It was a beautiful spring day, and I was itching to get some data from my new PowerTap Disc Brake hub. I was raring to go and had all of the mental prowess I could muster. After all, I had had my fancy new PowerTap for several weeks and had barely been able to use it before sustaining a very ill-timed and unfortunate fall down my stairs. The fall had left me unable to sit, stand, or walk for anything longer than 5 to10 minutes at a time - and only with a combination of Ibuprophin and muscle relaxers. To say the least, I was incapacitated for a solid 2 weeks.

I had fallen on a hard wooden stair which wedged itself between my lowest thoracic vertebrae, rendering me unable to either breathe or feel my legs for several seconds. After having my spine stabilized and being carted to the hospital, I was told that thankfully I did not break my back, but I would be in pain for a while, and I should take it easy. So after taking the proper precautions and staying off my bike for the full doctor-recommended 3 weeks, I felt I had paid my penance, and after that I should be in the clear and back to normal.

I was careful though and smart enough to stay off of the trails; it was going to be only road riding for a few weeks until I was strong enough to ride off road. Even still, I was ready and willing to suffer - on my knobby tires, on the road, in the name of data collection. I had it all planned out, two other riders (both on road bikes) would accompany, encourage, and push me. We would ride out to the time trial (TT) location and do two 10-minute TT efforts. During the first effort I would take off first and ride in an all-out manner which I could sustain for 10 minutes. Trailing me would be a junior rider who was just learning the ropes and had never attempted this type of exertion, and trailing him (in order to give us a head start) would be my husband, a retired cat 2 roadie who has never strayed far from his peak fitness.

After our warm-up ride I took off for interval number one like a bat out of hell with my trainee in tow attempting to keep up. I was so excited to be there, to be riding, to be seeing over 300 watts; this was spectacular - I am fitter than I have ever been – this season will be my best ever. What back injury? But then during about the 2nd minute, I noticed my power dropping, slowly at first, but I was able to respond and pushed it back up for at least another 30 sec before realizing that I might not be able to sustain 10 minutes of this effort. My legs and lungs were at full capacity and starting to protest. Fine. I can settle for just over 200 watts; that’s still a respectable power output for someone my size; that’s totally realistic; surely I could keep that wattage for the remainder of the effort. Meanwhile my trainee, who was instructed to go around me at any point that he felt he could, came around. I wasn’t quite ready to let that happen, so I pulled that last ditch effort and willed my legs to go harder. They did, and I pulled ahead of him just as my husband came flying past both of us like we were standing still. Oh well. We gathered ourselves while watching him disappear down the road.

With several minutes to go in the effort, I find that now all I can do is watch my power plummet, my work of breathing increase along with the pain in my legs and lungs, and all the while my heart rate was remaining the same. It had hit a plateau. My effort from the start was so over the top that my heart rate could no longer respond to even the drastic drop in power that my legs were now turning over. My heart rate was pegged up until the moment of absolution; I was at full cardiac output and even with partial system shut down, couldn’t decrease until the effort was completely over; I had gone into serious debt.

No worries though, I had one more TT with which to redeem myself. We all cooled down, and after several minutes, I caught my breath and decided the next effort should be a bit more controlled. I would start slowly bringing my power up to ~220 watts and keep the power there, not letting my excitement get the best of me. This time our trainee knew what to expect and was again instructed to start with me but pass at any point in order to sustain his own TT effort, and my husband would give us a little more of a head start.

So off we went. I started out controlled with my trainee trailing. After a bit we rode side by side, our paces matched, then I pulled ahead, then he passed, and this time he stayed passed while I focused on keeping my power consistent - at least that was the goal, but it would not stay put. My power was dropping again, and no amount of pedaling or shifting or adjusting or mental prowess was bringing it back up. My trainee was now out of sight, and shortly after my husband flew by. I continued to watch my power decline in a rate that was considerably faster than the time was passing. Would I even make it to 10 minutes? It wasn’t looking good, and I certainly wasn’t feeling good. Again I noticed that my HR was just sitting there mocking me with it’s stubborn plateau, exactly the same as the first effort, as if I was doing a consistent exertion when the only constant was my declining power.

I made it to 10 minutes – barely, about a mile from the point in the road where I had expected to finish. Was it the knobby tires? Was it the mountain bike? No. I knew what it was, and I do know better: it was way too soon to be doing such an effort, and the cost would be high. My legs, lungs, and now back were all toast, and all I could think of doing was lying on my couch with an ice pack. In hindsight, my decision to do a TT for data collection during the first week back on the bike after an injury was a bit aggressive. But it was worth it if only to convince me, once and for all, that the measure of power is the only valid measure of output.

Lesson learned – I will take the time to rebuild my fitness base and intensity while respecting the limits of my ability to both heal and recover. I have always used the measure of heart rate with some discretion but seeing the drastic difference during my two TT efforts, a constant heart rate while my power varied by ~200 watts, was a surprising reality. Power is the only true measure of effort and will be useful to utilize as I build back my fitness on the trail to higher power.