Endurance for the long haul: learning from the ultra-elites

New research

To try and provide some more definitive answers on the best approach for the long-term development of endurance, a team of Norwegian researchers has just published new research on XC ski athletes⁽¹¹⁾. Published in the journal ‘Sports Medicine Open’, what makes this research unique however is that the information on training practices was not gathered from a snapshot, but from three decades of data!

Six Norwegian female world-class XC skiers (categorized as tier 5 – ie world class⁽¹²⁾) were recruited for the study. To be included, all the athletes had to meet the following criteria:

·        All athletes competed at the senior level between 1988 and 2023.

·        Athletes who had achieved individual medals in the Olympic Winter Games (OWG) or World Championships (WCH).

·        Had systematically recorded their day-to-day training in detail from junior right through to senior & world-class level.

·        Had performed physiological testing at the Norwegian Olympic Training Center.

These athletes were then further divided into two groups based on their competitive results through their careers: the researchers assigned a class of ‘tier 5+’ to the athletes who had won eight or more medals from OWG/WCH, and a class of ‘tier 5’ to the athletes who had only(!) have won four or fewer medals. The key point was that as seniors, the group of tier 5+ athletes reached the podium in the WC, WCH, and OWG more than five times as often as the tier 5 athletes. In effect, what the researchers were trying to do was discover which training factors were most likely to be important for creating the very best world-class athletes – the crème de la crème.

What they did

The goal of the study was to investigate the development of training characteristics and factors that determine physiological performance over a long period of time. Therefore, to cover both the transition from junior to senior levels (19–23 years) and the point of reaching world-class level, 10 to 15 seasons of training were analyzed for each athlete, covering the period from junior age to world-class level. The researchers compared tier 5 athletes with tier 5+ athletes at the same time points in their careers. In addition, to minimize the influence of time-dependent improvements in on training and performance knowledge and practices (as we learn more, training practices tend to improve), each athlete was paired with another athlete performing at the same time-period within the same decade.

The training records that were investigated by researchers included information about training frequency, duration, training forms (endurance, strength, speed) and the intensity for endurance training sessions. All athletes used the five-zone intensity scale developed by the Norwegian Olympic Training Center (see table 1). However, for the data analysis, both the three-zone and the five-zone intensity scale were applied to enhance the clarity of findings (LIT = zone 1–2; MIT = zone 3; HIT = zone 4–5). As well as training data, the researchers also looked at the athletes’ fitness testing data accrued across the years. In total, the six athletes conducted a total of 455 physiological tests at the Norwegian Olympic Training Center; to ensure validity of the findings, only tests where the athletes were in tip-top condition (ie no illness or injury) and which were conducted in the general preparation period (August to November), were included in the analyses.

Table 1: The Norwegian Olympic 5-zone intensity scale

NB: this model is often described as a “polarized” or “pyramidal” training distribution (roughly 80% in zones 1–2, 10–15% in zone 3, 5–10% in zones 4–5). Zone 3 is deliberately narrow because Norwegian coaches believe spending too much time here (“gray zone”) gives poorer adaptations than polarizing toward zone 1–2 and zone 4–5. Lactate threshold heart rate is typically ~82–88% of HRmax in well-trained endurance athletes, which is why the percentages shift when using threshold instead of max HR.

What they found

The key findings were as follows:

·        There were large individual differences in the progression of training volume of the athletes (exactly as you might expect). In plain English, there was no ‘magic formula’ guaranteeing world class performance!

·        However, when it came to the evolutions of the athletes’ training, there was a clear difference in the way the tier 5+ and tier 5 athletes progressed through the years and in the transition from junior to senior world-class level; specifically, the tier 5+ athletes demonstrated a gradual, stepwise increase in training volume over a much longer period compared to less consistent progression observed in the tier 5 athletes.

·        This more noticeable increase in training volume in the tier 5+ athletes was primarily driven by an increase in the number of training sessions, while the duration of individual sessions only increased modestly.

·        Importantly, the increase in training volume observed in the tier 5+ athletes was primarily driven by increased volume of zone-1 low intensity training (see figure 1). There was no consistent pattern regarding the proportion or frequency of high-intensity sessions.

·        As time progressed, the tier 5+ athletes showed larger improvements in sustainable speeds for a given level of blood lactate and heart rate than the tier 5 athletes (see figure 2). For example, the tier 5+ athletes were able to increase their average speed at lactate threshold (the point at which/lactate and fatigue begins to accumulate in the blood) by around 14% over the years compared to an increase of just 7% in the tier 5 athletes.

·        The annual progression of strength and speed training was not significantly different between the tier 5 and tier 5+ athletes.

Figure 1: Annual progression of low-intensity training (LIT) for three tier 5 and three tier 5+ athletes

Light green = zone 1 training volume; dark green = zone 2 training volume. a/b/c and a+/b+/c+ represent the three periods of analysis across the three decades for the tier 5 and tier 5+ athletes respectively. Notice the more consistent increase in zone-1 training volume (light green) in the tier 5+ athletes.

Figure 2: Development of lactate threshold tests from tier 5 and 5+ athletes across three decades

a/b/c and a+/b+/c+ represent the three periods of analysis across the three decades for the tier 5 and tier 5+ athletes respectively. Red plots represent tests at junior level, green plots are the same tests at senior level. Look at the red/green lactate curves at the bottom of each graph. As they progressed, athletes moved from red to green curves. But notice how the tier 5+ athletes show a green (senior) test result much more shifted to the right compared to the red (junior) result. This shows that the as the tier 5+ athletes progressed over many years, they improved their ability to work hard before reaching lactate threshold more than did the tier 5 athletes over the same time period.

Practical implication for athletes

Very few endurance athletes reading this article will ever make it to world class level (although we’d like to think that some of the new research highlighted in SPB over recent years could help a little!). But what are the implications for recreational and amateur athletes, and can we use this info to help us develop better training plans and overall structure? The key take-home message is that gradual, sustained training evolution, focusing primarily on low-intensity training, is what counts for long-term performance gains.

For recreational and amateur endurance athletes pursuing long-term improvements, this highlights the need for sustainable, individualized strategies, emphasizing aerobic base-building rather than quick fixes or short-term interventions; amateurs should try and view their progress in the context of 5 to 10-year timescale rather than judging it over a period of a few weeks of months.

A particularly important finding in this study was that the progressive ramp-up in annual training volume in these elite XC skiers was achieved not by increasing session lengths, but rather by boosting session frequency (eg twice per day training) and prioritizing low intensity (zone-1) training for the bulk of sessions. Surprisingly, high-intensity training (zones 2 and 3) showed no clear link to elite success. For amateurs, this suggests structuring training so that around three quarters of the volume is low/easy intensity (you should be able to hold a conversation without struggling) in order to build a robust ‘aerobic engine’ without risking burnout.

Modest-duration sessions (eg 60-90 minutes) should be prioritised to minimize overuse injuries, with the number of sessions increased rather than session lengths increased to build volume. That’s not to say you should never perform long sessions in training (eg marathon preparation), but rather you should prioritize performing more sessions over longer sessions. Regular testing to check progress is also recommended; you don’t need a fancy laboratory to do this – a simple time trial test or 12-minute (running) Cooper Test can provide benchmarks to make sure you are moving in the right direction! Finally, if you are a young or junior athlete, it’s important to avoid building up to high volumes of training early on in your career. Not only will this increase your risk of burnout and injury, the evidence is that it provides no advantage in your performance as your career develops over the longer term!

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