Should ultrarunners lift weights?

Yes, primarily as injury insurance and muscle retention rather than as a growth stimulus. Two full-body sessions a week at moderate load through a block, with a particular emphasis on eccentric strength in the quadriceps because descent is what breaks ultrarunners.

Can you build muscle while ultra training?

Realistically no, at genuine ultra volume. The energy cost and the fatigue load leave no room for the surplus and recovery capacity muscle gain requires. Retention is the correct goal and it is achievable.

Why does downhill running cause so much damage?

Because it is maximally eccentric. Every descending stride decelerates your bodyweight with the quadriceps lengthening under load, which produces far more muscle damage than flat running at the same pace. A hard descent produces soreness comparable to a heavy leg day.

How many calories does ultra training burn?

Running costs roughly 1 kcal per kilogram of bodyweight per kilometre. A 155 lb runner at 70 miles a week is around 1,700 kcal a day above a sedentary baseline, which is far beyond what any activity multiplier will estimate.

What is the biggest nutrition mistake in ultra training?

Chronically under-eating relative to a training load that rose while intake did not. The consequences — reduced bone density, hormonal disruption, immune suppression, lost muscle — arrive slowly and get attributed to overtraining, which sends the athlete toward less training when the fix is more food.

Ultrarunning and Strength: What Survives Very High Volume

The descent problem

Downhill running is the highest-eccentric endurance modality there is.

Every descending stride decelerates your bodyweight with the quadriceps lengthening under load. On flat ground running is already thousands of eccentric contractions per session; on a descent the eccentric component is far larger, and the muscle damage that follows is substantial and slow to repair.

The practical consequences are direct:

A hard descent-heavy session is a lower-body session. Schedule it like one, not like aerobic volume.
Do not put heavy squats or deadlifts the day before or after it.
Count it as a hard session in your weekly total.
Recovery takes 48 to 72 hours, not 24.

This is also why eccentric-focused strength work has a specific place in ultra preparation. Training the quadriceps to tolerate eccentric load in the gym is directly protective of the tissue that descent damages — the repeated-bout effect is real, and a controlled version in a gym is preferable to discovering the limit at mile forty.

What to lift, and why

Two full-body sessions a week during a block. Eight to twelve fractional sets per muscle. Compounds at moderate load.

The purpose is retention and injury resistance, not growth. The dose required to maintain muscle is substantially lower than the dose required to build it, which is what makes this workable at all.

Priorities:

Emphasis	Why
Eccentric quad work — slow tempo squats, step-downs	Directly protective against descent damage
Single-leg strength — split squats, step-ups	Running is a single-leg activity
Posterior chain — RDLs, hip thrusts	Hamstring and glute durability over long durations
Trunk, anti-rotation	Postural endurance across many hours
Calf and foot	The most common site of the injury that ends a block
Upper body	Where a runner's muscle is most easily lost, and it costs almost nothing

Two to three sets at 2 to 3 RIR. Not to failure — you have no systemic fatigue to spare.

The energy problem, which is the one that actually breaks people

Running costs roughly 1 kcal per kilogram of bodyweight per kilometre, net of resting. For a 155 lb (70 kg) runner:

Weekly mileage	Extra daily cost
50 mi	~1,200 kcal/day
70 mi	~1,690 kcal/day
90 mi	~2,170 kcal/day

Those figures are far beyond what any activity multiplier produces. "Extremely active" in a standard calculator does not reach 1,700 kcal a day of training cost, and the gap between what such a tool suggests and what you actually need can exceed a thousand calories.

Chronic deficiency at that scale produces the full RED-S picture: falling bone density, hormonal disruption, immune suppression, poor recovery, lost lean mass. And every one of those symptoms is read as overtraining first, which sends the athlete toward less training when the fix is more food. What that looks like and how to tell them apart.

The only method that works at this volume does not predict expenditure at all:

weightChangeLb = trendWeight(today) - trendWeight(14 days ago)
energyBalance  = weightChangeLb * 3500 / 14
maintenance    = avgDailyIntake - energyBalance

Re-measure every four to six weeks through a block, because the number will move by several hundred calories as volume ramps. The full method.

The two blood markers to actually check

Ferritin. Endurance training depresses iron status, and running does so through foot-strike haemolysis — the mechanical destruction of red cells in the feet. At ultra volume this is not a theoretical risk. Low iron produces fatigue, declining performance and poor recovery, which are indistinguishable from overtraining and from under-eating.

Vitamin D, particularly at latitude and in winter, given the bone density stakes.

Do not supplement iron blindly. Excess iron is harmful and a blood test resolves in one step what months of training adjustment will not.

Ramp rate

Keep this week's volume under 1.3 times the average of the previous four. Past about 1.5 the injury-risk curve turns sharply upward, and it turns for connective tissue in particular — tendon and bone adapt on a slower timescale than muscle and cardiovascular fitness do, which is precisely why an ultrarunner feels great right up until they do not.

For an ultra block that ratio does double duty: a spike week is both an injury risk and a direct draw on the recovery budget your strength work is spending. The calculator.

The off-season

The only window where building is realistic, and it should be planned during the season while you still intend to.

Three weeks of genuine rest, then twelve to sixteen weeks of strength-primary work: three or four lifting sessions, 14 to 18 fractional sets per muscle, running held at easy volume only, eating at a small measured surplus.

Aerobic base decays slowly. Capacity to build muscle is at its highest when running volume is lowest.

What to do next

Measure your maintenance now at your current volume, and again in six weeks. The ultrarunners who lose muscle and pick up stress fractures are almost always the ones who never made that measurement, and the symptoms they get treated for are downstream of it.