What is Threshold?
Lactate Threshold Pace, Heart Rate or Power all refer to the maximum effort you’re able to maintain while your body can still remove the lactate acid being used by the muscles. For most trained athletes this is similar to the maximum effort they can maintain for an hour. Going above this threshold effort will result in a “burn” in the muscles and, after a few minutes, require stopping or slowing in order for the body to clear the lactate acid. As endurance athletes, we want to go as fast as we can for as long as we can. Therefore staying under or right at the lactate threshold allows us to go hard, but not so hard that we have to stop.
Lactate Threshold (LT) is also referred to simply as threshold. Lactate Threshold Power is also referred to as functional threshold power (FTP).
Why is Threshold Important?
Unlike VO2 max, which relies largely on an individual’s predisposed physiological characteristics such as lung capacity and body mass, lactate threshold can be improved consistently through training. Training below and above threshold will improve the body’s ability to clear lactate acid as well as tolerate higher concentrations of lactate acid.
As you gain fitness, your threshold increases. Your threshold is the basis around which your training or power zones are established - they are determined as a percentage of your threshold.
How is Threshold Determined?
Lab testing: To determine your threshold power, pace or heart rate you can go to a lab and do a graded test where blood or oxygen exchange samples are taken to determine the effort when you’re no longer able to clear more acid than you’re producing.
Field Testing: Without access to a lab, the next most accurate test is a 1-hour steady effort (such as a time trial on a bike). If doing a maximal 60 minute test is not possible, an athlete can do shorter, maximal tests and extrapolate their threshold. For example, Joe Friel recommends an athlete run alone and hard for 30 minutes, and use the average pace or heart rate for the last 20 minutes as your lactate threshold. Such methods of “field testing” may not be as accurate as lab testing but will still provide a sound estimation to base training zones off of, as well as measure fitness improvements over the season.
For details on some recommended methods of field testing, read Joe Friel’s Quick Guide to Setting Zones.
How is Threshold Used Within TrainingPeaks?
Your threshold is used to calculate TSS for each workout.
Your threshold is used to calculate Training Stress Score (TSS), which quantifies overall stress for each session. Since threshold is closely associated with your max effort for 60 minutes, we award 100 TSS points for a one-hour max effort. However, if you train at a lower effort you can still accumulate 100 TSS if your hold the lower effort for a longer period of time. Conversely, going at an effort greater than threshold for less than an hour can result in 100 TSS. How we calculate TSS for each sport.
TSS is used to measure fitness, fatigue and form
As you accumulate TSS from each session each day, your fitness improves. You can measure your overall long term fitness using Chronic Training Load (CTL) which is a rolling average of the previous 42 days of TSS accumulation. You can also measure fatigue, the short term effect of training, using Acute Training Load (ATL). ATL is your rolling 7-day average TSS.
We know we cannot solely focus on raising ATL and CTL since we also need to rest. Just as we use CTL/ATL to measure fitness and fatigue, we use Training Stress Balance (TSB) to measure your form.
- Fitness (CTL): Chronic Training Load, long term effects of workouts
- Fatigue (ATL): Acute Training Load, short term effects of workouts
- Form (TSB): Training Stress Balance
Fitness (CTL) – Fatigue (ATL) = Form (TSB)!
If your ATL is greater than your CTL, your TSB will be negative. If your ATL is less than CTL, your TSB will be positive. A positive TSB will indicate a trend towards improved rest as well as a reduction in fitness, similar to what you’d see during a taper period. At a certain TSB, your fitness and your fatigue will be in balance so that you are in peak “form” for your event.
All of this is calculated in the Performance Management Chart.
Your ATL, CTL and TSB are calculated and graphed within the TrainingPeaks Performance Management Chart (PMC). The PMC is a key tool in TrainingPeaks that allows you to gauge your fitness vs. fatigue over time, and be on peak form for your events.
Your threshold is also used to calculate Intensity Factor (IF) for each training session. If threshold is set inaccurately in TrainingPeaks, this statistic will also be inaccurate. Read more about IF.
How Does TrainingPeaks Calculate My Threshold?
As you upload sessions to TrainingPeaks that are over threshold TrainingPeaks will be able to alert you when we detect that your threshold may have improved:
- Heart Rate Threshold: We suggest a threshold increase if your Peak 60 Min OR 95% of your Peak 20 Min Heart Rate (whichever is higher) is greater than the currently set threshold.
- Power Threshold: We suggest a threshold increase if 95% of your Average Peak 20 Min Power is greater than the currently set threshold.
- Pace Threshold (Run Only): We suggest a threshold increase if your Peak 45 Min Average Pace is faster than the currently set threshold.
We may detect threshold improvements in more than one category. At this time, TrainingPeaks does not suggest decreases in threshold.