The evidence supporting strength training (and exercise in general) is so compelling that the U.S. Department of Health and Human Services recommends that adults do muscle-strengthening exercises for all major muscle groups at least twice a week. Ideally, this should be combined with at least 150 minutes of moderate (or 75 minutes of vigorous) aerobic activity per week, as well as balance and flexibility exercises. Strength and Power Training: A guide for adults of all ages, a newly updated Special Health Report from Harvard Medical School, offers the following tips—and more—for varying your routine, cranking up the challenge, and making strength training a lifelong endeavor.

Try new equipment. Substitute one type of equipment for another. For example, work out with machines instead of free weights one day a week, or switch from one brand of machine to another. Or try exercises using a medicine ball, resistance bands, or resistance tubing.

Change your pace. Vary your intensity—do one hard, one medium, and one lighter workout in cycles of seven to 10 days. This is a form of periodization, an exercise strategy that can enhance strength gains, help sidestep plateaus, and avoid overtraining while allowing more time for the body to heal after being thoroughly taxed. Because it can be difficult to put together a good periodization strategy, it’s essential to work with an exercise professional to come up with an effective plan that’s tailored to your needs.

Work out with a friend when you can. If your friend is careful about good form, too, this can be a way to help reinforce good habits. Some gyms have a buddy board to help members find workout partners.

Work with a trainer. Pay for a session or two with a certified personal trainer who can help you develop a well-rounded new routine.