Why your plan
looks like that
Our prescription tool gives you a weekly mix across Xfit, Xtend and the barbell room. Here is the reasoning behind it, in plain English, with the research it leans on and an honest account of what it does not prove.
Training two things at once does not ruin either
The old worry was the interference effect: the idea that conditioning eats your strength and muscle. It was based on early research and it has not held up well. A large review of concurrent training found that whether the aerobic work was running or cycling, whether people trained more or less than five times a week, whether they were trained or untrained, and whether the sessions were on the same day or different days, combining the two did not stop muscle growth or maximum strength improving.
What this means for your week. Doing Xtend and lifting in the same week is not a compromise. You are not choosing between an engine and strength, which is the whole point of having three lanes under one roof.
Source: Frontiers in Sports and Active Living, semi-systematic review of concurrent training, summarising Schumann and colleagues.
But the ratio matters, which is why we prescribe one
The nuance is that the amount and type of conditioning changes the result. A well cited meta-analysis found that interference was related to the modality, frequency and duration of endurance work, with running specifically producing decrements where cycling did not, and more frequent, longer endurance sessions associated with smaller gains in size, strength and power. There is also direct evidence on ratios: when strength and endurance were done in a three to one ratio favouring strength, strength gains held up, where an even split did not.
What this means for your week. If your goal is strength or muscle, we cap your conditioning rather than letting it run wild, and we tell you so on the card. If your goal is a race, we do the opposite. The mix is the prescription.
Source: Wilson and colleagues, Journal of Strength and Conditioning Research.
Strength needs its own sessions, not leftovers
Strength and muscle respond to how much hard work a muscle gets across a week. Reviews of training dose show gains rising as weekly volume rises, and that when total volume is held equal, how you split it across the week matters far less than doing it at all. Useful gains are possible on surprisingly little, with two sessions a week enough to move maximum strength in trained lifters.
What this means for your week. If getting stronger or building muscle is your goal, the plan protects lifting days first. Conditioning alone will not build a squat, however hard it feels.
Sources: Pelland and colleagues, resistance training dose-response meta-regressions; Schoenfeld and colleagues on training frequency.
If you double up in a day, lift first
When strength and endurance are done in the same session, order appears to matter over longer blocks. A meta-analysis of training sequence found that across programmes longer than eight weeks, doing strength before endurance was more favourable for lower body strength.
What this means for your week. Two sessions in one day is fine. Put the barbell first and the engine work after, and you keep more of the strength.
Source: Frontiers in Physiology, concurrent training sequence meta-analysis.
Running is built by running, mostly outside class
Distance is built through easy aerobic volume accumulated over weeks, while class time is best spent on the things you cannot do alone: intervals, running off a sled with your legs already gone, and coaching. That is why a plan aimed at a 5k or 10k gives you homework runs at conversational pace and leaves the hard running to us.
What this means for your week. If you have a distance goal and cannot run outside class, the plan says so honestly rather than pretending the timetable can cover it.
For the long game, the guidance is already written
If your goal is staying capable rather than winning anything, the target is not a mystery. World Health Organization guidance for adults is 150 to 300 minutes of moderate aerobic activity a week, or 75 to 150 minutes of vigorous activity, plus muscle strengthening work involving all major muscle groups on two or more days a week. For older adults it adds balance and functional strength work to help prevent falls.
What this means for your week. The long game prescription guarantees the two strength days first and builds the aerobic side around them, and if you are over sixty it tells you to add balance work, because almost nobody trains it.
Source: WHO Guidelines on Physical Activity and Sedentary Behaviour.
What we are not claiming
- This is population level evidence. It describes what tends to happen across groups of people, not what will definitely happen to you.
- Most of these studies were not done on people training three disciplines in a gym like ours. We are applying reasonable principles, not reading a recipe.
- Nobody has proven a single optimal ratio for any goal. Our numbers are a sensible starting point built on the evidence above and on coaching people here.
- Consistency beats precision. A plan you follow for eight weeks will beat a better plan you abandon in week two, every time.
- The tool is not medical advice. If something hurts, or you are pregnant, or you have a health condition, it stops and points you at a conversation instead. That is deliberate.
Your numbers beat any study
The research sets the starting point. What happens next is measured on the floor: your loads on the board, your times, your scans, your lifts. If eight weeks of a prescription has not moved the number you care about, we change it. That is the part no paper can do for you, and it is why every plan comes with a review date on it.