21. Physiological determinants of exercise performance Flashcards
What factors influence exercise and sports performance?
- Physiological
- Nutritional
- Environmental
- Biomechanical
- Psychological
What are the potential sites of fatigue?
- excitatory input to motor cortex
- excitatory drive to lower motoneuron
- motoneuron excitability
- neuromuscular transmission
- sarcolemma excitability
- excitation-contraction coupling
- contractile mechanism
- metabolic energy supply
What is the metabolic feedback from skeletal muscle?
Feedback from muscle to the brain via type 3 & 4 afferents.
In experiment involving fentanyl, feedback was blocked, but not motor nerves, showing that the metabolic feedback to the brain existed and the lack of it meant:
-increased capillary blood lactate
-higher power output initially, but then a bigger decrease as the muscle rapidly fatigues
(still has end spurt though)
List the potential factors in fatigue.
"Central fatigue" (CNS) Ionic disturbances (Na+, K+) Impaired excitation-contraction coupling Substrate depletion (ATP, PCr, CHO) Metabolic accumulation (Pi, H+, ROS) Fluid & electrolyte losses Hyperthermia Muscle damage
What are the essentials for sprint success?
Muscle mass to generate force & power
Fast twitch fibres
Neuromuscular recruitment
Fatigue resistance
Ability to generate & tolerate lactic acid (buffer capacity)
Fast reaction time
When would you have ~50/50 aerobic/anerobic oxidation?
Running ~1min.
> 1 min = increased aerobic oxidation
What are the fuels for sprinting?
Initially, heavy reliance on glycolytic and PCr ox. pathways, but gradually decreases as sprint duration increases .
Dietary creatine supplementation - what effects does it have on 2 successive bouts of 30s sprinting?
Increased ability to resynthesise Cr, and higher rate of ATP turnover means that you have greater power output —- greater total work output
In Bout 2, both control & Cr subjects showed lower total work output (evidence of fatigue), but Cr subjects’ total work output was still higher.
Muscle glycogen availability vs. high intensity ex. performance
15 x 6s sprints = initially no difference b/w controls and increased muscle glycogen subjects,
but then greater muscle glycogen subjects are better able to maintain their power output as the control group lose their ability to maintain PO (decreased muscle glycogen levels)
Time to fatigue much lower in low glycogen, higher when glycogen levels elevated.
What happens when the muscle is acidic?
When muscle is acidic, it protects the Cl- conductance and maintains excitability.
Induced alkalosis
Facilitates removal of H+ ions
Takes longer to reach acidic conditions with alkalosis trial, may be advantageous in 400m+ events
*Doesn’t change the muscle memb pH though as it is impermeable to bicarbonate
Essentials for endurance success
High VO2 max (>70ml/kg/min)
Ability to maintain high % VO2max (“fractional utilisation”)
High PO at LT - muscle oxidative capacity
Fatigue resistance
Efficient/economical technique
Ability to oxidise fat at high POs
What are the physiological determinants of endurance performance?
muscle capillary density SV max HR Hb-content aerobic enzyme activity distribution of PO
% ST fibres
anthropometry & elasticity
Which is a better predictor of endurance performance: cytochrome oxidase or VO2 max?
Cytochrome oxidase (muscle ox. capacity) - 81% of the variance in endurance time can be accounted for by the diff. in cytochrome ox.
49% with VO2 max.
Lactate threshold & muscle oxidative capacity relationship?
Strong correlation!
What is the r/ship between %VO2 max at LT & time to fatigue?
And b/w glycogen usage and %VO2 max at LT?
Well trained cyclists all had similar absolute VO2 max
Higher LT = greater time to fatigue, less glycogen usage due to one or both:
- better ability to distribute demands on active muscle(s)
- use of less glycogen
What is the effect of glycogen loading?
=increases glycogen availability
hence increases time to fatigue
CHO ingestion improves performance by…?
- prevents fall in blood glucose
- maintains muscle CHO ox. & brain glucose supply
- reduces perception of fatigue
- increases exercise time to fatigue & PO
How does hydration affect your exercise endurance performance?
Hydration = better performance
Dehydration = impaired performance
*affects your maximal CO & SV
What is the r/ship of fluid & CHO ingestion in terms of performance?
They both independently improve performance (possibly by different mechanisms), but their effects are additive.
What are the strategies to enhance fatigue resistance?
Training - physical, technical, mental
Nutrition - CHO, fluid, protein
Heat acclimatisation/cooling
Drugs/supplements/gene doping?
