7. Improving Muscle Mass & Strength Flashcards
6 factors contribute to develop & maintain mm mass & strength:
1) Genetics (gene doping?)
2) nervous system activation
3) physical activity—WE NEED ACTIVITY
4) nutritional activity
5) endocrine influences
6) environmental factors
Skeletal MM Adaptations that Incr Strength
1) Hypertrophy [incr cell size]: PCSA, hyperplasia [incr # of cells • Hyperplasia probably does NOT & that muscle hypertrophy is primarily the result of incr muscle fiber size NOT #]??
2) Fiber Type Alterations: incr the proportion of Type II fibers
3) Myofilament Packing: incr # of myofilaments and hence an incr in # of cross bridges that may be formed for the same PCSA
4) Neural Adaptations…that improve strength
o ↑ # of motor units recruited
o ↑ firing rate (freq) of Motor Unit
o ↑ Motor Unit synchronicity (coordination)
o ↑ activation of synergist muscles
o ↑ inhibition of antagonist muscles
Hypertrophic factors that incr strength
-muscle CSA (greater CSA→greater force production
-PCSA: sum of the CSA of all the muscle fibers within the muscle
-fiber type
• can’t incr the # of type II fibers but you can hypertrophy type II, so that the area is greater than type I→stronger (all about proportions)
-myofilament packing
• pennation angle of 30°…lose 13% of force capacity, BUT pack in more fibers→stronger muscle
Fiber Type Alterations
Genetic factors largely determine one’s predominant muscle fiber distribution.
• PRT may result in fiber type transformation from Type IIB to IIA
o Type IIB: highly fatigable, very anaerobic, GREATEST strength
o Type IIA: more aerobic
o CANNOT TRANSFORM TO TYPE I
• Endurance training DOES NOT alter fiber type transformation!!!
4-6week training of a novice individual—strength gains due to neural adaptations→after 6-8 wks other factors contribute
Excess Post-exercise Oxygen Consumption (EPOC)
Factors that contribute to EPOC?
After RT body uses more O2 before returning to normal (elevated metabolism up to 38 hrs after a single bout)
Factors that contribute to EPOC:
o Resynthesize ATP & PCr
o Reaynthesize lactate to glycogen
o Oxidize lactate in energy metabolism
o Thermogenic effects of elevated core temp
o Thermogenic effects of hormones (Catecholamines)
o Effects of elevated HR, RR, + other physiologic fxns
Neuromuscular Adaptations to Exercise
• mm contraction regulated by recruitment of motor units (MU)
• muscle fibers in different MU possess different metabolic capacities
• MU recruitment= progressive order from slow twitch to fast twitch
• MU recruitment during ex can influence muscle energy metabolism and blood acid-base balance.
**knowledge of MU recruitment + contributions of different muscle fibers to meet demands of ex, aids in understanding body’s adaptations to ex.
Innervation & Muscle Fiber Types
• Type of motor neuron innervating mm fiber dictates the fiber type
• Both nerve cross-innervation and artificial electrical stimulation of motor nerves have been shown to reverse the metabolic and contractile profiles of muscle fibers.
o Connecting mm fibers to an opposite motor nerve or stimulating a nerve in the opp freq & intensity converts the muscle fibers to reflect the muscle normally innervated by the nerve and stimulation profile.
Neural Adaptations with RT
• Accounts for majority of strength gain early (first 4 weeks) in a RT program
o Learning & familiarization
• 5-10% incr in strength upon subsequent testing
• Accounts for large strength gains observed in OLD PPL when hypertrophy is minimal/absent
• Specificity of training
o Training specifically at fast or slow contraction velocities results in different abilities to generate torque, without alteration in muscle fiber type proportions.
• Training at fast vel= improvements at high velocities (mainly)
• Training at slow vel= improvements across ALL speeds.
• Gender/Gains— neural/coordination adaptations with RT
o 48-54% MALE vs 67-70% FEMALE
Pyschological Facotrs influencing Strength
• ppl fxn @ a level of neural inhibition—protective reflex mechanism
• NM inhibition may derive from:
1) unpleasant past experiences 2) protective home environ 3) fear of injury (less likely to perform max effort)
• Motivation, encouragement, excitement of competition, use of dis-inhibitory drugs, or hypnotic suggestion often induces supramax performance bc of optimal motor neuron recruitment.
Electromyography (EMG): what does it do?
provides means to study NM adaptations during different mm actions. Reflects QUALITY & QUANTITY of electrical activity generated by mm.
Electromyography (EMG): greatest EMG activity?
EMG during concentric bidirectional mm work:
o Augmentation of tension output and greater EMG activity during concentric bidirectional work occurs than with unidirectional, concentric-only work.
o Probably the result of greater recruitment of motor units.
o ie: If the R & L limbs flex, then extend in alternating fashion, tension output and EMG activity of both limbs reaches higher levels than with single-limb activation.
Electromyography (EMG): EMG & Muscle Contraction
o Early stages of RT…EMG activity will incr suggesting neural adaptations. Later stages of RT…EMG activity will remain the same ore slightly decr
o Lower EMG activity is associated with ecc contractions approx 25% less EMG for same absolute workload as concentric)
Electromyography (EMG): strength
A. Strength Gains due to Neural Factors: proportional changes due to neural adaptations (incr activation, but same ratio)
B. Strength Gains due to Hypertrophy: incr strength, but no change is EMG
