Peripheral Fatigue - Max Exercise

Question 1

What is fatigue at maximal exercise?

Answer 1

• Inability to maintain a given power/work output

Question 2

Soderland et al (1993)

Answer 2

• Maximal electrically evoked isometric quadricep contractions
• 20 contractions
• 60% reduction in force production from 1-20 contractions

Question 3

Phosphocreatine hydrolysis

Answer 3

• Rapid reaction and resynthesis of ATP

- Maintain high rate of ATP turnover

Question 4

Glycolysis

Answer 4

• Breakdown of muscle glycogen
• Several more reactions (9) - 2 reactions produce ATP
• Produces lactate
• Ability to resynthesise ATP is lower due to more reactions

Question 5

What is the PCr reaction:

Answer 5

PCr + ADP + H+ (CK)= Cr + ATP

Question 6

PCr for subsequent bout of exercise - Trump et al (1996)

Answer 6

• Max intensity exercise to deplete PCr
• One group had a cuff on the leg to keep away re-synthesised PCr
• Following another max intensity sprint, cuff group produced significantly less work than control
• PCr plays a significant role in the subsequent bout of ATP

Question 7

How long before glycogen becomes depleted?

Answer 7

35-40 minutes

Question 8

Name the 2 ways that hydrogen ion accumulation happens:

Answer 8

1. • Hydrogen ion accumulation partly comes from glycolysis to convert lactate into pyruvate
2. • ATPase breaks down ATP to produce a hydrogen ion

Question 9

Spriet et al (1987)

Answer 9

• Strong correlation between increased lactate production and muscle acidosis
• However, the lactate accumulation doesn’t directly cause muscle acidosis, conversion of lactate to pyruvate causes the increased H+ which increases muscle acidosis

Question 10

Is muscle acidosis a limiting to max exercise performance?

Answer 10

• Normal muscle pH = 7.1 but reduced to around 6.4 during max intensity exercise
• In vitro -low pH limits phosphofructokinase (PFK) but not in Vivo unless <6.4
• PFK is a rate limiting step of glycolysis - therefore impair glycolysis can be impaired with increase muscle acidosis

Question 11

Hill et al (2007)

Answer 11

• Beta alanine increases carnosine (which buffers H+)
• 3.2-6.4g/day of BA increase carnosine by 40-60%
• 10% increase in muscle buffering capacity
• 20% increased force production during isometric contraction

Question 12

Cooke et al (1988)

Answer 12

• Increased Pi impairs velocity of muscle contraction in Vivo (impairs calcium handling)
• Hard to measure Vitro studies but we known that PCr rapidly depletes with exercise and coincides with fatigue, suggests Pi must accumulated and be associated with fatigue

Question 13

Calcium handling (Duke and Steele, 2001)

Answer 13

• Calcium release and reuptake by SR is essential of activation of muscle excitation-contraction coupling
• Stimulation of SR calcium release by caffeine can improve muscle force production, even with low pH
• Calcium uptake is an ATP dependant process, and PCr depletion can reduce SR uptake

Question 14

Extracellular potassium accumulation to cause fatigue

Answer 14

• Sodium-potassium pump is ATP dependant - when ATP is depleted we can’t pump K+ back into the cell
• Therefore, we get an extracellular potassium accumulation
• Force production is impaired due to reduced action potential

Question 15

Nielson et al (2003)

Answer 15

• Reduced extracellular K+ in trained vs untrained leg

Question 16

Nordsborg et al (2003)

Answer 16

• Prior arm exercise results in increase extracellular K+ in that leg
• Therefore impaired cycling performance after prior exercise due to increase extracellular K+