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Many runners feel that soaking their legs in a cold water bath after a long or hard workout helps with recovery by reducing post-run soreness. One theory behind this chilling treatment is that the reduction in skeletal muscle blood flow may help reduce swelling and inflammation. Previous studies have shown that cold water immersion for 10 minutes in 8 degree C (47 degree F) water results in about a 50% reduction in femoral artery blood flow for up to 30 minutes. Of concern however, is that the reduced blood flow may interfere with the muscle's ability to replenish supplies of glycogen which were depleted in the exercise bout. Since the first 30 minutes after an exercise bout are a prime time for glycogen re-synthesis to take place, this is a valid concern for those who do the post-run ice bath.

A recent study published in Medicine and Science in Sports and Exercise (Med. Sci. Sports Exerc., Vol. 45, No. 6, pp. 1174-1181, 2013) shed some light on this topic. Dr. Warren Gregson and his colleagues at the Research Institute for Sport and Exercise Sciences in Liverpool England studied 9 recreationally active subjects (all males) to determine how well they were able to replenish muscle glycogen after an exhaustive exercise bout. Subjects first depleted their stored glycogen with an exhaustive bout of intermittent cycling followed by a relatively low carbohydrate meal (<50g). The next morning they returned to the lab in a fasting state to perform a continuous bout of cycling to the point of exhaustion and this was followed by either 10 minutes of resting at room temperature (68 degrees F) or 10 minutes of lower extremity immersion in cold water (8 degrees C, 47 degrees F). Both the control and cold water immersion groups continued their recovery in a seated position for 4 more hours. The subjects muscle glycogen content was measured via biopsy at the end of the exercise bout, and 1, 2, and 4 hours later. Following the initial 10 minute recovery or cold water immersion, subjects were given carbohydrate at a rate of .6mg/kg body weight per hour. Although this rate of carbohydrate replacement would be considered sub optimal by many, it is likely similar to what most athletes consume on their own.

Not surprisingly, the researchers discovered that skin temperature as well as muscle temperature at 1, 2, and 3 cm depth was much lower in the cold-water immersion group than the control group, not only immediately but throughout the 4-hour recovery period. The authors noted "nevertheless, despite creating conditions that could compromise glycogen re-synthesis (i.e. reduced blood flow and low carbohydrate availability) we observed cold water immersion to have no detrimental effect on glycogen re-synthesis." Post-exercise muscle glycogen content progressively increased throughout the recovery period and was not different between the two groups.

So for those of you who find the post-run ice bath an appealing proposition, there's no reason to believe that you're interfering with your body's ability to replenish its skeletal muscle glycogen stores.

Feel free to chill-out if you like!

(Med. Sci. Sports Exerc., Vol. 45, No. 6, pp. 1174-1181, 2013)