How Muscle Grows

Chapter 2

Read pgs: 29-33, 35-38, 40-44

2 Ways a Muscle can Grow

• Hypertrophy- an increase in the size of individual muscle fibers

– Primary means for muscle growth

• Hyperplasia- an increased number of muscle fibers

– Controversial

Benefits of Resistance Training

• Increased muscle size• Improves muscle

strength• Improves bone health• Improves athletic

performance• RT benefits both men

& women

• Stay healthy & offset natural aging process

• Sarcopenia• Osteopenia• Osteoporosis

Fears of getting “too big”

• Women have fewer muscle fibers, esp. in upper body

• Hormone (testosterone) level is lower in women

• Difficult to develop large muscles without use of anabolic drugs

Foundation for Muscle Growth

• 1. Muscle must be stimulated• Well designed RT-program

• 2. Well balanced diet (adequate calories)• Increasing muscle size requires energy

• If either of these two principles are ignored, muscle will not adapt.

Foundation for Muscle Growth

• Carbohydrates, proteins & fats serve as building blocks to repair & remodel muscle.

• Timing of nutrient intake is important

• Sleep & a healthy lifestyle are important

Neural Adaptations to RT

• Strength increases during initial few weeks of an RT program

• Neural function improved, along with coordination, & agonist/synergist

Muscle Stimulus

• If Goal is HYPERTROPHY:– Moderate to heavy loads (70 - 85% of max

strength)– High Volume (8 - 12 reps for 3 or 4 sets)

– This program stimulates greater acute increases in natural occurring anabolic hormones in the body

Muscle Stimulus

• Shorter rest periods = greater metabolic stress (increased lactic acid in blood), stimulating hormone release.

• This stimulates muscle protein synthesis & increased muscle size

• 1-2min rest periods recommended

Process of Muscle Growth

• Motor units must be activated

• Adequate EX intensity• Size Principle• Low-intensity (type I)

exercises vs. High-intensity (type II) exercises to increase muscle size

Hormone Responses to RT

• RT sends signals to all organ systems of the body

• The systems then support muscle’s ability to produce force & contribute to recovery & growth of muscle– Cardiovascular system– Endocrine system (epinephrine, testosterone)– Immune system (tissue repair)

Hormone Responses to RT

• Epinephrine (adrenaline) helps muscles produce force.

• Testosterone and growth hormone stimulate muscle protein synthesis, sending signals to the muscle to regenerate & grow.

• RT increases anabolic hormones in blood during & approx. 1-hr post ex, allowing body to rebuild & add muscle at that time.

Hormone Responses to RT

• RT stimulates release of growth hormone from pituitary gland in brain

• GH travels in blood & stimulates prod. Of insulin-like growth factor in the liver & muscles

• This IGF-I binds to a muscle cell’s receptor, triggering increase in production of proteins

Hormone Responses to RT

• Maximizing hormonal response to exercise = increase in muscle size (hypertrophy)

• Workouts that are structured using high volume & intensity, short rest periods, & that use large muscle mass will maximize body’s natural capacity to stimulate muscle growth -Denmark study in 2001

Muscle Damage & Immune Response

• Microscopic damage occurs

• Leads to inflammation & swelling,soreness

• But, this provides stimulus for growth

• How? The immune response to damage.

• WBC’s cause increase blood flow to muscle

• Blood carries 02 & nutrients to muscle and helps remove waste product

Protein Synthesis

• Acute increase in anabolic hormonesin muscle stimulates increase in protein synthesis

• Actin & Myosin are contractile proteins located in muscle cell

• Increased # of contractile proteins = hypertrophy & strength/power

Protein Synthesis

• Amino acids cross cell membrane & enter skeletal muscle

• Increasing amino acid intake post-RT can increase availability of aa’s to assist in protein synthesis

Important Factors for Protein Synthesis with RT

• Amino acid availability

• Timing of post-RT intake (sooner is better)

• Hormonal regulation

• Mechanical stress (intensity, volume of RT)

• Cellular hydration

Protein Synthesis

• To maximize protein synthesis:– Eat a meal soon after exercise– Meal should contain carbohydrate & protein

– Carbohydrate will replace fuel stores (glycogen) in muscle

– Protein will facilitate repair & building of muscle