In a health or exercise context, “Borg” refers to the Borg Rating of Perceived Exertion (RPE) scale, a tool for measuring how hard physical activity feels to you. It’s not actually an acronym. The scale is named after Gunnar Borg, a Swedish psychologist who developed it during the 1960s and 1970s while studying how people perceive physical effort. The abbreviation you’ll see most often is RPE, which stands for Rating of Perceived Exertion.
What the Borg Scale Measures
The Borg scale translates a subjective experience, how hard you feel you’re working, into a number. Instead of relying solely on heart rate monitors or oxygen measurements, you rate your own effort based on how your body feels overall. The official instructions describe it as your “total, inner feeling of exertion,” combining physical stress, fatigue, breathing difficulty, and general effort into a single score. You’re not supposed to focus on one sensation like leg soreness or breathlessness alone.
The Two Versions of the Scale
Borg actually created two scales, and they work differently.
The 6-20 Scale
The original scale runs from 6 to 20, which seems like an odd range until you learn the reasoning: multiplying your rating by 10 gives a rough estimate of your heart rate during exercise. A rating of 12 (somewhat hard) would suggest a heart rate around 120 beats per minute. Borg proposed this 1:10 ratio in 1982, and later research refined it slightly, suggesting the formula works best for ratings between 11 and 16 with a small adjustment of 20 to 30 extra beats per minute. The correlation between RPE scores and actual heart rate isn’t perfect in everyday conditions (a meta-analysis found an overall correlation of 0.62 across healthy individuals), but in controlled settings like tethered swimming, the relationship has been measured at nearly 1.0, essentially a perfect match.
The CR10 Scale
The second version, called the Category-Ratio 10 (CR10) scale, runs from 0 to 10, with an “absolute maximum” option above 10 for truly all-out effort. This is the version most people encounter today. The labels are intuitive: 0 means nothing at all, 1 is very weak, 3 is moderate, 5 is strong, 7 is very strong, and 10 is extremely strong. Half-point increments allow for finer distinctions between levels.
The American College of Sports Medicine uses this 0-10 framework in its current exercise intensity guidelines. Moderate-intensity exercise targets an RPE of 3 to 4. Vigorous exercise falls between 5 and 7.
Why It Matters for Exercise
Heart rate is the most common way to gauge workout intensity, but it has a major blind spot. Certain medications, especially beta-blockers prescribed for high blood pressure, suppress heart rate artificially. If you’re on one of these medications and try to hit a target heart rate zone, the numbers won’t reflect how hard your body is actually working. The Mayo Clinic specifically recommends the Borg scale as an alternative for people in this situation.
Even without medication complications, perceived exertion captures something heart rate alone can’t: how your whole body responds to effort on a given day. Sleep quality, hydration, stress, temperature, and dozens of other variables affect how a workout feels. Two runs at the same pace can produce the same heart rate but feel completely different. The Borg scale accounts for all of that.
How Accurate It Is
The scale works well across a broad range of people. Research comparing normal-weight individuals with overweight and obese individuals found no significant difference in the relationship between RPE scores and actual physiological markers like percentage of maximum heart rate and oxygen uptake. In other words, people of different body sizes are equally capable of rating their effort accurately, particularly adults between roughly 21 and 59 years old doing low-to-moderate intensity exercise.
That said, the scale has limits. Personality and mental health influence how people perceive and report effort. Extroverted individuals tend to underrate how hard they’re working at higher intensities, and their preferred effort level for sustained exercise is higher than that of introverts. Anxiety and depression can also distort ratings. Research found that anxious or neurotic individuals had the most difficulty accurately processing how hard they were working. One study even demonstrated that perceived exertion could be shifted up or down through hypnotic suggestion, with corresponding changes in actual physiological responses, highlighting how deeply intertwined perception and physical performance really are.
How to Use It During a Workout
Using the scale is straightforward. At any point during exercise, pause mentally and assess your total feeling of effort. Consider your breathing, muscle fatigue, and overall strain together. Then assign a number. On the CR10 scale, if you can carry on a full conversation without any difficulty, you’re likely at a 2 or below. If you can speak in short sentences but not sing, you’re probably in the 3 to 4 range (moderate). If talking is difficult, you’re at 5 or above (vigorous).
For general health benefits, most guidelines recommend spending at least 150 minutes per week at moderate intensity (RPE 3 to 4) or 75 minutes at vigorous intensity (RPE 5 to 7). Tracking your RPE across workouts also helps you notice trends. If an exercise that used to feel like a 5 now feels like a 3, your fitness is improving, even if the stopwatch hasn’t changed.