ECOs Training Load Explained: A Coach’s Guide to Objective Load Equivalents

Table of Contents

• Key Takeaways for Coaches
• What Objective Load Equivalents Are
• How the ECOs Training Load Score Is Built
• Why a Hard Hour of Swimming Isn’t a Hard Hour of Running
• How We Read Intensity: Pace and Power Before Heart Rate
• What a Normal ECOs Score Looks Like
• If You Already Think in Training Stress Score
• How EndoGusto Calculates ECOs From Your Files
• Suggested References

A coach with a triathlete is really coaching three athletes at once. The swimmer, the cyclist, and the runner all share one body, one recovery budget, and one finish line. Yet each sport loads that body differently. So the simple question, “how hard was this week,” turns out to be hard to answer with a single number.

Two approaches are common, and neither accounts for the different stress each sport places on the body. The first considers only time, treating an hour as an hour, so a steady spin and a brutal track session look interchangeable. The second leans entirely on heart rate, which flatters easy work and underrates short, sharp efforts. Consider an easy 60-minute swim next to a 60-minute fartlek run. They cost the body very different amounts, yet a time-only or heart-rate-only view can rate them as near neighbors.

The ECOs training load score exists to fix that. It puts swim, bike, and run on one scale, while accounting for their different impact. This guide explains what the score is, how it is built, and how to read it.

What Objective Load Equivalents Are

ECOs is the Spanish acronym of Equivalentes de Carga Objetiva. Spanish sport scientists Roberto Cejuela Anta and Jonathan Esteve-Lanao developed it to quantify training load across endurance sports, and published the peer-reviewed article Training Load Quantification in Triathlon in 2011. In English, that translates to Objective Load Equivalents. We use the Spanish acronym in the app as a deliberate nod to the researchers who built and validated the method.

The method was built for triathlon, where the hard part is comparing a swim to a bike to a run on one scale. The authors set out to do a few things at once: combine all three sports, consider brick sessions, weigh both how long and how hard each effort is, and reflect the overall fatigue a week leaves behind. It also works for a single sport in isolation, which matters for EndoGusto, because the same logic scores a standalone run as cleanly as a full triathlon build.

How the ECOs Training Load Score Is Built

The ECOs score rests on three inputs: time, intensity, and sport. For each segment of a session, it multiplies the time spent in a zone by that zone’s intensity factor, then by a factor for the sport. Summed across every zone, those products give the session score.

ECOs uses eight zones anchored to physiological landmarks rather than round-number heart-rate percentages: the first and second lactate thresholds (LT1 and LT2) and the VO2max region above them, with LT2 marking the upper boundary of sustainable intensity. Anchoring to physiology rather than arbitrary percentages keeps the zones comparable across athletes of very different fitness.

The intensity factors do not climb in even steps. They run 1, 2, 3, 4, 6, 9, 15, and 50. Cejuela and Esteve-Lanao made the progression exponential rather than linear, so the scale levels the hardest sustainable effort in each zone for a given athlete. The logic is physiological: the higher the zone, the less time an athlete can hold it, so each step costs disproportionately more than the last. A minute in the top zone is not one increment dearer than the minute below it but several times dearer, which is why a few minutes of genuinely hard work can dominate a session’s total.

The table below shows the eight zones, the landmark each one relates to, and its intensity factor.

Zone	Common Terminology	Physiological anchor	Intensity Factor
Z1	Recovery	Below Aerobic Threshold (LT1)	1
Z2	Aerobic base	Aerobic Threshold	2
Z3	Tempo	Between Thresholds (LT1 and LT2)	3
Z4	Threshold	Anaerobic Threshold (LT2)	4
Z5	Above threshold	Between LT2 and MAP	6
Z6	VO2max	Maximal Aerobic Power (MAP)	9
Z7	Anaerobic capacity	Lactic Capacity	15
Z8	Neuromuscular	Lactic Power (Glycolytic Power)	50

ECOs also measures volume as time rather than distance, so efforts compare fairly across athletes of different speeds and across varied terrain. Forty minutes climbing and forty minutes descending carry the same volume, judged on duration rather than the distance the gradient allowed.

The exercise factor completes the calculation. After zone time and intensity factor, ECOs multiplies by a factor for the discipline: 1.0 for running, 0.75 for swimming, and 0.5 for cycling. The next section explains why those numbers differ.

Why a Hard Hour of Swimming Isn’t a Hard Hour of Running

The exercise factor is what makes ECOs a multisport training load score rather than three separate ones. The same hour, at the same relative intensity, does not cost the body equally in each discipline, so a single scale has to account for that or the comparison misleads.

How the Exercise Factors Were Scored

These factors are not guesswork. Cejuela-Anta and Esteve-Lanao rated each sport from one to four on four dimensions: how hard it is to hold technique, how much delayed muscle soreness it leaves behind, how continuous a typical session tends to be rather than broken up by rests, and its overall energy cost. Then they summed the four and set the highest total as the reference. The table below shows where each sport landed (Cejuela-Anta and Esteve-Lanao, 2011, Table 3).

Dimension	Swim	Bike	Run
Difficulty maintaining technique	4	1	2
Delayed muscle soreness	1	1	4
Typical workout density	1	2	3
Energy cost	3	2	3
Total	9	6	12
Exercise factor	0.75	0.50	1.00

Running scored the highest at 12, so it became the reference at 1.00. Every other factor is simply that sport’s total divided by running’s, which is why swimming’s 9 lands at 0.75 and cycling’s 6 lands at 0.50. The ratings are deliberately coarse, a one-to-four judgment rather than a lab measurement, yet they capture the real differences in how each sport taxes the body.

The mechanism is familiar to any coach. Running is weight-bearing, so it produces the most eccentric muscle damage and mechanical stress of the three. Cycling is supported by the bike and carries far less eccentric loading. Swimming sits in between: the water supports the body, yet technique and upper-body demand still add real cost.

The practical effect is striking. An athlete rides 90 minutes at threshold, then on another day runs 45 minutes at the same relative intensity. On a time-only view, the ride is clearly the larger session. On ECOs, the run lands close behind, because each minute of running counts double a minute of cycling. That is not a quirk of the formula. It mirrors what every endurance coach already manages around: most athletes can ride hard far more often than they can run hard, because cycling spares the legs the eccentric damage running inflicts.

Coaching tip: When an athlete’s weekly run ECOs creeps up while ride ECOs stays flat, watch the calf and Achilles complex before the lungs. The exercise factor is telling you where the mechanical bill is landing.

How Brick Sessions Are Scored

A brick stacks two disciplines back to back, and the second always feels harder than it would in isolation. The authors account for this with a transition premium, adding a small bonus to the second discipline’s load: roughly 0.10 when cycling follows another sport, and 0.15 when running follows, reflecting the measured rise in energy cost and the changes in running mechanics that show up off the bike (Cejuela-Anta and Esteve-Lanao, 2011). EndoGusto does not yet apply this premium; bricks currently score as the sum of their segments, each with its own exercise factor.

How We Read Intensity: Pace and Power Before Heart Rate

ECOs is only as good as the zone it assigns to each minute, so how we measure intensity matters as much as the formula itself. EndoGusto reads intensity in a fixed order: pace or power first, then threshold heart rate, then maximum heart rate, and finally rating of perceived effort. This order follows guidance from our advisor Marcos Peón, endurance coach and PhD researcher on Mental Fatigue and Endurance Performance at the University of Oviedo, and the method’s own authors flag the same heart-rate limitations that motivate it. The distinction is between external and internal load. Pace and power are external load, the work an athlete actually produced. Heart rate is internal load, the body’s response to that work, and as a response it is both lagging and noisy.

There are three reasons not to lean on heart rate alone. First, it lags. At the start of a hard interval, heart rate takes roughly 15 to 60 seconds to catch up to the effort, so short repetitions can finish before it ever reflects them. Second, it drifts. Over a long steady effort, heart rate climbs even when pace and power hold flat, pushed upward by heat, dehydration, and fatigue, the familiar aerobic decoupling. Third, it flattens at the top. Above threshold, heart rate stops separating efforts cleanly and eventually plateaus near maximum, so it cannot reliably distinguish a hard interval from an all-out one. For all three reasons, ECOs treats the upper zones as places where heart rate alone is insufficient and pace or power should lead.

Why Threshold Beats Maximum Heart Rate

When heart rate is the best signal available, ECOs anchors to threshold heart rate rather than maximum heart rate. Peón framed the distinction cleanly: “maximum heart rate describes capacity, while threshold describes performance. Two athletes can share an identical maximum heart rate and still have very different thresholds, very different fitness, and very different responses to the same workout.” Anchoring zones to threshold therefore ties the score to what an athlete can actually sustain, not to a ceiling they rarely touch.

Perceived effort sits last in the order, and it still earns its place. When no device data exists, it is the final fallback. It also serves as a check: when a session felt far harder than its numbers suggest, that gap is a signal worth a coach’s attention rather than noise to discard.

What a Normal ECOs Score Looks Like

A single session number means little without a sense of scale: a short recovery swim scores low, a long threshold set scores high. What most coaches actually track is the weekly total, since that reveals whether load is ramping, holding, or tapering into recovery.

So what counts as a normal week? For an elite short-course triathlete in full training, the weekly total lands near 1,000 to 1,150 ECOs, and an overload week can push past 2,000. Those are professional ceilings, not age-group targets. The value for a coach lies in the shape underneath the numbers: how the load divides across three sports, and how much or little of it comes from easy hours.

A Benchmark From Elite Short-Course Racing

The cleanest published reference comes from a full 47-week season logged for two elite Olympic-distance triathletes in Cardona, Cejuela, and Esteve-Lanao’s Manual para entrenar deportes de resistencia (2019). Their season gives you an anchor for what a complete, sustainable year of multisport training load actually costs.

Weekly ECOs (Objective Load Equivalents)	Triathlete A	Triathlete B
Typical week	1,135	1,033
Peak week	2,108	1,889
Swim, share of load	32%	31%
Bike, share of load	31%	30%
Run, share of load	37%	39%

A working rule of thumb for an elite short-course athlete is therefore roughly 1,000 to 1,150 ECOs in a normal week, rising to around 1,900 to 2,100 in a peak block. That peak sits about 1.7 to 1.9 times the average, which gives you the scale of a genuine overload week relative to baseline. Other athlete types in the same source scale down from there: runners peaked nearer 800 to 900 ECOs per week, while longer-course triathletes ran higher, up to roughly 1,600 to 1,800.

How the Week Splits Across Swim, Bike, and Run

The three sports sit remarkably even in that table. Load divides into near-thirds, tilted slightly toward running at 37 to 39 percent, and that balance is the whole point of a multisport training load score. Measured in ECOs, an hour of hard running and an hour of easy cycling are not the same currency, so the split reflects real physiological cost rather than time on the clock. It doubles as a sanity check: if an athlete’s swim is consuming half of weekly load, something is off, either the threshold pace is set wrong or the swim sets skew too hard.

Reading the Numbers for Your Own Athletes

This is the part that raw hours conceal. In that elite season, about 87 percent of training time sat in low intensity, yet that easy work accounted for only 45 to 50 percent of total ECOs load. A small slice of hard work, well under 15 percent of the time, swallowed roughly half the load. This is precisely what the non-linear zone weighting is built to expose, and it is why two athletes can log identical hours and still carry completely different loads.

For your own roster, treat the elite figures as a reference frame rather than a goal. The method’s authors stress this themselves: ECOs is designed to show relative trends, not absolute targets (Cejuela-Anta and Esteve-Lanao, 2011). Scale the expectation to the athlete in front of you, then watch the swim-bike-run balance and the easy-to-hard load ratio. Those two patterns hold across every level.

If You Already Think in Training Stress Score

If you already coach on Training Stress Score, you have a calibrated sense of what a week should total and what a hard day looks like. ECOs answers the same question, the cost of a session, with different machinery, so the two will not line up one to one. The biggest difference is how each handles different sports. TSS normalizes every discipline to its own threshold, so an hour at threshold reads near 100 whether your athlete ran, rode, or swam it. ECOs instead applies a separate exercise factor per sport, so the same relative hour costs more running than cycling, by design.

A worked example makes the gap concrete. Take sixty minutes held at threshold, which lands in Z4. Under TSS that hour is the definition of 100, closer to 111 for running, since graded pace inflates it slightly. Under ECOs the same hour scores 60 × 4 × the exercise factor: 240 running, 180 swimming, 120 cycling. Treat the absolute numbers as illustrative; the relationship is the point. A threshold hour of running costs twice a threshold hour of cycling in ECOs, where TSS holds both near 100.

There is no clean conversion factor between the two. Different units, different internal structure, and a different cross-sport rule mean no constant maps weekly TSS onto weekly ECOs. Your coaching eye transfers intact, but your absolute anchors reset, so rebuild them from two or three weeks of your athletes’ own data. For the full comparison, including where the two models actually agree and what transfers versus what you will relearn, see ECOs vs Training Stress Score: A Guide for TSS-Fluent Coaches.

How EndoGusto Calculates ECOs From Your Files

Everything above is the method. This is how EndoGusto turns it into a number. When an athlete uploads a session, the platform reads it moment by moment, assigns each stretch to one of the eight zones using the best available signal, applies that zone’s factor and the discipline’s exercise factor, and sums the result into a session score. Those session scores then roll up into the weekly totals most coaches actually watch.

Because ECOs reads pace and power first, the threshold values on each athlete’s Training Zones tab define where every zone boundary falls: Pace at LT (T-pace) for running, FTP for cycling, CSS for swimming, and LTHR where heart rate leads. Athletes with current thresholds get the most accurate read; the ones worth a quick review are those whose values are outdated or were never set.

ECOs gives endurance coaches one honest currency for training stress across three very different sports. The next guides in this series cover what changed when EndoGusto moved to ECOs, how the score lines up against the Training Stress Score you may already use day to day, and how the ECOs stress scores filter into the Performance and Training Load Balance graphs so you can track and plan your athlete’s performance over time.

Suggested References

• Cejuela-Anta, R., & Esteve-Lanao, J. (2011). Training load quantification in triathlon. Journal of Human Sport and Exercise, 6(2), 218–232. https://doi.org/10.4100/jhse.2011.62.03
• Cardona, C., Cejuela, R., & Esteve-Lanao, J. (2019). Manual para entrenar deportes de resistencia.