There are several ways to increase training stimulus in run training. Some runners respond very well to increased mileage. However, you can only make each run longer to a certain point. Running for 2 hours straight can be a quick recipe for injury, if the athlete even has time. The solution to increasing mileage for advanced runners: running twice a day. Double runs should be used with caution, but for advanced, injury-prone runners, they can provide a beneficial aerobic stimulus.
How to Use Double Runs
What are Double Runs?
Essentially, doubles are used when other logical approaches to increasing mileage have been used up. If you are running less than six days per week or less than 70-75 minutes most days, explore the options of increasing the number of days you run or how long most runs are. A majority of recreational runners will not ever use double runs, but there are a minority who will benefit from them as they chase ambitious goals such as a sub-3:00 hour marathon.
The Rationale for Double Runs
Generally, if an easy run would be longer than 75-80 minutes, you may want to consider programming a double run instead. Why? The answer boils down to both physiological (muscle damage and energy demands) and practical (time available). You will notice even elite runners take this approach, with easy runs generally capping at 75-90 minutes and then adding a second run of the day of 30-40 minutes.
Splitting a longer run into two runs promotes aerobic adaptation and recovery better than one big workout. Runs over 90 minutes deplete more glycogen and lead to more muscle breakdown – and thus longer recovery.
Daily runs over 90+ minutes may be a training approach that works for some elite and ultra–runners, but let’s always remember that those runners are often genetic anomalies with off-the-charts fatigue resistance. For most runners, daily runs of two hours can be junk miles at best, overtraining in most scenarios, and untreated exercise bulimia at worst.
Double runs spread out the mileage between two runs. Typically, one run is longer (60-75 minutes) and one run is shorter (20-40 minutes). The recovery time between runs is typically 4-8 hours, although nothing says you can’t run at 6 AM and 6 PM to fit in your double. The recovery time between the two runs allows glycogen stores to replenish.
Double runs should be short, around 20-30 minutes for most runners. When you first introduce them, start short, with only about 15-20 minutes for the first few weeks.
Double runs also allow you to increase mileage without sacrificing a rest day. Rest days are vital for adaptation. While many elites can train every day, they also can rest throughout the remainder of the day. Recreational runners often do not have the same luxury and need to dose enough rest for recovery through a weekly rest day. (It’s worth noting that one marked difference between American and Kenya models of training are Sunday rest days.)
How to Program Double Runs
Unless you are an elite, you should not be doing double runs most of days of the week. Most recreational to low-level competitive (including OTQ hopefuls) will do best with one to three doubles per week.
In terms of intensity, double runs should be done at a low intensity. Easy runs promote aerobic development with minimal fatigue. If you are new to double runs or completing them on the same day as a hard workout, you may pace them as a very slow recovery run.
Double runs will require more adaptation than other training stimuli. Generally, you will want to start with one double run per day. Initially, a double should be a very short run of 10-20 minutes. If you respond well to that, add in a second double run in the next training cycle or lengthen a double run up to 30 minutes.
(Note: Canova-style double threshold workouts are popular in world-class elites and are highly effective for the top <1% of athletes. This training approach is not appropriate for almost all non-elite runners.)
The Cons of Double Runs
Not every runner will respond well to double runs.
You should not do doubles if:
- Your easy runs are shorter than 60-75 minutes (and you have the time to fit in more in one run). One 60-minute run provides greater endurance adaptations than two 30-minute runs.
- You are not running six days per week.
- It is difficult for you to meet the nutritional needs of twice-per-day training.
- You are prone to injury/illness or recently injured.
- You experience symptoms of burnout or overtraining, such as fatigue, plateaued training, or irritability.
Alternative: Aerobic Doubles
In coaching, I have had success with aerobic doubles instead of double runs for some athletes in marathon or triathlon training. Aerobic doubles simply mean a second workout of the day that is aerobic yet low-impact: cycling, swimming, elliptical, cross-country, hiking, etc. These can be an introduction to running doubles or a stimulus in their own right.
Aerobic doubles can be a safer option for advanced yet injury-prone runners. Due to the lower impact, you can also experiment with aerobic doubles even if you do not run six days per week. For example, you may run five times per week, do a long bike ride or hike one day, and complete a short bike double once per week. Many triathletes will use aerobic doubles to fit in the necessary volume for Ironman or half Ironman races.
Should You Run Twice Per Day?
Like any novel training stimulus, double runs should be approached with caution. If you are running six days per week, injury-free, and ready to increase your mileage, they are a training option to explore.
When running twice per day:
- Monitor your recovery rates
- Scale back at the first sign of injury
- Be mindful to eat within your recovery windows after each workout and to eat enough
- Schedule the double run before a rest or an easy day
For more tips on how to handle twice a day workouts, reference this article.)