For years athletes have utilized interval training as a means to gain higher levels of fitness. Intervals are very simply periods of increased intensity exercise followed by a lower intensity recovery period which is repeated for a prescribed amount of sets. Typically the recovery periods are longer than the higher intensity phases of the workout, with the exception of more modern modalities of interval training such as High Intensity Interval Training (HIIT). HIIT is characterized by periods of very intense (VO2 Max) all-out efforts for a period of 20-50 seconds, followed by a brief recovery phase of 20-30 seconds before repeating. Sprinting is a very common means of utilizing HIIT. An athlete will sprint during the higher intensity period and jog or walk during the recovery period. A simple 20 minute HIIT workout would look something like: 10 minute light intensity warm-up jog, followed by five 30 second high intensity intervals with five 30 second low intensity recovery periods in between the high intensity bands. Conclude the workout with a 10 minute light to moderate intensity cool-down phase.
The benefits of HIIT include assisting an athlete in increasing speed and running form. By reaching VO2 max during workouts, athletes can improve lactate threshold over time, and also improve their running form at higher speeds. An athlete may struggle with maintaining an all-out sprinting effort for 3 minutes, yet by doing six 30 second HIIT intervals, the total time spend at all-out effort equals 3 minutes during the workout.
Keep in mind that most HIIT workouts typically last no longer than 20 minutes in total duration, which is including an adequate work-up and cool-down phase. I must stress the importance of warming up prior to getting into the interval phase of the workout, as exposing your body and muscles to all-out sprinting efforts can increase the risk of injury if the muscles are not warmed up. Same holds true for the cool-down phase, as the heart rate and cardiovascular system needs the opportunity to return to resting or near-resting rates gradually.
HIIT workouts allow the athlete to increase fitness in shorter duration workouts, which is the reason behind the growing popularity of this type of fitness training. This is especially appealing to the working-class athletes that simply do not have hours each day to devote to training. Using triathlon as an example, HIIT is an incredibly effective way to train for shorter duration events such as Sprint and Olympic distance races. HIIT can also be a very effective means to increase fitness for athletes training for longer distance events, yet should not be the sole focus of their preparation (longer events require a higher cardiovascular fitness base, which can only come from longer duration workouts). Many champion long distance triathletes credit the inclusion of HIIT workouts into their training programs as a key component to their success. I recommend including 1 to 2 shorter duration HIIT workouts to any long distance training programs to gain the explosive power and top-end fitness that come from high intensity training. One important thing in regards to HIIT workouts is the amount of recovery time needed between sessions. Due to the high intensity nature of this type of workout, the body does not respond well to back-to-back days of High Intensity Interval Training. It is typically accepted that the minimum amount of recovery between workouts is 1 day. For those athletes engaging in endurance type training, especially high-mileage training, I recommend extending the recovery period between HIIT workouts to at least 2 days.
One source I discussed recommended that as little as 15 minutes of High Intensity Interval Training can be just as effective, in terms of increasing fitness, as 1 hour of low to moderate intensity training. Shape Magazine reports that a study shared at the 2011 American College of Sports Medicine's annual conference proposed that 2 weeks of High Intensity Interval Training increases aerobic capacity as much as 8 weeks of moderate intensity training. If this research is even remotely accurate, the impact that HIIT can have on fitness and athletic ability is worth considering. I personally feel that everyone can benefit from moderate amounts of HIIT. It helps keep your training fresh and interesting, and the health benefits are an added bonus. Consider adding 2 to 3 HIIT sessions to your training programs each week as I can personally attest to the fact that you will see an increase in explosive power and fitness. Prior to beginning or increasing the intensity of your exercise routine, check with your healthcare provider to disksuss any risks of doing so.