What’s the least number of repetitions, sets, and days per week I can do strength training and still get results? —C.J., Midland, Texas

Good news: Unless you’re a bodybuilder or a serious athlete, a single set for each muscle group, twice a week, is all you really need. Beyond that, the benefits begin to taper off. As for repetitions, the general advice calls for 8 to 12 reps at a weight or resistance that’s challenging but lets you complete the set. If you’re frail or older than 65, substitute 10 to 15 reps at a slightly lower resistance. If you work out on consecutive days, switch off between muscle groups—say, the torso one day followed by arms and legs the next—since muscles need at least a day off to recuperate.