Terra study: Running is the hardest endurance sport across 9 sports and over a million sessions

A comparison of 9 endurance sports drawn from over a million logged sessions puts running on the top step for intensity. It is hard to find anything more demanding for the heart-and for the rest of the body.

Terra ranks running as the most intense endurance sport

To the perennial question, “which is the hardest endurance sport?”, the health and sports data platform Terra believes it has a data-led answer. After analysing training records from more than a million sessions across 9 different disciplines, running finished first, ahead of indoor cycling (turbo trainer) and cross-country skiing.

Released on 23 April 2026, the findings are presented as a chart showing the “cardiac signature” of each sport. The wave-like curves represent the distribution of heart rate (HR)-in other words, the average time spent in each heart-rate zone per session. Compared with other endurance activities, running’s curve is shifted furthest to the right, indicating more time at higher HR levels.

Terra also plotted the median for each sport using dotted lines, allowing a more precise comparison. On that basis, running drives the body to a median HR 9 beats per minute (BPM) higher than turbo-trainer cycling, and 14 BPM higher than cross-country skiing. Terra links this to the fact that running is not a weight-supported sport and involves no glide.

Three intensity bands across the 9 sports

Across the full set of 9 sports, Terra groups activities into three categories:

• High intensity: running, turbo trainer, cross-country skiing
• Moderate intensity: outdoor cycling, open-water swimming, ski touring
• Low intensity: walking, alpine skiing, hiking

Notably, the turbo trainer is placed above outdoor cycling because indoor riding offers no natural pauses-unlike outside, where you may stop pedalling on descents or be forced to ease off in traffic.

Where the analysis is limited

Terra also points out limitations in its work: “We have no demographic information (age, sex, fitness level), which prevents us from separating these effects from those related to the choice of sport. We also do not know the goal of the training (easy run or tempo session), which means our data mixes structured training and free activity.”

A further constraint is the measurement device itself. The dataset largely comes from wrist-worn optical heart-rate sensors (sports watches), rather than advanced chest straps. As a result, accuracy may vary between sports-particularly swimming or skiing-because of arm movement and environmental conditions.

Different intensity ratios, with a special case: walking

To round out the results, Terra also highlighted an intensity “ratio” for each sport, arguing that looking only at average HR can be misleading. The idea is that runners may, on average, be healthier individuals-not merely participants in a more physically demanding activity. Terra therefore combined data by comparing average HR against the maximum HR recorded per session.

Running again comes out on top, with the highest typical per-session peak: the average maximum HR is 168 BPM, which is Terra’s highest recorded value once more. Relative to other sports, running sits clearly above the rest.

Outdoor cycling also separates itself from indoor cycling, showing a much higher average session maximum HR-160 BPM versus under 145 BPM for the turbo trainer.

Walking ranks third for the highest intensity ratio, but this is mainly because there is little variation in effort intensity: whether the session is on flat ground or rolling terrain, the difference is modest compared with other sports. It naturally sits close to hiking.

Downhill skiing is not far behind, for a different reason. It is an intermittent sport, where intense descents are offset by uplift rides and time spent queueing in the cold-periods during which the body can drop to a relatively low heart rate.

93% of runner-cyclists train harder when they run

Finally, Terra also compared intensity within the same individual across disciplines. To avoid simply contrasting the fitness profiles of runners with those of cyclists, skiers, or hikers, the platform narrowed the analysis to 2,808 people “who had recorded at least five sessions in at least two disciplines”. The study’s approach was as follows:

“For each person, we used their maximum recorded heart rate as their personal maximum heart rate, then expressed the average heart rate of each session as a percentage of that maximum value,” Terra explains.

In a second chart, the results show that the same people who run at a median intensity of 78% of their personal maximum heart rate cycle outdoors at only 67% and walk at 52%. The dataset also indicates that, among 1,480 users who both run and cycle outdoors, 93% show a higher relative intensity when running.