If you're always tired from running and lifting, the cause is almost never that you're training too much — it's that you're eating too little for how much you train. Chronic fatigue in hybrid athletes is overwhelmingly a fueling problem: not enough carbohydrate (most people need 5–7 g per kg of bodyweight per day), not enough total calories, and not enough real recovery to absorb the workload. Left unchecked, that gap becomes Low Energy Availability (LEA) and eventually RED-S (Relative Energy Deficiency in Sport), which trashes performance, sleep, mood, immunity, and hormones. This guide gives you the warning-sign table, the numbers to eat, and the line where "eat more" stops and "see a doctor" starts.
Always Tired From Running and Lifting: Warning Signs and Likely Cause
Being always tired from running and lifting shows up as a cluster of signs, not one symptom — and reading them together tells you whether you're simply underfueled or sliding toward RED-S. Find your signs in the table below, then match them to the likely cause. The pattern most hybrid athletes see is several rows lighting up at once, which points hard at an energy deficit rather than any single exotic problem.
| Warning sign | What it feels like | Most likely cause |
|---|---|---|
| Dead legs | Heavy, flat legs on runs and warm-ups that never feel fresh | Depleted muscle glycogen — too few carbs |
| Stalled or dropping lifts | Weights that used to move now grind; reps disappear | Under-recovery + low fuel; poor training adaptation |
| Poor, broken sleep | Wired-but-tired, waking at 3 a.m., unrefreshing sleep | Low energy availability driving up cortisol |
| Frequent colds / niggles | One bug after another; slow wound and DOMS recovery | Suppressed immunity from chronic deficit (RED-S) |
| Low mood, low drive | Flat, irritable, no motivation to train | Under-fueling affecting brain fuel + hormones |
| Low libido | Noticeably reduced sex drive; (women) irregular or missing periods | Suppressed sex hormones — a red flag for RED-S |
| Performance plateau | Doing the work but times and loads won't budge | Body prioritizing survival over adaptation |
| Always hungry OR never hungry | Ravenous and can't fill up — or appetite has vanished | Both are deficit signals; blunted appetite is worse |
| Nagging or recurring injuries | Tendinopathy, stress reactions, bone pain that lingers | Poor recovery + low bone/tissue support (RED-S) |
One or two rows can be a bad week. Four or more rows together, for weeks, is the signature of underfueling — and if the RED-S-flagged rows (missing periods, recurring stress injuries, frequent illness, crashed libido) are lit, treat it as more than tiredness.
Why Underfueling Makes You Always Tired From Running and Lifting
The reason you're always tired from running and lifting is that hybrid training stacks two large energy demands on the same body. A run drains muscle and liver glycogen (your stored carbohydrate); a hard lifting session drains it too and adds heavy tissue-repair costs on top. Do both across a week and your daily energy bill is far higher than a pure runner's or a pure lifter's — but most people keep eating like they only do one sport.
When the fuel coming in can't cover training plus the basic cost of being alive, your body defends itself by down-regulating everything non-essential: it dials back reproductive hormones, thyroid output, bone building, and immune function to save energy. Sports scientists call that state Low Energy Availability (LEA), and it's measured as the calories left for your body after exercise is paid for. The rough threshold where problems begin is around 30 kcal per kg of fat-free mass per day of energy availability; drop below it consistently and fatigue, not fitness, is what you build.
From Tired to RED-S: When It's More Than Underfueling
If you stay always tired from running and lifting for months, chronic low energy availability can progress into RED-S — Relative Energy Deficiency in Sport. RED-S is the modern, both-sexes successor to the old "female athlete triad," and it describes what happens when the energy gap has been open long enough to impair multiple body systems at once, not just performance.
- Hormonal: suppressed testosterone in men; irregular, light, or absent periods in women (a major warning sign).
- Bone: falling bone density and a rising rate of stress fractures and stress reactions — especially punishing for runners.
- Immune: more frequent infections and colds, slower recovery from every session.
- Mood & cognition: low mood, irritability, poor focus, and depression risk.
- Metabolic: a body running cold — often low resting heart rate paired with feeling constantly, unshakably tired.
RED-S is not a diagnosis to self-assign lightly, but its early rungs — persistent fatigue plus one or two of the flags above — are exactly what an underfueled hybrid athlete looks like. The good news: caught early, the fix is the same as for plain underfueling. Eat more, recover more.
The Fix for Always Tired From Running and Lifting: Eat More Carbs
The single most effective fix when you're always tired from running and lifting is to raise your carbohydrate intake — it's the fuel your training actually burns, and it's what most hybrid athletes chronically under-eat while over-focusing on protein. Carbs refill the glycogen that gives you fresh legs and completed rep targets.
| Training load | Daily carbs | Notes |
|---|---|---|
| Easy / low-volume day | 3–5 g/kg | Recovery or rest days |
| Moderate hybrid training | 5–7 g/kg | The zone most tired athletes are missing |
| High volume (long runs + lifting) | 6–10 g/kg | Big double days and race prep |
For an 80 kg athlete, the moderate band is roughly 400–560 g of carbs a day — far more than most think they're eating. Concrete moves: add rice, potatoes, oats, pasta, or fruit to every meal; take 30–60 g of carbs during sessions over ~75 minutes; and eat a carb-plus-protein meal within a couple of hours after training. Don't forget total calories either — carbs fix fuel, but if overall intake is below your needs, the tiredness stays. If you're losing weight you didn't intend to, that's the deficit talking.
Protein and Recovery: The Other Half of the Fix
Carbs get you un-tired; protein and recovery keep you adapting. When you're always tired from running and lifting, under-eating protein slows tissue repair and lets muscle erode under the double workload. Aim for 1.6–2.2 g of protein per kg of bodyweight per day, spread across 3–5 meals of roughly 0.4 g/kg each — that upper end matters more for hybrid athletes than for pure lifters because endurance work also chews into protein.
- Sleep 7–9 hours. This is where hormones reset and tissue rebuilds; short sleep alone can mimic every fatigue symptom above.
- Take at least one true rest day a week — no "easy" run that becomes a hard one.
- Deload every 4–8 weeks: a lighter week lets accumulated fatigue clear so adaptation surfaces.
- Fuel around sessions, don't train fasted-and-empty on hard days if you're already flat.
- Manage life stress — work and sleep debt spend from the same recovery budget as training.
Recovery isn't the reward for training; it's the part of training where you actually get fitter. If you're eating enough but never resting, you'll stay tired anyway.
A Simple 2–4 Week Plan to Stop Being Always Tired
Turning around being always tired from running and lifting usually takes 2–4 weeks of consistent fueling and recovery — not a single big meal. Run this experiment before assuming anything is medically wrong:
- Weeks 1–2: raise carbs into the 5–7 g/kg band, hit 1.6–2.2 g/kg protein, and stop any accidental calorie deficit. Sleep 8 hours.
- Add a real rest day and cut one hard session's intensity while your fuel catches up.
- Track the signs from the first table weekly — dead legs and mood usually lift first, within 1–2 weeks.
- Weeks 3–4: if energy, lifts, and sleep are climbing, you've confirmed underfueling. Keep the new baseline and rebuild volume gradually.
Most cases resolve here. But if you've genuinely eaten more, slept more, and rested — and you're still exhausted after 2–4 weeks, or you have RED-S red flags like missing periods, recurring stress fractures, or repeated infections — that's your line. See a sports physician or a registered sports dietitian. Persistent fatigue can also stem from iron deficiency/anemia, thyroid issues, or other conditions that need proper testing, and those are not something to guess your way through. Eating more is the first move; a professional is the next one if it doesn't work.
Common questions
Why am I always tired from running and lifting?
Usually because you're underfueling — eating too few carbs and calories for the combined load of endurance plus strength work. Hybrid training burns through glycogen from both sides, so most athletes need roughly 5–7 g/kg of carbs a day. Chronic shortfalls become Low Energy Availability and drive constant fatigue.
How many carbs do I need if I run and lift?
Most hybrid athletes need about 5–7 g of carbohydrate per kg of bodyweight per day, rising toward 8–10 g/kg on very high-volume or race-prep weeks and dropping to 3–5 g/kg on easy days. For an 80 kg athlete that's roughly 400–560 g of carbs on moderate training days — far more than most eat.
Is my constant tiredness overtraining or underfueling?
For most people it's underfueling, not too much training. True overtraining is rare and usually follows sustained underfueling and poor recovery. Try eating more — especially carbs — and sleeping 7–9 hours for 2–4 weeks first. If dead legs, mood, and lifts recover, it was fuel, not volume.
What is RED-S and could I have it?
RED-S (Relative Energy Deficiency in Sport) is what chronic low energy availability becomes: impaired hormones, bone, immunity, mood, and performance in both men and women. Red flags include missing or irregular periods, recurring stress fractures, frequent infections, and crashed libido alongside persistent fatigue. If those appear, see a sports physician.
When should I see a doctor about training fatigue?
See a sports physician or registered sports dietitian if deep fatigue persists 2–4 weeks after genuinely eating more, sleeping 7–9 hours, and adding rest — or immediately if you have RED-S red flags like absent periods, recurring stress fractures, or repeated infections. Iron deficiency and thyroid issues also need proper testing.