Useful is a different question from optimal
Your plan says three sets, but today you have less time. Is doing only one pointless? No. A single set per exercise can be part of effective strength training. That is a narrower claim than saying one set will give you the same results as three.
First, clear up the wording: one set per exercise is not one exercise for your whole body, and it is not one workout ever. Research on this question compares programs repeated over weeks. A set of push-ups alone does not cover every muscle group.
What the research actually compared
In a study of previously untrained adults, both one-set and three-set programs improved tested strength. Three sets produced greater relative gains in the bench press and biceps curl. [1]
The participants used weights, and the training periods lasted nine weeks each. This was not a test of one quick bodyweight session. It supports the possibility of progress with fewer sets, while leaving a reason to do more when the goal and available time justify it.
ACSM’s 2026 guidance recommends two to three sets per exercise to optimize strength. [2] “Can help” and “best for this goal” answer different questions. You do not have to dismiss a smaller amount of training to acknowledge that more may offer an advantage.
Count the week, and name the tradeoff
Before cutting a session, look at what you are changing. Reducing sets while keeping the same exercise selection is different from keeping only your favorite exercise and dropping everything else. Also distinguish an occasional short day from a permanent change to your plan.
An invented example: you complete one set of each exercise in your existing plan instead of three, because your available time changed. Record that as a shorter session. It does not prove that you maintained the same training stimulus, but it is not an empty entry either. This example illustrates planning, not a personal exercise prescription.
Do not turn the missing sets into a debt
Our practical suggestion: if shorter sessions keep happening, make a realistic version of the plan with your coach or a suitable beginner program. Ask which exercises to retain, how often to train, and when to review the amount. Do not improvise a harder variation or an all-out set just to claim you made up for the missing work.
Keep a simple record of exercises, sets, repetitions, and effort. Review comparable sessions over time. If you later add sets, label the change rather than comparing only total repetitions. The useful next step is a plan you can evaluate, not a promise that less always delivers the same.