You know that feeling when you are absolutely jamming during a workout- you don’t have intervals/ intensity planned, but you feel absolutely phenomenal, so you push the pace anyway? You are an absolute beast- crushing this workout and life in general; you blast your favorite tune and go even faster. You felt pretty tired this morning getting out of bed (you’ve been stressed at work and putting a lot of training hours in lately too), but now you feel AMAZING!
This is my favorite feeling, and a situation I find myself in more often than not. In fact, even when I don’t necessarily start the workout with those amazing feelings, I find that if I just push a little harder, I tend to feel better and they start to go away. I am the absolute queen of hammering into this “feel good” zone- a zone I very non-scientifically like to call “high level-2”. I like to convince myself that I’m not reaching my anaerobic threshold, but let’s face it- I probably am. After years of experience with this, I now make an effort to be a little smarter. I will explain why below, but first, I’ll give some background on training zones so it all makes sense.
Training Zones
Training zones are a tool that can be used to help structure your training. Typically, they are calculated as a percentage of heart rate max, as a lot of people use heart rate monitors during training. Other metrics can also be used; for example, power for cycling and lactate has become increasingly popular with elite cross-country skiers during interval training. Heart rate is much simpler and doesn’t require you to get your finger pricked multiple times throughout a session, however, so we will stick with that. Here is the model we use at ETS for zones, which stems from our Nordic skiing background (so the zones are a little different than if you were to do a simple google search of training zones).
Zone 1: 55-72% HR max
Zone 2: 72-80% HR max
Zone 3: 80-87% HR max (~2mm-4mm of lactate)
Zone 4: 87-93% HR max (~>4mm, or around anaerobic threshold)
Zone 5: 93-100% HR max
To get your HR max, you need to do an effort where you go as hard as possible- this could be on a treadmill, an uphill running time trial, or on the bike. It also doesn’t need to be long- just long enough for you to feel like you have maxed out. The important part is to select an activity that you actually participate in regularly; for example, if you do 90% of your training on foot and rarely ride a bike, you won’t get very accurate numbers on a bike because your muscles aren’t accustomed to the motion.
If you aren’t a heart rate/ numbers kind of person at all, you can stick to my personal, non-scientific definitions:
Zone 1: Warm up, cool down; long, slow/easy distance pace (could do this for hours!)
Zone 2: You’re cruising, could do this for hours, but afterwards wouldn't call it an “easy” workout
Zone 3: Talking starts to get tough, but you can hold a conversation; this is the pace you’d go for longer intervals (>8 minutes) and could sustain for a race 1-3 hours in length
Zone 4: Race pace (think 5-10k or 20-30 min race); shorter intervals
Zone 5: Max effort/ end of a race/ hands on your knees/ possible collapse depending on your style
Zone 3 is just below your anaerobic threshold, or the point when you are working out when there is steep, nonlinear increase in ventilation, blood lactate, and Co2 production.1 Zone 4 is where you hit anaerobic threshold; zone 4 intervals should NOT feel comfortable. You should start to feel all the fun effects of lactate accumulating in your blood: heavy legs, breathing, possibly a little nausea - with tunnel vision starting to set in at zone 5.
Ok, so now that we’ve delineated training zones, time to talk about how much time should be spent in these zones during your training.
Polarized vs. Pyramidal Training
Back in the early 2000’s, research in Norway on elite Nordic skiers helped found the popular concept now known as “polarized” training. This research analyzed the distribution of time spent in each zone for these athletes; it was found that about 80% of training was performed at low levels of intensity, with 20% being higher-intensity interval training (above 90% VO2max). 2 This became known as the 80/20 rule, or polarized training. Over the years, various numbers regarding the time spent in each zone have been presented, but the general idea is that 70-90% of training should be done at low intensities (zone 1 and low zone 2), while 10-20% should be done at high intensity (zone 4-5). The zone to avoid under this model is zone 3, where you are approaching ventilatory, lactate, or anaerobic threshold.
Polarized training was recently criticized for the fact that it does not account for the fact that many athletes who participate in relatively longer races (think 1-3 hour range) do not need as much zone 4/L5 training. Instead, they should mimic the pace they typically race at, which equates to the L3/ sub-anaerobic threshold zone. This model has been coined as pyramidal training, stating that the majority of training should be performed in zone 1 (~70-90%), with zone 3 comprising (15-20%), and 5-10% in zone 4-5. 3
While there has been debate regarding which method is superior (polarized or pyramidal), numerous research studies have shown that endurance athletes respond best when a high percentage of training is performed at low heart rate and lactate levels. This is true across all disciplines: cross-country skiing, cycling, running, etc. 4
Excessive high-intensity training can cause a chronic inflammatory response that slows the recovery process from training. This can cause reduced cardiac output, mitochondrial efficiency, and reduce the body’s ability to produce ATP, which is necessary for sustained muscle contraction during exercise. 4
Put simply, it is crucial to have easy days to allow for the massive disturbance in homeostasis that occurs on harder training days. Not only do our bodies undergo heavy physiological change, but our tissues (tendons, bones, ligaments) are also subject to large stress as training intensity increases. It is crucial to prepare your body for the loads it will undergo during hard interval training, or else it starts to operate in a state of constant “fight-or-flight” (sympathetic nervous system is in charge). When the majority of exercise is performed at higher intensities above the ventilatory threshold, it takes longer for the autonomic nervous system to recover and to return to a state where the parasympathetic system is in charge again (think: rest and digest!). 5 This means elevated levels of epinephrine, norepinephrine, and cortisol- hormones that make it difficult for us to just “chill out”. Our bodies need to relax in order to perform basic physiological functions that are essential to recovery (think digestion, metabolism); if we don’t, then the stimulus of hard training actually backfires, leaving us without the energy to perform more high-intensity sessions. Thus, the quality of training decreases, and if we continue to keep pushing it , a vicious cycle starts to occur.
Easy is Easy, Hard is Hard
So, this brings me back to my intro, as someone who constantly likes to push into the sub-threshold (and sometimes even threshold) zone during training.
How do we alter our daily training to ensure we make maximal gains with training? Instead of thinking of easy distance training days prior to intervals as “recovery” days, it can be helpful to shift your mindset to viewing them as training “preparation” days.4 While its okay to drift into upper level 2 throughout a distance workout, it is important to not let yourself operate at high level 2 and into level 3 for the entire session- especially day after day. This is especially true during the racing season, when peak performance on “hard” days is more important.
Do we need to live and die by our heart rate monitors and zones? Certainly not; in fact, I rarely even use mine. At ETS, we are big believers in the fact that you can learn zones by “feel” after years of being in tune with your body. Factors like cardiac drift (the physiological response to training in the heat whereby your heart rate will naturally increase despite pace staying constant) often make training with a heart rate monitor tricky during the summer, anyway. Rather, the key is being cognizant of when you choose to drift into these higher zones- understanding that if this is something you engage in daily, you will start to move yourself backwards.
A great example is how David approaches distance training in the summer. When I was living in Albuquerque, David and I constantly rode our mountain bikes, and the trails there are chunky, rugged, and full of punchy climbs. It's tough terrain to keep your heart rate down if you just ride naturally. David actually stopped doing mountain bike rides the afternoon before he had intervals planned for the following morning, as he felt the quality was reduced by the fact that his effort was consistently too high throughout the session. Instead, he chose to mountain bike in the afternoon post morning intervals- keeping the hard day “hard”, and the easy days “easy”. After years of experience realizing how this was negatively impacting my own training, I have started to make similar alterations. I will pick easier trails/ gravel rides before planned intervals, even though I’d much rather hammer 24/7 to feel like I’m “getting fitter” at all times.
Throughout the ski season, both David and I are much more cognizant of going “true” level 1. One thing we have both noticed when racing on the World Cup is how the fastest skiers always seem to be going the slowest the day before the race. I actually first had this revelation as a junior skier, when I passed Sadie Bjornsen during race prep for the 10k skate. I thought to myself “wow, I’m going to have an AMAZING race today!”. Sadie then proceeded to win the race- probably beating me by 3-4 minutes in a 25 minute race. Needless to say, I learned my lesson there! I then went on to train with Sadie at APU, where I learned how she is the queen of this strategy. She always knew when to take it easy, and didn’t care if other athletes were passing her during the session. When it was time for intervals and racing, she was always the fastest; this was a big “ah-ha” moment for me (and a great example of how much we can learn from more experienced athletes!).
So, do we need to walk every uphill during a run to keep our heart rate down during a long distance session? Absolutely not, but its probably not a good idea to do this every day if we truly are going too hard. Instead, focus on good quality intervals, which will help improve your distance pace over time. What about classic striding in the tracks even though this is definitely an interval now? Sometimes its good to work on technique, and if you don’t have races or big intervals planned the next couple days, it's fine to do from time to time. The biggest thing is to not make a habit out of it, and to pick your battles. You are much better off sticking to a plan than allowing your effort to drift all over the map during workouts.
References
1. Ghosh AK. Anaerobic Threshold: Its Concept and Role in Endurance Sport. Malays J Med Sci. 2004;11(1):24-36.
2. Seiler S. What is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? International Journal of Sports Physiology and Performance. 2010;5(3):276-291. doi:10.1123/ijspp.5.3.276
3. Burnley M, Bearden SE, Jones AM. Polarized Training Is Not Optimal for Endurance Athletes: Response to Foster and Colleagues. Med Sci Sports Exerc. 2022;54(6):1038-1040. doi:10.1249/MSS.0000000000002924