Biomechanics III: Velocity-Based Training and Force-Velocity Profiling

Foundational Principles and Goals of Resistance Training

• Repetition Maximum (RM) Continuum: The relationship between load and repetitions follows a specific continuum that dictates physiological adaptations. Training goals vary based on the number of repetitions performed:   - Strength: Typically targeted with lower repetition ranges, specifically $\le 2$ to $6$ repetitions.   - Power: Overlaps with strength and hypertrophy ranges, often requiring explosive intent between $2$ and $10$ repetitions.   - Hypertrophy: Focused on muscle growth, generally ranging from $6$ to $12$ repetitions.   - Muscular Endurance: Developed through high-repetition sets, typically $13$ to $\ge 20$ repetitions.

• Significance of Strength and Power Assessment: Measuring these metrics is essential for several coaching and physiological reasons:   - Acute Performance Monitoring: Tracking fatigue and immediate responses within a training session.   - Chronic Response Tracking: Identifying long-term adaptations, progression, and appropriate overload to mitigate injury risk.   - Weakness Identification: Pinpointing specific physical deficits in an athlete's profile.   - Individualization: Engineering programs specifically based on the unique demands of a sport.   - Benchmarking: Comparing an individual athlete to normative, population-specific data sets.

The Window of Adaptation

• Targeting Performance Qualities: Athlete performance is enhanced most effectively when training specifically targets the qualities required by their sport.

• Concept of Efficiency: The greatest efficiency in training is derived from focusing on the components where the athlete is weakest.

• Component Contribution: All physical components contribute to an ‘overall window’ of adaptation.

• Law of Diminishing Returns: As a specific component becomes highly developed, its remaining window for adaptation shrinks. Once a component is highly optimized, it may be more effective to pivot the training program toward components that possess a larger window of adaptation.

• Implications for Profiling: Accurate profiling allows coaches to identify which windows remain open and which are nearing their ceiling, informing future training blocks.

Classification of Strength and Power Tests

• Maximal Strength:   - Focus: Maximal force exertion.   - Loading: > 90\% \text{ of } 1RM.   - Exercise Examples: Back Squat, Deadlift, Bench Press, Leg Press.

• Strength-Speed / Strength-Power:   - Focus: The ‘middle ground’ between force production and velocity.   - Loading: $70-80\% \text{ of } 1RM$ or $70-80\% \text{ of Bodyweight (BW)}$.   - Exercise Examples: Olympic lifts, Deadlifts, Squat Jumps (SJ), Countermovement Jumps (CMJ).

• Peak Power:   - Focus: The product of Strength $\times$ Speed.   - Loading: $20-45\% \text{ of BW}$ or $0-10\% \text{ of BW}$.   - Exercise Examples: SJ, CMJ, Bench Press Throws, Single-Leg SJ, Single-Leg CMJ.

• Speed-Strength / Power-Strength:   - Focus: ‘Middle ground’ favoring velocity over load.   - Loading: $BW - 10\% \text{ of BW}$.   - Exercise Examples: Depth Jumps, SJ, CMJ, Hurdle Jumps (Single-Leg).

• Maximal Velocity:   - Focus: Maximal movement speed.   - Loading: Bodyweight ($BW$).   - Exercise Examples: CMJ with arm swing, hopping, bounding, rapid plyometrics, sprints.

Contextual Factors in Assessment Selection

• The choice of diagnostic tests is dictated by specific contextual variables:   - The Sport: The specific physiological demands of the athlete's primary activity.   - Resources: Availability of staff expertise and specialized equipment.   - Athlete Demographics: The number of athletes being tested and their respective skill levels.   - Testing Batteries: Must be individualized to provide relevant data.

Traditional vs. Modern Strength Assessment

• Maximal Strength - Dynamic Assessment:   - Includes $1RM$ Squat isoinertial testing and Submaximal RM sets used for $1RM$ prediction.   - Measures absolute maximum force and relative force (force per unit of bodyweight).   - Captures dynamic Rate of Force Development ($RFD$) during concentric and eccentric phases.

• Benefits of Traditional Methodology:   - Easy to track over time.   - Logistically simple for large groups.   - Requires no specialized technological equipment.   - Load serves as a reliable correlate of intensity at near-maximal efforts (> 90\% \text{ of } 1RM).

• Drawbacks of Traditional Methodology:   - Uses bar load only as a proxy for force; load is not always the best indicator of true physiological output.   - Athletes may ‘go through the motions’ without maximum intent, which traditional methods cannot detect.   - Lacks the ability to quantify movement velocity or power output with the human eye.

The 3 I’s of Intensity in Strength Training

• 1. Intensity: Defined as the absolute weight on the bar, usually expressed as a $\% 1RM$ or as a specific Repetition Maximum (e.g., $5RM$, $10RM$).

• 2. Intent: The lifter’s mental and physical drive to move each repetition with maximum acceleration. Examples:   - Lifting $80\% \% 1RM$ with maximum intent might result in a mean velocity of $0.4\,m/s$.   - Lifting the same $80\% \% 1RM$ with submaximal intent might results in only $0.2\,m/s$.

• 3. Intensiveness: How close the athlete is to muscular failure (RM).   - Example: If the intensity is $80\% \% 1RM$, an athlete might perform $3$ reps (far from failure) or $7-8$ reps (point of failure).

• Limitations of Intensity Measures:   - RPE (Rating of Perceived Exertion): Can be subjective; issues arise if athletes are lazy or lack self-awareness.   - Fatigue: Can cause a higher RPE even when the athlete is working at a lower percentage of their $1RM$.

Technology in Velocity-Based Training (VBT)

• Core Calculations:   - Force: $F = m \times a$   - Power: $P = F \times v$   - Systems typically measure Displacement, Velocity, and Acceleration.

• Available Technologies: Tendo Units, PUSH, Gymaware, Myotest, and Linear Position Transducers (LPT).

• Validity Research (Sato et al.):   - Study Objective: Identify the accuracy of a wireless inertia sensor compared to a high-frequency motion capture system.   - Methodology: $5$ subjects performed $2$ dumbbell exercises for $4$ sets of $10$ repetitions at light intensity. Data sampled at $200\,Hz$.   - Results: High correlations ($0.80 - 0.92$) for peak and average velocity between the inertia sensor and motion capture. Left and right-side consistency was also high ($0.90 - 0.93$).

Measures of Velocity: Mean vs. Peak

• Mean Velocity (MV): Represents the average speed at which the load moves through the entire concentric phase.   - Relationship: Highly correlated with $1RM$ strength, especially at loads above $65\% \% 1RM$.   - Use: Best for monitoring changes or maintenance in absolute strength.

• Peak Velocity (PV): The highest velocity recorded at any single point during the concentric range of motion (measured in windows as small as $1-5\,ms$).   - Relationship: Closely related to explosive power-based movements like jumping, throwing, and Olympic lifting.   - Use: Monitoring adaptations in peak power output.

Surfing the Force-Velocity Curve (Velocity Zones)

• The Force-Velocity curve represents the inverse relationship between force and velocity: as speed increases, the force that can be produced decreases.

• Absolute Strength:   - Squat: < 0.5\,m/s   - Bench Press: < 0.35\,m/s   - Focus: $1RM$ and maximal loads.

• Accelerative Strength (Strength-Speed):   - Squat: $0.5 - 0.75\,m/s$   - Bench Press: $0.35 - 0.6\,m/s$   - Focus: Bridging max strength and power; the "force side" of power.

• Peak Power:   - Squat: $0.75 - 1.0\,m/s$   - Bench Press: $0.6 - 0.85\,m/s$   - Focus: Optimal load manipulation for maximum wattage.

• Speed-Strength:   - Squat: $1.0 - 1.3\,m/s$   - Bench Press: $0.85 - 1.1\,m/s$   - Focus: The "velocity side" of power; typical of game/competition speeds.

• Maximum Velocity:   - Squat: > 1.3\,m/s   - Bench Press: > 1.1\,m/s   - Focus: Movement speeds typical of field and court sports change-of-direction (COD); loads are usually BW to $20\% \% 1RM$.

Load-Velocity Profiling Protocol

• Method: Measure concentric MV over $4-6$ progressive load intensities ($30-85\% \text{ of actual/estimated } 1RM$).

• Recovery: Minimum of $3$ minutes of passive recovery between sets.

• Distribution: Loads should be spread enough to ensure a velocity decrease of at least $0.5\,m/s$ between the lightest and heaviest loads.

• Repetition Schemes:   - Light loads (v > 1.0\,m/s): $3$ repetitions.   - Moderate loads ($0.65 - 1.0\,m/s$): $2$ repetitions.   - Heavy loads (v < 0.65\,m/s): $1$ repetition.

• Analysis: Only the highest velocity recorded at each load is used for the profile. Maximum effort/intent is required for every repetition.

Mean Velocity Benchmarks by Load (m/s)

VBT Integration and Longitudinal Monitoring

• Periodization Stages:   - Anatomical Adaptation: Large ROM, low intensity. Velocity is largely irrelevant.   - Hypertrophy/Endurance: $3-6$ sets, $8-12$ reps, $\ge 70\% \% 1RM$. Time under tension is key; velocity is largely irrelevant.   - Strength: Loads creating velocities beginning at $0.5\,m/s$ and slowing down (> 85\% \% 1RM).   - Power: Load varies ($30-80\% \% 1RM$). Values near $80\% \% 1RM$ target strength-speed, while values near $30\% \% 1RM$ target speed-strength.

• Longitudinal Tracking of Strength:   - MV has a robust correlation with $\text{\% 1RM}$. An increase in MV at a submaximal load indicates an increase in absolute strength.   - Threshold for Change: A change in velocity of $0.07 - 0.09\,m/s$ at a given load between sessions equates to approximately a $5\%$ change in actual $1RM$ strength (Gonzalez-Badillo et al., 2010).   - Power Training: Athletes may stay with the same load for extended periods, aiming to increase the velocity (and thus power output) rather than adding weight to the bar.