Muscular contractions and energy pathways Flashcards
carb needs pre exercise
Pre exercise: glycogen
stores, hydration, gastro-
intestinal
comfort/discomfort, timing
carb needs during exercise
During Exercise: Goal will be
to sustain performance and
minimise glycogen
depletion, hydration
carbs needs post exercise
Post exercise:
RECOVERY AND
REHYDRATION IN ADVANCE
OF NEXT TRAINING OR
COMPETITION
Energy requirements vary on
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.
Energy requirement problems
- 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
types of carbohydrates and the general molecular formula
- (CH2O)n
- Monosaccharides
- Disaccharides
- Oligosaccharides
- Polysaccharides
Homeostasis
how the body maintains a consistent and stable environment
Excitation and contraction coupling
- 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.
Types of muscle fibres
Type I
Type 11a
Type 11x
short term acute responses to exercise
- 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
Long term chronic adaptations to exercise
- 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
Phosphocreatine hydrolysis
- 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.
Glycolysis
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)
Substrates for glycolysis
- Uptake of blood glucose
- GLUT4
- Once inside cell, hexokinase
converts free glucose to
glucose-6-phosphate - Breakdown of glycogen stores
Net ATP yield from Glycolysis
2 ATP (when blood glucose used) or 3 ATP when glycogen
used as source of blood glucose
Glycolysis relevance in sports nutrition
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
Oxidative Phosphorylation
- 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
Fat metabolism
- 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
Protein metabolism
- 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
ATP generation for short power events
- Explosive power events, short muscular contractions- need high rates of ATP regeneration and need it
quickly- PCr. - Anaerobic
ATP generation for sprinting
high rates of ATP but
muscular contractions of slightly longer
duration (approx. 6-60 secs)
* Combination of PCr system as well as
anaerobic glycolysis
ATP generation for middle distance events
- Combination of PCr, Glycoloysis, Oxidative
Phosphorylation - PCr, Glycogen, blood glucose, IMTG, (both
aerobic and anaerobic)
ATP generation for endurance events
- Endurance or ultra-endurance events – slower rate of contraction
- Glycogen, blood glucose, IMTG, plasma fatty acids, amino acids
Fuel stores Muscle glycogen
Approx 300g
Fuel stores Liver glycogen
approx. 100g
This can be released as glucose into circulation
Fat stores
triacylglycerol- adipose tissue
Triacylglycerol in skeletal muscle- can provide FA’s
for metabolism
12 kg/ww triacylglycerol
(Type I more than Type II)
Regulation of energy metabolism: What influences the rates of metabolic reactions to produce the energy for exercise
- 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
Fatigue in high intensity exercise
- ‘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
Fatigue in prolonged exercise
- 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
