Energy Production, Muscle during Exercise,
and Intensity/Fatigue
SPH K 212
Dr. Moscicki
Figure 2.1
Energy for
Cellular Activity
Energy Form Conversions
• Energy is easily converted from one form to another
• Law of Energy Conservation
– Energy can’t be lost, just converted in to another form
– Though not near 100% efficient
• Some energy is lost as heat
• That is why you get hot when you workout.
Energy system basics
• ATP (adenosine triphosphate) is the primary currency of energy in
the human body
• We use energy system to replenish ATP levels in active muscles
during activity
Energy Systems and Fatigue
• Different types of muscle primarily rely on different means of
energy production
• Two common categories:
– Anaerobic
• w/o oxygen
– Aerobic
• w/ oxygen
Processes to Replenish ATP
1.
2.
3.
Phospho-Creatine
Glycolysis
Mitochondrial
Respiration
1
Phospho-Creatine
3
Krebs
Cycle
2
Electron
Transport
Enzyme Basics
EnzymeProtein based structure used to
catalyze biochemical reactions
Enzymatic Pathway & Control
Overview of energy systems
Lactate + H+
H2O + CO2
ATP-PCr System
• Anaerobic
• ATP yield: 1 ATP:1 PCr
• Duration: ~10 seconds
• Because ATP stores are very limited, this pathway is used to
reassemble ATP
Glycolytic System
•
•
•
•
Anaerobic when directly utilizing Glycolytic enzymes
ATP yield: 2 ATP / glucose
Duration: 1 to 2 min
Breakdown of glucose via glycolysis
Overview of energy systems
1 atp
2 atp
Heat
Lactate + H+
H2O + CO2
Oxidative System
•
•
•
Aerobic (adequate O2 required)
ATP yield: depends on substrate
– 32 to 33 ATP/1 glucose
– 100+ ATP/1 Fatty Acid
Duration: steady supply for hours
Krebs
cycle
Fuel Utilization vs Intensity
Overall summary of Metabolism
Lactate + H+
MUSCLE USE AND CONTROL
Skeletal Muscle
• Structure
– 100’s to 1,000’s of muscle fibers(cells) controlled by many
neurons
Skeletal Muscle
• Muscle fibers are controlled in groups called
motor units
• Motor unit
– A single motor neuron and all the muscle
fibers it innervates (i.e.- connects to)
– Each neuron will innervate many fiber
around the muscle
Motor units Recruitment by Intensity
Type I
Slow Twitch
Type IIa
Fast Twitch
More
Mitochondria
Motor Unit
Recruitment
Type IIx
Fast Twitch
Less
Mitochondria
Low Force/Slow Tasks
High Force/Fast Tasks
Muscle force production
• Look at type of activity
– Walking/Jogging- low force activities that rely heavily on Type
I/Slow Motor Units
• Can perform long bouts due to Aerobic energy production
– Sprinting is a high force activity relying heavily on Type II/Fast
Motor Units
• Fatigue quickly
Energy systems and Fatigue
1 atp
2 atp
Heat
Lactate + H+
H2O + CO2
Reasons for Fatigue Relative to Intensity
High Intensity short activity
– Short time span
• Reasons for fatigue
– CP system depleted slowing ATP
resynthesis
– Build up of:
• Acidic byproducts
– Hydrogen builds up
• Waste byproducts
Lower Intensity long activity
– Long time span
• Reasons for fatigue
(Should be able to make ATP fast
enough)
– Run out of fuel stores for energy
pathways
• Glycogen stores depleted
– Dehydration
– Damage to muscles
– Heat
• End
Review- Not in your notes
OTHER SYSTEMS RESPONSE TO
EXERCISING SKELETAL MUSCLE
Changes in Body leading to Exercise Response
• Neural response
– Thinking about exercise and actually contracting muscles lead
to the changes
– Epinephrine release (among other hormones)
• Chemical changes
– Byproducts from active skeletal muscle get into blood stream
and lead to increase activity of other systems
• CO2 and H+
Cardiovascular system
•
•
•
•
•
é Heart rate
é Stroke volume
é Cardiac Output
é Blood pressure
Redirect blood flow around the body
– Shunt blood to active muscle
Respiratory System
• Due to CO2 in the blood, respiratory centers are excited
• é depth of breathing
• é rate of breathing
Skin Response
• Due to increase in Heat build up from energy metabolism
• é blood flow to skin
• é sweating