energy from the lower body to the upper body (baseball pitch, football pass)
  • Wind-up, stride, arm cocking, arm acceleration, arm deceleration, follow-through
• Jumping and landing mechanics are critical for performance and injury prevention in many sports (basketball, volleyball)
  • Proper technique involves hip, knee, and ankle flexion to absorb forces and maintain alignment
• Cutting maneuvers require rapid deceleration, change of direction, and acceleration (soccer, football)
  • Technique emphasizes maintaining a low center of mass, short ground contact times, and optimal foot placement
• Swimming strokes (freestyle, breaststroke, butterfly, backstroke) involve coordinated upper and lower body movements to propel the body through water
  • Efficient technique minimizes drag and maximizes propulsive forces
• Cycling pedaling technique involves a combination of downward and forward pedal forces to optimize power output
  • Proper bike fit and positioning are essential for performance and injury prevention

Injury Mechanisms and Prevention

• Acute injuries occur suddenly due to a specific traumatic event (ankle sprain, ACL tear)
  • Often result from excessive force, awkward landings, or collisions
• Overuse injuries develop gradually over time due to repetitive stress on tissues (stress fractures, tendinopathies)
  • Caused by training errors, improper technique, or muscle imbalances
• Biomechanical risk factors for injury include abnormal alignment, muscle weakness, and altered movement patterns
  • Valgus knee collapse during landing increases risk of ACL injury in female athletes
• Injury prevention programs focus on improving strength, flexibility, balance, and neuromuscular control
  • FIFA 11+ program reduces lower extremity injuries in soccer players
• Proper warm-up and cool-down routines help prepare the body for activity and promote recovery
  • Dynamic stretching before exercise, static stretching after exercise
• Load management strategies aim to optimize training and competition loads to reduce injury risk
  • Monitoring training volume, intensity, and recovery using tools like RPE and GPS tracking
• Equipment modifications can help prevent injuries in contact sports (helmets, padding)
  • Properly fitted and maintained equipment is essential for safety and performance

Practical Applications in Sports Medicine

• Gait analysis is used to assess walking and running mechanics in patients with neurological or musculoskeletal conditions
  • Identifies abnormal patterns and guides treatment decisions (orthotics, surgery)
• Rehabilitation protocols incorporate biomechanical principles to progressively load tissues and restore function
  • Eccentric exercises for tendinopathies, plyometrics for ACL rehabilitation
• Orthotic devices (shoe inserts, braces) are prescribed to correct alignment, redistribute pressure, and provide support
  • Custom foot orthotics for plantar fasciitis, knee braces for osteoarthritis
• Ergonomic assessments optimize workstation setup to reduce the risk of musculoskeletal disorders (carpal tunnel syndrome)
  • Proper chair height, keyboard position, and monitor placement
• Functional movement screens (FMS) assess an individual's movement quality and identify limitations or asymmetries
  • Used to guide exercise prescription and injury prevention strategies
• Sport-specific training programs are designed to enhance performance and reduce injury risk
  • Plyometric training for explosive power, resistance training for strength and stability
• Biomechanical feedback systems provide real-time visual or auditory cues to improve technique and motor learning
  • Motion analysis software, pressure-sensitive insoles, EMG biofeedback

Advanced Topics and Current Research

• Musculoskeletal modeling uses computational methods to simulate human movement and predict internal forces
  • OpenSim is an open-source software platform for developing and analyzing musculoskeletal models
• Finite element analysis (FEA) is a numerical method for solving complex biomechanical problems
  • Used to study stress distribution in bones, implants, and prosthetic devices
• Machine learning algorithms are being applied to biomechanical data for automated analysis and pattern recognition
  • Gait classification, injury risk prediction, and performance optimization
• Wearable sensors and smart textiles enable continuous monitoring of biomechanical variables during daily activities and sports
  • Inertial measurement units (IMUs), electromyography (EMG) sensors, and pressure-sensitive fabrics
• 3D printing technology allows for rapid prototyping and customization of orthotic and prosthetic devices
  • Patient-specific implants, personalized foot orthotics, and sports equipment
• Tissue engineering approaches aim to regenerate or replace damaged musculoskeletal tissues
  • Stem cell therapies, bioactive scaffolds, and growth factor delivery systems
• Motor control and learning research investigates the neural mechanisms underlying movement acquisition and adaptation
  • Implications for rehabilitation, skill acquisition, and performance enhancement
• Biomechanics of aging and age-related conditions (sarcopenia, osteoporosis) is an emerging area of research
  • Identifying factors contributing to functional decline and developing targeted interventions