HLTH2015 - Principles of Physical Conditioning: Fatigue, Physiology of Training, and Environmental Extremes

Training Principles

  • Training philosophy is crucial.
  • Principles, not formulas, are key to successful training.

Base Training Principles

  • Why train? Stress leads to adaptation.

Basis for Training

  • Achieved by the S.A.I.D. principle: Specific Adaptation to Imposed Demands.
  • Athletes must be subjected to workloads to which they are unaccustomed.
  • Athletes must be able to adapt and adjust to workloads imposed by training.
  • No adaptation = no survival!

Adaptation to Chronic Exercise

  • Requires a specific stress-evoked response.
  • Mobilization of the body’s energy reserves.
  • Mobilization of enzyme proteins.
  • Mobilization of the body’s tissue resynthesis and defense mechanisms.

Adaptation - Training Load and Performance

  • Application of correct training load is imperative.
  • Increasing stimulus (load) leads to adaptation and performance improvement.
  • Lack of stimulus results in a plateau and lack of improvement.
  • Excessive stimulus leads to maladaptation and decrease in performance.

Key Training Principles

  • Specificity.
  • Overload.
  • Progression.
  • Individuality.

Specificity in Detail

  • Energy systems.
  • Neuromuscular.
  • Joint angle.
  • Velocity.
  • Muscle groups.
  • Strength/Resistance Training vs. “Conditioning”/Continuous training.
  • Specificity does not mean only completing the specific movements in a given sport.

Athlete Needs Analysis: 3 Key Questions

  • The individual, the athlete.
  • The event or goal.
  • The time available to achieve the goal.

The Individual

  • What are the athletes' characteristics?
    • Training history status.
    • Fitness screening results/comparison.
    • Physiology (fitness testing): Aerobic, anaerobic, power, etc.
    • Pattern of fatigue.
    • Biomechanics (movement screen), injuries, etc.
    • Psychology (motivation).

The Event or Goal

  • Components of Fitness required.
  • Key movement patterns.
  • Movement speed.
  • Types of contraction.
  • Muscles used.
  • Common injuries.

Time Available

  • Determines:
    • How much improvement is possible.
    • How much training is required.
    • Training progression/periodization/intensity distribution.

Training Load

  • Intensity.
  • Volume.
  • Must be progressive.

Overload & Progression

  • Overload: attempting to induce through a training session.
  • Progression: attempting to manage through training session.

Managing Stress & Fatigue

  • What are the keys to managing Stress & Fatigue?

Individuality

  • Training response.
  • Genetic ceiling.
  • Ability to adapt.
  • Ability to recover.

Other Principles

  • Diminishing returns.
  • Reversibility.
  • Maintenance.

Adaption, Stimulus, and Recovery

  • For adaptation, stimulus (overload, fatigue) must occur.
  • To adapt, recovery (from overload, fatigue) must occur.

Sports Science and Fatigue Definitions

  • Sports Science is multidisciplinary which has resulted in different definitions and explanations of fatigue
  • Defn = “The loss of the ability to sustain work output” (R. Tucker) or
  • “The conscious awareness of changes in subconscious homeostatic control systems” (St Clair Gibson, 2003)
    • Physiological
    • Biochemical
    • Biomechanical
    • Psychological
    • Neurological

Sites of Fatigue

  • Muscle in vivo
    • Advantages: All physiological mechanisms present, fatigue can be central or peripheral, all types of fatigue can be studied, stimulation patterns appropriate for fiber types and stage of fatigue
    • Disadvantages: Mixture of fiber types, complex activation patterns, produces correlative data; hard to identify mechanisms, experimental interventions very limited
  • Isolated muscle
    • Advantages: Central fatigue eliminated, dissection simple
    • Disadvantages: Mixture of fiber types, inevitable extracellular gradients of O<em>2O<em>2, CO</em>2CO</em>2, K+K^+, lactic acid, mechanisms of fatigue biased by presence of extracellular gradients, drugs cannot be applied rapidly because of diffusion gradients
  • Isolated single fiber
    • Advantages: Only one fiber type present, force and other changes (ionic, metabolic) can be unequivocally correlated, fluorescent measurements of ions, metabolites, membrane potential, etc. possible, easy and rapid application of extracellular drugs, ions, metabolites, etc.
    • Disadvantages: Dissection difficult, environment different to in vivo, K accumulation and other in vivo changes absent, prone to damage at physiological temperatures, small size makes analysis of metabolites difficult
  • Skinned fiber
    • Advantages: Precise solutions can be applied, possible to study myofibrillar properties, SR release and uptake, AP/Ca² release coupling, metabolic and ionic changes associated with fatigue can be studied in isolation
    • Disadvantages: Relevance to fatigue can be questionable, may lose important intracellular constituents, relevant metabolites to study must be identified in other systems

Task Dependency

  • Not all fatigue is the same.
    • Open vs. Closed Loop Exercise.
    • Prolonged vs. High Int/Short Duration.
    • Contraction type (Conc. v Ecc.; Isometric vs. Isotonic).
    • Mode: run vs. cycle vs. row vs. throw etc.

What is Maximal?

  • Is maximal really obtainable?
  • Max in vivo muscle contraction < max. in vitro muscle contractions.
  • Pacing / teleoanticipation evident in so-called maximal and supramaximal exercise tasks.
  • Maximal ‘effort’ is an entirely different concept.

Models of Fatigue

  • Linear vs. Complex models of fatigue.

Linear Fatigue

  • Peripheral fatigue theory, accumulation/depletion models.
  • Catastrophic Failure.

Proposed Models of Fatigue

  • CV / Anaerobic Model
  • Energy Supply / Depletion Model
  • Neuromuscular Model
  • Biomechanical Model
  • Thermoregulatory Model
  • Psychological Model
  • Anticipatory regulation / Complex Systems Model

CV / Anaerobic Model

  • Performance limited by:
    • Ability of the CV system to supply oxygenated blood to the muscles.
    • Ability of the CV system to remove metabolites.
CV / ANAEROBIC FATIGUE
  • Cardiac Output Q=HR x SVQ = HR \, x \, SV
    • ↓Q↓Q … ↓↓ muscle oxygenation
    • a-v O2O_2 diff did not reach max at the point of fatigue; therefore, Q is not the sole cause of fatigue (Gonzalez-Alonso & Calbert, 2003)
  • Red Blood Cells
    • Altitude, EPO & Blood doping found to ↑↑ RBC count ↑↑ Cycling performance (Chapman, 2014) (Hanin & Gore, 2001)
  • Muscle Blood Flow
    • -ve linear relationship between muscle blood flow and power output (Saltin et al, 1998)
  • Oxygen Uptake
    • Mitochondria size and density, Myoglobin capacity, Aerobic enzyme activity (Hoopler & Fluck, 2003)
    • Capillarisation (Pringle et al., 2003)
  • Lac & H+H^+ Removal
    • AT occurs at a higher % of VO2MAXVO_{2MAX} among trained (Lucia et al. 2003)
    • Lac production-removal imbalance causes:
      • ↓↓ intramuscular pH
      • ↓↓ enzyme activity (PFK) - but perhaps not in vivo
      • ↓↓ Efficiency of NADH shuttle
      • ↓↓ myoglobin O2O_2 capacity
      • ↑↑ pain receptor activity?
    • But… Lactate conc is relatively low following endurance performance.

Energy Supply / Depletion Model

  • Fatigue due to:
    • Inadequate supply of ATP to the muscle.
    • Inadequate depletion of endogenous substrates.
ENERGY SUPPLY / DEPLETION
  • McCardle’s Disease
    • Metabolic myopathy affects 1/100K
    • ↓↓Capacity to store glycogen
    • Weakness & pain after exercise
    • Suggests [glycogen] causes fatigue
  • ATP Production
    • Failure to supply ATP via various metabolic pathways
    • Glycolysis & lipolysis (Shulman & Rothman, 2001)
  • Depletion vs. Supply
    • Depletion assumes fatigue is a direct rather than an indirect result of:
      • ↓↓Muscle/liver glycogen
      • ↓↓Blood glucose
      • ↓↓Phosphocreatine
  • Rate of Glucose Oxidation
    • Since muscle fatigue is not solely due to the availability of Glucose or ATP, some have concluded that the rate of muscle glucose oxidation is more important (Noakes et al. 2000) + See Rauch 2005 later in this lecture.
    • But…. Intramuscular ATP never below 40% even at fatigue (Green, 1997)
    • But… E ”value” of ATP as [P i][P \, _i] iCa2+ regulation at -50% [ATP] Possibly leading to cell death (in Grassi 2015) Is [ATP] an afferent signal?
    • Depletion vs. Supply
    • But… 60% & 86% ↓↓ in gastroc glycogen depletion after 90- 180 min running among rats. (Gigli & Bussman, 2002)
    • Not fully depleted so cannot be the sole cause of fatigue.

Thermoregulatory Model

  • Fatigue due to…
    • Reaching a critical core body temperature
    • ↑ Core, muscle, and skin temp places demands on other physiological systems/models…
    • CV, anaerobic, energetics, psychological
THERMOREG
  • Model
    • Core body temp = heat production (muscle metabolism) – heat removal (convection, conduction, radiation, evaporation).
    • ↑↑Environmental temp & hyperthermia are known to have –ve effect on performance
    • ↑3°C↑ 3°C may account for ~300ml/min ↑↑ VO2VO_2
    • However, this hasn’t consistently been observed in humans
  • Periph. Thermoregulation
    • Sweating and dissipation of heat have ↑↑CV demand due to supplying skin as well as muscles with blood (Nybo et al., 2001).
    • Skin flow plateaus, but core temp continues to rise during exercise placing extra CV demand (Nielsen et al., (1997)
    • Fatigue is related to the extra CV demand imposed by periph thermoregulatory changes
  • Central Thermoregulation
    • Exhaustion when cycling in heat occurred at 39.5°C (Nielson et al., 1993)
    • But… Tucker et al., 2004 saw the highest power when core body temp was greatest (39°C). core temp is not the sole cause of fatigue. Anticipation? Population?

Biomechanical Model

  • Fatigue due to a reduction in mechanical efficiency and economy which provokes…
    • ↑↑ CV system demand (CV model)
    • ↑↑ Energy consumption (Energy S/D model)
    • ↑↑ Metabolite production (Anaerobic model)
    • ↑↑ Core temperature (Thermoregulatory model)
BIOMECH. EFFICIENCY OF MOTION
  • Muscle Fibre Composition
  • Intermusc. Coordn. (Stretch/Shortening)
  • Muscle Activation Rate (e.g. cadence)
  • Energy consumption / heat generation
  • O2O_2 consumption and uptake
  • Accumulation of metabolite
  • % Type I / II recruitment pattern

Neuromuscular Model

  • Sites of Central Fatigue

  • Central Fatigue

    • is anything upstream of the anterior horn cell

  • Sites of Peripheral Fatigue

  • Peripheral Fatigue

Summary: Neuromuscular Model

  • Fatigue due to:
    • Inhibition of the neuromuscular pathway.
    • Reduction in central neural drive.
    • Reduction in responsiveness of the muscle to action potentials.
    • Failure of excitation-contraction coupling mechanisms.
    • “Functions involved in muscle excitation, recruitment, and contraction are what limit performance.” (Noakes, 2000)
NEUROMUSCULAR MODEL: MUSCLE FIBRE CONTRACTION
  • An action potential arrives at the neuromuscular junction
  • ACh is released, binds to receptors, and opens sodium ion channels, leading to an action potential in the sarcolemma
  • Action potential travels along the T-tubules
  • Thick and thin filament interaction leads to muscle contraction
  • Muscle shortens and produces tension
  • Thick and thin filament interaction relaxes
  • Calcium is resorbed, beginning relaxation cycle; ATP is required
  • Muscle lengthens and relaxes

Psychological Model

  • Fatigue due to psychological factors which…
    • ↓↓ Central activation & motivation.
    • ↑↑ Perceived exertion & fatigue.
PSYCHOL. MODEL
  • Rating of Perceived Exertion
    • The way peripheral sensations associated with exercise are perceived.
    • RPE scale - As task nears completion RPE rise with skin temp & HR (Amada-da- silva, 2004)
  • Emotion & Drive
    • Fatigue is an emotion or a ‘subjective feeling’ state dependent upon physiological and situational environmental factors. (St Clair Gibson et al, 2003)
    • Feelings of fatigue may be related to motivation, anxiety, arousal, and confidence.
  • Consciousness
    • We are not consciously aware of specific physiological functions e.g., muscle blood flow, blood pressure, glycogen depletion.
    • RPE is conscious awareness based on many afferent sensations.
  • Information Processing
    • Pacing strategies determined by information processing between the brain and physiological systems.
    • Knowledge of distance or time during an event provides crucial input to monitor and determine the overall pacing strategy (St Clair Gibson et al, 2006).
      • internal clock
      • endpoint knowledge
      • feedback

What’s Wrong with the Peripheral Fatigue Theory?

  • Peripheral (linear) fatigue models predict that exercise always terminates at an absolute, temporarily irreversible endpoint.
  • Linear system (power output a direct consequence of input variable e.g. [Bla] [Glucose]
  • Therefore, fatigue and the sensation of fatigue must coincide with the peripheral physiological input variable.
  • Often they often do not…

Complex Systems of Fatigue

  • Complex Systems & Homeostasis… Noakes, 2011.
  • Known as:
    • Central governor theory (CGT).
    • Teleoanticipation.
    • Anticipatory regulation.

Anticipatory Regulation

  • Basic premise is that:
    • Fatigue occurs not as a result of the disrupted homeostasis but to prevent it.
  • Attempts to answer the questions of how fatigue manifests e.g.
    • “How do you know when to slow down?”
    • “How is pacing achieved?”

Teleoanticipatory Governor Model

  • Prior Experience
  • Interpretation

Korsakov’s Syndrome

  • Sufferer’s are unable to form new memories, and must approach every situation as if they had just seen it for the first time.

How Does It Work?

  • Empirical & Theoretical Context

Anticipatory Regulation

  • Initial pace during the first moments (Feed-Forward).
  • Subsequent Pacing (Teleoanticipation).
    1. Knowledge of Endpoint
    2. Previous Experience
    3. Afferent Feedback
    4. Perceptions of and beliefs about the present and likely future

Previous Experiences

  • Previous experience and memory:
  • Exactness / Relevance

Anticipatory Regulation EFFERENT CONTROL

  • Previous Experience AFFERENT FEEDBACK
    1. Previous experience and memory:
      • Exactness / Relevance
      • Distortion / Accuracy
      • “Rose colored glasses”
    2. Pacing decisions are likely to be influenced by memory as well as perceptual experience - RPE.
    3. Memory/ Previous experience will affect the way we perceive and interpret afferent sensations. This provides a basis for ‘expected outcomes’.

Theoretical Context

  • EXOGENOUS REFERENCE SIGNALS
  • ENDOGENOUS REFERENCE SIGNALS

Evidence for Anticipatory Regulation

  • Fluctuations in power output (Tucker et al., 2006) and heart rate during exercise (Palmer et al., 1994) are more representative of a homeostatic system of control rather than a linear model.
  • Homeostatic regulation by the CNS could account for a continually changing pattern of muscle recruitment during exercise.
  • The presence of homeostasis in all organ functions helps support the model.

Integration of Signals

  • Homeostatic control is based on a complex ‘black box’ calculation (Ulmer, 1996) derived from the integration of multiple afferent signals (Lambert et al., 2005) e.g.
  • Rauch et al. (2005) signalling role of muscle glycogen concentration during prolonged cycling.

Models of Fatigue

  • The actual mechanism of fatigue is likely to lie somewhere between the peripheral theory and anticipatory regulation.
  • May also be situation specific.
  • And, therefore, complex.

Complex Systems Model

  • Fatigue is due to anticipatory regulation maintaining homeostasis through…
    • Integration of peripheral afferent signals and exogenous reference signals.
    • Determination of efferent muscular control.
    • Concepts of teleoanticipation, pacing, and perceived exertion.
    • Includes, and attempts to differentiate between, conscious and subconscious processes.

Summary

  • The brain is likely to govern any exercise effort receiving information from a variety of sources.
    • Peripheral and Central origin.
  • Mechanisms of fatigue may be:
    • Cardiovascular/ Anaerobic
    • Energy Supply/ depletion (or rate thereof)
    • Neuromuscular
    • Biomechanical
    • Psychological

Summary

  • Performance is determined by:
    • Continual afferent feedback.
    • Previous experience.
    • Expectations.
    • Beliefs and.
    • Interpretation.

Summary

  • Key principles of Physical conditioning
    • Specificity
    • Overload
    • Progression
    • Individuality
  • Good performance is about managing fatigue
  • Fatigue is a complex phenomenon.