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Posted in Team Finish Line.

November 6th, 2020

Training for Cycling as a Runner: Watts, Speed, Heart Rate and Where to Start

By Brendan Martin, PT, DPT, FAFS

While runners typically speak in terms of distance, pace, and maybe heart rate; cyclists often elect to use an entirely different metric, power, to guide their training and racing. 

Power is measured in Watts, (or Joules per second 🤓,) which represents how much work or output you are translating into the pedals per second. Another way of thinking about it is to imagine a lightbulb connected to your bike. The more gusto you are pressing into the pedals, the brighter the lightbulb will shine.

When I first started cycling more seriously, I assessed my training efforts strictly off of speed and distance, since :

  • A) that is what my GPS watch measured for me, and
  • B) I’m a runner and those are the measurements that we all use! 

However, I quickly realized that all it took was 10 mph winds to slow my ride down quite a bit.  Instead of letting a pretty average amount of wind devalue my training effort, I decided to look elsewhere. I invested in power meter pedals, and while it took some adjustment time, I quickly bought into the training-by-watts mindset.

First, you must perform a power test where you ride for 20, 30 or 60 minutes at a maximal effort. Using the average watts recorded, you can calculate your FTP, or Functional Power Threshold. This number is the key, as it will guide the majority of your training.  Threshold repeats are done at 95-105 % of FTP. Vo2 Max efforts are done at 130% of your FTP. Recovery rides are <70% of your FTP. And so on.  The beauty of training by power and power zones is that on a given day, no matter what the course or weather conditions are like, you are still able to achieve your training goals for that day.  A hill will slow your speed down, but you know you are working at the proper effort.  A headwind will slow your speed down, but you again are reassured that you are working at the proper effort.  If you’re going downhill, you need to pedal like crazy to make sure you are still putting in a meaningful amount of work/power. 

While on the surface it sounds like it complicates matters, power is very freeing in that it removes a lot of external factors from your training focus. 

After a series of productive weeks or months of training, you can perform a new power test and measure your progress and re-adjust your training zones.

Learning your power threshold can be a valuable resource for racing as well.  Since it tells you how much juice you are putting into the pedals, it is far more indicative of how quickly you will fatigue when compared with speed in mph.  If you are benefiting from a tailwind, you could be flying without putting in much effort at all. If you are pedaling up a steep hill into the wind, you might be working extremely hard but your speed is still only going to be 0.5 mph.  Nobody racing wants to see 0.5 mph, so if you were to go strictly off of speed, you might fry your legs and lungs trying to muscle up the hill and avoid the slow speed.  Power comes in to reassure you: “yes, you are working plenty hard – stay patient” as you are riding within your goal power zone for the distance.  It allows you to “pace yourself” for the duration of the event, even as your literal pace or speed varies depending on wind and terrain.

Training by power comes at a cost, though, in that you must upgrade either your crank or pedal to have a power meter in it. This can cost $500-2000, a potential barrier to training by power.  Luckily, heart rate monitors are quite a bit more affordable, starting at under $100.  They don’t provide the same measurements and information as a power meter, but are useful tools nonetheless.  Similar to how wattage would spike while grinding up a hill, heart rate will rise as you increase your work output.  The difference is that heart rate can be higher on a day where you are feeling very fatigued, or it is very hot, etc.  While heart rate tells you more about how your body and system are working on a given day, it will not tell you as much about your performance.  Power numbers would be down on a day that you are feeling “off” and not performing as well.  Heart rate is how hard the engine is working, power is how much effective work that same engine is putting out.  Both are useful and both can guide your training via “zones,” but they are different. 

It is worth noting that for experienced runners that are getting into cycling, they may have a seriously difficult time getting their heart rate up despite pedaling as hard as they can.  There are many potential explanations for this, but the most simple is that the runner lacks the cycling specific leg strength to work their extremely developed cardio system hard enough to get the heart working harder.  This is actually the main reason I caved and invested in power meter pedals. I would be riding so hard that my legs would be sore for days, but my heart rate would be lower than it is on a recovery shake out jog.  Power allowed me to see how much output I was producing, regardless of the disparity between my aerobic fitness and relatively weak cycling legs.  I was able to glean more meaningful insights into my efforts within a given ride by using watts. 

Side note; For the above reasons, there is a rule of thumb that runners-turned-cyclists adjust their HR zones by 10 beats (lower) when cycling. 

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