From the Coaches: Long slow duration and why it still has its place in your weekly training

Here at SYSTM (previously Sufferfest), we do love intervals, suffering, and working so hard that we leave a puddle of sweat and pain underneath our turbo trainers after a good, high-intensity session. And, of course, these high-intensity sessions are vitally important to our training: improving fitness, getting faster and just generally feeling badass when we get them completed. But there is still an important place in our training for low-intensity and longer durations so let’s dive into why this is the case…

We may not have the time available to train like the pros, who will be doing 25+ hours of training a week. But, interestingly enough, we probably do a similar amount of intensity each week as they do at times. So, what do they do differently? The answer is: a lot of long, slow duration training - which is used to facilitate more potential gains from the high intensity work that they do.

We can improve our aerobic power via a few different methods but many of them come down to something called PGC-1α (Peroxisome proliferator-activated receptor gamma coactivator 1-alpha). One of the primary things that PGC-1α does is to increase mitochondrial biogenesis, therefore increasing the number of cells within our muscles that oxidise fat, carbohydrates and lactate to produce adenosine triphosphate (ATP) - which is what our body uses to energise all muscular processes . Another benefit of increased PGC-1α expression is that insulin-stimulated glucose transport is increased (also called increased insulin sensitivity) via GLUT4 (Glucose Transporter Type 4). Essentially, this means that we can deal with carbohydrate loads better without the associated blood sugar highs and lows, as blood sugars remain more stable.

The first method of activating PGC-1α that we’ll discuss occurs due to high-intensity exercise and is achieved via the AMP-K (adenosine monophosphate-activated protein kinase) enzyme. The AMP-K facilitated PGC-1α signalling occurs during high-intensity due to the ratio of AMP:ATP increasing. This is because ATP is being used at a rate faster than it can be generated, such as during very high-intensity exercise that is not sustainable. So, those hard interval sessions in SYSTM will be contributing towards improving your aerobic function.

However, long duration low-intensity training sessions can also cause PGC-1α signalling to occur in a different way. When we contract our muscles, calcium is secreted into the cytoplasm from the sarcoplasmic reticulum. This in turn activates calcium/calmodulin-dependent protein kinase (CAMKII), which is itself a signalling molecule for p38 mitogen activated protein kinase (p38 MAPK). p38 MAPK not only increases PGC-1α after the initial uptake of exercise, but also increases the expression of PGC-1α as exercise continues, thus improving mitochondrial biogenesis, oxidative capacity and aerobic performance. Due to the continuous nature of this signalling pathway, long duration exercise is more beneficial than shorter in this respect. The only way to conduct this exercise sustainably is to perform it at lower intensities.

Another benefit of long duration exercise is something called angiogenesis, or muscle capillarisation, which is the creation of new capillaries within the muscle, allowing more oxygen to be transported around the muscle and therefore improving oxidative capacity. This can also be facilitated via PGC-1α signalling to a lesser degree. However, this driver for angiogensis is vascular endothelial growth factor (VEGF), which is secreted from the muscle fibres to the muscle interstitium. Additionally, studies have found that, as intensity increases, VEGF activation decreases and angiogenesis is hampered, which is why low-intensity exercise is so important for angiogenesis. These benefits are theorised to occur more in the long duration exercise due to, again, the continued muscle contractions over far longer time durations than for, say, 60 minutes of high-intensity training.

So, what is low-intensity training? Traditionally, it is referred to as Zone 1 or Zone 2 exercise, something that is easily maintainable over long durations while being able to maintain conversations. Physiologically, it is the moderate exercise intensity domain which refers to exercise that is below LT (lactate threshold), where the primary fuel oxidised is fatty acids and lactate production does not increase from base levels. A general rule of thumb for this is exercise performed at less than 70% of Functional Threshold Power, but LT for individuals varies in terms of their percentage of FTP and can also change based on environmental factors such as heat and even fatigue. Additionally, sub-LT is often an intensity that maintains the Heart Rate to Watts ratio without cardiac drift occurring. Cardiac drift, also referred to as aerobic-decoupling, is when HR increases compared to power in a non-linear fashion. So, either power stays the same and HR increases, power drops and HR remains static, or power increases but HR increases at a rate that is exponentially higher than would be expected.

What does this mean for everyone reading this? Fortunately, you don’t need to be doing 4+ hour rides 5 times a week to reap the benefits of long duration low-intensity training. Getting one or two longer rides at a low-intensity in at the weekend will help you significantly with your aerobic fitness, as well as providing a good base to build upon using high-intensity sessions. So, although suffering and doing sessions to make the Pain Cave earn its name are important, don’t forget the importance of those long slow endurance rides when you can fit them in.

For further reading on PGC-1α, have a look at this research paper: Jung, S., & Kim, K. (2014). Exercise-induced PGC-1α transcriptional factors in skeletal muscle. Integrative medicine research , 3 (4), 155–160.

For more info on angiogenesis, this is a great read: Gliemann, L. Training for skeletal muscle capillarization: a Janus-faced role of exercise intensity? Eur J Appl Physiol 116 , 1443–1444 (2016).


Are Z2 trainings interchangeable across sport? For example, would I see the same or similar angiogenesis benefits hiking a mountain or going for a jog so long as I maintain a Z2 HR? I’m a recreational athlete with a primary focus on building my mileage capacity on mountainous gravel roads.


Great question! You would still see aerobic benefits from doing things like hiking, swimming or jogging and maintaining that Z2 HR zone (might be slightly higher during jogging due to greater body muscle recruitment). I had a long period off the bike but walked a lot, was very surprised by how much my aerobic endurance was, however the maximal capacity suffered as I couldn’t do high intensity work


Would adding an extra 30 minutes of zone 2 onto the end of a HIIT session provide any benefits or does it need to be long slow rides?

I’m in a situation where I think I need more volume at zone 2 to improve but it’s very difficult for me to get out for longer than a 2 hours at a weekend.


There is some benefit to that yes, or even Z1 afterwards as an extended warm down as continuous muscle contractions will be occurring. You’ll additionally get some additional recovery benefits from the muscle skeletal pump system helping to circulate metabolites built up during exercise.
There’s also some suggestion that low carbohydrate availability can help in the endurance adaptations, so straight after a hard intervals session your muscle glycogen stores will be more depleted. Of course important to refuel well after the session!


Thanks @Coach.Andy.T I’m trying to work out how I can maximise any of those adaptations associated with LSD type rides. It’s certainly doable for me to do my normal week day workouts as per my training plan, fuel the same as normal, but extend some of the workouts by 30 minutes. I know I’d have to be careful to not let that compromise the HIIT workouts.

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Very interesting read!

You’ve mentioned to add Z1 on the back of some HIIT sessions. Are you leaning towards Z1 vs. Z2 as the caveat is that the added time is more important (than say added TSS) and because ideally it shouldn’t compromise the next HIIT session in a couple of days time?

As an aside, my gut feeling (which I guess is wrong) is that there ought to be fitness gains to be had by just adding some tough tempo 3hr rides. Your more scientific approach seems to suggest: do the 3hr ride as a slow steady effort which also allows you to do 1hr HIIT the next day or so (whilst I’m still recovering from the long temp effort!!).

Is there any benefit from doing a hard 3hr ride as part of training or is that really something that ought to just be done as a race/sportive/event etc?


@Coach.Andy.T - Thanks for easy to understand info regarding Cardiac drift/aerobic-decoupling!


Yep, it’s not something that I would add on to every session, and you need to monitor how the training load affects you

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My impression from all of the research I have done is that it is either or. In other words either low intensity or high intensity with nothing in the middle. Low intensity does as mentioned in this article and leaves you fresh enough to do high intensity properly. The bit in the middle( tempo/threshold) is too high to leave you fresh enough to do the high intensity workouts properly and still too high to allow the adaptations from the low intensity workouts. I think threshold/ tempo training is outdated these days with all the advances that have been made in fitness science. Check out polarised training by Stephen Seiler


After HIIT Z1 more for that additional period of time contracting the muscles, but limiting the additional stress yes. Especially as all our SYSTM plans are carefully designed to deliver the right amount of training load and use HIIT to elicit some of those big fitness gains. Therefore you don’t want to compromise them.

So riding a long ride at tempo can reduce some of the angiogenesis gains, thus removing/limiting one of the potential training benefits from your ride. This is why a more polarised approach to training is often taken, so super easy or super hard. Even a pyramidal model follows this approach quite closely. Tempo is sometimes referred to (unfairly for the most part) as a dead zone of training. You get some of the benefits of Z1/2 (not all of them) but more fatigue. So yes, 3hours Z1/2 should mean you’re fresh enough for HIIT the next day.

However, there is still a place for tempo riding. Tempo riding is useful for building resistance to fatigue, especially if doing events such as road races or gran fondos. Additionally, if your training goal is to say ride 100miles as fast as possible, tempo is the pace that you will have to be good at to achieve that. But to get a quicker ‘tempo’, the long slow endurance rides will be more beneficial than riding tempo too regularly.


So there are two approaches being debated currently, polarised and pyramidal. Polarised is the 80/20 split of as you said all (20% flat out) or nothing (80% very easy). This is based on the research into PGC-1α signalling and using that as the primary goal or endurance training.

However that method is flawed for a few reasons. Depending on your goal, you will not be competing at either of those intensities exclusively. For example, if your goal is to ride 100miles as fast as possible, then riding tempo is important and being able to deal with that build up of fatigue and rate of perceived exertion.

If your goal is a time trial, then you need to be able to pace your threshold effort and time at threshold is required. Road racing you need to be able to vary pace a lot across the whole spectrum. Track cyclists need a huge maximal and glycolytic power which if anything requires intentionally less PGC-1α signalling to maintain Type IIb fibres.

So a lot of the thinking now is more of a Pyramidal approach after a lot of studies determined that a polarised approach was not the most appropriate, especially for road racing. Pyramidal still requires mostly long slow duration riding, but has room in there for tempo, threshold, MAP, glycolytic capacity, and neuromuscular efforts. This is also the approach of the SYSTM plans nowadays, even with the efforts we have in the week, we still have easy recovery sessions, or even full rest days


Thank you for your replies to my post. I have come back into training at 67 years of age after well over 24 years off the bike and even before that I only started cycling at around 40 years of age for about 4 years. For the last year I have just been doing my own thing, mainly on a dumb trainer and got reasonably fit so was looking up all of the latest info on training methods and polarised training seemed to make the most sense to me. I decided to step it up a bit and get more organised so bought an interactive trainer and joined Systm 4 weeks ago but unfortunately yesterday my trainer broke down. I have moved the remaining 8 weeks plan one week forward hoping that it will be fixed by then and was looking to use the week to build up my aerobic threshold outside hence my post on here. I should have realised you guys know your stuff, ha ha thanks


Great article. I’ve read a lot about the benefits of HIIT workouts but always wondered why they don’t work well for me compared to longer low intensity workouts.
Is there a way to tell whether your physiology works best with HIIT or with low intensity?

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Getting some longer Z1/2 rides outdoors will help boost up the aerobic fitness, and are also nice to do when the weather is good :stuck_out_tongue_closed_eyes:


I’m glad you enjoyed it. In regards to working out what you responded best to training wise, I couldn’t say exactly how you would assess that. Trial and error is the only thing I could think of beyond genetic testing

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@Coach.Andy.T This stuff is great and only adds to the value that this training platform already offers so thanks for that!

Perhaps as a related topic are ideas on how to best integrate esports. Is it as simple as swapping out a similar SUF video and staying away from rest weeks or are there other considerations. I am interested in trying some of the crit and time trial offerings on RGT but don’t want to unbalance my training plan in the process. I also have other IRL races so would consider those as well.


That’s a great question. It’d be good to be able to use some of the e-racing offerings within RGT without spoiling yourself for your training plan.


I’m pretty sure this is something we’ll be integrating into the plans in the future with the acquisition of RGT. But for the most part you are right yes, that switching a similar session and avoiding doing them on rest weeks. But then of course there’s the consideration of if it’s a target event and needs to be tapered for beforehand. All depends on the importance of the event


@Coach.Andy.T hi, does long slow duration play a role for helping to increase time at threshold ? I mean that despite the fact that two individuals would have the same ftp, one of them could sustain a longer time at threshold (what I try to achieve for time trials). Thanks