Tuesday, September 3, 2013

High-Intensity, Sprint-Interval Training and Fitness

Fitness is a critical component of soccer performance. Studies show that during a match, players can cover anywhere from 5-8 miles. This requires them to be fit and have a tremendous aerobic capacity. However, the game also requires players to sprint, stop, start and jump – all anaerobic activities. Given this, what is the best way to improve fitness of a soccer team? How can players improve endurance capacity while increasing anaerobic power? Previously, we have talked about high-intensity interval or sprint-type training as a tool for increasing VO2max. In a recent research review, Danish investigators highlighted the physiological and performance changes that occur with this type of training. Their findings have a number of key implications for training footballers.


The investigators search the scientific literature and found 19 individual studies that matched their criteria of quality and consistency of training methods. In general, the training sessions included three to seven, 30 second “all out” sprints performed three times per week. The recovery interval between sprints two to five minutes. Most of the studies had subjects training on a stationary bicycle but others used running. The training programs lasted between two and eight weeks.

The various studies use some slightly different terms when describing their programs. Some used the term “sprint-interval” training (SIT) is used. Others use “high-intensity interval” (HIIT or HIT). For the most part, these refer to the same type of training – short, high intensity exercise bouts separated by a full (or almost full) recovery interval.

When all of the studies were taken into account, high-intensity SIT improves fitness or VO2max (maximal oxygen consumption) by 4-13%. When SIT training is compared to traditional endurance training (long, slow distance runs), the improvements in fitness were nearly similar. This means that similar gains in fitness could be accomplished with SIT training sessions that last about one-third of the time required by traditional training.

A unique adaptation SIT training is small improvements in running economy (typically does not occur the traditional training). This means that players use slightly less energy at a given exercise intensity. This change may be linked to better, more efficient running mechanics. When considering the course of a 90-minute match, any small energy savings could benefit the player during the latter stages.

Anaerobic performance is also increased following SIT. Power output during sprint-type activity was improved, as is the resistance to short-term fatigue. On the field, this should translate into improved repeated sprint ability. These changes are also somewhat unique when compared to traditional endurance training. For example, long duration running does not appreciably affect short-term high-intensity exercise performance.

Underlying these changes in performance are several key physiological and biochemical adaptations. Cardiovascular function is improved following training resulting in better oxygen delivery to the exercising muscles. Within the muscle, the capacity to utilize oxygen to produce energy is enhanced. Also, the amount of glycogen stored within the muscle is increased. What makes SIT training effective is that these changes in muscle metabolism occur in both fast and slow muscle. During traditional endurance training, fast fibers are not recruited or “trained”. Thus, adaptations are seen in slow fibers only. All of these changes result in greater aerobic metabolism and decreased reliance on anaerobic metabolism during prolonged, high intensity exercise.

What are the implications for training a soccer team? There are several. First, high-intensity SIT training improves both aerobic and anaerobic fitness. Both VO2max and short-term power output are increased, two critical components of performance on the field. Second, coaches are often limited in terms of the amount to time they can spend with their players. Working on technical and tactical aspects of the team can leave very little time for fitness training. A typical SIT session might involve five, 30-second sprints (~200m) with a 5 minute recovery. All totaled, this session would last 15 minutes. Compared to a long training run (30-40 min), a significant amount of training time can be saved.

Last year, we reviewed a study where SIT was used as part of an off-season training program with women collegiate players (LINK). The study found that both SIT and endurance running improved fitness to similar extents. However, the SIT program required about half of the training time.

So, a bigger bang for the training buck? SIT allows teams to improve fitness with less time invested in training – leaving more time to improve other aspects of their game.

References

Sloth M, Sloth D, Overgaard K, Dalgas U (2013) Effects of sprint interval training on VO2max and aerobic exercise performance: A systematic review and meta-analysis. Scandinavian Journal of Medicine and Science in Sports, doi:10.1111/sms.12092