Does HYROX build muscle or cost it?
Neither, by much, as long as you keep lifting. A race is 8 km of running, in eight runs of about 1 km, one before each station. The loads are real but moderate for someone who already trains for size: in Men Open the sled push is 152 kg including the sled, the farmers carry is 2 x 24 kg and the sandbag is 20 kg (Women Open: a 102 kg sled push, 2 x 16 kg and a 10 kg sandbag). You move them for distance, not for sets of eight.
In the first published study of the race, 11 recreational athletes each raced a simulated Open course alone in a gym. The runs took a median 51.2 of 86.5 minutes. Faster finishers had higher aerobic capacity and did more endurance training; grip strength and muscle mass percentage did not predict the time. The authors judged its maximum-strength demands moderate to low next to other functional fitness formats. It is a small sample, but it matches the race: if you already lift, HYROX training alone will not add much size, and your size will not carry you round.
The muscle is not at risk from the running so much as from what you drop to make room for it. If you are strong and the Open loads feel light, look at Pro: a 202 kg sled push and 2 x 32 kg kettlebells for men, and the Men Open loads for women. See Open or Pro.
What concurrent training does to muscle growth
Concurrent training means strength and endurance work in the same programme. For years the assumption was that the running eats the gains. A 2022 meta-analysis does not find that. Schumann and colleagues pooled 43 trials and 1,090 adults, comparing a strength programme alone with the same programme plus aerobic work for at least four weeks. Maximal strength came out the same across 37 of those trials, and muscle size came out the same across the 15 that measured it.
- Growth held. No difference by age, or between fewer and more than five sessions a week. Running against cycling is less settled; see below.
- Explosive strength lost out, most when both kinds of training shared a session rather than being at least 3 hours apart.
- The idea was already under question. Murach and Bagley argued in 2016 that the case for interference with growth in humans was weaker than assumed.
The trials lasted as little as four weeks, and that analysis did not separate advanced lifters from other active people. A 27-study analysis found that concurrent training blunted squat and leg press strength gains (one-rep max, not muscle size) in trained people but not in untrained or moderately trained ones. A 2018 review reached the same view: the more experienced you are, the more interference you meet, so if you have lifted for years, you are the athlete most likely to meet it. In the 27-study analysis the loss came when strength and endurance shared a session; in separate sessions more than 2 hours apart it was small and not significant.
A week that keeps both
The upper body costs the race little. Legs are where the two goals collide: the sleds, the burpee broad jumps, the lunges, the wall balls and every run all use them. A week that keeps both protects the heavy leg session and the hardest run from each other.
| Day | Size leads | Race leads |
|---|---|---|
| Mon | Upper body, heavy | Upper body, heavy |
| Tue | Lower body, heavy | Run intervals |
| Wed | SkiErg and rower intervals | Lower body, heavy and short |
| Thu | Upper body, volume | Easy run |
| Fri | Lower body, volume | Upper body, volume |
| Sat | Easy run, 30 to 40 minutes | Runs and stations, race order |
| Sun | Rest | Rest |
- Keep the load, cut the sets. Maintenance research finds that keeping the same relative load matters more than how many sets or sessions you do.
- Put a gap between legs and hard running. A different day is simplest. The detail on same-day doubles is in running and lifting.
- Pick lifts that carry over. Squats, split squats, deadlifts and carries feed the sleds, lunges and farmers carry. The strength guide matches lifts to stations.
Choosing which goal leads each block
Peaking for size takes high lifting volume, legs included. Peaking for a race takes running volume and race-style sessions. Both draw on the same recovery, so one goal leads and the other is held. A 2018 review of concurrent training puts numbers on it: when strength adaptations matter most, do two or three strength sessions for every endurance session; when endurance matters most, move to one for one, or one strength session for every two endurance sessions.
- Start from the race date. With no race booked, or one far off, size leads and the HYROX work is easy running and erg sessions.
- Find what limits you. If the loads are the problem, a strength block comes first. For a lifter it is usually the running, the biggest part of the race, so the race takes the lead earlier.
- In the race block, hold rather than grow. Fewer lifting sessions, same heavy loads, legs placed away from the key runs.
- After the race, switch back. Size leads again and running drops to maintenance.
In one trial, 70 adults trained their legs three times a week for 16 weeks, then 56 of them dropped to one session a week, or none, for 32 weeks. In the 20 to 35 year olds, one session a week kept the muscle even at one set per exercise; in the 60 to 75 year olds, neither dose did. A later review put the older floor at up to two sessions a week and two to three sets per exercise, as long as the relative load stays the same. Those people had not trained their legs with weights for five years and were not running a race block, so treat it as a floor, not a target.
Running volume and muscle
This is where the research disagrees. A 2012 meta-analysis of 21 studies found that running, but not cycling, reduced growth and strength, and that longer and more frequent endurance sessions went with smaller gains. The 2022 analysis found no difference between running and cycling for whole-muscle size, and none by session count. But a companion 2022 analysis by the same group, of 15 studies and 300 adults, found a small loss of muscle-fibre growth with concurrent training, and a larger one in type I fibres when the endurance work was running rather than cycling. Only three of its studies used running, and the authors call that result preliminary.
You cannot skip the running: it is the biggest part of the race, and more endurance training went with faster finishes in the first HYROX study. What you control is how it arrives.
- Add it in steps. Build weekly running gradually rather than adding a race block of running in one go.
- Share the load with the ergs. The authors of the first HYROX study suggest replacing or combining some running with the rower or SkiErg to limit overuse.
- Keep the hard work short. A 2018 review of concurrent training suggests that short, intense intervals interfere less with strength than long, frequent steady sessions. More in running for HYROX.
If you also play a sport, the same logic covers the whole week. See hybrid training.
Goals in Smash Coach
Once you know how much size matters this block, give it a place under the race, and move it when the block changes.
Your race sits at the top and everything is built around it. Under it you get three goals, in the order you care about them. On Home, find YOUR GOALS and tap MANAGE. Under Add a goal, OTHER GOALS offers common ones such as a pull-up, a stronger core or running faster, or type your own and your coach checks it reads as a training goal before adding it. Press and hold the grip handle on a card to drag it up or down: the higher it sits, the more of your training goes to it. The event card at the top cannot be moved or removed from here, so what you rank is everything under your race.
With Pro or during your trial, one rebuild runs when you leave the Goals page. On the free plan your goals are still saved, but your coach is paused, so your plan stays as it is. More in Set and rank your goals.
With Pro or during your trial you can ask your coach in chat about fuelling and hydration around a session, and nothing beyond that: no calorie targets, macros or meal plans. See What you can ask.