A few days ago, I received an email from my high
school coach asking me about the "correct" way to calculate
percentages of a given pace. This is a
question that I am asked fairly frequently, and the answer has a few
interesting angles, so I have decided to make a post about the details.

Many different training programs are predicated on
doing workouts, easy runs, and interval sessions at various percentages of a
particular pace, whether this is race pace or threshold pace or VO2 max
pace. But if you ask a group of people
how to calculate, say, 85% of 5:00 mile pace, you'll get two different
answers. The first camp will say,
"Simple, just multiply 5:00 per mile by
1.15, which gives you 5:45 per mile."
The second will say, "No, you have to divide 5:00 by 0.85, which
gives you 5:53." Who is correct?

In some sense, they are

*both*correct. To break down what each of these particular strategies actually*mean*, mathematically speaking, it helps to compare and contrast the result for a variety of percentages. So, sticking with our example of 5:00 mile pace, let's do the math on a few various paces, both faster and slower than 5min-miles. To make things simple, let's call one variant—85% = 5 x 1.15— the "multiplication method" and the other—85% = 5 / 0.85— the "division method."
So, looking at the table above, we can see how the
two methods break down. The multiplication method is the mathematically proper
representation of

*percentage of*—for every incremental change in the percentage, the running pace, in minutes per mile, changes by a consistent amount. Just like 90, 80, and 70% of $100 differ by $10 for each step, so too do 90, 80, and 70% of 5:00 mile pace differ by a consistent change in pace (30 seconds, in this case).**PACE**
The division method is the mathematically proper
representation of

*percentage of*—if we convert 5:00 mile pace into its true speed in meters per second, we can see that the division method results in a linear change in**SPEED***speed*(in m/s) for each incremental change in percent— 0.54 m/s in this case.
So, which is "correct"? That depends on
your perspective. From a convenience
point of view, I am partial to the multiplication method, To me, it makes a lot of sense for 110% and 90% of race pace to be an equal difference,
in pace, from the original race pace.
This is also the opinion of Renato Canova, the world-famous Italian who
has coached many of the great Kenyan distance champions. I have even taken to calling the
multiplication method "Renato Canova math" to distinguish it from the
division method, which you might call, in jest, "American math."

But there might be a good physiological argument
to be made for the division method.
After all, the increases in speed increments that occur with the
multiplication method may lead to an unacceptable ramp-up in effort per
percentage increase. Ideally, you'd have
a percentage system where linear increases in the percentage of race pace resulted in linear
increases in the

*effort level*and*energy expenditure*of the athlete. I don't have the physiology expertise to know how the math of that would work out, but it's pretty obvious that the ramp-up in effort from 100 to 110 to 120% will be more aggressive using the multiplication method than with the division method.
In the end, the important part is not which system
you choose to use. Rather, when
discussing training with athletes and coaches, it is important that you be

**consistent and clear**with your methods! If you were reading about some of Renato Canova's ideas on the critical importance of training at various percentages of race pace, for example, you'd get totally different paces if you used the wrong method! The difference is not so great between 90 and 110% of race pace, but at the extremes it becomes significant—over 30 seconds per mile when comparing 70% of 5:00 mile pace! For the record, all of my writings about training on this blog and elsewhere use the multiplication method. For all of the coaches and athletes out there, I'd like to hear your thoughts on this—how do*you*calculate percentages of race pace?
To close, I'll leave you with four useful formulas
(two for each method) for calculating the proper pace and percentage given a
particular race pace. While it is pretty
basic to figure out the right

*pace*given a particular percentage, the math can get you a bit confused when trying to figure out the*percentage difference*between two paces, especially when you aren't sure which method you're using! To alleviate that problem, I've done the algebra for you. These formulas are particularly handy for use in spreadsheets when preparing pace charts. Note that the dot operator (**·**) just means multiplication.
P = Percentage, in numeric form (i.e. 85, not 0.85)

Pace = desired pace to run

RP = race pace, or the "initial" pace
(representing "100% of pace")

**Multiplication Method**

**Division Method**

I'm glad to see that it's not straight forward, and it wasn't me being a bit thick!

ReplyDeleteYou have a typo in your introduction (2nd paragraph) - you say 90% when you clearly mean 85%.

Thanks for catching that! I'll fix that right up

ReplyDeleteGreat post and would be dog-eared if it was in printed form. Just one minor quibble. In the key you state "P = Percentage, in numeric form (i.e. 85, not 0.85)" But I think that for the division method P would have to be expressed in decimal form, no?

ReplyDeleteThanks for spotting that! The formula should be fixed now.

ReplyDeleteThank-you so much! I missed school the day they taught math, and this post helped me. Please verify I calculated correctly. I'm an 8 min per mile race pace runner in 5k and half-marathon, so using division method is 70%=685seconds, and 80%=600 seconds

ReplyDelete