Hills, HIIT or the Gym?

Trail RunningEndurance
Written by Cat Hoh
Trail running series · Part 2 of 5

Trail runners know they need to climb. The question is how to train for it: more hills, harder intervals, or time in the gym?

A 2026 randomised trial in masters trail runners put the three head to head for 12 weeks. This guide covers what each one changed, what the sessions looked like, why hills aren't a substitute for strength work, and how to fit both into a week.

For trail times, the uphill intervals did the work.

The trial's abstract reports which changes were statistically significant, not how big they were, so we show direction rather than size. The session details come from a published summary of the paper, and we've flagged them where they appear.

01

The Strength Puzzle

When French researchers tested elite trail and road runners side by side, the trail runners were clearly stronger. They were also less economical on the flat, and they trained far less.

Figure 1

Elite trail runners vs elite road runners

Maximal leg torque N·m, higher is stronger

Trail122
Road99

Maximal power watts, higher is more powerful

Trail726
Road626

Energy cost on the flat at 14 km/h J/kg/m, lower is more economical

Trail4.32
Road4.06

Group averages. At 10 km/h on the flat and at 10 km/h up a 10% slope, the two groups' energy cost was similar. The road runners also spent 81% more time training over the previous year. Bars for each measure start from zero. Source: Sabater Pastor et al. (2023).

The authors offer two explanations. Running up and down hills could work as built-in resistance training, or the sport could simply suit, and keep, runners who are naturally stronger. A snapshot of two groups can't tell those apart.

Read this carefully. This was 17 elite men (10 trail, 7 road), measured once. It describes the athletes at the top of the sport. It doesn't show that hill training builds strength, which is the question the trial in section 02 can test.
02

The Trial

Forty experienced trail runners aged 35 to 55 were randomly split into three groups for 12 weeks. Each did three extra sessions a week of one type, on top of the same three runs.

Who took part

According to a published summary of the paper, everyone had at least three years of trail training, ran at least 40 km a week and raced trails at least once a year. Each group was close to half men and half women. Five of the 45 who started withdrew with injury or illness.

The three groups

13 runnersCircuit training

Fourteen bodyweight and free-weight exercises, including box jumps, Romanian deadlifts, single-leg squats, lunges, calf raises, glute bridges and planks.

13 runnersUphill HIIT

Hard intervals on a treadmill set to a 10% incline. See section 03 for what a session looked like.

14 runnersCombined

One round of the circuit followed by an uphill interval in the same session.

All three groups also did one easy run, one tempo run and one long run each week, with one rest day.

Figure 2

What improved after 12 weeks

OutcomeCircuitUphill HIITCombined
Mountain trail time
Running economy, flat and uphill
Lean mass
Leg strength and jump power
VO2max
Anaerobic fitness
Leg stiffness
Balance
Improved (statistically significant)No significant change reported

From the trial's abstract, which reports significance but not the size of each change. Source: Panthong et al. (2026).

Every group got fitter. Only the two groups that ran uphill intervals got faster on the mountain, and only they became more economical. The circuit work built strength and lean mass, and the combined group got both sets of benefits from the same number of sessions.

03

An Uphill Session

The uphill group trained on a treadmill set to a 10% incline, with efforts of a few minutes at close to maximum heart rate.

Figure 3

The shape of a session in the first six weeks

Lower heart rate90 to 95% of max

Shown as described in a published summary of the trial, not from the full paper. Two efforts per session: 4 minutes each in weeks 1 to 6 and 5 minutes in weeks 7 to 12, at 90 to 95% of maximum heart rate, each followed by 2 minutes of active recovery at about 50%. Sessions ran about 45 minutes, rising to about 55. Bar heights show relative intensity, not measured values.

How the 12 weeks progressed

All three groups kept the same session count for all 12 weeks. At week 7 each one stepped up, by making the efforts longer or the exercises harder rather than adding sessions.

Figure 4

What changed at week 7

Circuit3 a week
2 × 15 reps14 exercises, 30 s between them. About 45 min.
Harder versionsFaster reps, higher jumps, single-leg and unstable-surface work. About 55 min.
Uphill HIIT3 a week
2 × 4 min90 to 95% HRmax on a 10% incline. About 45 min.
2 × 5 minSame intensity, a minute longer each. About 55 min.
Combined3 a week
Circuit + 1 × 4 minOne circuit round, then one uphill effort. About 46 min.
Circuit + 1 × 5 minHarder circuit, longer effort. About 55 min.

From a published summary of the trial. The combined group did half the uphill work of the HIIT group in each session, one effort instead of two, and its trail times still improved.

Taking it outdoors

A 10% treadmill slope is a steady, runnable hill: 100 m of climb for every kilometre. Outdoors, look for a hill at that kind of gradient that takes at least four or five minutes to run up hard. The walk or jog back down doubles as easy recovery, and it adds some of the downhill exposure from Part 1.

04

Make the Gym Count

The trial's circuit was light: bodyweight, a box and free weights, 15 reps at a time. It still built strength and lean mass in 12 weeks. Reviews of strength work in runners point to a stronger version.

Heavier beats lighter

Eihara et al. 2022Heavy lifting beat jumps

Pooling 21 studies, heavy resistance training improved running economy (g 0.32) and time trials (g 0.24) by small amounts. Plyometrics on their own gave trivial changes.

Llanos-Lagos et al. 2024aLoad matters

Across 31 studies and 652 runners, high-load training (at least 80% of a one-rep max) gave small economy gains, larger at faster running speeds.

Zanini et al. 2025It shows up late

Ten weeks of heavy lifting plus hops didn't change fresh economy in well-trained runners, but economy held up better at 90 minutes. That's the part of a trail race that decides it.

A session built for trail

Each group of exercises does one of the jobs the legs do on a trail. Pick one or two from each, twice a week.

3–4 × 4–6 each legLoaded step-ups

Knee-height box, dumbbells or a bar. Drive through the whole foot and stand tall at the top. The closest gym copy of a climb.

3–4 × 4–6Trap-bar deadlift

Heavy hip and knee extension in one lift, and easier to learn than a back squat.

3 × 5–6 each legRear-foot elevated split squat

Back foot on a bench. Heavy single-leg strength with less load on the spine.

Climbing shifts more of the work to the hip (Vernillo et al. 2017), so these load hip and knee extension together.

3 × 6–8 each legSlow step-downs

Lower off a step over three seconds, heel just touching the floor. Eccentric quad work, the same braking as Part 1's descents.

3 × 5 each legSingle-leg Romanian deadlift

Long spine, hips square. In one season-long study of track and field athletes it was linked to fewer hamstring strains (Otani et al. 2025).

3 × 4–6Tempo squat

Three seconds down, steady up. Heavy load through the range the knee works in on a descent.

Eccentric work causes soreness at first. Start these light and build over three to four weeks, the same way Part 1 builds downhill running.

3 × 15–20 contactsPogo hops

Quick, stiff ankles, minimal knee bend, off the ground fast. Done fresh, before the heavy lifts.

3 × 8–12 each legLoaded single-leg calf raise

Holding a dumbbell, full range. Do half the sets with a bent knee to load the soleus.

3 × 30–45 sHeavy isometric calf raise

Push into an immovable bar or a loaded machine at mid-range. Used alongside hops in the durability study above.

Hops work best paired with heavy lifting rather than on their own (Eihara et al. 2022; Llanos-Lagos et al. 2024b).

3 × 8 each legLateral step-ups

Step up sideways onto a box, pelvis level. Hip abductor work like this improved pelvic drop and knee control in injured runners (Lashien et al. 2024).

3 × 20–30 s each sideSide plank

Hips high and level. Add a top-leg lift once it's easy.

3 × 8 each sidePallof press

Band or cable at chest height. Resist the pull, which is the stride-to-stride job of the trunk.

Lower-priority than the other three. Fit these in at the end or on an easy day.

Build up to heavy: runners new to lifting should spend three to four weeks on lighter loads and good technique, like the trial's circuit, before moving to sets of four to six. Heavy means the last rep is hard but clean, not a max. The exercise list and set ranges are our reading of the research, not the trial's programme.
05

Hills Aren't a Gym

Hill running is often sold as strength training in disguise. Two earlier studies in well-trained road runners suggest it's better at some jobs than others.

Ferley et al. 2014Economy, yes. Power, no.

Thirty-two well-trained runners did six weeks of interval training on an incline or on the flat, or kept training as normal. Incline intervals improved measures of running economy, but they weren't enough to raise muscle power.

Barnes et al. 2013Harder hills, bigger gains

Twenty well-trained runners each did one of five uphill interval programmes. The highest-intensity programme gave the biggest improvement in running economy, about 2.4%, and was the best option for the neuromuscular measures too.

Putting it together

Uphill intervals give you

  • Faster mountain times (Panthong)
  • Better running economy, flat and uphill
  • A higher VO2max

The gym gives you

  • More leg strength and jump power
  • More lean mass
  • The things hill intervals didn't build (Ferley, Panthong)

Strength work and uphill intervals do different jobs. The combined group in the trial did both inside the same three sessions a week, and it came away with both sets of gains.

06

Build the Week

The trial used six training days a week. Most trail runners have fewer. Here's the trial's week next to a lighter version.

MonCombinedCircuit + uphill interval
TueEasy run55 to 80% HRmax
WedCombinedCircuit + uphill interval
ThuTempo run75 to 85% HRmax
FriCombinedCircuit + uphill interval
SatLong run50 to 90% HRmax
SunRest 

The combined group's structure as summarised from the trial. The day order is ours; the summary doesn't give it.

Day 1Uphill intervals2 × 4 min hard
 Rest or walk 
Day 2StrengthHeavy lifts + hops
Day 3Easy runConversational
 Rest 
Day 4Long trail runInclude descents
 Rest 

Our reading of the research, not a tested programme. It keeps one uphill interval session and one strength session, which between them cover what the trial's combined group improved.

Putting it into a programme

  1. Make one quality session an uphill one.In the trial, the uphill groups were the ones whose mountain times improved.
  2. Keep strength work in the week.It built the strength, power and lean mass that hill intervals didn't.
  3. Start with two efforts.The trial began with two 4-minute efforts and only lengthened them to 5 minutes after six weeks.
  4. Run them hard.The biggest economy gains in the Barnes study came from the highest-intensity programme.
  5. Separate the hard days.Put an easy day or rest between the uphill session and a heavy strength session where you can.
Leave room to recover: these were experienced masters runners, all with a weekly rest day, and five of the 45 who started still withdrew with injury or illness. Build the hard sessions in gradually, especially for runners new to intervals or strength work.
07

Evidence and References

What the studies found

In the trial, 12 weeks of uphill intervals, on their own or combined with circuit training, improved mountain trail time and running economy in masters trail runners. Circuit training on its own improved strength, jump power and lean mass but not trail time. All three groups improved VO2max, anaerobic fitness, leg stiffness and balance. In road runners, incline intervals improved economy but not muscle power, and the hardest uphill programme gave the biggest economy gain. Reviews of strength training in runners favour heavy loads over light ones and over plyometrics alone, with the biggest effect when heavy lifting and hops are combined.

What this research can't tell you

We could only access the trial's abstract, which reports significance but not the size of each change, so we can't say how much faster the uphill groups got. The session details come from a published summary rather than the full paper. The trial tested one mountain course over 18 km, so it may not apply to longer, steeper or more technical races, and it only included masters runners. The trail and road comparison was 17 elite men measured once, and the two earlier interval studies were in road runners. None of these studies tested a week like our four-day version. The strength session in section 04, its exercises and set ranges are ours, built from reviews that mostly studied road and track runners.

This is general guidance based on research. It doesn't replace individual advice from a coach or health professional. For more on strength work, see our Strength Training for Runners guide.

References

Figures and citations checked against the published sources, October 2026. Next in the series: Experience Beats the Lab.

Cat Hoh
Next

Races Are Lost on the Way Down