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
