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

Foundational Principles and Goals of Resistance Training

Uses of Strength + Power Assessments

• 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.

• Strength + 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.

Classification of Strength and Power Tests

• Maximal Strength: Maximal force exertion - > 90\% \text{ of } 1RM. (e.g Back Squat, Deadlift, Bench Press, Leg Press.)

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

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

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

• Maximal Velocity: Maximal movement speed - Bodyweight ($BW$). (e.g CMJ with arm swing, hopping, bounding, rapid plyometrics, sprints.)

Pros + Cons of Traditional Strength Assessment

• 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

• 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 $1RM$.

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.

How to create an F–V curve — practical steps (GymAware)

Protocol Essentials

• standardised warm‑up

• familiarisation

• fixed rest intervals

• progressive loads or velocity bands (e.g., sets covering >5 velocity zones).

• Use best rep per set and standardised technique/depth.

Data Collection

• GymAware records bar displacement → computes velocity v=Δd/Δt and acceleration.

• ‘Force = mass x acceleration’ and ‘Power = force x velocity’.

• Collect multiple loads (or target velocities) and plot force vs velocity to fit the linear load–velocity relationship.

How to create a torque–velocity curve — IKD (Isokinetic Dynamometer)

Protocol essentials

• careful axis alignment

• gravity correction

• familiarisation trials

• multi‑velocity testing (e.g., 60°/s, 180°/s, 300°/s), and standard rest.

• Report joint moments (Nm) across velocities to produce a torque–velocity profile.

• Use peak torque and work metrics per velocity.

Key outcome measures to master (what they mean and how coaches use them)

• F₀ (N or N·kg⁻¹) = theoretical max force at zero velocity.

• V₀ (m·s⁻¹) = theoretical max velocity at zero force.

• Pmax (W) = peak power (occurs near mid‑spectrum).

• RFD = early time‑window force slope.

• Slope / FV imbalance = indicates force‑ vs velocity‑deficit and guides whether to emphasise heavy or fast training.

Validity, reliability and common sources of error

GymAware

• generally high validity for mean/peak velocity when compared to gold standards

• more affordable

• easy to use / non specilaised operators needed

• easy to scale and implement for athletes/teams for load monitoring

• device placement, exercise type, and bar path introduce error (noise that affects reading)

• uses an indirect force estimation so errors in displacement and accleration translate into force and power (Grgic et al, 2020)

• follow standardised protocols to reduce noise.

IKD

• high internal reliability for torque measures using direct measures

• clinical gold‑standard for isolated joint testing

• controlled velocity testing to give exact figures

• excellent for building velocity profiles to inform rehab for isolated joints

• lower ecological validity for multi‑joint sport tasks.

• alignment, gravity correction and familiarisation strongly affect validity.

• expensive

• need trained operators to operate it

How the data should inform S&C practice (actionable rules)

• Identify deficit - use F–V slope to classify athlete as force‑deficient (train heavy, low‑velocity) or velocity‑deficient (train light, high‑velocity).

• Autoregulation - use velocity zones and velocity‑loss thresholds (e.g., 10–30% loss) to control volume, fatigue and effort intensity and to target adaptations.

• Rehab and RTP - use IKD torque profiles and limb symmetry indices to make objective return‑to‑play decisions.