It’s worth noting the use of ‘arbitrary units’ on the y-axis, and the fact this graph is not based on real-world data, but is purely a hypothetical relationship. Both of these facts have understandably been heavily criticised.
However, in defence of Coggan, he’s very clear that this graph was only ever intended as conveying a concept, rather than being an accurate depiction of the relation between intensity, and training effect (Overton, 2020).
Sweet Spot Base Training Benefits & Drawbacks
We know that sweet spot training can result in some of the adaptations we’re looking to achieve in the base period. These include increased mitochondrial content and Type I muscle fibre size, as well as improved markers of fat oxidation, and a potential shift in muscle fibre type from Type IIa to the more aerobically-adapted Type I fibres (Gollnick et al., 1973, Howald et al., 1985; Jarstad, & Mamen, 2019).
However, in understanding whether sweet spot is truly effective in the base period, the fundamental question we need to answer is:
“Does sweet spot training result in better adaptations vs low-intensity training for the same overall weekly time-commitment”.
In other words – is the increase in intensity worth it?! By “better adaptations”, we specifically mean those that we’re looking to attain during the base phase (i.e. improved fat oxidation, aerobic capacity of muscles, endurance and economy, muscular strength and so on).
This question isn’t very easy to answer, as there are very few scientific studies looking at this question.
The Science Supporting Sweet Spot
The best study we’ve come across to help answer our question is from Stöggl & Sperlich (2014). This study compared 9 weeks of training with a high-volume, low-intensity program (HV), with 9-weeks training on a lower-volume program where the majority of sessions were are sweet spot (the SS program).
In the HV program, lactate levels were maintained below 2mmol/L in all but one session per week, which is very similar to a traditional base training plan. In the SS program, lactate levels were between 3-5mmol/L in most sessions.
The HV program averaged approximately 11.4 hours/week vs 9.4 hours/week for the SS program.
Various performance/fitness outcomes were measured, but the outcome of greatest relevance to our research question was ‘cycling economy’. However, unfortunately, there were no discernible changes in cycling economy for either training program! This is probably because the athletes were well-trained, and the training load too low to elicit measurable fitness improvements in a 9-week period.
It’s worth noting that the researchers did detect a drop in VO2max with the SS program, whereas VO2max remained stable for the HV program, suggesting that the HV program may have been more beneficial for some fitness attributes. That said, VO2max isn’t something specifically targeted in the base phase, and therefore isn’t as relevant to answering our question!
On the other side of the argument, the most convincing paper we’ve seen in support of sweet spot training is a paper by Gollnick et al. (1973). The study involved 6 participants, who were recreationally active, but hadn’t done any endurance training in the past 2 years. The training intervention lasted 5-months, throughout which the participants trained 4x per week. Each session lasted 1-hour and was performed at 75% VO2max or above (with athletes being encouraged to ride at a higher power if they could manage it).
A key finding of the Gollnick study was a 95% increase in SDH activity. SDH is an enzyme found only in mitochondria and is a marker of mitochondrial density. A 95% increase in SDH activity is very large, and it’s been argued that since this is a bigger increase than has been seen in studies with lower training intensity and similar volume, it illustrates that sweet spot is more potent for improving mitochondrial density than lower-intensity riding.
Anecdotally it does seem that certain people respond very quickly to sweet spot training, and see fairly sizeable improvements in things like threshold power, which would tend to support the large improvements in mitochondrial density seen in the Gollnick study.
While the Gollnick study is very intriguing, it does need to be noted that the athletes were untrained and so were highly likely to see big fitness improvements from any training program. As the study didn’t directly compare the sweet spot program to a lower-intensity program in a controlled way, we can’t use this paper as strong evidence to support sweet spot on its own.
It’s also worth noting that there are numerous studies that have found no improvement in important aspects of base fitness after following a sweet spot-centric training plan (e.g. Wilson et al., 2012, Stöggl & Sperlich, 2014; Jarstad, & Mamen, 2019). In our experience, there’s considerable viability in how people respond to sweet spot training, and it’s certainly not a ‘magic bullet’ that works for everyone.
Our take on things so far: At this point, we’re still a little unclear on the usefulness of sweet spot in the base phase, although the large increases in mitochondrial density in the Gollnick are very intriguing, and for lower-level athletes at least, it seems sweet spot could be quite potent.
Theory Supporting Sweet Spot
As there is very little robust scientific research we can call upon comparing the direct effects of sweet spot training to lower intensity training, we need to turn to some theory.
The original theory behind sweet spot was based on the premise that a large training stress results in a large adaptive response.
However, this theory is flawed, because we know that different training intensities elicit different training adaptations. So we can’t simply say that sweet spot results in the best adaptive response because we get the biggest training stress… it depends what adaptive response we’re looking for!
Moreover, training stress was calculated based on the ‘training stress score’ (TSS), which ascribes a score to a given session based on its intensity relative to FTP, and its duration. TSS is also inherently flawed because the score is anchored around FTP. Due to differences in physiology, when one athlete rides at a given percentage of FTP, this may not result in the same training stress/stimulus as it does for another athlete.
Thus the argument that sweet spot is good because it results in a higher overall training stress just isn’t a strong or valid argument, in our view.
Nevertheless, if we look to some other theory, we can start to build up a moderately convincing argument for using sweet spot in the base phase. In particular, training at a higher intensity results in recruitment of more muscle fibres (Sale, 1987).
We know that when muscle fibres are worked, they become more aerobically adapted, increasing things like capillary supply and mitochondrial density (Howald et al., 1995; Ingjer, 1979). So it makes very logical sense that by riding at a higher intensity, we can train more of our muscle fibres at once, leading to more time-efficient base training.
It’s also been argued that by riding at sweet spot intensity, muscle fibres are depleted of glycogen more rapidly. Low glycogen levels are thought to be a key stimulus for a range of aerobic adaptations (Almquist et al., 2021), and so in this sense we may also get a more potent stimulus for aerobic adaptation.
Finally, there’s an argument that riding at sweet spot also forces the muscles to contract under higher force which contributes to muscular strength and strength endurance (the ability to repeatedly contract forcefully without fatigue).
Our take on things so far: There are some convincing theoretical arguments for why sweet spot training could be effective in the base period, particularly with regard to increasing mitochondrial and capillary density around a higher proportion of muscle fibres than would be achieved with low intensity riding of a similar duration.
Does energy system use make a difference?
While these theoretical benefits are all well and good, another thing to consider is the role of energy system usage. At different intensities, you’re working different energy systems to different extents. And so the adaptations you stimulate from training at a lower intensity may not be the same as training at a higher intensity, and we might not get all the benefits that low-intensity training provides.
One particular concern relates to fat oxidation. This is something we typically want to develop through the base season as it contributes to both endurance and threshold power. The rate of fat oxidation is maximised when training at roughly 65-80% FTP, and then falls off quite quickly above this intensity.
Thus at a sweet spot intensity, reliance on fat oxidation is low (Achten & Jeukendrup, 2004), and there’s an argument that sweet spot training doesn’t adequately develop the fat oxidation system. This is particularly true in more well-trained cyclists, who may need their training to be more optimised (you may have noted that earlier in the article, we mentioned that sweet spot can improve fat oxidation, but this is always in less well-trained athletes, who respond favourably to almost all types of training!).
Now, the argument that the best way to train fat oxidation is to ride at an intensity where fat oxidation is maximised (the so-called ‘FatMax’ intensity) is not quite as simple as it might seem. We have some evidence, for example, that adding sprints to an endurance ride may enhance the fat oxidative adaptations achieved by these low-intensity rides, even in very well-trained athletes (Almquist et al., 2021). So higher intensity training, can in some cases be beneficial.
Nevertheless, anecdotally, we’ve found that people who do a lot of sweet spot training at the expense of low-intensity riding do tend to rely more on carbohydrate oxidation than fat oxidation. So we’re not convinced that sweet spot training is a particularly effective way to develop fat oxidation, unless you’re starting out from a relatively low fitness level.
Our take on things so far: From our experience, training at sweet spot doesn’t seem to be a good way to develop fat oxidation ability in moderate to well-trained cyclists, and these cyclists likely need to keep some lower-intensity riding and/or employ other strategies for developing fat oxidation in their base phase in order to adequately train this ability.
Other Sweet Spot Training Benefits/Drawbacks
Before wrapping up, let’s look at some of the broader benefits and drawbacks of sweet spot in the base phase.
One very key advantage of sweet spot is that many people really enjoy riding in this zone. It feels challenging but not painful. It’s the sort of intensity people tend to ride at if they were told to just go out and ride as they feel.
It’s really important for training to be enjoyable through the base phase, because racing is a long way off, and you want to minimise the risk of mental burnt-out when racing gets nearer and training is far more important. So in this regard sweet spot can play a really useful role in keeping training fun.
Conversely, a big concern with sweet sport training is that it can cause significant fatigue. We’ve encountered many athletes who have become overtrained after following a training plan that includes a high proportion of sweet spot.
Indeed, while sweet spot may feel subjectively easier than a high-intensity interval session, Seiler et al., (2007) showed that the fatigue response of the autonomic nervous system to spending 30-mins at a tempo/sweet spot intensity, is markedly similar to the response seen after a set of classic ‘VO2max’ intervals (6x 3-min efforts, at 96% VO2max).
In contrast, spending 2-hours riding below the first ventilatory/lactate threshold (i.e. at a Zone 2 intensity) elicited a very different fatigue response, suggesting that the top end of Zone 2 is a crucial tipping point, beyond which there is considerably more fatigue accrued.
Our Base Training Approach
Overall, we think that there’s some good evidence to support the inclusion of sweet spot training as part of the base phase for athletes who don’t have the time for traditional high-volume, low-intensity training.
The clearest benefits of sweet spot seem to be that it stimulates a higher rate of mitochondrial biogenesis (i.e. growth) in the muscles compared with lower-intensity riding, and importantly, is a form of training that many people find fun and may help maintain motivation when racing is quite distant.
Theory also suggests that sweet spot may also help with other aspects of fitness such as capillary density and muscular strength/resistance to damage. However, the evidence for this doesn’t appear as strong.
We’re less convinced that sweet spot helps develop other important attributes of fitness that are typically targeted in the base phase, including fat oxidation, endurance in long (e.g. 4H+) rides and economy. Furthermore, the risk of burn-out is high when riding is predominantly done at a sweet spot intensity.
For these reasons, we think it’s important to also include a balance of lower-intensity riding within a base training plan. This will help develop those aspects of fitness that aren’t targeted so well by sweet spot, and allows some recovery between harder sessions. In our view, sweet spot training plans like TrainerRoad’s Sweet Spot Base plan include far too much sweet spot riding, particularly in the higher volume plans.
Other training strategies are also worth considering for time-crunched athletes. As mentioned above, including sprints within low-intensity rides seems to be a potentially promising strategy to enhance fat oxidation. Carbohydrate-restricted training is another such strategy, which if implemented right, can give rise to significant improvements in fat oxidation and other aerobic abilities (see here). Finally, strength training may be a good way to improve cycling economy and endurance (Rønnestad & Mujika, 2014).
In our view, the main best-practices to follow through the base period are:
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Don’t include more than 2-3 sweet spot training sessions per week.
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Aim to include at least one longer ride each week, which can include some sweet spot riding, but also some lower-intensity riding too.
Here’s an example training week from one of our Autumn/Winter Base Training Plans: