The effect of caffeine or protein co-ingestion with carbohydrate on post-exercise muscle glycogen synthesis rate

Muscle glycogen has been recognized as an important fuel source during
prolonged exercise. To optimize glycogen synthesis rates adequate amounts of
carbohydrate (CHO) should be ingested. Several studies have examined the amount
of carbohydrate that should be ingested to optimise post-exercise glycogen
synthesis. These studies revealed an ingestion rate of 1.0-1.2 g/kg/h to be
most effective. Elevated insulin levels may further increase glucose uptake and
glycogen synthase activity, the latter of which forms the major factor in
determining the rate of glycogen synthesis when substrate supply is adequate.
Several studies have attempted to increase post-exercise insulin levels by the
combined ingestion of carbohydrate, protein and leucine. Whether protein and
leucine co-ingestion in addition to a carbohydrate intake of 1.2 g/kg/h could
further accelerate post-exercise muscle glyocgen repletion remains to be
established.
Recently Pedersen et al. showed that the addition of caffeine to a CHO (1.0
g/kg/h) recovery drink increases the rate of muscle glycogen synthesis by 66%
compared with CHO ingestion only. However, other studies investigating the
effect of caffeine on muscle glycogen synthesis have shown variable results.
Therefore, the effect of caffeine co-ingestion with carbohydrate warrants
further investigation.

The aim of the present study is to investigate the effect of added
protein+leucine or caffeine to 1.2 g/kg/h CHO on the rate of post-exercise
muscle glycogen re-synthesis in healthy, recreational athletes.

Subjects will perform 3 randomized tests, each separated by at least one week.
During those tests subjects will first perform an intensive cycling protocol to
deplete their muscle glycogen stores. Thereafter, subjects will rest for 6
hours during which the will receive one of the 3 recovery drinks. The drinks
will be provided in a randomized order and will contain carbohydrates only, or
combined with protein hydrolysate and leucine, or caffeine. Muscle biopsies
will be taken within 15 min after exercise and after 6 h recovery to determine
muscle glycogen levels. Blood samples will be taken throughout the test for the
measurements of blood glucose and insulin levels.

The test starts with a intensive cycling exercise of approximately 90 min. to
deplete muscle glycogen levels. 15 min after cycling the first muscle biopsy
will be taken. Subsequently, subjects will recover for 6 hours during which
they will receive one of the test beverages every 30 min. A blood sample will
be drawn every 15 min for the first 90 min and every 30 min thereafter. After 6
hours a second muscle biopsy will be taken.

The risks involved in participating in this experiment are minimal. Insertion
of the catheters in a vein is comparable to a normal blood draw and the only
risk is of a small local hematoma. This is the same for the muscle biopsy. The
incision made for obtaining the muscle biopsy (performed by am experienced
physician) will heal completely. The test beverages are made from normal
nutritional ingredients and for this reason do not form any health risks.