General Development Phase in Trail Running: Build Endurance and Strength (3/5)

The general development phase is the quiet core of successful preparation. It’s where you build the endurance, consistency, and strength that will help you handle heavier loads later. After the base phase and before specific race prep, this is where trail runners build their durability. It’s long, methodical, sometimes monotonous — but absolutely essential.

Understanding the phase

This phase comes after recovery and marks the progressive return to structure and discipline. The goal: develop all the fundamental qualities needed for trail running — endurance, strength, and staying power.

For short to medium trail races (up to 60 km), it typically lasts 6 to 8 weeks. For ultras, it can extend up to 12 weeks. Volume increases gradually, hill work is introduced, muscles are strengthened, and paces are tested.

Key focus areas

  • Base endurance is the cornerstone: most of your training time, at low intensity, on flat or gently rolling terrain. It develops the aerobic capacity that lets you go long without burning out.
  • Long runs, often hilly, last 1.5 to 2 hours for mid-distance races, longer for ultras. They build muscular endurance and teach pacing over time.
  • Hill work builds strength and power endurance, with 1- to 2-minute uphill repeats or standing climbs on the bike.
  • Specific pace work (zone i3) builds stability at a steady pace, simulating race-day effort.
  • VMA intervals and fartlek (30 seconds to 3 minutes) keep the cardiovascular system responsive.
  • General strength training (core work, resistance exercises, proprioception) ensures stability and prevents injuries.

Finding the right intensity balance

Coaches often refer to the 80 / 15 / 5 rule: 80% of volume at low intensity, 15% at moderate intensity (aerobic threshold, zone i3), and 5% at high intensity (VMA, short intervals). You need to know how to run slow to get faster.

Sample week

  • Monday: easy 45–60 min run on flat terrain. Nothing more.
  • Tuesday: hill workout, e.g. 2 sets of 8 × 1-minute climbs, jog down to recover, short cooldown.
  • Wednesday: light activity — cycling, swimming, or easy jog.
  • Thursday: specific pace session: 20 min warm-up, 30 min at marathon or long trail pace, cooldown.
  • Friday: 30-minute strength session + 30-minute jog.
  • Saturday: the key session — 1.5 to 2 hours on rolling trails, walking if necessary.
  • Sunday: rest or very easy jog.

This 6–8 hour weekly structure provides a solid base. Experienced runners can add a VMA session or extend the long run up to 2.5 hours.

Measuring progress: the VMA test

To fine-tune intensities, know your Maximal Aerobic Speed (VMA). The half-Cooper test is simple: run 6 minutes at a steady, maximal pace on flat ground, record the distance, and divide by 100. Example: 1,450 m = 14.5 km/h.

  • Easy endurance: 60–70% of VMA
  • Tempo: 75–85%
  • Threshold: 85–90%
  • Long intervals: 90–95%
  • Short VMA: 100–105%

Adapting to your profile

Beginners or busy runners: three sessions per week is enough — one long run, one hill or VMA session, one easy run. Intermediates can aim for four to five sessions, balancing volume and intensity. Advanced athletes may train six to eight times a week, sometimes with double sessions, where mastering the balance between intensity and recovery becomes crucial.

A phase to embrace

On the surface it may seem like nothing’s happening. But under the hood everything is coming together: muscles grow more resilient, the heart more efficient, the mind more stable. It’s not about chasing PRs — it’s about building the foundation, because every easy step you take now powers your performance later.

This article is part of the series “Build your trail season”: 1/5 Planning your season · 2/5 The base phase · 3/5 General development · 4/5 Specific development · 5/5 Tapering