Wk7


Objectives

  • Understand the common domains of force expression found in athletic movements.

  • Understand how to classify different strength qualities.

  • Understand the tests used to monitor strength qualities.

What is Strength?

  • Defined as the capacity to express force against an external object.

  • Typically measured in either kg (mass) or Newtons (force).

  • The definition should reflect how we express “strength” in the context of movement.

Domains of Force Expression

  • Domains are categorized by time constraints (slower to faster) and external load (less to more).

  • The domains include: Isometric Strength, Heavy Dynamic Strength, Fast Dynamic Strength, Reactive Strength, and Explosive Strength.

Maximal Isometric Strength

  • Defined as the highest level of force that can be expressed against an immovable object.

Ballistic Isometric Strength

  • Refers to the measurement of force during the early stages of an isometric test.

  • Includes variables such as:

    • Rate of force development.

    • Time-specific impulse.

    • Force at specific time-points.

Heavy Dynamic Strength

  • Refers to strength tested through dynamic tasks with a high external load.

  • Examples include:

    • xRM testing.

    • Loaded jumping.

  • Changes in performance during these tests are impacted by:

    • Changes in physical capacity.

    • Changes in motor behavior.

Fast Dynamic Strength

  • Characterized by the expression of high levels of force against little to no external load.

  • Characterized by the use of slow stretch-shorten cycle elements.

  • Movement time is greater than 0.3 seconds.

Reactive Strength

  • Defined by the ability to express high levels of force using fast stretch-shortening cycle elements.

  • Has a strong relationship with movements that entail high eccentric strength demands.

Which Strength Qualities Should We Test?

  • Testing should align with the strength qualities that are most important for the sport.

  • Should also align with the purpose of testing.

Continual vs Structured Testing

  • Two types of testing include continual and structured testing.

Structured Testing

  • Describes the periodic benchmarking of athletes.

  • Athletes are benchmarked against:

    • Normative data.

    • Teammates.

Continual Monitoring

  • Testing needs to be frequent to ensure we can detect meaningful changes in performance or fatigue.

  • Selected tests must be simple to perform, non-fatiguing, and provide actionable information.

Which Test to Select

  • Test selection criteria:

    • Validity.

    • Reliability.

    • Equipment.

    • Time.

    • Availability.

    • Sensitivity.

    • Rationale.

The Importance of Validity & Reliability

  • Validity: The degree to which a test measures what it is supposed to measure.

  • Reliability: The consistency and repeatability of a test.

Test Options - Domains of Force Expression

  • Maximum Isometric:

    • IMTP (Isometric Mid-Thigh Pull).

    • ISqT (Isometric Squat).

  • 'Ballistic' Isometric:

    • IMTP.

    • ISqT.

  • Heavy Dynamic:

    • xRM.

    • Loaded Jumps.

  • Fast Dynamic:

    • CMJs (Countermovement Jumps).

    • SJs (Squat Jumps).

  • Reactive:

    • Drop Jumps.

Tests of Maximal Isometric Strength

  • Two main options in applied environments:

    • Isometric mid-thigh pull.

    • Isometric squat.

  • Can also use single-joint dynamometry which requires specialized rack and force-plates/load-cells.

The Isometric Mid-Thigh Pull

  • Designed as a test to monitor maximum force output in weightlifting athletes.

Isometric Mid-Thigh Pull – Set-up

  • Body posture and bar position matches the second pull of the clean.

  • Hip angle: 140−150∘140-150^{\circ}.

  • Knee angle: 130−145∘130-145^{\circ}.

  • Position must be standardized if using the test to monitor force over time.

The Isometric Mid-Thigh Pull – Common Errors

  • Incorrect posture or positioning.

  • Pre-tension or countermovement at the start.

The Isometric Mid-Thigh Pull - Positioning

  • Variables measured include peak force (PF) and force at different time points (F50, F90, F150, F200, F250).

The Isometric Mid-Thigh Pull - Testing Protocol

  • Correct posture (knees 125−145∘125-145^{\circ}, hips 140−150∘140-150^{\circ}).

  • Countdown: '3, 2, 1, PUSH!'

  • Instructions: "Push your feet into the ground as fast and as hard as possible".

  • Upright trunk.

  • Clean grip, hands strapped & taped to bar.

  • No pre-tension, rigid torso.

  • Standardized grip and foot width.

  • Acceptable trials: minimal pre-tension (<50 N) or countermovement at the start.

  • 1-2 mins rest between trials.

The Isometric Mid-Thigh Pull - Reliability

  • Intraclass Correlation and Coefficient of Variation (%) are used to assess reliability.

The Isometric Squat

  • Fundamentally similar to the isometric mid-thigh pull.

  • Three typical positions that the test is performed in:

    • 120∘120^{\circ} knee flexion.

    • 90∘90^{\circ} knee flexion.

    • Position that matches the IMTP.

The Isometric Squat - Reliability

  • Reliability measures include Intraclass Correlation Coefficient and Coefficient of Variation (%)

Tests of Ballistic Isometric Strength

  • Typically, the tests used to assess ballistic isometric strength are the same as tests of maximum isometric strength:

    • Isometric mid-thigh pull.

    • Isometric squat.

  • Still requires the use of force-plates or load-cells to obtain a force-time curve.

Tests of Ballistic Isometric Strength

  • Force-time curve data is analyzed to assess ballistic isometric strength.

Why Not Use Traditional Isometric Testing Protocols

  • Traditional isometric testing protocols may not accurately capture ballistic strength characteristics.

Ballistic Isometric Strength – Testing Protocol

  • Correct Posture

    • Knees: 125−145∘125-145^{\circ}

    • Hips: 130−145∘130-145^{\circ}

  • Clean grip

  • Hands strapped and taped to bar

  • Limited Pretension

  • Rigid Torso

  • Stable Baseline ≥1\geq 1 second

  • “3, 2, 1, PUSH!”

  • ~ 1 s trial

  • Upright Torso

  • Standardise position, posture, grip

  • ~20 s between trials

  • “Push your feet into the ground as fast and as hard as possible”

Ballistic Isometric Strength Assessment - Reliability

  • Reliability is assessed using Intraclass Correlation and Coefficient of Variation (%) for force, rate of force development (RFD), and impulse.

Heavy Dynamic Strength

  • Typically assessed using repetition maximum testing:

    • 1RM, 3RM, 5RM etc.

  • Number of repetitions in the xRM test can depend on the biomotor ability that you’re trying to assess.

Heavy Dynamic Strength

  • xRM tests can also be used to predict 1RM via various formulas.

Heavy Dynamic Strength - Reliability

  • Reliability is assessed using Intraclass Correlation (ICC) and Coefficient of Variation (CV).

Heavy Dynamic Strength - Alternatives

  • Strength testing can be fatiguing/time-consuming.

  • Strength might be variable from day to day.

Heavy Dynamic Strength - Alternatives

  • Velocity based training (VBT).

Heavy Dynamic Strength - Alternatives

  • Almost every study performed with free-weights has found that predictions of 1RM from barbell velocity are inaccurate.

Fast Dynamic Strength

  • Most commonly assessed domain of force expression.

  • Typically assessed using vertical jumping tasks:

    • CMJ (Countermovement Jump).

    • SJ (Squat Jump).

  • Allows for the assessment of the athlete’s ability to express force under no load.

The Countermovement Jump

  • Used for performance profiling, neuromuscular fatigue assessment, and return from injury.

Pre-Testing Checklist

  • Standardize testing conditions.

  • Ensure proper warm-up.

  • Familiarize athletes with the testing protocol.

Fast Dynamic Strength – Testing Protocol

  • Start Position: Stand as still as possible, hands on hips.

  • Jump Phase: Lower to self-selected depth, jump as FAST and as HIGH as possible.

  • Landing: Land as softly as possible.

Importance of Precise Data Collection

  • Precise data collection is crucial for accurate assessment of jump performance.

The Countermovement Jump

  • Force-time curve analysis provides detailed information about jump performance.

Fast Dynamic Strength – Alternative Methods

  • Alternative methods include different landing techniques and variations in jump execution.

CMJ – Alternative Testing Protocols

  • Landing: Land in the same COM position as take-off.

  • Jump Phase: Lower to self-selected depth, jump as FAST and as HIGH as possible.

  • Start Position: Stand as still as possible, hands on hips.

Fast Dynamic Strength – The Squat Jump

  • Landing: Land in the same COM position as take-off.

  • Jump Phase: Lower to required depth and pause, jump as FAST and as HIGH as possible.

  • Start Position: Stand as still as possible, hands on hips.

Tests of Reactive Strength

  • Tests of reactive strength involve the elastic components of the stretch-shortening cycle.

  • Most common test is the drop jump.

  • Important to balance the need for short contact times vs the need to jump as high as possible.

Tests of Reactive Strength - The Drop Jump

  • Reactive strength is assessed using the drop jump test.

Using Strength Testing to Guide Training

  • Strength testing can inform training periodization and individualize training programs.

Periodisation of Training

  • Different training methods target different strength qualities.

Benchmarking

  • Benchmarking allows comparison of an athlete's performance against normative data or teammates.

Case Study #1

  • Athlete A: Good strength at slow velocities; lacking pure and explosive strength.

    • Training emphasis: Heavy rack pulls; weightlifting derivatives from the hang across a range of loads.

  • Athlete B: Good pure and explosive strength; lacking strength at slow velocities.

    • Training emphasis: Heavy strength training through full ranges of motion that use the SSC.

Case Study #2

  • Player A: Good reactive strength; poor slow SSC strength at fast velocities.

    • Training emphasis: Combined heavy strength, loaded and unloaded ballistic tasks.

  • Player B: Good slow SSC strength at fast velocities; poor reactive strength.

    • Training emphasis: Plyometrics with instructions to maximize jump heights or distance with minimal contact times.

Ratios

  • Common to use ratios of two variables from vertical jump tasks to guide training.

  • Also common to use ratios to monitor neuromuscular status/adaptation to training.

  • Examples: Reactive Strength Index, Reactive Strength Index modified, Dynamic Strength Index, Eccentric Utilization Ratio.

Dynamic Strength Index

  • Variety of ways that this can be calculated:

    • CMJ peak force / IMTP peak force.

    • SJ peak force / IMTP peak force.

    • BP peak force / IBP peak force.

  • Guidance:

    • <0.6: Focus on rapid force expression

    • 0.6 – 0.8: Balanced

    • >0.8: Focus on maximal strength

Reactive Strength Index

  • Calculated from jump height during a drop jump and contact time.

  • Typically used a continual monitoring tool as a measure of “explosiveness”.

  • Requires close attention to data collection, particularly standardisation of drop height.

Reactive Strength Index Modified

  • Calculated from CMJ jump height and overall movement time.

  • Similar to RSI, typically used as a measure of “explosiveness” in the context of continual monitoring.

  • Only really able to be calculated if using force plates.

The Problem with Ratio Statistics

  • Any change in RSI/RSImod/DSI requires a change in something else.

  • Sometimes, the information provided can be misleading.

  • The accuracy of the ratio is dependent on the accuracy of the underlying data.

Conclusion

  • Questions and contact information.