Physiology Lecture #4 Neuromuscular System: Strength & Endurance

What is exercise?

Adaptation → stimulus on the body and seeing how body changes/adapts to it

What are the 7 training principles that optimize adaptation?

1. FITT(E) variables: Frequency Intensity Time Type (Enjoyment)

2. Overload

3. Periodization

4. Reversibility

5. Individuality

6. Progressive Overload

7. Specificity

FITT(E) variables

Frequency Intensity Time Type (Enjoyment)

How often, how much, how long, which specific exercise

Overload

demand must be greater than levels encountered during ADL’s for training effects to occur

Periodization

gradual cycling of specificity, intensity, and volume of training to achieve peak levels of fitness

Start: high volume, low intensity

Progress: low volume, high intensity

Reversibility

Training programs must include a maintenance plan to ensure gains from training are not lost

Individuality

consider specific needs & abilities of the patient

Progressive overload

training stimulus must be progressively increased as the body adapts

Specificity and variables to consider

Training effect is limited to the muscles or muscle groups involved in the activity

Variables to consider:

• muscles involved

• recruited fiber types

• principle energy systems (anaerobic vs. aerobic)

• contraction type

• contraction velocity & type of activity

• order of exercises

• progression of exercises 

• rest intervals

Muscular endurance

ability to perform repeated muscle contractions or to sustain a contraction over time

Cardiorespiratory endurance

the entire body’s ability to sustain prolonged, dynamic exercise using large muscle groups

Strength

maximal force a muscle group can generate

Anaerobic systems

ATP-PCr

Anaerobic glycolytic system

Aerobic system

Oxidative system

What system do you use for short sprints with higher intensity and shorter duration (<15 sec)?

ATP PCr system

What system do you use for longer sprints with middle distance (15 sec to 2 min)?

Glycolytic system

What system do you use for longer distance, lower intensity, longer duration (>3 min)?

Oxidative system

What part of the heart hypertrophies with training?

Left ventricle: more efficient pumps → pumps less often because more blood with each pump

What are some cardiovascular changes/adaptation to aerobic endurance training?

Blood flow to active muscles is increased due to increased:

• capillarization

• capillary recruitment

• blood volume

• left ventricular size/strength

• stroke volume/contractility

Blood pressure + HR at rest & during submaximal exercise is reduced

Describe the make up of Type I mf

red muscle

high # of mitochondria

Describe the make up of Type IIa mf

mixed muscle

medial # of mitochondria

glycolytic

Describe the make up of type IIx mf

white muscle

low # of mitochondria

Therefore doesn’t really use oxygen

Can you change one muscle type to another?

Yes, you can change fiber type IIx to IIa, but you can’t really go from IIa to IIx

Type I fiber type (chart)

• slow-twitch fibers

• oxidative

• high # of oxidative enzymes + mitochondria

• high fatigue resistance

• low specific tension

• slow shortening velocity

• high efficiency

Type IIa fiber type (chart)

• intermediate fibers

• fast oxidative glycolytic

• moderate # of oxidative enzymes

• moderate fatigue resistance

• high specific tension

• intermediate shortening velocity

• moderate efficiency

Type IIx fiber type (chart)

• fast-twitch fibers

• fast- glycolytic

• small # of oxidative enzymes

• high # of glycolytic enzymes

• low fatigue resistance

• higher specific tension

• fast shortening velocity

• low efficiency

How do muscle fibers adapt to aerobic endurance training?

• increased size of type I fibers

• transition of type IIx → type IIa

• transition of type II → type I

• increased # of capillaries per mf & in a given cross-sectional area of muscle to help with oxygen delivery for aerobic metabolism

Effects of aerobic exercise on metabolism (graph)

O2 uptake improves with training → you plateau instead of dropping off

Metabolic adaptations to aerobic endurance training

Increased:

• oxidative enzymes

• # of mitochondria

• VO2 max/ oxygen uptake

• ATP generating capacity

Lactate threshold increases due to:

• increased clearance of lactate & hydrogen ion

• decreased production of lactate

• increased efficiency of aerobic metabolism

Maximal oxygen uptake (VO2 max)

• indicator of cardiorespiratory endurance & aerobic fitness

• normal active untrained college students = 38-42 ml/kg/min

What are the contributing factors of oxidative capacity?

• # of mitochondria

• fiber type composition

• oxidative enzyme activity w/in muscle

• endurance training

• age: after age 25-30, decrease ~1% per year

What systems benefit from aerobic training?

ATP-PCr

Glycolytic

Energy system adaptations to anaerobic training

• increased ATP-PCr system enzyme activity

• increased activity of key glycolytic enzymes

• no effect on oxidative enzyme activity

  • no increase in capillary density (O2)

  • no effect on VO2 max

Metabolic system adaptations to anaerobic training

Increased:

• anaerobic metabolic function

• short term, high intensity capacity

• acid base imbalance tolerance (can handle lactic acid better)

• ATP-PCr and glycolytic enzymes

Neuromuscular adaptations to anaerobic training

Increased:

• # of motor units recruited w/ improved synchronicity → improved force

• efficiency with reduced coactivation of agonist & antagonist muscles

• mf recruitment

• cross-education

Decreased:

• inhibitory mechanisms (golgi tendon organs, antagonists)

Adaptations to resistance training

• increased strength & power

• neural mechanisms leading to strength gains:

  • increased frequency of stimulation, # of mu’s, synchronicity of recruitment

Rate coding

Explains how the intensity of a stimulus impacts the rate in which it stimulates the muscle

More intense stimulus = more frequent contraction = more force + power

Force production increases with:

Increased:

• recruitment of mu’s

• frequency of stimulus

• type II recruitment (more force + mf’s)

Larger vs. smaller muscle groups (glute max vs. med)

What are the 3 rules of adaptions with resistance training?

1. neural adaptations are always first and accompany strength gains

2. transient (acute) muscle hypertrophy results from edema

3. chronic muscle hypertrophy reflect actual structural changes in the muscle (increased size of individual mf’s)

When do you see neural activation and fiber hypertrophy?

first 6 weeks = MU recruitment & Co-activation

• early gains in strength are more influenced by neural factors

10-16 weeks:

• long-term strength increases due to mf hypertrophy

Transient (acute) hypertrophy

Increase in muscle size that immediately follows a single exercise bout

• fluid accumulation in interstitial & intracellular space from blood plasma

Chronic hypertrophy

Increase in muscle size after long-term resistance training

• facilitated by post exercise nutrition

• net increase in actin & myosin synthesis

• changes in mf size

Types of resistance training

• static contraction (isometric)

• free weights

• eccentric training

• isokinetic training

• variable resistance (theraband)

• plyometrics (explosive movements)

What do you do when you want to enhance strength development?

low-repetition, high resistance

What do you do when you want to optimize muscular endurance?

high reps, low resistance

Resistance training programs chart: volume, intensity, frequency, rest

Acute muscle soreness

• accumulation of end products (H+) of exercise in the muscles or edema

• usually disappears minutes or house after exercise

Delayed onset muscle soreness (DOMS)

• Soreness is felt 12-48 hours after strenuous bout of exercise

• primarily from eccentric muscle activity

• more muscle breakdown than protein synthesis

Prevention:

• initial training at lower intensity w/ gradual increases

• reduce eccentric component during early training

Isometric measurement of strength

• Hold contractions 3-5 seconds

• advantage: simple, only 1 point tested

• disadvantage: most activities are dynamic (full ROM

Free weight measurement of strength

1 Rep Max:

• isotonic measurement

• max weight an individual can lift at once

Methods: free weight & adjustable resistance machine

Advantage: low cost, dynamic

Disadvantage: risk of injury as weight increases

Isokinetic measurement of strength

• maintains constant speed w/ varying resistance through ROM

• Advantage: provides feedback on differences in force through ROM

• disadvantage: lots of money + time

Variable resistance measurement of strength

• resistance changes through ROM in conjunction w/ change in joint angles

• eliminates joint mechanical advantages & inertial effect

• Advantage: maximizes muscle force through full ROM

• Disadvantage: uniformity b/t trials, time

Clinical measure of exercise intensity: VO2 max

• highest rate of O2 consumption attainable during max exercise

• can be improved with endurance training

Clinical measure of exercise intensity: talk test

Light intensity: should be able to sing during activity

Moderate: can carry conversation

Vigorous: winded or too out of breath to hold conversation

Clinical measure of exercise intensity: Target heart rate

• Based on max heart rate

• 220 - age = HR max

• HR max x 0.6 = target HR

• verify by taking pulse

Clinical measure of exercise intensity: Rating of perceived exertion

• subjective measurement that can be used to determine intensity of aerobic workout

Determined by:

• cue of increased rate of breathing

• ask if patient senses their HR is faster

• ask how hard does it feel like you’re working?

Want to workout b/t 12-16 (50-85% HR max)

Overtraining

• Excessive overload w/ inadequate recover → accumulated training stress

• signs & symptoms:

  • extreme fatigue, illness, injury, hormone disturbance

• Long-term performance losses

Detraining

• loss of accumulated physiological adaptations with reduction in frequency, volume, and intensity of training

• if you don’t use it, you lose it

• Magnitude depends on length of detraining period & initial status

• quicker gains with return to training → muscle memory

Muscle atrophy

• inactive muscle with injury, immobilization or cessation of training

• transition of type IIx → type IIa

• decreased strength, protein synthesis, cross-sectional area

• muscles can recover when activity is resumed