Backwards running will almost certainly never be as fast or efficient as regular running. A study back in 2011 showed that it should takes about 30% more energy to run backwards at a given speed. Why? It depends on how foot muscles respond during both types of strides. In normal running, landing on the balls of your feet and pushing off on the toes allows muscles to coil up and then release elastic energy, propelling you forward. When running in reverse, the muscles are unable to stretch and release in the same way.
Current world records in the backwards 5k and marathon are substantially slower than the corresponding forwards records: 19:31 and 3:38:27 compared to 12:37 and 2:01:39, respectively. I assume that if the strongest distance runners trained for backwards running, they could improve on those backwards times, but they'd still be at a disadvantage, from an energy perspective.
I'm a college runner, so I figured I'd try to experiment a bit at practice today to better understand the mechanics of what's going on. We already do some backwards jogging as a warm-up drill, so I figured I'd just modify that. I ended up doing three sets of sprints on a standard outdoor track, with each set consisting of one forwards 40-meter sprint at a controlled pace and one backwards sprint of the same distance, as fast as I could go. I made some observations:
- I ended up taking about 1.75-2 times as many steps while traveling backwards, on average; I was forced to shorten my stride because my motion felt limited.
- While running backwards, I was forced up onto my toes more; if I tried to use the balls of my feet at all, I ran the risk of falling.
- I definitely felt much less spring in my step when I pushed off running backwards. It was a little bit awkward, biomechanically.
- I was able to run straight without looking over my shoulder, by keeping my head fixed on a target I was running away from. However, I was on a straightaway, and inside a lane. On a course with turns, I would be hard-pressed to stay close to the inside, like I would normally do.
Some of these could be overcome through training, especially at a young age, but I'm pretty certain that the lack of a spring in my step could be problematic. It definitely got me less bang for my buck.