Chapter 7: Muscular Fatigue and Nutritional & Hydration Strategies

Muscular Fatigue Mechanisms

• Key Knowledge:
  • Muscular fatigue mechanisms linked to varied sport and exercise intensities and durations.
  • Nutritional and hydration strategies to enhance performance, delay fatigue, and improve recovery.
• Key Skills:
  • Explain muscular fatigue mechanisms associated with the 3 energy systems.
  • Describe nutritional and hydration strategies to enhance performance, delay fatigue and improve recovery.

Assessment

• Outcome 1:
  • Analyze primary data from physical activity to refine movement skills using biomechanical and skill-acquisition principles.
  • Marks allocated: 45
• Outcome 2:
  • Use data from practical activities to analyze body and energy systems, explain fatigue factors, and recommend recovery strategies.
  • Marks allocated: 45
• **Contribution to final assessment:
  • School-assessed Coursework for Unit 3 contributes 20% to the study score.

Fatigue Mechanisms

• Fatigue and Recovery Overview
  • Neuromuscular factors: Decreased CNS firing, impaired Na^+ and K^+ gradients
  • Fuel depletion: Intramuscular ATP, phosphocreatine, muscle glycogen, blood glucose
  • Elevated body temperature: Dehydration, redistribution of blood away from muscles
  • Metabolic by-products: H^+ ions, inorganic phosphate (P_i), ADP, Ca^{2+} ions
  • Considerations: How long until the next event or training?
• Recovery
  • Fuel restoration: High-GI vs low-GI sports drinks and gels
  • Active recovery
  • Passive recovery
  • PC restoration

What is Fatigue?

• A reduction in the ability of muscles to produce power or force.
• Fatigue varies based on:
  • Duration: Longer events increase the likelihood of fuel depletion (CHO stores last 60-90 mins).
  • Intensity: Higher intensity increases the contribution from anaerobic glycolysis (accumulation of H^+).
  • Level of physical fitness.
  • Age.
  • Diet: PC and CHO stores limit system capacity.
  • Environmental conditions: High temperatures require cooling, reducing oxygen available for aerobic ATP production.
  • Types of contractions occurring.
  • Muscle fiber type being used.

Fatiguing Factors

• Exercise physiologists believe that fatigue is multi-factorial
• Thermoregulatory Fatigue
  • Very high core temperatures.
  • Increased rates of dehydration.
  • Redistribution of blood to assist cooling.
• Fuel Depletion
  • Intramuscular ATP.
  • PC.
  • Muscle Glycogen.
  • Blood Glucose.
• Accumulation of metabolic by-products
  • H^+ in plasma and muscles.
  • Inorganic phosphates (P_i).
  • Adenosine diphosphate (ADP).

Central vs. Peripheral Fatigue

• Central Fatigue
  • Occurs in the CNS, causing a decrease in muscular function due to CNS impairment.
• Peripheral Fatigue
  • Occurs at the muscles where internal processes become disrupted.

Levels of Fatigue

• Local Fatigue
  • Causes, signs and symptoms: Fatigue experienced in a specific muscle or muscle group. Occurs when the same muscle group is repeatedly used without sufficient recovery. Muscles feel heavy, tingling pain, or cramp.
  • Fatigue indicator (out of 10): 2-4
  • Examples: After completing a weight station (e.g., eight bench presses at 80% of repetition maximum) or in biceps/triceps after a game of squash or badminton.
• General Fatigue
  • Causes, signs and symptoms: Fatigue occurs after completing a full training session or competitive game. Performers feel that all muscles are 'weakened' and may experience psychological fatigue.
  • Fatigue indicator (out of 10): 6-8
  • Examples: After completing a circuit session or a 'full-on' game of hockey.
• Chronic Fatigue
  • Causes, signs and symptoms: An unhealthy breakdown of the immune system caused by overtraining, poor training program design, inappropriate recovery strategies, and/or excessive competition demands. Often accompanied by increased susceptibility to illness/infection, persistent muscle soreness, and reduced motivation.
  • Fatigue indicator (out of 10): 10
  • Examples: Diagnosed as chronic fatigue syndrome (CFS) or sometimes glandular fever.

Fatigue and Recovery: ATP-PC System

• Fatiguing factor:
  • Fuel Depletion: ATP & PC
    • Limited stores of ATP (<2secs) & PC (around 10secs) in muscles
    • When PC depletes, the body breaks down glycogen to resynthesise ATP
    • Results in decreased contractile force and energy production rate.
• Recovery Strategy:
  • Fuel Depletion: ATP & PC
    • Facilitated by passive recovery (during the rapid part of EPOC).
    • Low pH levels (high H^+ levels) and a slow/low supply of O_2.
    • Greater aerobic power assists with speedy PC recovery; anaerobic athletes still require aerobic training.
• Recovery time:
  • 30secs - 70% PC Stored
  • 60secs - 75% PC Stored
  • 3mins - 98% PC Stored
  • 10mins - 100% PC Stored

Fatigue and Recovery: ATP-PC & Anaerobic Glycolysis

• Fatiguing factor:
  • Accumulation of metabolic by-product - P_i
    • Slows the release of calcium ions and reduces the contraction force of muscles.
    • Occurs when ATP-PC & Anaerobic Glycolysis systems contribute more to energy production.
  • Recovery:
    • Removed best during passive recovery where high levels of O_2 are available
  • Accumulation of metabolic by-product - ADP
    • Accumulates during explosive activities; reduces muscle power.
    • Occurs when ATP-PC & Anaerobic Glycolysis systems contribute more to energy production.
  • Recovery:
    • Removed best during passive recovery where high levels of O_2 are available

Fatigue and Recovery: Anaerobic Glycolysis

• Fatiguing factor:

  • Accumulation of metabolic by-product - Hydrogen Ions (H^+)
    • H^+ accumulates when the LIP is exceeded.
    • Increased muscle acidity slows glycolytic enzymes and glycogen breakdown.
    • Occurs when Anaerobic Glycolysis has a higher contribution.

• Recovery Strategy:

  • The quicker H+ can be removed, the quicker the performer can recover
  • Best removed when oxygen levels remain elevated with increased blood flow.
  • Active Recovery: Maintain elevated O_2 intake and blood flow.
  • Massage: Elevated blood flow only.
  • Contrast bathing: Elevated blood flow only.

Lactate Inflection Point (LIP)

• L.I.P. has been exceeded when lactate appearance in the blood is greater than lactate removal from the blood. (Lactate rises from a steady state)

• When L.I.P. is reached, most energy is still supplied aerobically; however, an increased reliance on the Anaerobic Glycolysis energy system due to an increased intensity results in the lactate increase

• Remember: It is not the lactate itself that causes fatigue. The rise in blood lactate is a good indicator of the amount of H^+ that is in the muscle

• When the body produces ATP via the anaerobic glycolysis system, lactic acid is produced (by product of metabolising glucose when oxygen isn’t present) thus produces METABOLIC BY PRODUCTS = LACTATE AND HYDROGEN IRONS (H^+). It is the accumulation of metabolic by products, namely H^+, that interferes with muscle contractions hence causes fatigue. In the presence of oxygen, lactate is converted back to glucose to use as fuel however it is the accumulation of H^+ that causes a drop in muscle pH which increases muscle acidosis.

• Passive Recovery:

  • Min lactate removal time: 1 hour
  • Max lactate removal time: 2 hours

• Active Recovery:

  • Min lactate removal time: 30 mins
  • Max lactate removal time: 1 hour

Fatigue and Recovery: Aerobic Energy System

• Fatiguing factor:

  • Fuel Depletion: Glycogen
    • Muscle glycogen is used first, then liver glycogen
    • Considered a fatiguing factor after 60mins of continuous exercise
    • Will ‘Hit the wall’ 2-3hrs into an endurance event
    • Energy production form glycogen is 50-100% faster than the rate from fats

• Recovery Strategy:

  • Restored through replenishment during and post exercise bout (best results with high GI in first 30mins after completing exercise)
  • Glycogen depletion can be minimised by carbohydrate loading (learn more later in the course)
    • Post event glycogen intake (High GI)
      • Within 1 hour - 55% in 5hrs, 100% in 24hrs
      • 1-2 hours - 100% in 24-48hrs
      • 5+ hours - Up to 5 days

• Fatiguing factor:

  • Thermoregulation
    • Body heats when producing ATP (you take your jumper off when you start exercising)
    • To regulate rising body temperature, body sweats leading to water evaporating from the bloodstream
    • To do this, the body redistributes blood AWAY from muscles to the skin
    • Therefore, less oxygen for ATP production (so cannot work as high “aerobically”)
    • This process also leads to dehydration meaning blood loses water so thicker (increased viscosity) so the heart has to pump harder to move blood around (leads to increased heart rate for same intensity)

• Recovery Strategy:

  • Cool body temperature by consuming fluid (as you will most likely experience dehydration)
  • Recovery in cool environment (e.g. under a tree)

Fatigue: Neuromuscular Factors

• Fatiguing factor:
  • Decreased firing of the CNS
    • Brain detects fatigue – weaker signals sent to muscles to reduce intensity (self-protection)
    • As intensity increases, Acetylcholine release slows down, resulting in less forceful contractions
• Recovery - Passive recovery is the best
  • Loss of Electrolytes- Impaired sodium and Potassium Gradient
    • Electrolytes lost due to sweat
    • Without electrolytes, nerves cannot communicate with each other or perform their essential functions
    • Impaired sodium–potassium pump function can restrict muscular contractions.
  • Recovery- Sports and electrolyte drinks can help to maintain and replenish electrolyte levels

Lactate Inflection Point (LIP)

• The highest intensity at which the body can remove lactate at the same rate it is being produced.
• OR The point beyond which lactate accumulation exceeds the removal.
• Any intensity beyond this point will see a dramatic increase in blood lactate levels, as lactate is being produced faster than it can be oxidized or broken down.
• Aerobic training improves (DELAY) LIP, so athlete can work at higher intensities for longer durations aerobically.

Recovery Rates and Strategies

• Recovery time
  • 30secs - 70% PC Stored
  • 60secs - 75% PC Stored
  • 3mins - 98% PC Stored
  • 10mins - 100% PC Stored
• Passive Recovery:
  • Min lactate removal time: 1hour
  • Max lactate removal time: 2hours
• Active Recovery:
  • Min lactate removal time: 30mins
  • Max lactate removal time: 1hour

Recovery Strategies for Energy Systems

• ATP-CP System
  • Passive recovery to replenish PC stores more rapidly than active recovery
• Anaerobic Glycolysis
  • Active recovery to remove accumulated metabolic by products - hydrogen irons (H^+)
• Aerobic
  • CHO replenishment within 30 minutes to replace lost glucose/glycogen. CHO load.
  • Active recovery to remove accumulated metabolic by products - ADP & Pi
    • Increasing blood flow assists with removal of MBP (H^+).
    • Muscle pump through active recover & massage & contrast therapy.
    • Assist body to regulate temperature by hydrating before and cooling body after.
  • A well developed aerobic system assists more rapid replenishment of ATP and PC stores
  • A well-developed aerobic system assists more rapid removal
  • Active recovery should be used to remove accumulated metabolic by products - hydrogen irons (H^+) when exercise involve increased contributions from anaerobic glycolysis.

Nutritional Needs of the Athlete

• Appropriate nutrition is vital for all of us, not only in the choice of foods we ingest, but also with timing and quantity of foods consumed.
• The essential nutrients that are required by all athletes include:
  • Carbohydrates, fats, proteins, vitamins, minerals, water and fibre.
• Athletes must develop their own individual eating plans to achieve maximum results from their training programs.
• Not only does the athlete need to take into consideration the specific nutritional requirements of the sport that they participate in, they also need to consider their individual energy expenditure, metabolism and state of health
• Good nutrition and hydration strategies should be practised for both training and competition.
• For the first 2 hours during recovery blood is being blood is still being sent to muscles in large quantities and muscles are still receptive to taking up glucose and enzymes conducive to converting glucose to glycogen.

Pre, During, and Post Training/Competition Nutrition

• Pre-training/competition
  • Aim is to keep the athlete from feeling hungry before and during exercise, and maintain optimal levels of energy stores for the activity that follows.
• During training/competition
  • Acts as an alternative fuel source and maintains fluid lost throughout the exercise bout.
  • Note: Some evidence suggests that top-up fuelling is beneficial for events lasting longer than 30 minutes, as the body preferentially uses glucose from the blood due to it being a faster fuel source.
• Post-training/competition
  • Ingested within 30 mins for 100% restored glycogen in 24 hrs for best recovery.

Nutritional Recovery Strategies: Carbohydrates

• The body uses glycogen at rate of 1 gram per minute during moderate intensity exercise and slightly higher at higher intensities
• Carbohydrates should be consumed during exercises lasting longer than 1 hour to replace the glycogen used to produce energy (roughly 60 grams/hour)
• The effects of glycogen depletion can be minimized by not only refueling during the event, but also ensuring you have adequate stored before training or competition.
• Pre-exercise
  • Carbohydrate loading which involves a higher intake of carbohydrates for 4-5 days prior to competition in combination with tapering (maintain intensity, decrease duration)
• During exercise
  • Carbohydrates should be consumed regularly throughout the activity as this is an effective way to enhance endurance and performance.
  • High glycaemic index ranked foods are recommended to be consumed during exercise as these types of foods are rapidly digested and absorbed, and therefore are more readily available as an immediate energy source.
  • Could include Hypertonic sports drinks (both carbs and rehydration), Carb gels, sports bars, etc…
• Post-exercise
  • It is critical to replenish used glycogen as quickly as possible during recovery.
  • Muscles are able to store greater amounts of carbohydrates within the initial couple of hours after exercise.
    • High GI foods should be consumed as soon as possible to ensure rapid restoration of Muscle glycogen (first) and liver glycogen (second)
      • Post-event glycogen intake (high GI)
        • Within 1 hour - 55% restored in next 5 hours, 100% restored within 24hrs (1 day)
        • 1-2 hours - 100% restored within 24-48hrs (2 days)
        • 5+ hours - Up to 5 days

Hydration Strategies

• Post exercise hydration should aim to reverse fluid loss throughout training/competition
• Athletes rarely have just water as a sports drink will aid a faster recovery
• General guidelines:
  • Consume approximately 200–600 millilitres of fluid prior to their event
  • Strive to replace approximately 500–1000 millilitres of fluid per hour during the actual event
  • Begin drinking early in exercise and consume small volumes (200–300 millilitres) every 15–20 minutes if possible.
• A fluid volume equal to 150% of the fluid deficit should be consumed within 2-4 hours after exercise to completely rehydrate the body
• Water
  • Rehydrates lost fluids due to sweating during exercise.
  • Adequate rehydration fluid for activities less than 1 hr duration
• Sports drinks
  • Rehydrates
  • CHO
  • Electrolytes
  • Encourages thirst
  • More Palatable (so less chance of dehydration)
  • Greater absorption than water
  • Decrease urine loss

Nutritional Recovery Strategies: Protein

• Protein has several important functions in the body. These include:
  • Muscle construction and repair
  • Promoting glycogen resynthesis
  • Playing an important role in the immune system
  • Facilitating the transmission of nerve impulses throughout the nervous system
  • Preventing sports anaemia (low iron) by promoting an increased synthesis of haemoglobin, myoglobin and oxidative enzymes.
• Protein is an important part of an athlete’s diet as it plays a key role in post-exercise recovery and repair.
• Nutritionists recommend that protein contributes up to 15 per cent of total daily food intake; however, strength and endurance athletes may require additional volume of protein for growth of muscle tissue

Glycaemic Index (GI)

• The glycaemic index refers to a scale that ranks carbohydrates by how much they raise blood-glucose levels over a two-hour period compared with pure glucose.
• Foods are ranked from 0 to 100.
• Foods that have a high glycaemic index (70 and above) are digested quickly, resulting in a rapid and high increase in blood-glucose levels.
• Foods with a low glycaemic index (55 and less) are digested more slowly, resulting in a more gradual and less rapid rise in blood-glucose levels

Protein Consumption for Muscle Repair

• To repair and build muscles, athletes must refuel with high-protein foods immediately after exercise, especially after resistance training.
• Recommended to consume 30-40 grams of protein that includes 3-4 grams of leucine per serving to increase protein synthesis.
• Whey is an optimal post-workout protein due to its amino acid composition.
• Athletes should also consume protein regularly throughout the day after training to stimulate protein synthesis for up to 48 hours
• Post workout shakes as they can combine carbohydrates, protein and also help rehydrate
• Protein is optimally absorbed 30-60 mins after training or competition. This is because there has been micro-trauma at the muscles, so they are more susceptible to uptake protein for repair and growth

Combining Carbohydrates and Protein

• Combining is optimal as consuming both CHO and protein means muscle construction and repair and greater promotion og glycogen resynthesis.
• A carb/protein snack provides an excellent combination and can include snacks as;
  • Yoghurt and cereal bar or banana
  • Sports protein bar
  • Liquid meal supplement
  • Cereal and milk
  • Cheese and tuna sandwich
• Only having a small amount of protein post-exercise is required to increase muscle protein synthesis
• Athletes aiming at increasing muscle mass benefit more from pre-work out snacks
• Foods containing protein should be consumed at least 45-60mins before exercise to allow for digestion and absorption
• Real foods will allow for a more sustained release which will aid repair over a longer period of time