Cold water immersion cools muscle growth

When training athletes, resistance training should be executed with the same zeal and importance as skill and endurance training. However, this is rarely the case. Athletes tend to enjoy playing the sport the most and therefore gravitate toward drills and endurance play. Some find being stuck in the weight room boring and fail to see the payoff in performance. Others don’t want to suffer from delayed onset muscle soreness (DOMS) because they feel it negatively impacts performance.

Despite it being low on the list of favorite activities, athletes will begrudgingly troop to the gym and slog through a workout. To prevent DOMS many will take a dip in the cooling tub after resistance exercise. After all, they see their sports heroes do it all the time (see figure 1). But does icing improve outcomes?

Figure 1: Andy Murray posts photo in an ice bath

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Another practice that athletes seem to embrace with gusto is the post-workout protein shake. Since resistance training breaks down muscle as it stimulates building new muscle, after-exercise protein gives the body what it needs to repair and rebuild. Typical dosing for this is 20 grams of high-quality protein taken shortly after exercise.

Researchers in the Netherlands wanted to find out if cooling after resistance training was the best practice for muscle development⁽¹⁾. After all, if the athlete worked against adequate resistance and then ingested the required amount of needed protein, it would be a shame to stunt the desired muscle growth by unnecessarily cooling the tissues. They enrolled 12 recreationally active young men in a study and hypothesized that cooling muscles immediately after resistance exercises would decrease the uptake of available dietary protein by the muscle and thus lower the rates of muscle protein synthesis. They further hypothesized that the decrease in myofibril protein production would continue even after two weeks of resistance training if the cooling after exercise also continued.

The researchers performed a rigorous protocol that involved an infusion of an amino acid tracer at the onset, followed by a 45-minute lower-extremity exercise protocol.  Immediately after exercising, the subjects immersed one leg in water at 8ºC and the other in water at 30ºC for 20 minutes. The investigators then extracted muscle biopsies from the vastus lateralis of each leg before allowing the subject to ingest a protein-rich (20g) beverage, which also contained 45g of carbohydrates. Muscle biopsies were retaken after resting for two and then five hours.

The participants performed the same exercise routine, with resistance increased as needed to remain at about 80% of 1RM, for the next two weeks. They completed a total of seven training sessions. After each session, they performed the same cooling protocol on the same leg as at the first workout. The investigators again extracted muscle biopsies in the same way at the final session.

Muscle cooling on the rocks

They found that core temperature did not change significantly as a result of lower leg cooling. The skin temperature on the thigh of the leg in 8ºC water lowered significantly and remained so for about 3 hours after the cooling event. The actual muscle temperature of the cold water immersion leg was significantly lower than the other leg for about two hours after the treatment.

Blood work showed that the ingested protein was adequately available in the bloodstream for an appropriate amount of time after drinking the beverage. However, uptake of said protein was up to 26% lower in the muscles of the cooled leg than the control leg five hours after intake⁽¹⁾. Two weeks later, the myofibril production rate in the muscles of the leg immersed in cold water was still significantly lower than the control leg.

The study suggests that cooling lowers the temperature of the superficial and deep tissue of the leg, but also reduces the rate of uptake of dietary protein needed for muscle synthesis after resistance training. Whether due to an interruption of the chemical pathways or the restriction of vessels with accompanying decreased blood flow, is yet to be determined.

The study also recorded inflammatory markers in the muscles of both legs, noting that a reduction of inflammation is often the purpose of icing. Interestingly, not only was the cold water immersion no less effective in reducing signs of inflammation, the muscle of the cooled leg showed an increase in inflammatory markers immediately after immersion.

Practical implications

This study was conducted on a small, recreationally active population of men only. Therefore, extrapolation to other populations should be done with caution. That said, the research was meticulous and thorough in its execution of protocol and measurements, even trying to keep additional dietary protein similar by providing the subjects with the same dinner each night and requesting they keep a food diary.

The findings of this study call into question the ‘tried and true’ everyday actions and recommendations to athletes. There are two take-aways from this study that sports injury professionals should consider. The first is whether icing after a strength workout is beneficial. While it may ‘feel good’ to an athlete, the study shows that it inhibits the uptake of dietary protein needed to make desired strength gains. Therefore, perhaps the advice to athletes should be to wait to immerse in a cooling bath until at least five hours after protein ingestion.

This concept especially applies to injured athletes undergoing rehabilitation. Does the routine ice pack after a rehab workout stunt the desired muscle growth? Again, if the cooling is used to control pain and perceived or real inflammation, perhaps it should be applied at least five hours after exercising.

The second consideration is the importance of dietary protein for muscle synthesis. Do injured athletes understand the importance of continued post-workout protein? If not, they may not be maximizing the results from the rehab protocol. Encourage continued ingestion of 20g of high-quality protein after strength training, whether in the sports gym or the rehab clinic.

Reference

1. J Physiol. Accepted Author Manuscript. doi:10.1113/JP278996