Metabolism drugs in sport (caffeine)

Question 1

timeline of caffeine in doping

Answer 1

in 1984 having urinary [caffeine] above 15ug/ml was banned. the next year the threshold was reduced to 12

WADA added caffeine at 12ug/ml to its banned list in 2000. in 2004 it was removed and placed on the monitoring list.

Question 2

caffeine and metabolism

Answer 2

see increased [FFA], mostly just at rest. little evidence of caffeine affecting fat oxidation during exercise.
no change to respiratory exchange ratio.

As such it is inconclusive that caffeine ingestion spares muscle glycogen.

Data has suggested that caffeine lowers the threshold for exercise induced B-endorphin release however.

Caffeine increases the rate of muscle glycogen resynthesis during recovery when coadministered with carbs.

Question 3

Adenosine mechanism

Answer 3

inhibits A2A receptors which form a mutually antagonistic complex with D2 receptors. as such, antagonism of A2A increases catecholamine signalling.

The stimulation of the CNS from caffeine reduces pain, reduces perceived exertion, and delays muscle fatigue.

Question 4

Caffeine and glycogen resynthesis

Answer 4

Caffeine increases the rate of muscle glycogen resynthesis during recovery when coadministered with carbs.

Proposed to do this through AMPK. caffeine stimulates calcium-calmodulin-dependent kinases - increases AMPK activity. this stimulates GLUT-4 to increase transport of glucose into the muscles.

Question 4

Neuromuscular effects of caffeine

Answer 4

Caffeine acts at the sarcoplasmic reticulum. RyR1 receptors bind to calcium and increase the contraction of muscles.

Caffeine acts allosterically at the RyR1 potentially increasing binding sensitivity of calcium.