Lately I've been thinking a lot about what it means to run as hard as you can. We take it for granted that running as hard as you can, or giving a maximum effort, is necessary to achieve the objective of completing a race in the shortest amount of time possible. The thing is, in long-distance running events (heck, even in relatively short running events), you can't achieve the fastest time by starting the race at a full sprint and trying to sustain an absolute maximum effort all the way to the finish line. You have to hold back, pace yourself, calculate, apportion your energy, whatever you want to call it. The notion of running as hard as you can must be considered in relation to distance. And this reality certainly complicates the notion of running as hard as you can.

Exercise scientists used to think they knew what it meant to run as hard as you can. When the muscles encountered certain hard limits such as a maximum tolerable concentration of lactic acid, they failed, and the runner faltered. So running as hard as you could meant running at the fastest steady speed you could sustain without hitting one of these limits and faltering before the finish. But recent research has shown that these limits are theoretical only, and are never reached in practice, because the brain self-protectively causes fatigue to occur before they are ever reached. There seems to be some flexibility in these mechanisms, such that the body is allowed to work closer to its true mechanical limits in some circumstances than in others. This complicates the notion of running as hard as you can still further.

There are all kinds of examples of the fluidity of running as hard as you can. For example, every exercise scientist knows that experiments involving exercise bouts to exhaustion are highly irreproducible. In these experiments, subjects climb aboard treadmills or stationary bikes and work at a fixed intensity until they can continue no longer. When such experiments are repeated more than once with the same subjects at the same intensity in the same circumstances (with rest days between them, of course), their times to exhaustion vary considerably. The subjects always feel they have given it their all, but their "all" is seldom the same twice.In fact, it's usually not even close to the same.

Another example from my own experience is the influence of split times in races. More than once I have found myself really struggling in the middle of a race--running as hard as I could and beginning to falter--when I've passed a mile marker and received a split time that informed me I was on pace to set a personal best for the distance. And what happened next? Suddenly I was able to run harder to the finish. So apparently I wasn't running as hard as I could earlier, when I thought I was running as hard as I could.

I am beginning to believe there is really no such thing as running as hard as you can. But what you can do is run harder than you ever have before. That's the purpose that goals serve--especially time-based goals. If you ran 41:12 in your last 10K, you might set a goal to run under 41 minutes in your next 10K. If you pull it off, you won't know whether you ran as hard as you could, but you will know that you ran harder than ever before. Now it's time to run even harder!