How We Read A Study: One Worked Example

Short Answer

Before a study changes what we tell a client, we check who was studied, how many studies or people were in it, how long it ran, how big the effect was, and whether a better analysis agreed. Worked example: a 2016 review of ten trials (PMID 27102172) found muscles trained twice a week grew more than muscles trained once, with an effect size of 0.49 against 0.30.

Updated 7 October 2026

Who was studied?

The first check is whether the people in the study look like the person asking. The training-frequency review by Schoenfeld, Ogborn and Krieger (Sports Medicine, 2016, PMID 27102172) only counted trials on human participants without chronic disease or injury.

That tells us the result applies to healthy adults who are lifting. It does not tell us how someone with a joint problem should train, and we do not use it that way. If a study’s group does not match the client, the finding is background, not a recommendation. We also note where a paper was published: this one is in Sports Medicine, a peer-reviewed journal, so other researchers checked it before it was printed.

How many studies or people were in it, and how long did they run?

Next we count. The 2016 review pooled ten studies that directly compared different weekly training frequencies, and each trial had to run at least four weeks. Ten short trials is a useful signal and a small base.

A single trial of 20 people can point the wrong way by chance. Pooling ten trials reduces that risk but does not remove it, and four weeks is short for measuring muscle growth. So we read the result as a reason to look closer, then look for a larger analysis, which is the fourth check. We also look for how the authors searched for trials, because a review that does not say how it found its studies cannot be repeated by anyone else.

How big was the effect?

A result can be real and small. The review reported that higher training frequency was linked to a larger effect on muscle growth than lower frequency: 0.49 ± 0.08 against 0.30 ± 0.07, with a P value of 0.002.

Those are effect sizes, which express a difference in standard deviations. They are not percentages of muscle. The gap is 0.19. That is a modest advantage, and a P value of 0.002 says it is unlikely to be chance, not that it is large. We keep the numbers in the units the paper used. Ask "larger than what?" every time: an effect of 0.30 for once a week still means muscle grew, and it is the comparison that is smaller.

Did a better analysis agree?

Seven years later, Currier and colleagues (British Journal of Sports Medicine, 2023, PMID 37414459) compared training plans across 119 hypertrophy studies with 3,364 participants. Its authors reported that all of the plans they compared promoted muscle growth about equally well.

The highest-ranked plan for muscle growth was higher-load, multiple-set, twice-weekly training, with a result of 0.66 against no exercise (95% credible interval 0.47 to 0.85). So the larger analysis agrees that twice a week works. It does not show that twice a week is the only way, and the first review’s gap looks smaller once many plans are compared.

What do we tell a client after reading both?

The 2016 authors concluded that, with volume matched, training a muscle twice a week promoted better growth than once, and that major muscle groups should be trained at least twice a week. They also stated a limit: an analysis of session frequency could not be carried out because the sample was too small.

So our plain reading is this. Training each muscle twice a week is a sound default for most healthy lifters, a once-a-week split can still work, and the difference is modest. We do not promise a result from it. The full article, with the same citations, is on our science page.

Read the full training-frequency article · Titan Forge science library

Titan Forge Fitness provides fitness and nutrition coaching. It is not medical care, and nothing here diagnoses, treats, or replaces advice from a physician or physical therapist. If you have a medical condition, an injury, or symptoms that concern you, get clinical clearance before starting or changing a training program.