Intervals - how long?

"How do I decide on the right duration for my intervals?"  An interesting question posed by a friend at work. She is training for a triathlon and wondered if there was a formula (or guideline) to define the optimal interval length (perhaps, she speculated,  related to the duration of the ride one isplanning).

I suspect that there is an "upper limit" beyond which a longer interval will not provide additional training benefits. And one also needs to remember the importance of rest, that is the duration of the rest interval - too short and the muscles/CV system do not have time to recover and let you maximize the next effort, too long and you aren't stressing your performance to the max.

I did find this from the literature - as relates to sprint intervals: In order to enhance aerobic endurance and increase VO2max towards its upper, genetic limit, interval training should consist of 3-5 minute work bouts with a 1:1 work to rest ratio or less. The intensity should equate to 90-100% VO2max.

My advice would  be to set 3 to 5 minutes as the maximum length for your sprint intervals - where you are pushing your absolute maximum to train for that sprint at the end of a ride or preparing to respond with a chase to a early breakaway rider.

For endurance riding, the idea of stressing your CV system to improve still holds. But if you just want to pick up your average performance from 60% VO2max to 65%, then a half mile or even mile ridden at the faster pace qualifies as an "interval" and if you work in a half dozen during your ride, you will improve.

The final answer to "how long" the interval is, as in many things, "it depends" and more on the level of exertion of the interval than the length of your total ride.

Dick

Improving Your Performance - Intervals

You have done your prep work - 1) you have your base miles to minimize injuries as you push up the miles, 2) you have mapped out your personal  training program (based on a few principles we discussed in April), and 3) you have made a decision as to how you will track your level of training exertion (either a heart rate monitor or perceived exertion).

Now the final piece - intervals to provide that improvement in your cardiovascular performance.

An ideal training week should include one long ride at a reasonable pace and a rest day or two. Rest is important, and if you ignore it, thinking that 7 days of riding = optimal training, then you will fail to reach your personal best. But more about over training next time.

That leaves you with 3 more riding days during your training week. One (or perhaps two) are going to be interval days - and these will be the key to your performance improvement. Intervals are based on pushing your anaerobic threshold, and it is this "stress" on the cardiovascular system that leads to adaptation and improvement (just as weight training improves muscle strength).

Intervals are most effective when they are :

• limited to twice a week during the peak training season
• when the interval sessions are separated by at least 48 hours to allow adequate recovery. (For example, if your long ride is on the weekend, Tuesday and Thursday make good interval days.)

Short exercise intervals are generally 15 to 90 seconds and almost always anaerobic in intensity, while longer intervals may be up to 3 to 5 minutes duration. Once you decide on the duration for your interval training for that day, pace your effort to exercise at your maximum throughout that period (if you can't make it through the entire interval, you need to cut back your effort a bit and not the length of the interval). The goal should be a total of 10 to 20 minutes of hard pedaling during the intervals themselves (don't count warm up, recovery, or cool down). If you are just beginning an interval program, start with 5 minutes of peak effort per riding session (total interval time) and work up from there.


To get the maximum benefit from interval training, it is important to allow adequate recovery time between intervals. Subsequent intervals should start before your heart rate and oxygen uptake have returned entirely to normal. If you are using a heart rate monitor, wait for your heart rate to drop to 60 or 65% of your maximum heart rate. If you are using perceived exertion (i.e. how you feel) to decide, wait until your breathing has returned to it's normal depth and rate.

For those of you interested in more specifics and ideas, there is more information @ http://www.cptips.com/intervl.htm
 
But just as rest days are important, setting reasonable interval training objectives is important as well. If you set the bar too high, burnout and training drop out rates rise.