MUSCULAR FATIGUE MECHANISMS Flashcards
(20 cards)
fatigue
—> Fatigue is a gradual and multifactorial process, which means multiple types of fatigue are always present and occurring simultaneously (i.e. fuel depletion, accumulation of metabolic by-products and elevated body temperature). However, at any one point in an effort, one fatigue mechanism will be contributing most to the reduced intensity
fuel depletion
Fuel depletion refers to the depletion of the body’s energy fuels, which, through their breakdown, allow ATP resynthesis to occur.
- ATP is the body’s energy currency; it powers all of the muscle cells’ metabolic activity, including the ability to contract at a specific force and speed. The types of fuel depletion experienced within the muscle cells include CP depletion and glycogen depletion.
Central Fatigue
occurs when muscular function is decreased due to our central nervous system
Peripheral Fatigue
is at the muscle which occurs when muscle function is disrupted.
Factors affecting the rate and onset of fatigue:
- Type of activity
- Intensity of activity
- Fitness levels
Factors contributing to fatigue
- Thermoregulation
- Fuel depletion
- Metabolic by products
ATP ENERGY SYSTEM LIKELY CAUSES OF FATIGUE FUEL DEPLETION
—> Fuel depletion refers to the depletion of the body’s energy fuels, which, through their breakdown, allow ATP resynthesis to occur.
- ATP is the body’s energy currency; it powers all of the muscle cells’ metabolic activity, including the ability to contract at a specific force and speed. The types of fuel depletion experienced within the muscle cells include CP depletion and glycogen depletion.
Creatine phosphate depletion
During maximal intensity efforts of short duration, the existing stores of intramuscular ATP are used up within the first few seconds. This activates the energy systems to maintain the required rates of ATP within the working muscles.
As the muscle demand for ATP is high during maximal efforts, the muscles will use the ATP–CP system — specifically, CP as a fuel — to rapidly replenish ATP from ADP and Pi.
CP depletion occurs in:
- single maximal efforts of short duration.
- repeat intermittent maximal efforts where there is inadequate recovery time to fully replenish CP stores (see figure 7.3). Recall, that approximately 98 per cent of CP stores are replenished after three minutes of passive recovery. This length of recovery is rarely afforded to performers in team sports.
- long duration, continuous exercise in which submaximal effort is interspersed with periods of high or maximal intensity
ANAEROBIC GLYCOLYSIS ENERGY SYSTEM LIKELY CAUSES OF FATIGUE
Metabolic by-products: Substances produced as a result of chemical reactions within the body associated with the production of energy for ATP resynthesis.
Lactic acid: = lactate + H+ ions
–Impaired isometric muscle contraction force
–Impaired isometric muscle velocity force
–Is used as a cheaper measure of hydrogen ions
Hydrogen ion accumulation (H+)
– Hydrogen ions make the muscle more acidic (lowers pH) which slows down the enzyme activity
– Decreases the rate at which glycogen can be broken down (glycolysis) and results in a decrease in intensity (energy for ATP resynthesis occurs at a slower rate and therefore muscle contractions slow down).
– Occurs when the lactate inflection point (LIP) is exceeded
LIP occurs when H+ ions start to accumulate due to insufficient oxygen being supplied to enable them to be broken down.
When this happens they accumulate quickly and fatigue sets in shortly after this.
ADP ad inorganic phosphate (Pi)
—> The rising level of ADP and Pi interferes with the power of muscle contractions, predominantly with the role that calcium plays
AEROBIC ENERGY SYSTEM LIKELY CAUSES OF FATIGUE
- Fuel depletion
- Thermoregulation
- Neuromuscular factors
FUEL DEPLETION
When you move from glycogen to fats, this means u will hit the wall for energy supply
—> Muscle glycogen is the preferred fuel source during aerobic activities. Unfortunately, the stores of glycogen are limited, and deplete around 90-120 minutes mark of prolonged, submaximal exercise.
the order of fuel depletion
- glycogen stores are depleted
- increased reliance of fat metabolism
- fats have a greater oxygen cost and a more complex process to break down
- energy for ATP resynthesis is produced at a slower rate
- muscle contractions must slow down
HOW CAN WE REPLENISH GLYCOGEN
Exercise makes muscles more responsive to insulin, which results in a greater intake of glucose from the blood, by muscles
- This improved insulin response only lasts for about 30-45 minutes following exercise. High-GI foods should be consumed as soon as possible after events to ensure rapid restoration of muscle glycogen (first) and liver glycogen (second)
- The closer after the event that you eat high Gi foods, the glycogen stores will return to pre-exercise levels faster
THERMOREGULATION
Evaporation
- When sweat is produced to try and cool the body through evaporation of water
- Effective, but can lead to dehydration if the fluid lost is not replaced
- Can result in reduced muscle strength and endurance and heat stroke
Convection
- Is the movement of air past and away from the body which can have a cooling effect e.g. fan
Radiation
- When the body radiates the heat from the skin into the environment (above 37 degrees it is ineffective)
Vasodilation
- Blood is directed to the skin, away from the working muscles
- Decreases physical performance (intensity) and reliance on anaerobic energy production and the production of toxic waste products
NEUROMUSCULAR FACTORS
Decreased CNS ‘firing’
- When the brain detects fatigue it sends weaker signals to working muscles to reduce intensity and slow down work rate (self-protection)
Loss of electrolytes
- Electrolytes are salts which control cell membrane stability and carry the electrical charges for muscle contractions caused by nerve impulses.
- When we sweat electrolytes keep water balance, so that our muscles and organs continue functioning
DOMS
- Normal response to unaccustomed exercise or heavy eccentric work, normally felt 24-48hrs after exercise
recovery
- Passive recovery
- Active recovery
PASSIVE RECOVERY
Link to fatigue factor = Depletion of CP
Explanation:
Our muscle’s fuel CP is rapidly resorted when recovery involves total passive rest.
Recovery time % creatine phosphate restoration
30 seconds 70%
60 seconds 75%
90 seconds 93%
120 seconds 95%
150 seconds 97%
180 seconds 98%
10 minutes 100%
ACTIVE RECOVERY
Link to fatiguing factor = Accumulation of metabolic by-products (H+ ions)
Explanation:
Performing an active recovery at a low intensity which speeds up the removal of H+ ions by:
- Maintaining higher blood flow and therefore oxygen delivery to the muscles
- Creating a muscle pump where muscles create a squeeze on surrounding blood vessels enhancing blood flow
- Preventing venous pooling (therefore bringing blood pressure back to normal levels)
- Decreases muscle stiffness
E.g.
AFL – 20 minute cool down and consuming food/fluids immediately after training/game
1500m run – complete a low intensity 4-5km jog after a major even
DOMS stands for
delayed onset muscle soreness)
