Muscular contractions and energy pathways

Question 1

carb needs pre exercise

Answer 1

Pre exercise: glycogen
stores, hydration, gastro-
intestinal
comfort/discomfort, timing

Question 2

carb needs during exercise

Answer 2

During Exercise: Goal will be
to sustain performance and
minimise glycogen
depletion, hydration

Question 3

carbs needs post exercise

Answer 3

Post exercise:
RECOVERY AND
REHYDRATION IN ADVANCE
OF NEXT TRAINING OR
COMPETITION

Question 4

Energy requirements vary on

Answer 4

Need to:
* Ensure athlete sufficiently fed for
their sport and health
* Consume sufficient calories to
sustain training and maintain
body weight
* Meal planning, snacks, energy
dense foods etc.

Question 5

Energy requirement problems

Answer 5

• Can be difficult to eat enough
• Previous work – CHO requirements often not achieved by elite
  athletes
• Low energy availability common
• Females, aesthetic sports, sports which emphasise leanness
• Females: LEA- can affect menstrual cycle
• Intense training can suppress appetite
• GI discomfort
• Logistics: travel, training times, work

Question 6

types of carbohydrates and the general molecular formula

Answer 6

• (CH2O)n
• Monosaccharides
• Disaccharides
• Oligosaccharides
• Polysaccharides

Question 7

Homeostasis

Answer 7

how the body maintains a consistent and stable environment

Question 8

Excitation and contraction coupling

Answer 8

• Action potential arrives at the neuromuscular junction
• ACh released, binds to receptors, opens sodium ion channels
  -leads to an action potential in the sarcolemma
• Action potential travels along the T-tubules
• Muscle shortens and produces tension.

Question 9

Types of muscle fibres

Answer 9

Type I
Type 11a
Type 11x

Question 10

short term acute responses to exercise

Answer 10

• CVS
• Cardiac output increases (increase in HR and
  Stroke Volume)
• MABP Increases
• Increase in coronary artery flow
• Blood flow changes (to skin and skeletal
  muscles)
• Respiratory
• Increased pulmonary ventilation- tidal
  volume, Resp Rate
• Hormonal responses
• Immune responses

Question 11

Long term chronic adaptations to exercise

Answer 11

• CVS (SV, cardiac muscle hypertrophy, RBP
  down)
• Respiratory
• Musculoskeletal
• Size and number of mitochondria
• Increased ability to store glycogen and use
  fat stores
• Increase in capillaries to muscles
  (endurance training)
• Hypertrophy
• Increase in bone mass
• Increased strength of tendons/ligaments

Question 12

Phosphocreatine hydrolysis

Answer 12

• Anaerobic metabolism. Immediate source
  of ATP.
• High power output however stores are
  limited (seconds)
• Creatine kinase breaks down
  phosphocreatine to creatine and the
  phosphate is donated to ADP to form ATP
• Reversible reaction- when energy
  available from other sources creatine and
  phosphate will re-form PCr.

Question 13

Glycolysis

Answer 13

Aerobic or Anaerobic
* Occurs in the cytosol.
* Glycolysis involves a series of reactions that breaks down glucose into 2 x 3-carbon pyruvate
* Pyruvate then either converted to lactate (anaerobic) or travels to mitochondria and converted to
Acetyl CoEnzyme A (aerobic)

Question 14

Substrates for glycolysis

Answer 14

• Uptake of blood glucose
• GLUT4
• Once inside cell, hexokinase
  converts free glucose to
  glucose-6-phosphate
• Breakdown of glycogen stores

Question 15

Net ATP yield from Glycolysis

Answer 15

2 ATP (when blood glucose used) or 3 ATP when glycogen
used as source of blood glucose

Question 16

Glycolysis relevance in sports nutrition

Answer 16

Net energy yield
* 2 or 3 ATP
* Large stores of carbohydrates
* Glycolysis is a relatively rapid
process
* For athletes performing intense
exercise- vital energy pathway
* Fast, quick, anaerobic mechanism
* 800m runner may metabolise
100g of carbohydrate to lactate

• Ultimate limitations
• Availability of co-factors for
  reactions
• Lactate reduces pH
• Inhibits some of the enzymes
• Painful stimulus

Question 17

Oxidative Phosphorylation

Answer 17

• Mitochondria
• Pyruvate converted to Acetyl Co Enzyme A
• Enters a series of reactions- Krebs or Tricarboxylic Acid Cycle
• Electron transport chain- oxidative phosphorylation of ADP to make ATP
• Other sources of Acetyl Co-Enzyme A – Fatty acid oxidation – so metabolism
  of fats and carbohydrates share a final common pathway

Question 18

Fat metabolism

Answer 18

• Intramuscular triglyceride stores or fatty acids from plasma
• Lipolysis is the breakdown of fat stores
• Beta oxidation pathway- cleaves 2 carbon units off the fatty acid each time
• Yields a number of 2 carbon acetyl co-enzyme A
• Acetyl Co-enzyme A into TCA and electron transport chain

Question 19

Protein metabolism

Answer 19

• Intramuscular or plasma AA sources
• Can be oxidised in the muscle for energy
• <5% of whole-body substrate oxidation but can increase during
  exercise
• Increases with duration, low carbohydrate availability, negative
  energy balance

Question 20

ATP generation for short power events

Answer 20

• Explosive power events, short muscular contractions- need high rates of ATP regeneration and need it
  quickly- PCr.
• Anaerobic

Question 21

ATP generation for sprinting

Answer 21

high rates of ATP but
muscular contractions of slightly longer
duration (approx. 6-60 secs)
* Combination of PCr system as well as
anaerobic glycolysis

Question 22

ATP generation for middle distance events

Answer 22

• Combination of PCr, Glycoloysis, Oxidative
  Phosphorylation
• PCr, Glycogen, blood glucose, IMTG, (both
  aerobic and anaerobic)

Question 23

ATP generation for endurance events

Answer 23

• Endurance or ultra-endurance events – slower rate of contraction
• Glycogen, blood glucose, IMTG, plasma fatty acids, amino acids

Question 24

Fuel stores Muscle glycogen

Answer 24

Approx 300g

Question 25

Fuel stores Liver glycogen

Answer 25

approx. 100g
This can be released as glucose into circulation

Question 26

Fat stores

Answer 26

triacylglycerol- adipose tissue
Triacylglycerol in skeletal muscle- can provide FA’s
for metabolism
12 kg/ww triacylglycerol
(Type I more than Type II)

Question 27

Regulation of energy metabolism: What influences the rates of metabolic reactions to produce the energy for exercise

Answer 27

• Availability of substrate
• Accumulation of an end product
• Energy requirements of the reaction
• Enzymes and co-factors
• Temperature
• Hormonal regulation (Insulin, Glucagon, Growth Hormone, Cortisol)
• Catecholamines

Question 28

Fatigue in high intensity exercise

Answer 28

• ‘Fatigue is the inability to maintain a given or expected force or
  power output and is an inevitable feature of maximal exercise’
• Decline in anaerobic ATP, increased ADP
• Lactic acid & reduced pH. Hydrogen ions may inhibit force unclear
  the exact importance of this in fatigue because of recoverability
  demonstrated in studies.
• Calcium ions
• Reduced PCr resynthesis during repeated bouts of activity

Question 29

Fatigue in prolonged exercise

Answer 29

• Sustained for 30-180 mins
• Rate of ATP demand relatively lower
• Muscle glycogen can fuel approx. 80-90 mins of marathon running pace. Exact
  factors for assoc. between glycogen depletion and fatigue unclear.
• Some mechanism of fatigue before absolute depletion of ATP and rigor or
  irreversible damage
• Hypoglycaemia may be a factor – may be indirectly via the CNS ‘central fatigue’
• Rate of ATP re-synthesis from fat oxidation can’t keep up with requirements above
  50-60% Vo2 max