Applied Exercise Physiology Section 5: Body Systems Topic 1: Muscular System Prepared by Mr. Cerny Niagara Wheatfield Senior High School
Types of Muscle
40% of total body mass
It is the number of muscle fibers packed into a given muscle cross-sectional area that determine overall force-generating capacity
Macrostructure Skeletal muscle c.s. 40x
basic functional unit of muscle
Striated (light & dark bands)
Contains ACTIN & MYOSIN filaments that are responsible for contraction
Actin & Myosin
Using the list of “characters” below, create a storyboard showing the many different steps involved with the sliding-filament theory. Each step should contain a colored drawing (labeled if necessary) and a short explanation.
Calcium (Ca ++ ) Troponin Tropomyosin ATPase ATP Myosin Actin
Role of ATPase:
Enzyme that allows ATP on the myosin head to release energy ( ADP + P) so that it can form a cross bridge on actin
Needed again to detach
After myosin head attached and “pulls” on the actin
What is rigor mortis?
In relationship to the sliding-filament theory, explain how rigor mortis occurs.
Where did the Ca ++ come from?
Ca ++ is stored and released from the sarcoplasmic reticulum (SR)
SR is a network of tubules within the muscle fiber
Nerves & Muscles
An action potential (signal traveling along a neuron) causing contraction is termed Excitation-Contraction Coupling
Action potential travels along neuron by the temporary changing of charges
Nerve impulse causes the release of acetylcholine (ACh).
ACh travels across neuromuscular junction, binding to muscle cell membrane.
ACh binding initiates an electrical impulse which travels across membrane and into T tubules.
Impulse stimulates release of Ca +2 from SR.
Ca +2 binds with t-t complex of the actin filaments, shifting it's position, exposing myosin binding sites.
Myosin binds to actin; Ca +2 presence also causes enzymatic actions of myosin to breakdown ATP into ADP + P + energy.
Energy of ATP degradation causes shape change of myosin head, pulling actin molecule toward center of sacromere.
After sliding, a new ATP binds to myosin, breaking the myosin-actin bond, releasing the myosin head.
If Ca +2 is still present, the process repeats itself until sacromere has shortened completely.
If a nerve impulse ceases, the Ca +2 is reabsorbed by the SR and the muscle relaxes.
What is it?
Decline in force-producing capabilities over time
What’s the point?
Prevents exhausting of metabolic (energy-producing) reserve (like enzymes)
Limits the buildup of harmful products
Reduces the likelihood of damage to the contractile elements (ex.: sarcomeres)
Muscle Fatigue 1
What causes it?
1) Reduction in ATP
Under high stress, ATP utilization reduced faster than ATP production
2) Peripheral metabolic bi-products
H (and other free radicals)
Increases temp = decreases contractile properties
4) Decrease nerve signals/action potentials
5) Reduction of Ca
“ leakage ” 1
From decrease nerve connection
Specificity of Muscle Fiber Recruitment
Each activity will recruit different groups & different numbers of muscle fibers
Thus…in order to increase force production for a particular activity, you must train those specific muscle fibers used in that activity
Specificity of Muscle Fiber Recruitment
What does this mean for training ?
In order for optimum adaptation to occur during training, muscles should be trained in a manner similar to the way they are expected to perform during competition
What does this mean for rehabilitation ?
Return to work in a timely manner requires you to look at exactly what that worker will be doing
Difference dependant on contraction time (rate of cross-bridge cycling) NOT amount of force produced
“Twitch”: response of skeletal muscle fiber to a single electrical stimulus
Slow twitch (Type I)
Fast twitch (Type II)
Muscle Types nonoxidative Few Sprinting /bursts No Few Fast Same (slightly more) Fast twitch (II) Oxidative Many Endurance Yes Many Slow Same (slightly less) Slow twitch (I) Oxidative / nonoxidative # capillaries Activity Resistance to fatigue # mit. Speed Force
“ Delayed onset muscle soreness”
Damage to sarcomere properties
Actual protein molecules in sarcomere
Exacerbated by dehydration
Recovering faster with steroids
“ Bigger” muscles:
Usually NOT increase in muscle cells (hyperplasia)
Usually an increase in existing tissue size (hypertrophy)