Manipulating the Neural System for Exercise Outcomes

Flexibility

Definitions

• Flexibility: Range of motion about a joint (active or passive).
• Mobility: Ability to produce force within a range of motion.
• Importance: Mobility improves activities of daily living and quality of life, especially in geriatric populations.
• Focus: Functional range of motion over just flexibility.

Factors Affecting Flexibility

• Joint Structure: type (e.g., ball and socket, hinge, elipsoidal)

• Age: Flexibility decreases with age.

• Sex: Females are generally more flexible than males.

• Muscle and Tissue: Musculotendinous unit Tendon Ligament Fascia Joint capsules Skin All these impact elasticity and plasticity

• Neural Control (CNS &PNS): Afferent and efferent mechanisms

• Muscle bulk

• Activity level

• Stretch tolerance

• Stretch Tolerance: Individual pain tolerance when stretching.

Stretching Implications

1. Static Stretching: Slow, sustained stretch held at discomfort point (e.g., toe touch for hamstrings). Prevents stretch reflex.
2. Proprioceptive Neuromuscular Facilitation ( Mobility) (PNF): Uses spindles and GTO manipulation. Two techniques:
   • Contract (Contract-Relax): Contract muscle, then stretch further.
   • Hold (Hold-Relax): Isometric contraction, then stretch further.
3. Ballistic Stretching: Repetitive bouncing at end range of motion (not recommended due to injury risk).
4. Dynamic Stretching: Sport-specific movements using the range of motion.

Static Stretching

• Requires no voluntary muscular activity, instead, relies on external force •What would be considered an external force? A partner, gravity, bands
• Slow stretch– prevent stretch reflex
• Stretch 15-30 seconds; effects may last 60-120 minutes
• Long stretch – activate GTO + 6 sec. “autogenic inhibition” Muscle of interest
• Stretch very long: myoclonus(spasms)
• Could it cause a decrease in power or muscle strength? “stretching-induced force deficit” •Decreased vertical jump – 3-7.3% •Decreased strength up to 28%
• Stretching= Joint laxity

Static Stretching Effects

• Does static stretching before or after exercise -- prevent delayed onset muscle soreness (DOMS)?
• decrease balance? Yes because of joint laxity -decrease reaction time? Yes no Elastic recoil
• Are women more flexible than men? Yes
• Does resistance training affect flexibility? Yes kind of if muscle bulk increases flexibility decreases

Proprioceptive Neuromuscular

Facilitation -- PNF

• Forces contraction during ROM
• PNF stretching (autogenic inhibition) Requires Partner – 6-10s push phase, then 6-10s relaxation phase
• Contract – relax technique
• Max – isometric contraction of muscle •*call on GTO
• Passive stretch – reflex contraction of antagonist (R.I. stretching) •*reciprocal inhibition

PNF stretching options

• Calves and ankles
• Chest
• Groin
• Hamstrings
• Quadriceps and hip flexors
• Shoulders

Plyometrics

• Definition: Exercises that enhance power using the stretch shortening cycle (SSC).
• Jump Training or rebound training
• Call on stretch reflex
• More motor units fire synchronously
• Jump down – gravity load on eccentric phase
• Tendon and muscle stretched when land •Muscle contracts sooner on jump up

Stretch-Shortening Cycle (SSC)

• Three Phases
• Phase I-Eccentric (stretch of the agonist muscle)
• Elastic energy is stored in the SEC - Series Elastic Compartment
• Muscle spindles are stimulated. ( Gamma motor neurons) • Phase IlAmortization (pause between phases I and Il)
• la afferent nerves synapse with alpha motor neurons. - Alpha motor neurons transmit signals to agonist muscle group.
• Phase Ill-Concentric (shortening of agonist muscle fibers)
• Elastic energy is released from the SEC. - Alpha motor neurons stimulate the agonist muscle group.
• Example: Box jump sequence.

Low Back Pain and Exercise

• Prevalence: 80% of Americans experience it by age 50.
• Underlying Causes:
  • Lack of balanced strength in the core – particularly in the abdominals, hip flexors, hamstrings
• Poor flexibility in low back and hamstrings
• Excess body weight
• Poor posture and body mechanics
• Effects: Anterior or posterior pelvic tilt affecting lower back, hip, knee, and foot.
• Correction: Balance strengthening and flexibility exercises.
• Interesting Fact: Number one cause is tight hip flexors causing excessive lordotic curve.

Balance- Highly dependent system

• Feedback (visual, somatosensory, and vestibular)

• Integration

• Output

• Postural control

• Postural orientation, Control of body alignment and tone with respect to gravity, the support surface, the environment, and internal senses

• Postural equilibrium •Integration and coordination of sensorimotor strategies to stabilize the COM during voluntary and externally triggered disturbances in postural stability

• Importance: Highly delicate and complex control; essential for postural control.

• Training: Use of unstable surfaces (foam boards, sand pits) to improve balance and postural control.

Strategies to Maintain Balance

1. Reactive: Responding to unexpected disturbances (e.g., slipping).
2. Predictive: Planning movements in anticipation of a disturbance (e.g., reaching for handrail on moving bus).
3. Proactive: Avoiding potential disturbances (e.g., avoiding slippery areas).

Mechanisms to Regain Balance

1. Fixed Support:
   • Ankle Strategy: Swaying around ankles on stable surfaces.
   • Hip Strategy: Moving hips to adjust center of mass on less stable surfaces.
2. Change of Support:
   • Stepping Strategy: Stepping to enlarge base of support when necessary.

Aging and Balance

• Decline: Less activity leads to fewer Type 2x fiber recruitment.
• Inner Ear: Reduced fluid affects spatial awareness.
• Exercise Benefits: Maintains fluid balance, calcium content, and Type 2x fiber recruitment.

Conclusion

• Importance of integrating neural system knowledge into exercise principles.
• Reminders:
  • Stay on top of material and take notes.
  • Engage in group discussions and presentations.
  • Prepare for the exam and seek help when needed.