Training for Your First 100K — 22 Weeks, Plainly

A 100K (62 miles) is the quiet middle of ultrarunning. Less iconic than the 100, more demanding than the 50-miler, and the distance where most runners learn to handle real night running and serious fueling. It's also the perfect bridge race before a 100-miler.

Who this plan is for

• You've finished a 50-miler in the last 18 months
• You're running 45–55 mpw comfortably
• You have 22 weeks of consistent training
• You're either targeting a 100-miler in the year ahead, or want a true ultra without the 100-mile commitment

Three phases

Weeks 1–7 (Base): 45 → 55 mpw. Long runs 16 → 22 mi.

Weeks 8–18 (Build): 55 → 75 mpw. Long runs 22 → 36 mi. Heavy back-to-backs.

Weeks 19–22 (Taper): 75 → 50 → 35 → 25 mpw.

A peak week (week 17)

• Monday — rest + 25 min strength
• Tuesday — 8 mi easy with strides
• Wednesday — 10 mi with 6 × 5-min hill repeats
• Thursday — 8 mi easy
• Friday — rest
• Saturday — 32 mi long, on race-similar terrain
• Sunday — 16 mi back-to-back, easy pace

Total: 74 mi. The 32/16 weekend is the workout that makes your race possible.

Night running — the new skill

A 100K takes 14–18 hours for most first-time finishers. That means at least 4–6 hours of night running. This is the new variable from a 50-miler:

• Train in the dark. At least three long runs in the build phase done partially or fully in the dark.
• Headlamp practice. Use the same headlamp you'll race with. Get familiar with battery swapping at speed.
• Pace shift. Night running is 10–20% slower than day running for most. Plan splits accordingly.
• Mental. The first hour of night running is the lowest psychological point of the race for most. Push through it; it gets easier.

Fueling — the gut-stretch zone

A 100K runs 3-4 hours longer than a 50-miler. Cumulative calorie need: 8,000-12,000 cal. Absorption max: 250-300 cal/hr trained gut. The gap is where the bonk lives.

From week 9 of training, every long run includes 250 cal/hr fueling at race pace. Same gels, same flask mix. By week 17, your gut should reliably handle 280 cal/hr without protest. If it can't, the race will surface that limit.

The drop bag rehearsal

A 100K is the first race where drop bags really matter. Practice the drop-bag swap during your build-phase BTBs:

• Set up a "fake aid station" at your halfway point — water, gels, a sock change, body glide.
• Do the swap in under 5 minutes.
• Test what doesn't work (gels you don't want at hour 7, socks that take too long to change, etc.) and fix it before race day.

Race-week routine

• Tuesday: last hard effort — 5 × 3 min at threshold
• Wednesday: 5 mi easy
• Thursday: rest
• Friday: 2 mi shake-out + strides
• Saturday: rest, hydrate, carb-load
• Sunday: race

Race-day pacing

The first 30 miles of a 100K should feel insultingly easy. You're holding back. Walk the climbs. Eat constantly. The race begins at mile 35.

The night-section transition (typically miles 40-60) is the deciding section. If you've trained night running, this is where you make up time on runners who haven't. If you haven't trained for it, this is where you bleed time.

What's next

A 100K is the ideal bridge to a 100-miler. You've now done 14-18 hours of running, tested night-running fitness, and exercised your fueling protocol at near-race-day duration. The 100-mile gap (38 more miles, ~10 more hours) is incremental from here. Most 100K finishers who continue into a 100-miler within 12 months finish their first 100. Plan accordingly.