Lecture 6 - Task Specific Strength

What is max muscular performance

• the highest amount of force, power, or velocity you can produce when not restricted

  • ex: vertical jump (fast speed is required to produce a lot of force)

What is peak muscular performance?

• the peak amount of power, force, or velocity you can produce achieved at one specific parameter

  • Ex: you can produce more force on a 4kg shot put than on a 7 kg shot put

  • Ex: often tested with isometric measurements because it shows the most you can produce because you are not able to overcome the resistance and it takes time to produce the maximum amount of force

  • can never be more than max performance, but may be equal

External factors affecting performance

• isotonic resistance

• isometric resistance

• isokinetic resistance

• elastic resistance

• hydrodynamic resistance

Isotonic resistance

resistance is fixed and is typically a selected parameter for the task

• Ex: dumbell

Isometric resistance

muscle length does not change regardless of force production

Isokinetic resistance

muscle contraction velocity is predetermined by external resistance and independent of applied force

• only used in research/rehab —> machine to test quad strength after ACL surgery (leg extension movement)

Elastic resistance

the magnitude of force is determined by the displacement of elastic material

• Ex: resistance band (F = k₁ x D)

Hydrodynamic

predominant in water sports

• speed and force are directly correlated in water (max force is achieved at the same time as max velocity)

Intrinsic Factors affecting performance

• rate of force development

• stretch shortening cycle

• eccentric actions

What does the force velocity-curve represent?

• the greater the force, the slower the velocity of the movement and vice versa

• most sports fall somewhere in the middle of the curve

• maximal power is achieved in the intermediate range of force and velocity:

  • 30% of max velocity and 30% of max force

• Power = Force x Velocity

  • main purpose of strength training for athletes is to improve their power

  • goal is to increase the area under the curve to increase power

Rate of force development

• important in sports like volleyball where it is important to cut and move quickly

• explosive strength: the ability to produce maximal force in minimal time

Explosive strength deficit

• the gap between max force and peak force being produced

• advanced athletes should train to decrease this deficit by working on speed (rate of force development)

  • ex: plyometrics

• beginners often times don’t have a deficit so to work on rate of force development they should work on getting stronger

How to increase rate of force development

• Apply force rapidly against high load

  • think fast, move slow

  • resistance training

  • exercises performed well rested

• Apply force rapidly against low-moderate load

  • think fast, move fast = plyometrics

  • ballistic exercises = med ball throws against wall

• Improve stretch-shortening cycle

  • only necessary if your sport uses it

    • ex: swimming doesn’t use it, running does

Stretch-Shortening Cycle

• muscle lengthening under tension followed immediately by muscle shortening

  • ex: think of running mechanism

  • used in any sport where change of direction is made

• increases force output

• increases power output

• decreases energy expenditure

• Made up of 3 phases:

  • Eccentric (muscle stretching/lengthening)

    • force increases

  • Amortization (transition from lengthening to shortening)

    • develops isometric force

  • Concentric (muscle shortening)

Factors of Stretch-Shortening Cycle

• Since force increases during the eccentric (stretching) phase, the time available to reach maximal force is increased the more that the muscle is stretched

  • elastic energy is stored during muscle and tendon stretching

• Isometric force is produced during the amortization (transition) phase

• The stored elastic energy is released during concentric (shortening) phase

  • the stiffer the muscle, the more potential (elastic) energy is able to be stored = advanced athletes store more

Role of neural reflex mechanism in stretch-shortening cycle

• During rapid stretching under a load, the muscle spindle and golgi-tendon organ reflexes contribute to final force:

  • muscle spindles are activated to stimulate contraction = lengthen muscle

    • length-feedback component

  • GTOs are activated to inhibit contraction = shorten muscle

    • force-feedback component

  • force production is the sum of these reflexes

Eccentric Muscle Action

• forces from eccentric muscle action are 50-100% stronger than isometric forces

• creates a high degree of muscle damage and soreness, but this decreases the more you train

  • the eccentric movement is where athletes get hurt because your body isn’t strong enough to withstand the force

    • Ex: planting my foot and tearing my ACL