The Mechanisms of Muscle Hypertrophy and their Application to Resistance Training Flashcards
What is hyperplasia?
Results in an increased number of fibres within a muscle
What happens when skeletal muscle is subjected to an overload stimulus?
Causes change in myofibers and related extracellular matrix. This sets of chain of myogenic events which lead to increase in size and number of actin and myosin and total number of sarcomeres in parallel.
How do satellite cells mediate hypertrophy?
Usually dormant but come active when enough mechanical stimulus is imposed on skeletal muscle. Once aroused, satellite cells increase rapidly in number and fuse to existing cells to create new myofibers, providing precursors needed for repair and subsequent growth of new muscle tissue.
How do satellite cells facilitate muscle hypertrophy?
Donate extra nuclei to muscle fibres, increasing capacity to synthesize new proteins.
Exercise-induced muscle hypertrophy is facilitated by a number of signalling pathways, what are they?
- mTOR
- MAPK
- CA2+ dependent pathways
How does the Akt/mTOR pathway work?
Acts as master network regulating skeletal muscle growth. When activated, Akt signals mTOR, which exerts effects on various downstream targets promoting hypertrophy in muscle tissue.
How does the MAPK pathway work?
Master regulator of gene expression, redox status, and metabolism. Specific to exercise-induced skeletal muscle hypertrophy, MAPK links cellular stress with an adaptive response in myocytes.
What does elevated anabolic hormone concentration increase the likelihood of?
Receptor interactions, facilitating protein metabolism and muscle growth.
What are the 3 most widely studied hormones?
- Insulin-like GF
- Testosterone
- Growth Hormone
What is the role of IGF-1?
Thought to provide main anabolic response for the body as a whole and shows enhanced effects in response to mechanical loading.
What is availability of IGF-1 controlled by?
IGF-1 binding proteins - these either stimulate or inhibit effects of IGF-1 after binding to a specific IGFBF.
IGF-1 activates L-type calcium channel gene expression causing…?
An increased intracellular Ca2+ concentration. This leads to activation of multiples anabolic Ca2+ dependent pathways .
As well as muscle tissue, what else does testosterone interact with?
Neuron receptors, thus increasing number of neurotransmitters released.
What does testosterone bind to in the blood?
Albumin (38%), steroid hormone binding globulin (60%), circulating in the blood (2%)
How does testosterone reach the chromosomal DNA inside a cell?
Unbound testosterone binds to androgen receptors of target tissues (located in cytoplasm). Causes a conformational change which transports testosterone to cell nucleus.
What does testosterone do to satellite cells?
Promotes satellite cell replication and activation, resulting in an increase in number of myogenically committed satellite cells.
What does resistance training do to androgen receptor content in humans?
Upregulates it.
What does Growth Hormone do?
Acts as a repartitioning (dividing) agent to induce fat metabolism towards mobilization of TG and stimulate cellular uptake and incorporation of amino acids into various proteins, like muscle.
What secretes GH?
Anterior pituitary gland.
Greatest nonexercised secretions during sleep.
What type of exercise maximises cell swelling?
Exercise which relies heavily on glycolysis. The resultant lactate accumulation acts as primary contributor to osmotic changes in skeletal muscle.
What 3 primary factors are responsible for initiating hypertrophic response to resistance exercise?
- Mechanical tension
- Muscle damage
- Metabolic stress
Load <?% 1RM is considered insufficient to promote substantial hypertrophy/
65%
Why are high reps inferior to moderate/low reps in eliciting hypertrophy?
Load is inadequate to recruit and fatigue highest threshold motor units.
What systems are low AND moderate reps reliant on?
- Low = PC system
- Moderate = anaerobic glycolysis.
How would you get a ‘pump’?
Veins taking blood out of working muscle are compressed while arteries continue to deliver blood, creating an increased concentration of intramuscular blood plasma. This causes plasma to seep out of capillaries into interstitial spaces, build up of this fluid causes extracellular pressure gradient, causing flow of plasma back into muscle causing a ’pump’.
(?) Volume programs mediate GH release
High
What is ‘overreaching’? (in terms of volume)
Planned, short-term increase in volume/intensity intended to improve performance.
Is overtraining due more to volume or intensity?
Volume.
Why is frequent exercise rotation needed to fully maximise hypertrophic response?
To stimulate all fibres, varying exercise parameters cause different activation patterns within muscle compartments.
Why are short rest intervals used?
To generate metabolic stress, heighten anabolic processes associated with metabolite build up.
Why are long rest intervals used?
Afford full recovery of strength between sets.
Why are moderate rest intervals a good compromise?
Most strength is regained within 1 min of set completion. Traning with shorter rest = adaptations allowing lifter to sustain higher % 1RM during training.
What is a positive AND a negative about training til failure?
P = TTF hypothesized to activate more MUs
N = TTF may increase potential for overtraining.
To increase hypertrophy, should concentric reps be fast or slow?
Fast (some argue moderate speed)
Should eccentric component of rep be fast or slow?
Slow
