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Sports Biomechanics

Gait analysis and running biomechanics are key to understanding how we move. By breaking down the gait cycle and examining factors like ground reaction forces, we can see how our bodies adapt to different speeds and terrains.

Running economy plays a huge role in performance. From stride length to muscle fiber composition, many factors affect how efficiently we run. Footwear and surfaces also impact our biomechanics, influencing everything from impact forces to injury risk.

Gait cycle phases and biomechanics

Stance and swing phases

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  • Gait cycle divides into stance phase (60%) and swing phase (40%), each with distinct biomechanical features
  • Stance phase subphases include initial contact, loading response, midstance, terminal stance, and pre-swing
  • Swing phase subphases encompass initial swing, midswing, and terminal swing
  • Joint kinematics during gait involve complex interactions between hip, knee, and ankle joints
    • Hip joint exhibits flexion during initial contact, extension during stance, and flexion during swing
    • Knee joint demonstrates flexion during loading response, extension during midstance, and flexion during swing
    • Ankle joint shows plantarflexion at initial contact, dorsiflexion during stance, and plantarflexion during push-off
  • Muscle activation patterns alternate between agonist and antagonist groups for efficient movement
    • Quadriceps activate during early stance for shock absorption
    • Hamstrings engage during late swing for deceleration
    • Gastrocnemius and soleus muscles activate during push-off for propulsion

Gait analysis parameters

  • Center of mass displacement follows sinusoidal pattern in vertical and lateral directions
    • Vertical displacement approximately 5 cm during normal walking
    • Lateral displacement about 2-3 cm from side to side
  • Temporal parameters quantify timing aspects of gait
    • Stride time measures duration of complete gait cycle (typically 1-1.2 seconds)
    • Stance time represents duration of foot contact with ground (about 60% of gait cycle)
    • Swing time indicates duration of foot in air (approximately 40% of gait cycle)
  • Spatial parameters assess distance-related aspects of gait
    • Step length measures distance between heel strikes of opposite feet (usually 60-80 cm)
    • Stride length represents distance between consecutive heel strikes of same foot (typically 120-160 cm)
    • Step width indicates lateral distance between feet during double support (around 5-15 cm)
  • Velocity combines temporal and spatial aspects, typically ranging from 1.2-1.5 m/s for normal walking

Running economy and performance factors

Biomechanical and physiological influences

  • Running economy defined as steady-state oxygen consumption for given submaximal running speed
  • Biomechanical factors affecting running economy
    • Stride length optimization balances energy cost of leg swing and ground contact
    • Ground contact time reduction generally improves economy (optimal range 150-200 ms)
    • Vertical oscillation minimization reduces energy expenditure (typical range 6-8 cm)
    • Arm movement patterns influence upper body stability and overall efficiency
  • Physiological factors impacting running economy
    • VO2max sets upper limit for aerobic capacity (elite runners often exceed 70 ml/kg/min)
    • Lactate threshold determines sustainable pace (typically 80-90% of VO2max in trained runners)
    • Muscle fiber composition affects efficiency (higher proportion of slow-twitch fibers generally improves economy)

Anthropometric and environmental considerations

  • Anthropometric characteristics influence running economy
    • Body mass impacts energy cost (lighter runners generally more economical)
    • Limb dimensions affect leverage and moment of inertia (longer legs may improve economy at higher speeds)
    • Body fat percentage influences metabolic cost (lower body fat generally associated with better economy)
  • Environmental factors significantly impact running economy and performance
    • Temperature affects thermoregulation (optimal range 10-15°C for most runners)
    • Humidity influences heat dissipation (high humidity reduces evaporative cooling)
    • Altitude decreases oxygen availability (approximately 1% decrease in VO2max per 100m elevation gain)
    • Wind resistance increases energy cost (headwind of 5 mph can reduce performance by 1-2%)
  • Training adaptations enhance running economy over time
    • Neuromuscular coordination improvements reduce unnecessary muscle activation
    • Metabolic efficiency enhancements optimize substrate utilization
    • Structural adaptations in muscles and connective tissues improve energy return

Ground reaction forces in running

Components and patterns of ground reaction forces

  • Ground reaction forces (GRFs) in running characterized by three components
    • Vertical component largest in magnitude (typically 2-3 times body weight)
    • Anterior-posterior component reflects braking and propulsion (about 0.5 times body weight)
    • Medial-lateral component smallest, contributes to lateral stability (approximately 0.1 times body weight)
  • Vertical GRF exhibits distinctive double-peak pattern
    • First peak represents impact forces (occurs within first 50 ms of ground contact)
    • Second peak reflects propulsive forces (occurs during push-off phase)
  • Anterior-posterior GRF shows characteristic braking-propulsion pattern
    • Initial braking force decelerates body's center of mass
    • Subsequent propulsive force accelerates body forward
  • Magnitude and rate of loading of impact forces associated with injury risk
    • High impact forces linked to stress fractures and other overuse injuries
    • Loading rates exceeding 70 body weights per second may increase injury risk

Factors influencing ground reaction forces

  • Running speed significantly affects GRF characteristics
    • Faster speeds result in higher peak forces (both vertical and horizontal)
    • Ground contact times decrease with increasing speed (from about 250 ms at jogging to 150 ms at sprinting)
  • Foot strike patterns alter GRF profiles
    • Rearfoot strike typically shows distinct impact peak and higher loading rates
    • Midfoot and forefoot strikes often exhibit reduced impact forces and loading rates
  • Body weight directly influences magnitude of GRFs
    • Heavier runners experience proportionally larger forces
    • Weight reduction can decrease overall loading on musculoskeletal system
  • Running surface stiffness affects force attenuation
    • Harder surfaces (concrete) result in higher impact forces
    • Softer surfaces (grass, synthetic tracks) can reduce peak forces and loading rates

Footwear and surfaces impact on running biomechanics

Footwear characteristics and their effects

  • Cushioning in shoes alters impact forces and joint loading
    • Highly cushioned shoes can reduce peak impact forces by 10-20%
    • Excessive cushioning may decrease proprioception and stability
  • Stability features influence foot motion and lower limb alignment
    • Medial posts can reduce overpronation in some runners
    • Motion control shoes may alter natural foot mechanics
  • Heel-to-toe drop affects foot strike pattern and joint kinematics
    • Traditional running shoes typically have 8-12 mm drop
    • Lower drops (0-4 mm) may promote midfoot or forefoot striking
  • Minimalist shoes and barefoot running promote forefoot or midfoot strike
    • Can lead to increased cadence and reduced stride length
    • May alter muscle activation patterns, particularly in lower leg

Surface characteristics and biomechanical adaptations

  • Running surface stiffness affects impact force attenuation
    • Concrete surfaces increase leg stiffness to maintain constant overall stiffness
    • Softer surfaces like grass allow for reduced leg stiffness
  • Surface inclination alters joint kinematics and muscle activation
    • Uphill running increases hip and knee flexion, ankle dorsiflexion
    • Downhill running increases impact forces and quadriceps eccentric loading
  • Interaction between footwear and surface influences injury risk
    • Matching shoe characteristics to running surface may optimize biomechanics
    • Sudden changes in surface or footwear can increase injury risk
  • Adaptation periods necessary when transitioning between footwear or surfaces
    • Gradual transitions allow for neuromuscular and biomechanical adjustments
    • Typical adaptation period ranges from 4-8 weeks for significant changes
  • Preferred movement path concept suggests unconscious biomechanical adaptations
    • Runners tend to maintain comfortable motion paths regardless of footwear
    • Individual variations in adaptation strategies highlight importance of personalized approaches
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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.