Muscle Stimulation & Exercise 4-5 November 2014

Response to Stimulation Muscles have graded responses – they contract to different degrees, depending upon the frequency and strength of stimulation

Response to Stimulation If a nerve fires once (unusual), the muscle contracts and relaxes in a twitch If the nerve fires rapidly in succession, then the muscle does not relax fully in between impulses – resulting in tetany (a smooth, prolonged contraction)

Response to Stimulation Note: tetanus ≠ tetanus Tetanus (the type of muscle contraction) is different than tetanus the disease caused by a bacteria (commonly called lockjaw)

Response to Stimulation The strength of contraction also depends on how many muscle fibers are stimulated. The more muscle fibers stimulated, the greater the contraction of the muscle.

Quick Review What vocab word describes the fact that muscles may contract to different degrees? What two factors determine the extent to which a muscle contracts? Graded response Frequency of stimulation and number of cells stimulated

Muscle Metabolism Muscle contraction requires enormous amounts of energy in the form of ATP. The amount of ATP stored in the cell only lasts for ~5 seconds! The rest of the ATP must be regenerated, using one of three pathways.

Muscle Metabolism Pathway 1: Direct phosphorylation by creatine phosphate Fast! No O2 required Quickly used up Only in muscle cells

Muscle Metabolism Pathway 2: Anaerobic glycolysis and lactic acid formation Medium speed No O2 required Less efficient Produces lactic acid Only in muscle cells

Muscle Metabolism Pathway 2: Anaerobic glycolysis and lactic acid formation Misconception alert! Lactic acid build-up is not responsible for muscle soreness the day after exercise (that’s due to cell damage).

Muscle Metabolism Pathway 2: Anaerobic glycolysis and lactic acid formation Lactic acid build-up is responsible for the burning feeling during exercise. Also, lactic acid build-up increases muscle fatigue (inability of muscle to contract when stimulated)

Muscle Metabolism Pathway 3: Aerobic respiration Slow Long-lasting All cells Requires O2

Muscle Metabolism Which energy pathway is better? CP and anaerobic supply energy at a fast rate (for maximum performance) but for a short term only. Examples: Sprinting Any sport with bursts of energy & quick changes (e.g. Volleyball, b-ball) Start of exercise

Muscle Metabolism Which energy pathway is better? Aerobic can provide energy for hours without fatigue But, muscles are not working at peak levels Examples: cycling, marathon

Muscle Metabolism Sports & Energy Systems

Muscle Metabolism Oxygen Debt All non-aerobic energy use causes changes in the muscle that need to be reversed after the exercise is over O2, ATP, creatine phosphate, and glycogen reserves need to be replenished Lactic acid needs be broken down Oxygen debt is the extra amount of oxygen that must be taken in for these restorative processes. This is why you breathe deeply for a while after intense exercise. These processes all require oxygen

Think, Pair, Share Scholar with shorter hair: Name the reactants and products of each energy system. Which two energy systems are only used in muscles? Scholar with longer hair: Which two energy systems lead to oxygen debt? Which energy system(s) predominate in the following activities: running for your life, hiking, lifting heavy furniture These processes all require oxygen

Critical Thinking 1 The graph below indicates the amount of lactic acid produced by muscle cells as a function of power (energy / time). Describe how lactic acid production varies with power. Explain the shape of the graph using your knowledge of energy systems These processes all require oxygen

Critical Thinking 1 Lactic acid increases very slowly from 150 W to 250 W but begins to increase dramatically at about 275 W. At around 275 W, the rate of energy required by the muscle cells is too high, so the body switches from aerobic metabolism to anaerobic metabolism. This point is known as aerobic threshold. These processes all require oxygen

Exercise & Muscles Isotonic vs Isometric Contractions Isotonic contractions occur whenever the muscles shorten, causing movement (e.g. weight lifting, running, swimming, jumping, etc.) Isometric contractions occur whenever the muscle’s tension increases without actually shortening. This happens when you try to move an immovable object. (e.g. pushing against a wall; many yoga exercises, etc.) These processes all require oxygen

Exercise & Muscles Aerobic vs Resistance Exercise Aerobic exercise (aka endurance or cardiovascular) – builds the aerobic endurance of muscles Examples: jogging, biking Increases blood supply to muscles; # of mitochondria, & amount of stored oxygen Benefits Greater resistance to fatigue Better heart and lung function Improved digestion Improved bone density Reduced risk of metabolic disorder Increased immune system function These processes all require oxygen

Exercise & Muscles Aerobic vs Resistance Exercise Resistance exercise (aka weight training) – focuses on isometric contractions & forcing muscle to contract with as much force as possible Examples: weights, some yoga exercises, pushups, situps, Increases the number of actin and myosin fibers, resulting in larger muscles Benefits Greater strength Greater muscle mass = greater metabolism Increased bone density These processes all require oxygen

Exercise & Muscles Exercise recommendations for healthy adults age 18-65 from CDC These processes all require oxygen

Exercise & Muscles Muscle tone and muscle wasting Muscles quickly deteriorate when not used Lose 5-10% muscle mass per week with bed rest Lose 20% muscle strength in one week of bed rest Muscle strength plateaus at ~30% original strength after ~6 weeks of bed rest Our body maintains muscle tone by systematically stimulating and partially contracting muscles around the body Electrical muscle stimulators can also help prevent muscle atrophy following a stroke, injury, or surgery These processes all require oxygen

Think, Pair, Share Compare and contrast isotonic and isometric exercises, and provide an example of each Compare and contrast resistance and aerobic exercise, and provide an example of each Why is exercise necessary for our muscles? How does exercise help our body function? These processes all require oxygen

Closure What were our objectives today? What did you learn about these objectives? How does what we learned today tie to our unit question? These processes all require oxygen

Critical Thinking 2 – Exit Ticket The graph below indicates the amount of lactic acid produced by muscle cells as a function running pace. Describe the data. Explain the data using your knowledge of energy systems and exercise These processes all require oxygen