Why am I not building muscle?

The usual causes are too little progression, not enough hard sets, eating at or below maintenance calories, low protein, poor sleep, or simply not having trained long enough to see change. Check calories and progression first, because between them they explain most cases.

Work through the list honestly

• Are you eating enough? Muscle gain in a deficit is difficult and slow. If bodyweight has not moved in a month, you are not in a surplus regardless of how much it feels like you are eating.
• Is your protein adequate? Aim for roughly 1.6 to 2.2 g per kg per day and actually count it for a week rather than estimating.
• Are your sets hard? Sets stopped five reps short of failure do very little. Most people who feel they train hard are further from failure than they think.
• Is there enough volume? Below about 8 to 10 hard sets per muscle per week, progress is usually slow.
• Does the programme progress? If your logbook looks the same as three months ago, that is the answer.
• Are you sleeping? Chronically short sleep reduces training quality, recovery, and appetite regulation.

Have you actually given it time?

Eight to twelve weeks is the minimum window in which visible change appears, and many people restart the clock every few weeks by changing programmes. Pick a plan, run it for three months without changing it, and then judge.

Are you measuring properly?

Without four-weekly photographs, tape measurements, and a training log, real progress is easy to miss. A great many people who believe they are not growing simply have no record to compare against.

The genuinely harder cases

Advanced trainees, people in a deliberate deficit, and those with high daily activity or high stress all progress more slowly, and that is expected rather than a problem to solve. If you have addressed everything above and still see nothing across six months of good records, it is reasonable to speak with a doctor about anything affecting appetite, hormones, or recovery.

The full framework is set out in Hypertrophy and Muscle Growth and Principles of Strength Training.