Interval Training 101

Ed McNeely – Peak Centre for Human Performance

Interval training is a popular form of training amongst many athletes. While most rowers will use intervals at some point in the year few really understand the purpose of intervals or how get the most from this valuable training method.

 Physiology of Interval Training

Interval training involves alternating periods of high intensity work with periods of lower intensity work, usually, but not always above and below anaerobic threshold. By alternating periods of higher intensity work with lower intensity work several things are accomplished:

The amount of high intensity work is maximized. If you were to try to hold an intensity above anaerobic threshold for as long as possible you would fatigue in just over 20 minutes. If you were to do 6 x 5 minute work intervals with a rest period in between you would have done 30 minutes of work above threshold. Since the volume of work above threshold was higher it should give you a greater training effect. The same holds true for VO₂ max and anaerobic intervals.

During the work period of the interval you will be producing lactate and other metabolic by probducts, which your body will have to deal with during the rest period. Active slow twitch muscle fibers are capable of using lactic acid as an energy source. Repeatedly exposing your body to moderate levels of lactate and then allowing it to recover gradually trains your body to become more efficient at lactate removal as your body develops the enzymes necessary to convert lactate back to glycogen or glucose. This will translate into lower lactate and faster times during a race since you will be able to deal with the lactate as it is produced. Of course this training effect will only happen if you have done adequate base training.

The aerobic capacity of fast twitch fibers is improved with interval training. The more often a fiber is activated the greater it’s oxidative capacity. Interval training is the only ways to activate the fast twitch fibers frequently enough to improve their aerobic capacity, making them behave more like slow twitch fibers.

 Designing an Interval Training Program

Interval training is high intensity and needs to be planned very carefully in order to avoid overtraining. The most important component of an interval program is the base work that is done prior to starting intervals. The initial 6-8 weeks of your training should be devoted almost exclusively to low intensity long duration training, 60 minutes or more per session. This will prime the slow twitch fibers and improve their fitness, so that they can accept the lactate that will be produced when intervals are started, allowing you to make effective use of interval training.

The Work Period

The duration of the work period will vary depending on the intensity of the interval. A work load just above anaerobic threshold will need long intervals, 5-10 minutes, while higher intensity anaerobic intervals can be as short as five seconds. Consistency is the most important factor in interval training. The power output or split time should be the same for each work piece of an interval session. In other words if you are doing 5 minutes at 200 watts  on the first interval all other intervals should be done at the same pace. This ensures that you are maintaining the appropriate intensity and recruiting the same muscle fibers in each interval, improving the training effect. It does very little for you to do an interval session where the first interval is 18 km/hr the next is 16 km/hr the next 15 km/hr etc. Be sure to choose an interval duration and split time that allows you to be consistent throughout the workout.

Choosing paces for the work intervals requires a little up front work on your part. You need to have an idea of your splits for both anaerobic threshold and VO₂ max.

The Rest Period

The rest period is as important as the work period. The purpose of the rest period is to allow time to remove the lactate created during the work interval, and allow the anaerobic alactic energy system to replenish itself. During aerobic intervals, intervals longer than two minutes, the rest period is active, meaning you continue to row but at a lower intensity. The duration of the rest period will depend on the duration and intensity of the work period. Aerobic intervals will vary for a 1:1 to a 1:4 work rest ratio. Anaerobic intervals were covered last year in another article. When choosing the duration of your rest period, follow these simple guidelines: 1). The longer the work the shorter the rest

Longer intervals are normally done at lower intensity, requiring a shorter rest period. A five minute interval just above anaerobic threshold will produce moderate levels of lactate requiring less time to recover so a 1:1 or 1:1.5 work to rest ratio can be used. A higher intensity two minute interval will produce more lactate and therefore require a longer recovery. 2). Adjust the duration of the rest period so that you can maintain a consistent split during the work period. It may happen that you decide to do 5 minutes of work followed by 5 minutes of rest, repeated 5 times. Half way through the workout you notice that you can’t hold the same work split. Finish the training session, coming as close as possible to the desired splits. For the next session increase the duration of the rest period by 50%. If you still cannot hold the desired splits for all the work periods drop the splits for the rest period by about 10% for the next workout.

Table 1: Work and Rest Period for Various Interval Intensities

Most athletes will use some combination of all four types of intervals in their training program. For those doing short races, less than 30 minutes the VO₂ max and anaerobic sprints should make up the bulk of your interval training, while those doing only longer races will focus their interval training on anaerobic threshold intervals.

While interval training is a great way to improve speed, it is easy to overdo it and do yourself more harm than good so take it easy when starting by doing only one session per week and increasing by one session per week every two weeks until your are doing at most three sessions per week.

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