12.1 Strength training biomechanics

Strength training biomechanics explores how forces and movements shape our workouts. It's all about understanding the physics behind lifting weights and how our bodies respond. From Newton's laws to lever systems, these principles guide effective exercise selection and technique.

Force-velocity and length-tension relationships are key to optimizing strength gains. By manipulating variables like load, speed, and muscle length, we can target specific adaptations. This knowledge helps us design smarter workouts and achieve our fitness goals more efficiently.

Biomechanics of Strength Training

Foundational Principles

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  8.6 Forces and Torques in Muscles and Joints – Biomechanics of Human Movement View original

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  8.6 Forces and Torques in Muscles and Joints – Biomechanics of Human Movement View original

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• Newton's laws of motion underpin forces acting on the body during strength training exercises
  • First law explains inertia and resistance to movement
  • Second law (F = ma) relates force, mass, and acceleration in exercises
  • Third law describes action-reaction pairs in lifting movements
• Mechanical specificity dictates adaptations are specific to the type of loading imposed on the body
  • Training with free weights improves stabilization more than machines
  • High-velocity movements enhance power output for explosive sports
• Moment arm length affects torque produced at a joint
  • Longer moment arms increase torque and difficulty (barbell curls vs concentration curls)
  • Shorter moment arms decrease torque and muscle activation (close-grip vs wide-grip bench press)
• Stability relates to base of support for proper form and injury prevention
  • Wider stance increases stability in squats
  • Narrower grip decreases stability in bench press

Biomechanical Analysis and Adaptation

• Lever systems analyze mechanical advantage in strength movements
  • First class (fulcrum between effort and load): neck extension
  • Second class (load between fulcrum and effort): calf raises
  • Third class (effort between fulcrum and load): bicep curls
• Progressive overload drives continuous adaptation and improvement
  • Gradually increase weight, sets, reps, or decrease rest periods
  • Manipulate exercise variables to create new stimuli (tempo, range of motion)
• Stretch-shortening cycle explains importance of eccentric and concentric phases
  • Eccentric phase stores elastic energy
  • Amortization phase transitions between eccentric and concentric
  • Concentric phase utilizes stored energy for greater force production
  • Examples: countermovement jump, bench press touch-and-go

Force-Velocity and Length-Tension in Strength Training

Force-Velocity Relationship

• Muscle force production varies with contraction velocity
  • Inverse relationship: higher velocity decreases force production
  • Maximal force at zero velocity (isometric contractions)
  • Maximal velocity at zero load (unloaded movements)
• Impacts exercise selection and training adaptations
  • Heavy loads for maximal strength (low velocity, high force)
  • Light loads for speed and power (high velocity, lower force)
  • Moderate loads for hypertrophy (balance of force and velocity)
• Isotonic, isometric, and isokinetic contractions have distinct characteristics
  • Isotonic: constant load, varying velocity (free weights)
  • Isometric: no movement, maximal force (wall sits, planks)
  • Isokinetic: constant velocity, varying resistance (specialized machines)
• Time under tension relates to force-velocity curve for specific adaptations
  • Longer durations at moderate loads for hypertrophy
  • Short, explosive movements for power development
  • Sustained holds for isometric strength gains

Length-Tension Relationship

• Muscle force production changes with muscle length
  • Optimal length produces maximum force (active tension)
  • Extreme shortened or lengthened positions decrease force
• Influences exercise range of motion and effectiveness
  • Full range of motion targets all points on the strength curve
  • Partial range of motion can overload specific portions of the curve
• Optimal muscle length for force production guides exercise design
  • Mid-range typically produces highest force output
  • Example: chest press machine set to slight stretch at bottom of movement
• Actin-myosin overlap explains physiological basis
  • Maximum overlap at optimal length allows most cross-bridge formation
  • Less overlap at shortened or lengthened positions reduces force capacity
• Pennation angle in muscle architecture affects force production
  • More pennation increases physiological cross-sectional area
  • Trade-off between force production and contraction velocity
  • Examples: pennate (quadriceps) vs fusiform (biceps) muscles

Strength Training Modalities and Adaptations

Equipment-Based Modalities

• Free weights vs machines impact muscle activation and coordination
  • Free weights engage more stabilizers and improve balance
  • Machines isolate specific muscles and control movement path
  • Examples: barbell squat (free weight) vs leg press machine
• Variable resistance alters force curve throughout range of motion
  • Bands increase resistance at end of concentric phase
  • Chains gradually increase load as they're lifted off the ground
  • Applications: band-resisted push-ups, chain-loaded deadlifts
• Blood flow restriction training influences adaptations with lower loads
  • Increases metabolic stress and muscle hypertrophy
  • Allows strength gains with 20-30% of 1RM
  • Examples: BFR leg extensions, BFR bicep curls

Contraction-Specific Modalities

• Eccentric overload techniques affect muscle damage and gains
  • Greater force production during eccentric phase
  • Increased muscle damage leads to greater hypertrophy
  • Methods: supramaximal loads, partner-assisted negatives
• Plyometric training impacts stretch-shortening cycle and power
  • Enhances rate of force development and neural adaptations
  • Improves explosive strength and athletic performance
  • Examples: box jumps, depth jumps, medicine ball throws
• Isometric training affects strength at specific joint angles
  • Increases neural drive and maximal force production
  • Useful for sticking point training and rehabilitation
  • Applications: isometric mid-thigh pull, wall sits

Advanced Training Methods

• Velocity-based training impacts power and force-velocity profiling
  • Uses movement speed to guide load selection and volume
  • Enhances power output and sport-specific strength
  • Tools: linear position transducers, accelerometers
• Accommodating resistance combines multiple modalities
  • Integrates free weights with bands or chains
  • Matches strength curve of exercises more closely
  • Examples: band-resisted squats, chain-loaded bench press

Biomechanical Principles for Program Design

Exercise Technique and Selection

• Proper form based on biomechanical principles maximizes activation
  • Align joints for optimal force transfer (stacked joints in overhead press)
  • Maintain appropriate ranges of motion (depth in squats)
  • Control movement speed for desired training effect
• Exercise selection considers individual biomechanics
  • Limb lengths affect leverage and muscle activation (sumo vs conventional deadlift)
  • Muscle insertion points influence strength curves (high vs low cable flyes)
  • Joint structure dictates safe movement patterns (hip anatomy in squats)
• Functional movements mimic sports or daily activities
  • Enhance transfer of training effects to performance
  • Examples: farmer's walks for grip strength, landmine rotations for rotational power

Program Structure and Progression

• Periodization incorporates biomechanical variability
  • Target different aspects of force-velocity curve throughout training cycle
  • Undulating periodization varies load and volume within microcycles
  • Block periodization focuses on specific adaptations in mesocycles
• Joint stress and load distribution prevent overuse and imbalances
  • Balance pushing and pulling movements for shoulder health
  • Incorporate unilateral exercises to address asymmetries
  • Vary grip positions to distribute stress (pronated, supinated, neutral)
• Corrective exercises address muscular imbalances
  • Based on biomechanical assessments (Functional Movement Screen)
  • Target weak links in kinetic chain
  • Examples: face pulls for upper back, glute bridges for hip extension

Assessment and Optimization

• Biomechanical analysis tools assess and optimize performance
  • Force plates measure ground reaction forces and power output
  • Motion capture analyzes joint angles and movement patterns
  • EMG monitors muscle activation during exercises
• Utilization of analysis informs program adjustments
  • Identify technique flaws for correction
  • Quantify improvements in force production and power
  • Optimize exercise selection based on individual response