I hit my LTHR (Lactate Threshold Heart Rate) during a 5k PB at around the 1.5k mark.
So what? You rightly ask.
Well the LTHR is a point that when you perform above that point your body starts to accumulate too much lactic acid/lactate/H+ ions which, at SOME POINT, will cause you to stop.
But where is that ‘SOME POINT’. Well clearly for me based on that race it is AT LEAST 3.5kms (ie from 1.5km to 5km) and in fact I have stayed above it for 26 mins in a 10k and for 37 mins in a duathlon. In fact if you are fitter than me then you can keep at that level for over an hour…but probably not for a Half Marathon or a 2 hour duathlon/triathlon.
Going back to 5km then people can, apparently get their HR above that level for all but the first 30 secs or so. I’m not sure how though. As in my case to get my HR that high would require me to run a VERY fast first KM – which kind of goes against the idea of an equal split over all the 5ks of a 5k race to get a PB.
Any thoughts from your experience?
Related articles
- 5k Taper Plan: Abstinence vs Doing It Properly And a Duathlon Variant (the5krunner.com)
- Great Running Plan! (wtamu.wordpress.com)
- Running is the New Black (diaryofadomesticdiva.com)
- Keeping Yourself Motivated After Your Goal Race (wildthingsrunfree.com)
- How do I get a 5k parkrun PB next month? (the5krunner.com)
- 5k: the5krunner gets back to running … strange that (the5krunner.com)
- Lsd (long Slow Distance) (lennonfitness.com)
- The slow run (briandmains.com)
- VO2max and Metabolic Testing: “Are You a Sugar Burner or a Fat Burner?” (bodythrive.wordpress.com)
- Interval training: how and why (boomerathlete.wordpress.com)
- 5K run last evening (starlitstudio.typepad.com)
Last Updated on 2 October 2026 by the5krunner
Small things I always use
- Garmin 90-degree charging adapter: Charges your Garmin from any USB-C cable. Essential when travelling. I use one.
- Body Glide: The blue anti-chafe stick swimmers and runners carry. I use it.
- Speedo earplugs: Fewer ear infections and no cold-water dizziness. I use them.
- Dryrobe Advance: My winter changing robe for open-water swims. I use one. A cheaper option is the AONYIYI changing robe.
- Maurten: Race fuel that stays easy on the stomach. I use them.
- Garmin charging puck: The quickest way to top up before a session. I use one.
- Injinji: Toe socks that stop rubbing, so you run more. I use them.
- Ultimate toe protectors: Stop black toenails on long runs. They work. I use them.
- Compressport R2 v2 calf sleeves: My calf sleeves of choice. I use them.
- Cellucor C4: My pre-workout before hard sessions.
- TPU tubes: Schwalbe Aerothan, Tubolito and Pirelli SmarTube. Light, tiny spares. I use all three.
- G8 insoles: Adjustable insoles that are good. I use them.
- Cycplus Cube: A 97g electric pump that gets a road tyre rideable in two minutes. I carry one. 5% off with code THE5KRUNNER.
Watches and sensors
- Polar H10: My daily driver for waking HRV.
- Polar Verity Sense: My backup arm-worn HR sensor.
- Nomad bedside charger: Charges my iPhone and Apple Watch overnight. I use it, and many of their bands.
- Train.Red: The best muscle oxygen sensor I’ve used.
- Tymewear: Accurate heart rate and reliable ventilatory zones. I use it to pace endurance rides over an hour.
- Garmin Forerunner 970: A pro-grade triathlon watch. I use this.
- Apple Watch Ultra 4: My daily smartwatch. No phone needed on rides.
- Garmin Fenix 9 Pro: I’ve just bought one.
On the bike
- Continental GP5000 for everyday riding, and Aero 111 on the front for special occasions.
- Helmets: Specialized S-Works Evade 3 for road riding, and Rudy Project Wing for TT-style races. I use both.
- Ravemen FR300: A front light that mounts under your Garmin or Wahoo. I use one.
- Wahoo TRACKR Radar: I use it on one bike and Varia on the other. They perform the same.
- Garmin Varia RTL515: Radar that warns you of cars from behind. I use this model.
- Wahoo ELEMNT Roam 3: The bike computer that’s easy to use. I use mine on most rides.
- Favero Assioma Pro RS2: Accurate power pedals that swap easily between bikes. I use this model.
Home and indoor training
- NPE Runn: Makes my basic treadmill smart, sending more accurate speed and distance to my watch and Zwift. I use it.
- Google Wifi: Keeps Zwift connected in my pain cave. I use it.
- Apple TV 4K: Zwift on the big screen. I use two.
- Google Nest Doorbell (wired, 2nd gen): My video doorbell, running in both Google Home and Apple Home. I use it.
Health, recovery and sleep
- FreeStyle Libre 3 Plus: Shows how my blood sugar responds to diet.
- hDrop: Measures my sweat loss in summer and indoors.
- Fourth Frontier Zone: Checks my heart under load in hard sessions.
- Oura Ring 5: My partner’s recovery tracker of choice.
- Kineon MOVE+: Red light therapy for niggles. It works.
- Eight Sleep: A cooling mattress cover my partner and I use nightly.
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tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID
