Why some people progress faster: what we know about training response

Two people join the same gym in the same month, run the same programme and eat much the same food. Six months later one of them has added 25 kg to their squat and everyone asks what they are doing; the other has added 10 kg and their shirt fits exactly as it did in March.

This is not a vanity question. The answer decides whether you change the programme, change your expectations, or stop hunting for a culprit that is not there. Research has a solid, well-established part and a larger part that is still open, so it is worth separating the two.

What is reliably known

The spread of results on an identical programme is enormous. When a group trains on the same supervised plan, the average that eventually gets published — say a 5 per cent gain in muscle mass — usually describes almost nobody in that group. Some gain twice the average, others gain barely anything measurable. The evidence here is consistent: the same pattern shows up for strength, for muscle size and for aerobic fitness, across age groups and in both men and women.

Strength and size do not always move together. The same person can be slow to add muscle but quick to add weight on the bar, or the other way round. A large slice of early strength comes from the nervous system, technique and simple tolerance of heavy loads, and that slice runs on its own clock. Track at least two things — the numbers on the bar and tape measurements or photos — because one can sit still for months while the other moves.

Training age explains more of the gap than people assume. A beginner can add 40 to 60 per cent to the main lifts in the first year; someone with five serious years behind them is fighting for 2 to 5 per cent a year. Before you compare yourself with anyone, check how long they have actually trained, not how long they have held a membership.

What the programme does not show often matters more than the programme. Sessions completed over a year, how hard the sets really are, sleep, honest food intake and life stress are rarely measured properly, and any of them can create a several-fold difference. How close to failure you actually take your sets is the single most common hidden gap between two people apparently following the same plan.

Part of the apparent difference is measurement error. A one-rep max can swing 3 to 5 per cent from day to day, tape measurements depend on hydration and on who is holding the tape, and body composition devices carry their own error. When the same people are tested twice, a good share of those who looked like non-responders the first time land squarely in the average the second time.

What is likely but not settled

The inherited part is real, but you cannot buy a test for it. Family and twin comparisons consistently suggest that trainability is substantially heritable. They just as consistently show that no single gene explains how much any individual will gain — the contribution is scattered across many tiny effects. Genetic tests promising a training plan from a saliva sample are selling a certainty that does not exist.

The mechanisms are informed guesses. Muscle fibre type distribution, the number of fibres you were born with, how satellite cells respond, muscle belly length and where the tendons attach are all sensible explanations for why one person grows faster or simply looks more muscular at the same body weight. In humans this is still poorly researched and hard to measure, so it stays at the level of plausible rather than proven.

Individual volume needs. The idea that one person thrives on 10 hard sets per muscle per week while another needs 25 sounds right and many coaches see it in the gym. The evidence is weaker than the confidence around it, because genuine individual response is very hard to separate from random variation without repeated testing. Treat it as a working assumption, not a law.

Recovery. That people differ in how fast they recover — through sleep, age, stress and food — is close to certain. How much, and how to measure it in one individual, is not resolved. Read watch data and heart rate variability as a rough steer, not a verdict.

What gets reported badly

• “I am a non-responder.” That label comes from short trials of 8 to 12 weeks using a single measure. Extend the timeline, add volume or change what is measured, and most of those people move. A permanent non-responder is far rarer than the internet suggests.
• Body types. Sorting people into ectomorph, mesomorph and endomorph has no standing as a basis for prescribing training or diet. It describes how you look now, not how you will respond.
• The hardgainer. When intake is actually recorded for a few days, most people who say they eat everything and never gain turn out to be eating noticeably less than they estimate.
• Headlines about new findings. A group average is not a forecast for you, and a statistically significant difference need not be visible in the mirror. Reading study headlines without being taken in saves a lot of money here.

What this means for your training and food

Judge a programme in blocks of 8 to 12 weeks, not week by week. Measure at the start and the end under the same conditions: same time of day, same equipment, same person holding the tape. Anything shorter mostly measures noise.

Fix the best-supported things first. Sets taken genuinely hard — last rep landing 0 to 3 reps short of failure — and a gradual increase in load or reps over time. That is the signal the muscle actually registers, and it is where most self-declared non-responders are leaking progress.

Adjust volume in steps. Start at 10 to 15 quality sets per muscle group per week. If two blocks pass with no movement and recovery looks fine, add 3 to 5 sets per group per week and measure again. Jumping from 10 to 30 overnight gives you fatigue, not information.

Food carries its share. Roughly 1.6 to 2.2 grams of protein per kilogram of body weight covers what is well established; beyond that, extra rarely adds anything. Gaining muscle needs a modest calorie surplus, around 0.25 to 0.5 per cent of body weight per week — faster gain mostly means more fat, not more muscle.

Sleep and consistency. Seven to nine hours of sleep and completing 85 to 90 per cent of planned sessions across a year separate people far more than exercise selection does. An average programme run consistently beats a perfect one run occasionally.

If everything stalls for months and you feel flat, adding sets is not the answer. Check the signs of accumulated fatigue, take a deload week and come back on lower volume.

When to see a doctor

A drop in strength and energy that does not lift after 7 to 10 days of reduced training, unplanned weight loss, heavy breathlessness or chest pain on exertion, persistent dizziness, a missing menstrual cycle, or any suspicion of low iron, thyroid problems or anaemia are reasons for a check-up and basic blood work, not for a new programme. The same applies if you take medication affecting heart rate, blood pressure or blood sugar.

In short

• Differences in response to identical training are large, repeatable and well documented — they are not an excuse.
• The inherited component is real, but no test available today can tell you how big yours is.
• Most of what gets blamed on genetics is training age, effort, consistency, sleep, food and measurement error.
• Judge progress over 8 to 12 week blocks and with two measures, not one week and one number.
• If you genuinely are a slow responder, that changes the pace you expect, not the decision to train — the health returns from strength and fitness arrive regardless.