If a great Shakespearean protagonist had, anachronistically, joined a gym, his internal existential inquiry might have been, "To lift or not to lift?". Many centuries later, the identical inquiry, or controversy, persists. Joining a gym (health club) usually implies the new club member is going to engage in strength training in one form or another. Such exercise provides an abundance of benefits and is a valuable lifestyle choice for most people. But the possibility of injury exists. The key to safe, beneficial exercise is to learn how to do strength training correctly, then develop a plan, and follow the plan.
Government health and wellness guidelines recommend doing 150 minutes of (at least) moderate exercise per week. This translates to at least 30 minutes of exercise five times per week. Strength training is an important component of any exercise program designed to fulfill these recommendations. In combination with cardiorespiratory exercise, strength training greatly improves muscular capabilities and endurance. Your body becomes fit, toned, and honed, and as a result, you become much better equipped to successfully manage the mechanical stresses and strains that everyone encounters during the course of a normal day.1-3
If you are new to strength training or haven't done this form of exercise in a while, then the most important rule is to start slowly. Scientifically determine how much weight you should be lifting by experimentation. Choose a very light weight and see whether you can do eight repetitions with that weight comfortably. If it's difficult to do eight reps, then start over with the next lighter weight. If it's too easy to do eight reps, then start over with the next heavier weight. If eight repetitions feels just about right, then that's the weight with which to begin that particular exercise. Follow these steps for each of your exercises and you'll have established your beginning routine on a personal and safe foundation.
Strength training need never become boring, as you can change your routine with almost infinite variety. For example, for a 12-week period you could do chest and back exercises one day, then leg exercises a second day, and shoulder and arm exercises a third day. You would do your cardiorespiratory exercise on the remaining two days (for a total of five weekly days of exercise). During a different 12-week period, you could do cardiorespiratory exercise on three days and do arm and leg exercises on one day and chest, back, and shoulder exercises on a second day. Or you could choose to "work light" and exercise all your body parts on a single day. You could do your total-body strength training two or three days a week, filling in the other days with cardiorespiratory exercise. The only guideline in the context of these routine designs is whether the routine works for you. If it works, then it works.
As with all exercise programs, the more consistent you are, the greater long-term benefit you'll derive. Be sure to build-in recovery time by taking a week off here and there for rest and recharging. A modern Hamlet would find his or her exercise time enjoyable and rewarding, and would answer the perplexing question with a resounding, "Yes. I will lift."
1Granacher U, et al: The importance of trunk muscle strength for balance, functional performance, and fall prevention in seniors: a systematic review. Sports Med 43(7):627-641, 2013
2Grier T, et al: The effects of cross-training on fitness and injury in women. US Army Med Dep J Apr-Jun:33-41, 2015
3Liu Y, et al: Effects of combined aerobic and resistance training on the glycolipid metabolism and inflammation levels in type 2 diabetes mellitus. J Phys Ther Sci 27(7):2365-2371, 2015
These are very good points. With expanded research funding it may be possible to fulfill the assumptions of parametric analysis with greater confidence.