In the endurance world, and even in HYBRID space like HYROX, we spend a lot of time talking about our ‘thresholds’; “what’s your threshold pace?” is as ubiquitous in endurance circles as “what’s your bench?” is in strength sport. Threshold pace – is a metric gaining increasing footing in training programming and load monitoring in HYROX. Physiologically speaking, ‘threshold’, is defined the transition from steady-state to non-steady-state physiological responses to exercise. That is, above this second threshold – commonly referred to as the “anaerobic threshold”– physiological variables such as oxygen consumption, circulating lactate concentrations, and muscle and blood acidity cannot stabilise, which means that fatigue inevitably and progressively develops.
Whilst knowledge of this second threshold is definitely of significance to HYROX athletes, we argue that it is knowledge of the first physiological threshold – often referred to as the “aerobic threshold” or more accurately “lactate threshold” –that is of equal significance to HYROX athlete. In this blog, we are going tobriefly describe what this first threshold is, why it is useful, and how might go about identifying it at an individual level.
What is it?
The first threshold – which as mentioned is conveniently referred to as anything from the “aerobic threshold” or “lactate threshold” to LT1 or VT1 – defines the boundary between ‘moderate’ and ‘heavy’ exercise-intensity domains. Below this threshold, blood lactate concentrations are stable and essentially equal to baseline, whereas above it blood lactate concentration may stabilise, but at concentrations above baseline (4, 5, 8). It is this physiological definition that makes “lactate threshold” the most appropriate terminology. Similarly, when exercising at or below the lactate threshold, utilisation of rapid energy systems like the pyruvate-to-lactate pathway or phosphocreatine metabolism will be minimal, meaning that acidity is not meaningfully developed in the muscles and blood (4, 5, 8). Exercise below the lactate threshold is ‘conversational’ – or easy enough that it is possible to simultaneously hold a conversation without undue effort. Thus, exercise at and below this threshold can typically be sustained for multiple-hours in well-trained endurance athletes. Of course, generally below HYROX race pace for most individuals, but still of significance for training adaptation, and consistency.
Why is knowledge of this threshold important?
The lactate threshold is critical in the HYROX athlete as it defines the upper limit for moderate-intensity training sessions designed to result in minimal physiological stress and allow rapid recovery (11, 13, 15). Indeed, in well-trained athletes, the lactate threshold appears to delineate the intensity below which post-exercise autonomic disturbance – measured through HRV – is minimal (12). When training above the lactate threshold, disturbances in autonomic balance are more likely, and the fatigue and recovery time required following training is increased. Thus, when training below the lactate threshold is accurately programmed and emphasised in the training plan, larger overall training volumes can be attained. That is why many higher performing athletes adhere to what is called a pyramidal or polarised training intensity distribution, with upwards of ~75-80% of total training time accumulated at intensities below the lactate threshold (13, 14). That is not to say that all of our training should take place below the lactate threshold; just that we want to be very specific about when and how we go above it, such that stress, recovery, and adaptation can be managed successfully. Easy training easy, and hard training hard! This means we are substantially increasing our chances of consistent training, lowering the risks of injury, over-training, and illness. Consistent training is your best chance to hit a PR at your next HYROX!
How do we identify it?
That is the big question we have to grapple with. Ideally, the best approach for identifying your lactate threshold is to go into a laboratory and get it tested. This will involve exercising at progressively increasing workloads, with heart rate and blood lactate concentration – typically from a fingertip or earlobe – measured in each stage. This allows the exercise physiologist to construct a workload vs.lactate curve, and therefore report back your lactate threshold power or speed and heart rate. Knowledge of your lactate threshold heart rate might also be really important when trying to regulate your training intensity such that it remains easy 2, 3, or 4 hours into a session. However, our research has shown that it is quite possible your lactate threshold power will decline after multiple hours of exercise – a series of recent studies showed this is the case for the second threshold (1–3)).
Now, we appreciate that not everyone has frequent or affordable access to laboratory testing. That begs the question; can I estimate this threshold myself? Phil Maffetone has proposed the‘MAF’ estimate of lactate threshold heart rate (180 minus age in years, with some adjustment for training status) (7), although the accuracy of this method has not been tested empirically, and the possibility of meaningful error at an individual-level can’t be overlooked. Legendary physiologist Martti Karvonen also tried to estimate the heart rates that should be used for different training intensities as far back as 1957 (6), with his ‘Karvonen formula’ using percentages of the heart rate reserve (maximum minus resting rates).Specifically, ~40-60% of heart rate reserve has been referred to as ‘moderate-intensity’, though this is not anchored to other physiological responses. So, for example, if an individual had a maximum heart rate of 185bpm and a resting heart rate of 40 bpm, we would calculate an HRR (185-40) of145 bpm. The Karvonen formula suggests taking 40-60% of this number and then adding back on your resting heart rate. E.g., 60% of 145 bpm = 87 bpm; 87 bpm +40 RHR = 127 bpm. This would be the suggested upper end of moderate-intensity exercise. Indeed, in our experience having tested numerous athletes in the laboratory using metabolic and lactate data, this number appears much lower than an expected aerobic threshold in athletes.
One ready-to-use method that has seen some attention in the literature relates back to my point about exercise below the lactate threshold being ‘conversational’ in nature. The“Talk Test” is a method by which the lactate threshold is identified as the workload at which an athlete can no longer comfortably talk. The effectiveness of this test for identifying the lactate threshold power and heart rate was examined ina cohort of 18 well-trained cyclists back in 2013 (9). In this study, thecyclists performed an incremental test in the laboratory to estimate the lactate threshold on two occasions: once with physiological measures, and oncewith a talk test. In the latter test, participants were asked to read a standardised paragraph (38 words) aloud at the end of each stage, with the lactate threshold identified when the participants could not talk comfortably.There were no significant, systematic differences between lactate threshold pace or heart rate estimates using the physiological data or the talk test, with strong correlations observed between the two measures, and relatively tight limits of agreement. Therefore, this test could easily be done at home and may provide a useful means of estimating the all-important lactate threshold. There has also been a new paper published recently by Foster et al(16), that supported the effectiveness of the talk test to ascertain the first aerobic threshold.
Have a go!
Why not have a go at this at home? If you fancy it, here are some instructions you could follow for a running-based test.
- Choose a 30-40 word paragraph you are familiar with (e.g. words to your national anthem or from your favourite poem.
- Put on your heart rate monitor.
- After a 10-min warm-up, start the test at a running pace that is very easy (perhaps ~40-50% of FTP).
- Increase your pace in the treadmill by 0.5 or 1 kph (depending on level) every 3 minutes (keep the treadmill at 1.5% gradient).
- Read the passage aloud during the last 30 seconds of each stage
- Stop the test when you can no longer comfortably read the passage aloud (i.e. you have to breathe heavily after every few words)
- Use the running pace of the last stage that you could read comfortably in as your lactate threshold power estimate, and take the heart rate from 2:00-2:30 of that stage as your lactate threshold heart rate estimate (reading the passage may interfere with your heart rate, so don’t use the last 30-seconds whilst you were reading!)
The ENDUROX Calculator
Establishing your training zones is really important for training. You can also estimate your Level 2 training zone (top of VT1/aerobic threshold), as a percentage of your 5 km time. Using the VDOT formulae, established by Jack Daniels, we can estimate critical run pace ((CRP)(VT1/Anaerobic threshold)), and then derive the aerobic threshold as a %.
To establish your running training zones, take a look our specific Calculator here. This is best to be done on your Desktop, not your tablet or smartphone.
Rowing and Ski Erg Training Zones
Don’t forget — the SkiErg and RowErg are also powerful tools for building your critical endurance base in HYROX. This calculator includes training zone estimators for both the Ski and Row Ergs, based on your best 5-minute time trial performance. Simply enter the average 500 m split you can sustain during an all-out 5-minute effort on either the Ski or Row Erg to get your personalised training zones.
Predict your Race Pace Targets for your next HYROX
Based on your 5 km race pace time, and CRP, use the suggested target HYROX race pace, to ensure you have optimal pacing on race day.
References
1. Clark IE, Vanhatalo A, Bailey SJ, Wylie LJ, KirbyBS, Wilkins BW, Jones AM. Effects of two hours ofheavy-intensity exercise on the power–duration relationship. Med SciSports Exerc 50: 1658–1668, 2018.
2. Clark IE, Vanhatalo A, Thompson C, Joseph C, BlackMI, Blackwell JR, Wylie LJ, Tan R, BaileySJ, Wilkins BW, Kirby BS, Jones AM.Dynamics of the power-duration relationship during prolonged endurance exerciseand influence of carbohydrate ingestion. J Appl Physiol 127:726–736, 2019.
3. Clark IE, Vanhatalo A, Thompson C, Wylie LJ, BaileySJ, Kirby BS, Wilkins BW, Jones AM.Changes in the power-duration relationship following prolonged exercise:estimation using conventional and all-out protocols and relationship withmuscle glycogen. Am J Physiol - Regul Integr Comp Physiol 317:R59–R67, 2019.
4. Jones AM, Vanhatalo A. The ‘critical power’ concept: Applications tosports performance with a focus on intermittent high-intensity exercise. SportsMed 47: 65–78, 2017.
5. Jones AM, Wilkerson DP, DiMenna F, Fulford J, PooleDC. Muscle metabolic responses to exercise above and below the “criticalpower” assessed using 31P-MRS. Am J Physiol - Regul Integr Comp Physiol 294:R585–R593, 2008.
6. Karvonen MJ, Kentala E, Mustala O. The effects of trainingon heart rate; a longitudinal study. Ann Med Exp Biol Fenn 35:307–315, 1957.
7. Maffetone P, Laursen PB. Maximum aerobic function: Clinical relevance,physiological underpinnings, and practical application. Front Physiol 11:296, 2020.
8. Poole DC, Ward SA, Gardner GW, Whipp BJ.Metabolic and respiratory profile of the upper limit for prolonged exercise inman. Ergonomics 31: 1265–1279, 1988.
9. Rodríguez-Marroyo JA, Villa JG, García-López J, Foster C.Relationship between the talk test and ventilatory thresholds in well-trainedcyclists. J Strength Cond Res 27: 1942–1949, 2013.
10. Rogers B, Giles D, Draper N, Hoos O, GronwaldT. A new detection method defining the aerobic threshold for enduranceexercise and training prescription based on fractal correlation properties ofheart rate variability. Front Physiol 11: 596567, 2021.
11. Seiler KS, Kjerland GØ. Quantifying training intensity distributionin elite endurance athletes: Is there evidence for an “optimal”distribution? Scand J Med Sci Sport 16: 49–56, 2006.
12. Seiler S, Haugen O, Kuffel E. Autonomic recovery afterexercise in trained athletes: Intensity and duration effects. Med SciSports Exerc 39: 1366–1373, 2007.
13. Seiler S, Tønnessen E. Intervals, thresholds, and long slowdistance: The role of intensity and duration in endurance training. Sportscience 13:32–53, 2009.
14. Stöggl T, Sperlich B. Polarized training has greater impact on keyendurance variables than threshold, high intensity, or high volumetraining. Front Physiol 5: 1–9, 2014.
15. Sylta Ø, Tonnessen E, Seiler S. From heart-rate data totraining quantification: A comparison of 3 methods of training-intensityanalysis. Int J Sports Physiol Perform 9: 100–107, 2014.
16. Foster, C. et al. “Physiological drift duringsteady-state exercise based on the incremental Talk Test” Human Movement 2025doi: 10.5114/hm/199730
