Carbohydrate Consumption During Recovery from Exercise | Body ...

A significant proportion of the recovery from prolonged, moderate- to high-intensity
exercise is the replacement of the body?s stores of carbohydrate. Adequate glycogen
replacement following exercise depends upon the provision of exogenous carbohydrate.
In the event that carbohydrate is not consumed following exercise, the rate of
muscle glycogen synthesis is rather low, and assumes a rate of 7-12 mmol?kg?1dw?h?1,
with much higher rates (20?50 mmol?kg?1dw?h?1) occurring when carbohydrate is
provided in the correct time frame and sufficient amounts.

Carbohydrate intakes are typically expressed as grams of carbohydrate consumed
per kilogram of body weight per hour (g?kg?1?h?1). Provided that sufficient carbohydrate
is consumed, complete restoration of glycogen stores within 24 h has been
shown. Such a time frame is adequate for most individuals who do not regularly
fully tax their glycogen stores, especially when combined with the fact that several
meals will be consumed within this period. However, maximizing glycogen synthesis
takes on greater importance for athletes who significantly deplete their glycogen
stores on consecutive days of training or, as is very common, perform more than one
training session per day.

There appears to be a rapid and a slow phase of glycogen synthesis following
exercise-induced glycogen depletion. An initial rapid period (30?60 min) is characterized
by an insulin-independent translocation of glucose transporters (GLUT-4),
with a more extended period (up to 48 h) characterized by an insulin-dependent phase
of glycogen synthesis at a slower rate.

Resynthesis of glycogen following exercise isthus heavily dependent on the timing and amount of carbohydrate consumed. Withholding provision of carbohydrate results in significantly lower levels of
muscle glycogen synthesis. Glycogen synthesis rates are 45% lower when post-exercise
carbohydrate ingestion is delayed by 2 h. A delay in administration reduces
the amount of glucose that can enter the cell and subsequently be incorporated into glycogen. Thus, immediate (within 30 min of completion of exercise) consumption
of carbohydrate is necessary to ensure adequate glycogen synthesis.

Provision of a sufficient amount of carbohydrate is important in order to maximize
glycogen synthesis rates. The highest rates of glycogen synthesis are observed
when carbohydrate is provided immediately after exercise and at frequent (every
15?30 min) intervals in amounts sufficient to provide 1.2 g?kg?1?h?1.

Providing this same hourly amount less frequently results in slower glycogen synthesis. Supplying
more than 1.2 g?kg?1?h?1does not seem to result in higher glycogen synthesis rates.
Research has also focused on the addition of amino acids or protein to the carbohydrate
in attempts to further stimulate glycogen synthesis, perhaps by further elevating
insulin levels or providing an additional gluconeogenic substrate. Increased
glycogen synthesis rates have been observed when amino acids are added to moderate
amounts of carbohydrate (0.8 g?kg?1?h?1).

Jentjens and colleagues investigated
the addition of amino acids to a drink containing 0.8 or 1.2 g?kg?1?h?1 carbohydrate
and found that the addition of amino acids was beneficial only in the group receiving
the lower amount of carbohydrate. Therefore, the presence of protein or amino acids
in post-exercise supplements does not appear to be necessary as long as sufficient
(1.2 g?kg?1?h?1) amounts of carbohydrate are present, although the addition of protein
or amino acids may possibly assist with muscular growth and repair.

Endurance-trained individuals possess significantly higher rates of glycogen synthesis.
For example, one study determined that trained cyclists demonstrated glycogen
synthesis rates over two times higher than untrained cyclists. Muscle GLUT-4 content
was also three times higher in the trained individuals. Further research has illustrated
that just 10 weeks of training in previously untrained individuals resulted in significantly
greater muscle glycogen synthesis rates and increased levels of GLUT-4.

The magnitude of glycogen depletion plays a very important role in its subsequent
synthesis. Glycogen inhibits its own formation, and it appears that the absolute
amount of glycogen remaining in the muscle (and not the relative percentage that
has been depleted) strongly controls the rate of glycogen synthesis. Thus, it is the
glycogen concentration remaining in the muscle that determines its subsequent rate
of synthesis.

The type of prior exercise can affect the degree of subsequent glycogen synthesis.
Activities that result in significant amounts of exercise-induced muscle injury (such
as downhill running or prolonged exercise) have been shown to reduce glycogen synthesis
rates by up to 25%, even when large amounts of carbohydrate are ingested.76
Consumption of CHO in the post-exercise period is therefore essential to ensure
high rates of glycogen re-synthesis. Consumption of carbohydrate should commence
immediately after exercise, and should be consumed at the rate of 1.2 g?kg?1?h?1 for
4?6 h in order to maintain maximum glycogen synthesis rates.

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Source: http://mybodyhealth.net/carbohydrate-consumption-during-recovery-from-exercise/

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