My experience 3 weeks off running; cycling everyday cross-training.

For someone highly trained enough (relatively speaking) like you, your anecdotal observation that “nothing will replace running” is correct in the sense that any other form of cross training will be suboptimal in comparison. However, studies have shown that aqua jogging in particular especially in combination with other cross training can maintain something like over 85% of the pre-injury fitness. I can pull out those papers if there’s interest.

For less fit people more along the hobbyjogger spectrum than you, cross training with any aerobic activity and strength training can (seemingly counterintuitively) result in increased running fitness because time off from running allowed them to systematically fix their bottleneck weaknesses, so the silver lining about being forced to take time off from running or significantly reduce intensity is that it’s an opportunity to fix longstanding strength or activity-neutral aerobic bottlenecks.

It will come back quickly. I used to run 100mpw but take one week off and the following week i would feel like ive never run before. And i start low with 20mpw the first week back. Im actually injuried now for really the first time and trying to bike most days. Since beens been so long im now starting to do workouts on the bike.

I've found this to be the case too. There's just no perfect substitute for the physical demands of running. But you know you're better off for doing all of that cycling. You'll be able to build back up a lot easier with some semblance of an aerobic base. Without anything in those three weeks, things would only have been more difficult.

Pull ... thx

Klaas Lok author of book "Easy Interval Method" once told me that the ellipical is not so bad for cross training. However, I personally have no experience with it.

In plain english

runnersconnect.net

Aqua Jogging for Runners: Workouts, Technique, and Benefits

Injuries happen, but what can you to to maintain fitness while injured from running. Pool running is a good cardio replacement. Here are the benefits of aqua jogging, and 7 workouts to use in the pool.

Link:runnersconnect.net/coach-corner/aqua-j...

citing the two articles below with very similar findings, one over 4 weeks and another over 6 weeks.

“Before and after the deep water run training, subjects completed a 5-km race on the treadmill using a computer based system, a submaximal run at the same absolute workload to assess running economy, and a combined lactate threshold and maximal oxygen consumption test. No significant differences were found for (mean ± SEM): 5-km run time (pre, 1142.7± 39.5 s; post, 1149.8 ± 36.9 s; P = 0.28), submaximal oxygen consumption (pre, 44.8 ± 1.2 mL·kg-1·min-1; post, 45.3 ± 1.5 mL·kg-1·min-1; P = 0.47), lactate threshold running velocity (pre, 249.1 ± 0.9 m·min-1; post, 253.6 ± 6.3 m·min-1; P= 0.44), or maximal oxygen consumption (pre, 63.4 ± 1.3 mL·kg-1·min-1; post, 62.2 ± 1.3 mL·kg-1·min-1; P = 0.11).

also i recommend aquajogging without a belt, it makes it much more challenging, my go to workout was 

15 minutes of aquajogging

10x (1 min of aqua "sprinting", 1 min doggy paddle)