To combat this lack of warm-up space, my coach and I came up the best solution we could think: static stretch in the shower!
In retrospect, this was potentially the worst warm-up possible, as static stretching directly before a race is believed to impair performance. Unfortunately, this practice still happens at many crowded meets.
The role of a warm-up is to:
"reduce the disturbance in blood acid-base balance during the swimming exercise. Warm-up was found to be beneficial and not a hindrance to performance. Warm-up swimming can be used for reasons other than performance improvements (e.g., environmental familiarization, injury prevention, psychological focusing, neuromuscular facilitation). If it produces additional physiological benefits then its justification is even further supported (Robergs 2011)".
Even the well respected Lou Sharp suggests the physiological effect of warm-up diminishes 15-20 minutes after it is performed.
However, mimicking the intensity of your swimming race is essential, even when water is absent.
A proper out of water warm-up is non-specific, while moving in every plane of motion; most importantly, it must prevent injuries. Secondly, it will dilate arteries for increased blood flow to muscles, and lastly, it enhances specifics for the sport, as improving blood flow, vasodilation, is suggested to improve performance by 7%.
However, excessive warm-up impairs performance up to 5 seconds in the 100. However, excessive for one may be just right for someone else, making this process more subjective than scientists enjoy.
As Robergs stated, in swimming, getting in the water to regain feel is important, but some situations are less than ideal; especially if the swimmer is only able to move at a snail's pace in the warm-up pool. Mimicking the neural demands of swimming outside is impossible, but vasodilation, injury prevention, and intensity matching are possible.
You will never find a research study outlining a proper out of water warm-up. However, knowing the research on warm-up and applying this research to your knowledge on swimming, it is possible to create an ideal out of water warm-up appropriate for your needs.
If you are looking for an out of water warm-up to do at overcrowded meets, interested at the idea of reducing the amount of “non-race pace” swimming due to motor control theory, or looking for a method to help reduce injuries, then an out of water-up may be an option for you. Therefore, an out of water warm-up, prior to the swimming warm-up is likely the best mode for overall success. To reiterate, swimming is the best mode for swimming warm-up, however if you want to prevent injuries in combination of warming-up or if you don’t have space, try this out of water warm-up outline:
5 Minutes of multi-planar dynamic jogging (forward and backwards, side-steps, cross-braiding, etc.) to induce vasodilation.
Shoulder blade stabilization, core stabilization, and dynamic mobility exercises for injury prevention.
After this, hop on the block and do a few race pace dives and I think you'll be happily surprised with the results. If plan on implementing this at a meet, make sure to practice this new routine before the competition, tweaking it as necessary to optimize it for your personal physiology.
Remember, evidence-based coaching is the unison of personal experience and research. Unite these two realms for optimization for each individual. This is likely the best route of success, as one size fits none.