Intensity VS Pace
by Luke Humphrey, Jan. 9, 2010
Intensity VS Pace
Intensity VS Pace
So, winter has finally hit us here in Southeast Michigan, but I know you folks on the West Side have been getting nailed for some time. With all the snow and the less than ideal running conditions come a lot of emails regarding paces. This is especially true with those looking to do some form of speed work. The typical email is, “Why is it that I feel like I am running really hard, but all my times are slower?” Well, the truth is, you will be slower in the slush and cold, but the work that you are doing is very similar to what you were accustomed to during the rest of the year.
I think one common mistake is a simple misunderstanding of the terms intensity and pace. Intensity is often described as a percentage of VO2max or maximal hear rate (%HRmax). What it is describing is, here we go, the intensity of the work. Now, pace should probably be referred to as velocity. It is referring to the velocity at which you are running. It is describing how fast you are running at a given intensity. For example, if your VO2max is 75 ml/kg/min, or 100% of maximum. Let’s say your velocity (pace) at VO2max is 4:00/mile. See the difference? Putting it together, let’s assume that in the summer, you were running your 400 meter intervals at 1:15 per 400 and that was equal to 95% of your VO2max. Your intensity is 95% and your pace is 1:15 per 400. Now, in January, you are lucky enough to find a snow-free track and want to do the same workout. Now your effort, or intensity, is still 95%, but you can only muster 1:20 per 400. Your intensity remained the same, but the pace was slower. In this case, you ran slower to work just as hard. In fact, what will happen many times is that a runner will attempt to run harder (intensity) to hit the desired pace of 1:15 per 400. So, now they are working harder to reach the same pace. This rule of thumb translates throughout the range of paces-from easy runs to repeats.
Why does the cold affect pace so much? Besides the obvious answers of slippery footing and windy conditions, the cold temperatures directly affect your intensity and pace. First, the cold temperatures promote a greater loss of glycogen stores. Partly, this is due to an increase in shivering. I also believe that it is also due to an increase in body weight due to the increased amount of clothing that one wears in the winter. Since VO2max is a factor of body weight, if you weigh 5 pounds more due to sweaty clothing, then your intensity will automatically increase. This becomes particularly important when you are trying to run fast (speed work) or runs of 90 minutes, or more. These are where glycogen stores are most susceptible to depletion and have the greatest impact on performance. Besides the susceptibility of the glycogen stores, heat loss is greatly accelerated through sweat loss. As sweat accumulates in our clothing, it not only weighs more, but it also provides a direct link for heat to escape the body and into the environment. As we get colder we will automatically slow down to try and save energy.
How do you cope with doing workouts? Unfortunately, the winter is also the prime training time for those running spring marathons, like Boston or Bayshore. With a lot of my runners, we try and schedule their long tempo runs on the treadmill. As boring as it may sound, the pace of the tempo run is very important to me. Most of the time, they are trying to run their goal marathon pace and I want them to practice running that pace for long periods of time. If they go out and trudge through the snow, the effort will be there, but they will have no idea what the pace feels like. Speed work is different. For most of my athletes, the speed is just part of maintaining the training balance, so I am more concerned with the effort than I am the pace. In this case, there are a couple of options. One is to run fartlek workouts where we focus on a set amount of time at a perceived effort rather than trying to run a given distance at a set pace. It takes the necessity of finding tracks or perfect conditions out of the daily training routine. Plus, it is a good break from traditional speed work. The other option is again the treadmill. However, if you are like me, trying to run 5-10k pace on the treadmill is downright scary! What one can do, is to run a manageable speed, but take the grade of the treadmill up to the 4-6% range and the effort will be very high. It is a great way to approach your maximum intensity while keeping the pace manageable.
With a little luck and some careful planning, one can maintain and improve their fitness through the tough Michigan winters. As always, be safe and be seen!