RPE, MHR%, LT1/2, LSR, GCT… WTF!?

With the explosion of running in this boom we've seen over the past few years, comes an explosion of information, application of coaching and in the area of running training plans, you might have used in the past you have likely encountered a dizzying array of acronyms: RPE (Rate of Perceived Exertion), MHR (Maximum Heart Rate, often accompanied by percentage values), LT (Lactate Threshold 1 and 2), and LSR (Long Slow Run), and GCT (Ground Contact Time) to name just a few. It’s enough to make any runner’s head spin. But here’s the thing: you don’t need to feel overwhelmed by all these metrics. In fact, embracing their variety, and ignoring what doesn't need to be a concern, can help you make your training more enjoyable, effective, and fun.

Don’t Sweat the Acronyms

The key to mastering these concepts is to remember this simple truth: they’re all just tools for understanding and improving your performance, often kind of saying the same thing in different formats. They’re not rigid rules to follow or barriers to entry. Instead of being distracted by the latest buzzword or acronym, focus on finding what works for you and your body.

For example, a coach might prescribe a run based on RPE, a subjective measure of how hard you feel you’re working on a scale of 1-10. This is a favourite of mine, especially for beginners. Over time, you might notice that your RPE 7 corresponds to running at 85% of your MHR. That’s useful information, but it doesn’t mean you need to ditch RPE for heart rate monitoring or vice versa. These metrics complement each other. The danger though with RPE is that especially for those who have not done endurance sports before, and don't know yet what their limits are, RPE can take a while to figure out as a beginner.

Start With What Feels Natural

When you’re starting out though, your perception of effort—RPE—is a fantastic guide. It’s simple, accessible, and requires no equipment. For instance, a conversational pace might feel like RPE 3-4, while an all-out sprint is closer to RPE 9-10. Once you get comfortable tuning into these sensations, you can start correlating them to other metrics, for example:

• MHR (%): If you’ve calculated your maximum heart rate (220 minus your age is a common estimate but not bulletproof), you might notice that an RPE 5 effort aligns with about 70% of your MHR, while RPE 8 is closer to 90%. Once you join the dots, you're empowered, but this doesn't have to happen early in your training, or at all - it's just added insights.

  
  

• LT (Lactate Threshold): This is the point where your body shifts from primarily aerobic energy production to anaerobic. It ranges on a curve based on effort levels and duration, moving from LT1 (basically a steady run that generates low amounts of lactate) to LT2 (where it's manageably hard) It often feels like an RPE 7-9, where talking becomes challenging but at the top end, sustainable for a 20-40 minute hard effort.

  
  

• LSR (Long Slow Run): This is much more of a simple one to grasp, but how do you know what constitutes as the "right" slow, and what is too slow or too quick? Again with this for example, the whole benefit is aerobic development and muscoskeletal development through time on feet, and when you realise what slow feels like, you can match this to a coaches set RPE levels, or MHR% instructions.

  
  

• GCT (Ground Contact Time): Amidst all the talk of heart rates, thresholds, and effort scales, there’s one lesser-known but increasingly popular metric to consider: Ground Contact Time (GCT). This measures the amount of time your foot spends on the ground with each step, typically expressed in milliseconds. While it’s often associated with biomechanics and efficiency, GCT can also provide valuable insights when combined with metrics like RPE, MHR, and LT. Efficient runners typically have shorter ground contact times (GCT), but this varies with intensity, e.g:

• Low-Intensity Runs - GCT is naturally longer with relaxed, steady strides.

• Threshold Runs - GCT shortens as speed increases; longer GCT here may indicate fatigue or poor form.

• Sprints - GCT is shortest at maximum effort, reflecting explosive power.

Understanding these shifts can help optimise your form across different run types.

use variety to Gamify Your Training

Once you’ve built awareness of how these metrics connect, you can use them to make your training more engaging. Think of it as a way to gamify your runs, setting mini-goals and challenges for yourself, when you feel comfortable with the data and what it means. As training weeks go by, taking a unique focus for the variety in your week can put the fun back in running.

For example:

• Run by RPE during a long run, aiming for a steady RPE 4-5, and then review your heart rate data afterward (not during) to see how it aligns. This can allow you also to trust your feelings when running to gauge effort better in the future.

• During interval training, focus on hitting a specific percentage of MHR for your race pace / hard efforts (e.g., 85-90%) and check how it feels compared to your RPE and how it stacks up to the race pace you may be targeting.

• For threshold runs, aim to maintain the intensity you associate with your LT level—usually an RPE 7-8 and see how long you can sustain it.

• When running short intervals and strides, try and focus on minimising GCT to support quick, light steps to boost running economy, efficiency and speed, reviewing the data after to see how it may have improved from last time and how it affected pace.
  

Embrace Variety

The beauty of these metrics is that they provide different lenses through which to view your training. One day, you might focus on the numbers from your heart rate monitor. Another day, you might leave the tech behind and simply run by feel and review afterwards. Both approaches have their place, and together they can help you develop a deeper understanding of your body.

The most important thing is not to get bogged down by the acronyms or feel pressure to master every metric immediately. Start with what feels natural, build awareness of how it correlates to other measures, and use that knowledge to make your training more varied and enjoyable, using a mix of focal points for running, that ultimately will allow you to be more in tune with yourself. Using the support of a coach is useful here too. She or he can assess some of the data for you, draw alignment and join some dots, giving you the freedom to apply the variety with the rationale left to another supporting person (i.e the coach)

The Takeaway

RPE, MHR, LT, LSR. GCT... the list goes on —they’re not enemies; they’re allies. Each one provides valuable insights into your training and performance, and together, they can help you find your rhythm. But importantly they don't matter half as much as tuning into your own body and feeling your way around the efforts that are prescribed. So don’t let the jargon distract you, but f you are interested then embrace the variety of insights we're blessed with have fun with it, and remember that the best training plan and language used is the one that works for you. When you do understand the application of these areas and their uses and relationship, with the support of a coach - you can use them as tools to help you move forward.

Get in touch if you need support making sense of and applying the range of metrics and measures available to you on your running journey.