In today’s world of endurance sport, there are probably more metrics than one can keep count of! Technology is advancing daily and with that comes increased amounts of data that can be implemented and applied to your own training regimen. The question is, what cycling metrics really matter? Do different power metrics matter to different individuals? The following metrics highlighted are some of the core values that endurance athletes should have a basic foundation of, in order to interpret their workout data properly.
RPE: Rate of Perceived Exertion
I am sure many did not think this metric would be listed, but RPE (rate of perceived exertion) is a tried and true metric that is as important for athletes as it is for coaches. RPE is a subjective scale of how a given effort feels. While your bike computer may be telling you one thing, your body may be saying another.
RPE uses a 0-10 scale, where 0 is barely noticeable effort (recovery efforts) and 10 is all out, lay on the floor after maximal effort. While during a session you are analyzing multiple metrics; power, heart rate, cadence, be sure to always remember RPE. Why? It is important for you to understand your body and to be in tune with how you feel during efforts. Not every training day will find you feeling amazing, but understanding how your body feels at threshold, above threshold, below, etc can help you get the most out of your training. It can allow you to know if today is a good day to push through the pain, or if your body is sending signals that it may be best to back off a little bit.
A key piece to RPE is, to be honest with yourself. What does this mean? It means ignoring other data factors: heart rate/power, and analyzing how you feel during a given effort. For example: riding at 260 watts can yield an RPE of 5 for one rider, and an RPE of 9 for another, everyone feels the same during an RPE of 10…horrible. Only you can tell if you are operating at an RPE of 6.5 instead of 5 or 7. Honesty matters.
Just like heart rate, RPE can be affected by external factors as well. Did you sleep poorly the night before? Are you dehydrated? Is the weather outside excessively hot and humid? Your RPE will be altered because you are not performing at your optimal levels. It is important to understand these factors occur and to not get bogged down if you are not hitting your intended targets for the day!
TSS: Training Stress Score
TSS is a score given to tell you how hard a workout was. For example: if you were to ride at threshold for 1 hour, it would surely be more stressful to your system than if you were to ride at threshold for 30 minutes. TSS takes into account both intensity as well as the duration of an activity and paints a more complete picture of how hard a workout was comparative to your overall training. In simplest terms, TSS determines the “cost” a workout has had on your body. Typically the higher the calculated TSS score, the more fatigued you will feel.
TSS is calculated by the following equation:
TSS = (sec x NP x IF) / (FTP x 3600) x 100
sec: the total number of seconds in the session
NP: Normalized Power (more on this in a bit)
IF: Intensity Factor (more on this in a bit)
FTP: Functional Threshold Power (power you can hold for the 60-minute duration)
3600: total number of seconds in an hour
If you do not have a power meter, or for example are trying to determine TSS for an activity that is not heart rate or power-based, then using RPE is a good estimate to gauge your TSS for an activity. You will need to gauge the perceived exertion of the activity and then factor in the duration of the activity as well.
A key piece to stress regarding TSS is that this metric does not work as well when determining the cost of a session that is low in volume, but high in intensity. TSS scores can also be misrepresented in multisport athlete’s training when it comes to swimming, especially high intensity or power-focused swim sessions. When swim sessions result in a power focus, there are larger amounts of rest involved during the session, therefore the total volume of yards/meters swum will most likely be lower than say a distance-focused swim session. A TSS score for a session where a high volume of distance was recorded in X seconds at a lower intensity percentage, will most likely yield a higher TSS score, than a session where all-out speed was the focus with a drop in the volume swum in X seconds. Does this mean the power/speed-focused session was less metabolically costing? No. But at the moment, TSS equations do not reflect proper cost on high-intensity work due to decreased volume.
NP: Normalized Power
During any given session, your power can be variable. Not all power is the same, and this is where Normalized Power plays a pivotal role. This value is a rolling weighted average power for the session, giving more “credit” for efforts above FTP. The idea of NP is to provide a better representation of the physiological cost of a workout beyond average power or total energy output.1
Normalized power is calculated by factoring in differences between a steady workout, and one that is fluctuating. Take for example the following session: Rider A holds 220 watts steady for 1 hour straight, therefore their average power is 220 for the session. Rider B also averages 220 for a 1-hour session, but during the session completed intervals above 400 watts for 1-minute durations and then recovered below 220 between efforts. Though both riders ended their 60-minute rides with the same average power, the feel of the ride was quite different for both. For Rider B, they experienced a higher metabolic cost, and therefore due to fluctuations in their power, they would have a higher Normalized Power reflected in the post-workout metrics. The nuances of power can be hard to encapsulate into average power alone, and that is why Normalized Power can reflect these variances. While TSS may be similar for two different sessions, due to intensity or duration, Normalized Power shows how hard you had to work to achieve the TSS.
IF: Intensity Factor
Intensity Factor allows us to determine how intense a session was relative to our own threshold. IF is represented as any percentage of 1, with 1.0 being your threshold. For example: if your session calculates an IF of 0.5, then this can be read as: the session was performed at 50% of your threshold.
IF is calculated by taking a ratio of your NP to your threshold power. If your FTP is 200 and your normalized power for a session is 180, then your IF would be 0.9. Typically general endurance sessions fall between the 0.6-0.7 range, while higher intensity sessions can fall under the 0.8-0.9 and sometimes depending on the event, can exceed 1.
While the cycling metrics that are available to us can at times feel overwhelming, having an understanding of the key basics can help make a difference in the interpretation of your data. Always keep in mind that numbers only tell one side of the story when it comes to training and racing. Learning how your body feels and responds to given efforts is just as (if not more!) important as hitting your target numbers. Knowing how to apply these metrics properly to your training can help shape you into a more informed, and well-rounded athlete.