Now, to be clear, I ran for 8 weeks, or 17 total runs. Hardly anything to write home about. My mileage was relatively low, and I think my biggest week was race week, where in 8 days I did 35 miles. That may sound like a lot (and even writing it sent me back to double check) but it came in the form of a 12 mile long run 1 week out, and 2 short runs during the week followed up by race day. The key though was the intensity of each of the runs.
I’m definitely not an expert on running, but I do know I was on the razor edge of injury. The night before the race I was limping around with ankle and hip pain. That week had been brutal on my fragile non-runner body. Looking back, I had done too much intensity too fast leading up to the race, which is exactly what I needed, but I just wasn’t ready for the pounding. Though, I didn’t have much choice with such a short window in which to train (if I wanted to go fast), so I rolled the dice and won out; barely.
The Saturday before race day I went out and ran 12 miles at a low end threshold heart rate (for me, 170bpm). I had no idea what pace to target for the race, so this was my last ditch effort to determine just that. The run felt comfortable until the last mile, so I figured I was close, and decided a low 170’s target on race day was a safe bet.
Tuesday came and I went out for a fast 4 mile trail run with a friend. He pushed me hard and I was in mid to upper threshold the entire run. This actually ended up being the run that started cracking my body. Until that point I had held it together a bit, but after this run, joint pain set in hard. However, it was another threshold workout.
Race day came and thankfully, the nagging pain left 3 miles in and I felt great. I pushed myself to the absolute limit of what my body could deliver, and averaged 175bpm for the duration of the race. Smack dab in the middle of my threshold range. That left me with 220 minutes of threshold over 8 days, which is quite a substantial training strain on the system. I had no idea if and how running at threshold would translate to bike fitness.
One interesting discovery I found during this experiment is that running at threshold is far more comfortable and logistically easier than riding at threshold. I can go out and hammer at threshold for miles and not have to stop for lights, worry about traffic, trail conditions, or my speed. On a bike, unless you have a long climb or exceptionally flat and quiet road, its challenging to do a sustained workout at threshold without encountering an interruption, especially when you live in a city. So here I was with some of the best threshold training of my life completed, and none of it was on the bike.
Would it transfer though? It honestly wasn't even on my mind. Riding and running are very different activities that use similar muscles in unique ways, so it never even crossed my mind that I could see any gains in my bike fitness. It's the off season, so I hadn't been riding hardly at all. I was expecting my fitness to plummet as a result.
Anyone who has run more than a minute can tell you that running requires more energy than riding does. The number of muscles involved and the level of load they are required to manage while propelling you forward is substantially greater than what the body encounters while propelling a bicycle. Bikes didn’t earn the title of the most efficient form of human powered transportation for nothing! But because of this greater load incurred on your muscles when running, your muscles inevitably develop a greater respiratory capacity, in a shorter amount of time, by mere necessity.
The benefits of run training for biking are limited though to aerobic capacity because of the fundamental difference between the actions involved in riding versus running. While running, your muscles elongate (lengthen) while under tension which is known as eccentric contraction. This specifically differs from riding where your muscles are experiencing a concentric contraction, or shortening, under tension.
The temptation then to train bike fitness more quickly by running, would not be feasible because of the difference in how the muscles operate during those two activities. Bike specific fitness must still be trained primarily through riding, but from what I found, the benefits of running lie within the development of oxygen efficiency of the muscles.
I discovered this all accidentally when I went on a mtb ride and specifically loaded my muscles with a sub threshold interval before I hit the trails. Once on the trails, I pushed the climbs and hammered around for fun with friends, working hard enough to tire my legs further. 2 hours in I headed back out of the woods onto the road and presumed I would not be able to push at threshold for very long given that I hadn’t ridden a threshold interval in months during the off season.
What I found out over the next 30 minutes, was thus fairly shocking. I set out to do a sustained effort as close to threshold as possible, and it was no problem, strangely enough. The running had been hugely beneficial in jump starting my fitness, and had brought me back to levels I hadn’t seen since mid-season last year! I expected to have no high end or sustainable power, yet, it was all there. The running had brought me back to a threshold capacity that formerly I only believed riding could.
Now, like one would expect, the running didn’t fully supplement riding. My endurance is still lacking because of my low mileage through the off season, and I find that riding 3-4 hours sub threshold in zones 2 and 3 are tough as they should be. That is my expectation though, and confirms the science of muscle specificity I have been growing to understand. Nothing can replace miles on the bike for getting you race ready. Your leg muscles need that motion in order to become highly efficient at that motion. It would seem though that the incorporation of cross training at threshold can be extremely helpful though in developing the aerobic efficiency needed while running or riding at threshold for those intense race efforts.
It is now clear to me that running at threshold can provide very tangible benefits to riding fitness. But what about the opposite? Can riding provide benefits to runners?
A study was done back in 2003 with a team of collegiate runners. Between the cross country and track seasons, half the team was directed to substitute 50% of their run training with cycling during a 5 week recuperation period. At the end of the of 5 weeks, the entire team was tested at the 3000m distance to see how their fitness had changed during the rest period and the difference in training loads in running/riding vs just running. The results were that those doing both riding and running had been able to recuperate better by doing less running but were still faster by 13 seconds over 3000m!
It is the same principle I experienced this fall. With a reduced riding load, I was able to take time to rest and recover off the bike. Meanwhile, I was still able to maintain a high level of fitness from the running I had done.
There are a lot of variables in this and my experience is far from a carefully controlled scientific study. I do believe this gives you a basic view into the main benefits possible from cross training between riding and running. These are exercises that are similar enough to develop the engine for both sports, but different enough to not work your muscles in an identical fashion, thus allowing some recuperation in one while still participating in the other. So grab your shoes and your bike. They'll both help you with either sport.
Do you cross train? Let me know what you've observed from it in the comments.