Flexibility

Question 1

• Flexibility
  what is flexibility and what does it determine? operationally defined as a joints….? how can it be?

Two fundamental components:

• Flexibility vs “mobility”?
  mobility=? passive stretch vs. active control…?

Answer 1

• Flexibility
• “Flexibility is the intrinsic property of body tissues which determines the range of motion achievable without injury at a joint or group of joints
• Often operationally defined as a joint’s available range of motion
• This can be active or passive, static or dynamic
• Joint tissues
• Cartilage, capsule, ligaments, bone
• Surrounding soft tissues
• Muscle, tendon, fascia, nerves
• Flexibility vs “mobility”?
• Passive stretch vs “active control through a range of motion”?
• Mobility = “The ability to move”?

Question 2

Why do we stretch?
* Stretching primarily used to increase…?

• Thought to improve… and reduce…
• stretching is generally universally agreed on… its impact on performance and injuries is more…
• Consider type of … and …
• Consider potential for acute reductions ….

Answer 2

Why do we stretch?
* Stretching primarily used to increase joint range of motion

• Thought to improve subsequent performance and reduce
  likelihood of injuries
• Although the ability to increase ROM through stretching is generally universally agreed, its impact on performance and injuries is more controversial
• Consider type of activity and ROM requirements
• Consider potential for acute reductions in performance following
  prolonged stretching

Question 3

How are flexibility changes measured. example?
Muscle tendon unit stiffness is assesed via what?
how can muscle stiffness be distinguished from MTU stiffness? what does it account for?

Answer 3

Flexibility changes are measured by changes in joint/movement ROM.
Example: Maximum tolerable stretch.

Muscle-tendon unit (MTU) stiffness is assessed via the slope of the torque-angle curve during passive joint movement.

Muscle stiffness can be distinguished from MTU stiffness using techniques like ultrasonography.

This accounts for length changes in muscle vs. tendon

Question 4

Types of stretching

• Static stretching
• involves? how can it be done?
• Dynamic stretching
  controlled movement repetitively?
• Ballistic stretching
  variation of what? higher? actions at the end?
• Proprioceptive Neuromuscular Facilitation (PNF)
  sequencing of what contraction? take advantage of reflex…?

Answer 4

• Static stretching
• Involves lengthening a muscle until either a stretch sensation or the point of discomfort is reached, and then holding the muscle in a lengthened position for a prescribed period of time
• Can be active (involving the contraction of e.g., antagonist muscle)
  or passive
• Dynamic stretching
• Uses a controlled movement through the ROM of the active joint
• Ballistic stretching
• Variation of dynamic stretching
• Typically involve higher velocity movements than dynamic stretching, with bouncing actions at the end of the ROM
• Proprioceptive Neuromuscular Facilitation (PNF)
• Involves sequencing of agonist/antagonist contraction and
  relaxation with static holds
• Purports to take advantage of reflex mediated relaxation to induce greater increases in ROM

Question 5

what does passive force in soft tissues arise from?

Soft tissues (muscle, tendon, fascia) are viscoelastic, meaning they exhibit…

stiffness depends on … rate. Viscoelastic materials show…

Answer 5

Passive force in soft tissue arises from stretching structures like:
Titin, cell membranes, interstitial connective tissue (e.g., perimysium).

Soft tissues (muscle, tendon, fascia) are viscoelastic, meaning they exhibit:

Elastic properties: Resist deformation and return to original shape after force removal.
Viscous properties: Time-dependent resistance to deformation.

Stiffness depends on strain rate.
Viscoelastic materials show hysteresis:
Loss of elastic energy during loading and unloading.

Question 6

Creep and stress relaxation

Answer 6

Creep:
- When a tissue is held under constant tension (stress), it continues to stretch (increase in strain) over time.

Example: Holding a static stretch for a long time might allow your muscles or tendons to lengthen gradually.

Stress Relaxation:
When a tissue is held at a constant length (strain), the force (stress) required to maintain that position decreases over time.

Example: If you stretch a muscle and hold it at the same length, it feels less tight after a while because the internal tension reduces.

Question 7

what happens to passive force during static stretching and why

short reduction in passive stiffness is what? examples

Answer 7

Passive force decreases during static stretching due to stress relaxation

Acute reductions in passive stiffness are temporary.

Example: 8 minutes of calf stretching:
Stiffness decreased immediately but returned to baseline within 20 minutes.
Comparing durations (2, 4, and 8 minutes of calf stretching):
All reduced stiffness immediately after stretching.
The 2-minute group returned to baseline faster than the 4- or 8-minute groups

Three successive 45 second hamstring stretches were separated by 30s.

Stress relaxation occurred in all of them, but stiffness returned to baseline levels by beginning of next stretch!

Question 8

Longer/more intense stretch program
may decrease…

Program:

Outcome:

Answer 8

may decrease muscle stiffness

5 x 30s for 4 different calf stretch exercises, (10 min of total stretch time), 5 x weekly for 6 weeks

Significant decreases in stiffness after 10, 20, and 30 sessions

Question 8

Study details:
Program: 5 x 45-second stretches, twice daily for 3 weeks.

Chronic changes in stiffness with flexibility training:

Outcome: ….. muccle length after stretch training

Answer 8

Chronic changes in stiffness with flexibility training:
No lasting decreases in muscle stiffness after 3 weeks of hamstring stretching.

Outcome:
Increased peak angle (greater muscle length) achieved after stretch training

Question 9

Flexibility training increases ROM but the mechanism…

some studies show reduced…

others show…

differences may be due to

early flexibility improvements are mostly due to changes in the…

Answer 9

Flexibility training increases range of motion (ROM), but the exact mechanism is unclear.

Some studies show reduced stiffness (changes in passive torque-angle).

Others show no significant changes.

Differences may be due to stretch intensity.

Early flexibility improvements are mostly due to changes in the sensory system, with minimal structural changes to the muscle-tendon unit (MTU)

Question 10

What is PNF stretching?

what are the techniques…
CR and CRAC

mechanisms

effectiveness

Answer 10

PNF Stretching: Developed in the 1940s for spasticity rehabilitation, combining contraction and relaxation phases.

Techniques:
Contract – relax (CR): Passive stretch + isometric contraction of target muscle.
Contract – relax – antagonist contract (CRAC): Adds antagonist muscle contraction for enhanced stretch.

Mechanisms:
Autogenic inhibition: Target muscle relaxes after contraction.
Reciprocal inhibition: Target muscle relaxes when the antagonist contracts.

Effectiveness: Sometimes increases ROM more than static stretching, though evidence is mixed.

Question 11

Can reciprocal inhibition influence response to PNF?

what does PNF use?

techniques with the biggest ROM have the…?

this means that reflex resistance..?
reflex resistance?
muscle relaxation doesn’t directly affect?
ROM improvements are due to …. not…

Answer 11

Reciprocal Inhibition in PNF:

PNF uses feedback from the antagonist muscle to reduce resistance during stretching.

Techniques with the biggest ROM gains also have high muscle activation.

This means:
Reflex resistance is minimal.
Muscle relaxation doesn’t directly affect ROM.
ROM improvements are due to tissue elasticity and better stretch tolerance, not reduced muscle resistance.

Question 12

changes in stress relaxation after spinal cord injury

identical response in SCI in both subjects suggest…?

conclusion
stretch response is better explained by …..

Answer 12

No change in stress relaxation after spinal cord injury (SCI).

Identical responses in SCI and healthy participants suggest that decreased passive force is due to mechanical factors, not reduced muscle activity.

Conclusion:
Stretch response is better explained by the viscoelastic properties of tissue and improved stretch tolerance rather than reduced muscle resistance.

Question 13

PNF Summary:
PNF can lead to greater…

proposed mechanisms include

improved ROM from PNF may be due to

pain inhibits… suggests that PNF…

Answer 13

PNF Summary:
PNF can lead to greater acute ROM increases compared to static stretching.

Proposed mechanisms include autogenic and reciprocal inhibition.

Improved ROM from PNF may be due to increased pain modulation.

The idea is that “pain inhibits pain,” suggesting that PNF may reduce discomfort and enhance stretch tolerance.

Question 14

Pain Perception During Stretch:

muscle mechano-nociceptors respond to

receptive endings are mainly found

the exact mechanisms are

may involve changes in

Answer 14

Muscle mechano-nociceptors respond to high levels of mechanical load (e.g., stress or strain on the muscle).

Receptive endings are mainly found in the collagenous extracellular matrix (e.g., perimysium).

The exact mechanisms for increased stretch tolerance are not well understood.

It may involve changes in peripheral (local) and/or central (nervous system) components.

Question 15

Acute Impact of Static Stretching on Muscle Performance:

performance decrements. drop in muscle performance

dose-dependent. impact depends on … of stretch. shorter durations

recovery. effects are negated by…

Answer 15

Performance decrements: drop in muscle performance 3-5 minutes after static stretching. less power or strength

Dose-dependent: The impact depends on the duration of the stretch.
Shorter durations: <60 seconds typically have minimal effects.

Recovery: Effects are mostly negated by adding dynamic movements after static stretching.

Question 16

different modes of stretching

PNF stretching is thought to improve … Thru…

primary mechanism by which ROM is increased following training is …

reductions in MTU …. but these dont…

prolonged static stretching may …. . the reduction may be due to….

the effect is….. and negated by ….

Answer 16

• Different modes of stretching include static, dynamic, ballistic, and PNF stretching
• PNF stretching traditionally thought to improve ROM through reflexive inhibition
• Primary mechanism by which ROM is increased following flexibility training seems to be increases in stretch tolerance
• Reductions in muscle tendon unit stiffness may occur, but these don’t seem necessary for ROM improvements
• Prolonged static stretching may acutely impair power performance
• Effect may be due to reduction in central motor output (i.e., “central fatigue”)
• This effect is dose dependent and negated by performing dynamic movements RIGHT AFTER the
  static stretching