In the military, working out twice a day is almost a requirement to build actual strength and fitness. If you rely on the typical morning routine performed and it’s reliance on high-rep bodyweight movements and long, relatively slow, aerobic efforts you’ll probably end up with big holes in your overall fitness.

If you’ve checked out any of my training programs the first thing you’ll probably notice is that there are a number of days where you’ll be working out more than once. Typically following a morning endurance session and an afternoon strength & conditioning session format.

I’ve written about (and can talk at length about) the benefits of reducing your overall running volume in favor of higher intensity efforts but you have to remember that this model really only works if you’re also following a well-structured strength & conditioning program.

This strength and conditioning ‘base’ is just as important (if not more so) than the actual endurance training and if you miss it, your lower volume endurance training isn’t going to get you very far (pun not intended). On the flip side, if you spend all your time jacking weights like a bodybuilder you may end up looking great with your shirt off but you’ll probably be fairly useless when it comes to the dynamic athletic movement required of the vast majority of the military and tactical community.

So, you need to be doing both.

In fact, numerous studies have pointed to the benefits of concurrent strength and endurance training (**when programmed correctly) including improvements in the rate of force development and it’s positive impact on running economy.

**I mention “when programmed correctly” as there are a number of studies that point to an interference effect on strength when you include an aerobic training program concurrently. However, the program design in many of these studies is ridiculous at best and there are a number of factors to consider when designing a concurrent program. Additionally, a meta-analysis (study of studies) of this topic backs up my point that any interference effects (e.g. reduced strength or aerobic power gains) are affected by the modality, frequency, and duration of the endurance training.

When you consider that one study showed concurrent training to have negative effects on strength and a similar study, with a different training population, showed significant gains in strength the topic become even more confusing. So, once again, there is no easy right or wrong answer to this question and the success of your program is going to be determined by the overall program design.

But here is what we can conclude from the research (and my experience):

To maximize strength and power gains, athletes should avoid longer duration (30mins+) steady-state endurance training performed at high frequency (3+ days per week).

If your sport (or, in your case, life) depends on being strong and powerful (it does) then your endurance training should be kept shorter and the intensity should be cranked up (shouldn’t be shocking info unless you’re new here).

Doing so has been shown to result in lower interference of hypertrophy, strength, and power compared to the longer duration stuff in a concurrent training program.

Okay, so hopefully you agree that training twice per day isn’t going to ruin all of your gains so now we need to talk about how long to wait between workouts to achieve the maximal adaptations from both workouts.

Recovery between workouts

I’m going to draw from a few pools of knowledge here as I think it will give you the best idea of how to practically implement your own training, especially if you’re working out twice a day a few times each week.

First, I’ve been recommending ±3 hours of recovery between your strength & conditioning work and endurance work if you are following the CrossFit Endurance model. This is something we teach at the seminars and something all of the coaches has recommended for as long as I’ve been around. This recommendation is based largely in anecdotal evidence (i.e. We’ve seen it work in actual athletes).

The purpose of this recommendation is to ensure that the athlete is able to attack each workout with the same (or very similar) energy in order to ensure a high-quality workout at both training sessions. On a logistics level, this recommendation also serves to make sure coaches instruct their athletes that attending the CrossFit class immediately before or after the endurance class is less than optimal (although it is still very common).

Personally, I think 3 hours is kind of short and more importantly, it doesn’t really fit into most people’s lives. So, for this reason, I suggest individuals attempt to separate workouts by a minimum of 6 hours.

If you think about this minimum recommendation you could finish your first workout at 0700 each day and then hit your second workout at lunch (1300) and be good to go. However, more rest tends to be better, so I’d say if you can wait to hit that strength & conditioning session after work (1600+) then there is a good chance that the workouts won’t interfere with each other at all.

In a study by Robineau et al. it was noted that coaches should avoid scheduling training sessions with less than 6-hours of recovery in between. This study did note a difference (benefit) between the 6-hr and 24-hr recovery groups, with the 24-hr group showing greater improvements, however, the data suggest that this increase is trivial to small and no real significant changes were observed.

So it seems like that 6+ hour mark is a pretty solid number to shoot for if you are going to be performing multiple workouts each day.

Additionally, this recommendation also tends to work well when it comes to planning your nutrition. As I talked about in the Post Workout Nutrition article I mentioned that if your second workout of the day is greater than 6-hours after your first then you really don’t have to worry about the post-workout recovery window as much as long as you are eating a real meal within 90 or so minutes.

Wrapping it Up

So despite now having the requisite formal education (M.S. Kinesiology), I still think that experience and anecdotal evidence can reign supreme here, especially when dealing with a diverse group of athletes. Or, in your case, dealing with your individual situation.

Let’s sum this up:

  • You probably need to be training both strength & endurance
  • Long slow distance endurance training does not play nice with strength & power training
  • So keep you endurance training short and high intensity
  • Waiting 24-hours between workouts is probably the MOST optimal
  • However, it isn’t practical (considering the incompleteness of most unit daily PT)
  • You should aim for 6+ hours between workout when training twice per day.
  • While studies show 6-hours isn’t as absolutely optimal as 24-hours, it’s definitely good enough
  • When training twice per day, aim for a morning workout and a late afternoon or evening workout.
  • Listen to your body, rest more when you need it
  • It doesn’t matter if you run in the morning and lift at night or vice versa
References

Docherty, D., & Sporer, B. (2000). A Proposed Model for Examining the Interference Phenomenon between Concurrent Aerobic and Strength Training. Sports Medicine, 30(6), 385-394.

Robineau, J., Babault, N., Piscione, J., Lacome, M., & Bigard, A. (2015). The specific training effects of concurrent aerobic and strength exercises depends on recovery duration. Journal of Strength and Conditioning Research, 1-25. [epub ahead of print].

Wilson, J., Marin, P., Rhea, M., Wilson, S., Loenneke, J., & Anderson, J. (2012). Concurrent Training: A meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307.

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