If you missed the introduction to Training Zones click here.
Zone 3 is the most controversial of the training zones with some singing its praises and some telling you to never be caught dead in Zone 3. There is truth to both sides of the argument but Zone 3 can be useful if used correctly. First, let’s address the issues with Zone 3. It is often considered the “no man’s land” of training zones. This is because the Zones above and below it all have a clear energy system and training stimuli they are targeting and thus training in those zones provide very specific and obvious benefits. Zone 3 is the all-arounder in the middle where there’s some benefit in various areas, but no clear singular benefit being maximized. I.e., spending all you time in this zone will make you good at everything but great at nothing.
The other issue with Zone 3 is that people inadvertently spend a lot of time in Zone 3 at the detriment to their maximally training the other zones. In Zone 3 you can ride/run/swim hard-ish for long-ish, which a lot of people like because it feels like a great workout, they cover ground quickly, the average speed stats look great when they are done, etc. So when there is no plan for a workout, people often gravitate to this Zone. If people workout in groups this problem can be exacerbated as they like competing and going faster and will often find themselves unknowingly entering Zone 3 to push their friends or to keep up with their friends.
Why this is a problem is because too many of your workouts and too much of you total workout time can wind up in Zone 3. So on one end if you should be performing a Zone 2 workout but get excited and it turns into a Zone 3 workout than you miss out on the benefits that that Zone 2 workout was going to provide you. Also you could be more fatigued going into the next day’s workout and thus not perform that workout optimally thus not maximizing your benefit from that workout as well. An interval workout could also seemingly morph into a Zone 3 workout if your effort during recovery between intervals is too high, i.e., in Zone 3. Then for example when you perform your Zone 4 intervals, you are fatigued and they turn into high Zone 3 intervals, thus turning the whole workout into a Zone 3 workout.
Now, with all that being said, Zone 3 workouts do have a benefit. If the distance of your event is long-ish then you will probably need to go hard-ish, a.k.a. Zone 3 during your event. For said event you would need to train in Zone 3. As also stated above, Zone 3 is an all-around training zone meaning you get a little better at everything. A lot of times having the ability to do a little of everything is beneficial. For example, if you are in a bike race with a variety of climbs and is of a medium distance, being able to be comfortable in a variety of zones including a lot of zone 3 throughout would be critical to your success.
If your confused on whether to use Zone 3 or not at this point, I get it. The answer is that you should use it, but use it correctly. For single sport endurance athletes, I would use it as you third ‘hard’ day of the week. Generally, in the build up to your priority races/events you would have 2 hard days during your week that prepare you for the specific demands of your race/event. Let another day be a Zone 3 medium-hard day. For multi-sport endurance athletes, I would utilize Zone 3 in some of your brick workouts as you probably already have a hard workout day for each sport during the week. Using during bricks gets you some practice switching sports on pre-fatigued legs without over doing it. A caveat to both single and multi-sport endurance athletes would be if you races/events incorporate a lot of Zone 3 effort. For example, if you are training for a half or full marathon, your goal race time may be a Zone 3 effort. In this case, you would want to do some race specific Zone 3 workouts enroute to your race.
Now that we got all the complicated stuff out of the way, performing Zone 3 workouts are pretty simple. The most time in a given workout I would recommend you should spend in Zone 3 (assuming it’s a Zone 3 workout) is around 60min. This could take the form of 6x10min, 4x15min, 3x20min, 2x30min or 1x60min with the longer the duration without rest being more challenging. You should also work your way up to 60min over time, so your first Zone 3 workout in your training plan may be 3x10min and by the end of your plan you may be up to 1x60min. Recovery between Zone 3 intervals can be 5-10min of Zones 1-2. Another way to utilize Zone 3 for someone training for a half marathon for example to end their long run with 10-15min Zone 3 to get used to running goal race pace on tired legs. Probably more important than how to use Zone 3, is how to NOT use Zone 3, i.e., don’t be in Zone 3 unless that is the goal of that part of the workout.
Lastly, we need to discuss ‘Sweet Spot Training’. Essentially the sweet spot is the high end of Zone 3 and just above Zone 3, but not quite Zone 4. The sweet spot has traditionally been used in cycling, but the principle could be used for running and swimming as well. The purpose is essentially to maximize the benefits of training in Zone 3 by increasing the effort a little higher without crossing the Zone 4 barrier which would start the build-up of lactic acid (and its waste products) which will start to really limit the duration of these efforts. These workouts can be structured similar to other Zone 3 workouts, but are harder so the duration of intervals and total duration typically is slightly lower. I think these workouts make a great deal of sense. Their ideal uses would be as a progression of Zone 3 workouts, if your race/event requires a lot of Zone 3 and/or sweet spot efforts, or your race/event requires a lot of Zone 4 efforts and getting an extra workout training near Zone 4 would be beneficial. A lot of times workouts can be designed to include combinations of Zone 3, sweet spot, and/or Zone 4 to increase or decrease difficulty or to work on specific adaptations.
~92% of FTP 92-99% of FTHR 3-4 RPE
Cycling 76-90% of FTP 84-94% of FTHR 3-4 RPE
Swimming FTP + 1-5sec/100yds(m) 7-8 RPE
Sweet Spot (Cycling) 88-93% of FTP 92-98% of FTHR 4-5 RPE
Duration: 10-180min (Can do as intervals or longer ride)
Interval Duration: 10-30min intervals with 5-15min recovery or 30-60min ride
Continue reading about Zone 4 here.