Advantages of High-Intensity Interval Training
HiiT training can be beneficial in both an athletes off-season or training season. As the research below explains, it can also be a great economical way to stress the body and get just as much out of it as a training session that is 2-3x as long. Now, I am not endorsing that HIIT is the end all for training. Systematic long steady state endurance training is tantamount to good overall cardiovascular training, but interspersed HIIT sessions can be a boon to the metabolic system as well as general neurological development. Read below for a great summary of the benefits and research on Soccer players.
Soccer is a unique sport where the average player covers up to 7 miles per games by running forward, backward, and sideways. Intermittent sprints are quite frequent, with players performing them around every 90 seconds. Players may also change directions nearly 1,000 times a match. Whether it is walking, jogging, or sprinting, some type of movement is always occurring. Given that the length and intensity of movements are somewhat random, it is very difficult to make a fitness-training program that adequately mimics the physical demands that are required of a soccer match. Traditional methods of fitness training such as going on a long distance running do not mimic the physical demands of a match, and thus may not be the most effective training method for soccer players. A more progressive training regime that has been labeled as high-intensity interval training (HIIT) has become popular amongst athletes in order to increase their fitness capacity.
Many sports scientists have classified it as a “hybrid” sport, in reference to it requiring training of both the aerobic and anaerobic energy systems. Maximal oxygen consumption or VO2max is generally considered the best indicator of an athlete’s aerobic capacity and his/her ability perform exercise for long periods of time (cardiorespiratory endurance). Athletes that are considered “elite”, typically have a higher VO2max than those who are less competitive. Professional male players have VO2max values above 60 ml O2/kg.min, whereas female college players average in the mid 50’s. Because of the aerobic demands of the sport, a high VO2max gives a soccer player a distinct fitness advantage allow for a better performance on the field, especially during the later stages of the match.
HIIT is a program whereby an individual performs several intense, near maximal bursts of anaerobic activity lasting between 30 seconds and four minutes. These bouts are separated by fixed periods of less-intense activity, which might include light jogging, walking, or even complete rest. An example would be, an individual that runs a 150-200-meter sprint at maximal intensity, followed by a 2-minute recovery period of light jogging or walking. This is then repeated 4-6 times until the workout is completed. Does this type of training actually work? Does HIIT improve VO2max in soccer players?
Does HIIT Work?
A number of research studies have shown that HIIT increases aerobic capacity in untrained individuals. In addition, studies are emerging that show important effects on trained athletes and soccer players. They show that VO2max is increased between 6-8%. An excellent example of how HIIT can improve fitness in soccer players is a study carried out by researchers at Willamette University in Oregon. They compared HIIT and endurance running during an “off season” training period. They were interested in determining which form of training is better for improving fitness. The HIIT group performed five-30 sec maximal sprints separated by 3.5-4.5 minutes of recovery. The other group underwent 40 minutes of continuous running at 80% of their aerobic capacity. Training was conducted twice per week for 5 weeks. In both groups, VO2max increased by 4%, from 50.7 to 52.7 mL O2/kg/min. Also, performance on the Yo-Yo intermittent endurance test was equally improved.
HIIT has also been compared to other forms of soccer fitness training. For example, a recent study found that both small-sided games and HIIT improve VO2max by 7-8%. In terms of match performance, HIIT also results in players spending more time engaged in high intensity running efforts.
Research also shows that repeated sprint performance and exercise economy are improved following HIIT. Both of these changes are important for the athlete. One could argue that soccer is essentially a 90 minutes test of repeated sprint performance. Thus, HIIT offers a very sport-specific training adaptation. An increase in exercise economy means that he or she is using slightly less energy when performing the same amount of work. Some think that HIIT may improve running and sprint mechanics leading to less wasted energy. Whatever the cause, improving exercise economy could lead to important energy savings over the course of a match.
Based on these research studies, it is clear that HIIT does indeed improve VO2max in soccer players. Also, HIIT improves other aspects of performance like exercise economy and repeated sprint performance. Each of these improvements would be expected to translate to increased performance on the pitch.
How Does HIIT Work?
VO2max is determined by two key physiological variables. The first is cardiovascular performance and the heart’s ability to deliver oxygen to the muscle. Stroke volume or how much blood the heart pumps per beat is key to oxygen delivery. The second variable is the muscle’s metabolic capacity or its ability to extract oxygen from the blood and use it to produce energy. Improvements in VO2max following endurance training typically result from a 50/50 combination of cardiovascular and muscle adaptations. However, HIIT seems to increase VO2max by improving the muscle without affecting the cardiovascular system. That is, muscle metabolism is increased while stroke volume remains relatively unchanged.
Within the muscle, mitochondria (called the powerhouses of the cell) are the most affected by HIIT. These structures, located inside each muscle fiber have the machinery needed to combine oxygen with fuels like glucose, glycogen and fat to energy. Research shows that HIIT stimulates the muscle to produce more mitochondria. This means that the muscles of HIIT-trained players are better able to use oxygen than their endurance-trained competitors. HIIT also leads to increased muscle glycogen and a slower rate of glycogen use during exercise. Muscle glycogen is a critical fuel source for the player. The ability to slow glycogen depletion could pay dividends later in the match.
Thus, while HIIT and traditional endurance training both accomplish the same goals, they do so in somewhat different ways. Endurance training improves both the cardiovascular system and muscle metabolism. On the other hand, HIIT seems to cause greater improvements in muscle metabolism.
Why Might HIIT Be Better?
The fact that HIIT improves muscle metabolism has important implications for the soccer player. Soccer players generally have very high cardiovascular function. However the start-and-stop, sprint-jog-run nature of a match places a high demand on the muscle’s aerobic and anaerobic energy systems. Since HIIT relies on repeated high intensity sprints, it is very likely that both of these energy systems are stressed. Thus, a training program that and simulates the movements and energy demands encountered during a match is important for the player. HIIT training should give him or her the ability to jump, start, stop and change directions more effectively during the end of a match when fatigue starts to set in.
The second key advantage of HIIT is the time commitment. In the Willamette University study, the HIIT athletes trained 20-25 minutes per session compared to almost twice that time for the endurance group. This, HIIT can be a more economical way to improve fitness. For teams that have limited practice time on the field, this can be a huge advantage. Being able to improve fitness with a lower time investment leaves more time to work on other technical and tactical aspects of the game.
Using HIIT
Dr. Martin Gibala at McMaster University suggests that a combination of HIIT and endurance training may be best. Substituting 15-25% of the traditional training volume with HIIT or incorporating 2-3 sessions per week. Obviously this routine depends on the time of year and whether players are in-season, pre- or off-season. A greater number of HIIT sessions can be used during the off- and pre-season when the emphasis in on developing fitness. While in-season training may use HIIT once per week to maintain fitness.
The bottom line is that, research shows that HIIT is an effective and economical way to improve aerobic capacity in soccer players. In fact, the effects of HIIT on the exercising muscle and the minimal time commitment may make this mode or training preferable to traditional endurance running.
-- Jeremy Williams
Jeremy Williams is currently a graduate student at Florida State University and assistant with the women’s soccer team.