The aerobic exercise guidelines from the American College of Sports Medicine and other fitness groups are precise: You should aim for 150 minutes a week of moderate aerobic exercise (such as walking), or 90 minutes of vigorous exercise (such as running).
However, the same organisations are less precise when it comes to resistance (strength) training.
They call for two or three sessions a week, but make no reference to total time. To add to the confusion, strength training can seem complicated, with all those contraptions and weights and methods of lifting them.
Coming to the rescue, a new paper simplifies the variables, and offers a practical and proven programme that can be done in less than an hour a week.
The study was published in the journal Applied Physiology, Nutrition, and Metabolism, was written by a team of American and British strength-training experts.
Their investigation aimed to determine if relatively short strength-training sessions utilising different lift techniques could improve strength. It also looked into blood glucose levels before and after experiment.
Participants of the study involved 62 experienced, strength-training subjects (26 males; group's average age 40) who were placed into one of three protocols.
Sessions of strength training a week researchers are recommending.
A control group performed all exercises with two seconds of concentric muscle contraction and four seconds of eccentric contraction - that is, two seconds of the kind of contraction from lifting and four seconds of the kind of contraction from lowering.
A slow group did the same exercise with 10 seconds of lifting, 10 of lowering. A very slow group did 30 seconds of lowering, 30 seconds lifting, 30 seconds lowering.
All subjects followed a routine that consisted of two different strength sessions, of nine exercises each, that emphasised the chest press, leg press and pull down. Subjects performed each session once a week for 10 weeks.
At every workout, subjects did the assigned exercises to "momentary failure", which took about 12 lifts with the control group, four to five for the group doing 10-second contractions, and just one lift at 30:30:30. As a result, subjects spent the same "time under load" in each of the three protocols - about 90 seconds.
After 10 weeks, subjects in all three groups had gained a significant amount of strength, but there was no difference between groups. All groups also had a lower blood glucose level.
This result was not statistically significant, but the authors believe it "might be clinically relevant", as the drop lowered subjects into a different quartile of blood-pressure risk.
"Our paper showed that you don't need to spend two hours in the gym five times a week, as many people think," says lead investigator James Fisher, from Southampton Solent University in England.
"Even trained individuals continue to make gains with less than an hour a week. My own workouts take less than 20 minutes, twice a week."
For the next steps, consider making time in your schedule for two short strength-training sessions a week. Don't sweat over the details.
You can lift at whatever pace you feel comfortable with but it is important, Fisher believes, to reach the point of momentary failure where you can't do any more. Don't practise explosive, high-speed lifting that could lead to injuries.
"Stay relaxed and maintain your breathing pattern," he advises. "Don't hold your breath."
This approach should be even more effective with untrained lifters, who will have more to gain from beginning a strength programme.
"The main message is that resistance training can be relatively simple and still effective," says Fisher. "It doesn't have to get complicated by various training methods and protocols."