Wednesday, May 7, 2008

Is a Re-Warm-Up Needed Before the Second Period?

A previous post addressed the pre-match-warm up. It was noted that one of the goals of a warm-up is to increase muscle temperature which improves performance and lowers the risk of muscle injury. During the half-time period, muscle and core temperature decreases. Depending on the duration of the half-time, muscle temperature can return to near pre-warm-up levels. Interestingly, several studies clearly show that that performance and the intensity of play are reduced during the initial phase of the second half. Could this be due to the “cool-down” period of the half-time? Should players undergo a re-warm-up prior to the start of the second half?

Reduced performance at the start of the second period may be the result of not having a re-warm-up during the half-time interval. Most players spend 30-45 minutes warming-up prior to the start of a match. The main effect of the warm-up is to increase muscle temperature. Muscle temperature during the warm-up increases by about 5°F from ~98°F to near ~103°F and remains fairly consistent during the first period (core temperature rises to over 100°F but is well below the danger zone of 104-106°F). During a 15-minute half-time break, temperature declines towards normal and it isn’t until ~15 minutes into the second period that temperature returns to match levels. Thus, many players seem to spend the initial minutes of the second period re-warming-up.

Surprisingly, there is very little research focused on a strategy for preparing players to compete in the second half of a match. However, two recent studies indicate that a half-time warm-up may be beneficial during the first 15 minutes of the second period. These studies examined the effects of an active re-warm-up during the half-time interval on performance during the second period. In the first study, by Dr. Mohr at the University of Copenhagen, players participated in a 90-minute match which included a 15-minute half time. During the half-time, one group rested for the full 15 minutes while a second group spend the last 7 minutes of the intermission exercising at a moderate intensity. The researchers found that the players who exercised during half-time were able to start the second half with muscle temperatures near match levels. They also performed better on a spring test administered immediately before the start of the period. By the end of the match, sprint performances were similar for each group.

In the second study by Dr. Lovell at the University of Hull University (UK), subjects either rested during half-time, exercised during the final 8 minutes or used a warm bath to help maintain muscle temperature. Only the exercising group was able to maintain performance during the initial minutes of the second period. They argue that an active re-warm-up is needed to maintain muscle temperature rather than simply passively heating the muscle.

Based on these tow studies, it appears that some sort of active re-warm-up is needed during the half-time interval. A ~7-minute period of moderate exercise, either sprinting or continuous running, seems to be effective in re-warming the muscle and insuring that sprint performance at the start of the period is not adversely affected.

It is important to point out that the studies described here utilized a 15-minute half-time period. They were for the most part, directed towards matches that utilize a full half-time period (professional, college or high school matches). Many youth matches allow only a 5 minute period. While muscle temperature will decline quickly during recovery, the decreases will not be as great as those that occur during a 15-minute interval. Thus, a much shorter re-warm-up would be needed to re-increase muscle temperature and should include stretching and light sprints.

A final word of caution. When discussing temperature (even muscle temperature) and performance, it is very important to take into account the environmental conditions of the match. On hot, humid days, it is probably more important to hydrate and cool the athletes down during the intermission rather than focus on a re-warm-up. This is especially true for young players who have less developed thermoregulatory systems. The effects of heat illness and injury can be severe and certainly outweigh any importance of match performance. On hot days, it is best to allow players to passively recover in a shady area and drink a cool beverage. The most important consideration is avoiding and lowering the risk heat-related problems. At most, a re-warm-up should be short, including stretching and easy sprints.

While research concerning the benefits of a half-time re-warm-up is somewhat limited, there seems to be enough information to recommend. For matches where there is a 15-minute intermission, a short ~7 minute re-warm-up seems to prevent decreases in performance that occur at the start of the second period. For matches that include a shorter, say 5-minute half-time, the re-warm-up is probably less important, but a few minutes of stretching and sprinting might be beneficial. Above all, consideration should be given to the environmental temperature and inclusion of a re-warm-up should be weighed against the potential risk of heat-related problems.

References:

Mohr M, Krustrup P, Nybo L, Nielson JJ, Bangsbo J (2004) Muscle temperature and sprint performance during soccer matches – beneficial effect of re-warm-up at half-time. Scandinavian Journal of Medicine and Science in Sports. 14:156-162.

Lovell RJ, Kirke I, Siegler J, McNaughton LR, Greig MP (2007) Soccer half-time strategy influences thermoregulation and endurance performance. Journal of Sports Medicine and Physical Fitness, 47:263-269..