Scientists reviewed studies on elastic resistance bands, and concluded that strength training with elastic bands could cause the same gain in strength as lifting heavy weights for both the upper and the lower body (SAGE Open Med, Feb 19, 2019;7:2050312119831116). Training in the studies ranged from 2-5 times a week for 4-12 weeks. The studies found no difference in strength gain between:
• older and younger people (Arch Gerontol Geriatr, 2013; 57(1): 8-15)
• competitive athletes and ordinary exercisers
• healthy people and those with heart or lung disease, osteoarthritis (Arthritis Rheum, 2008; 59(10): 1488-1494) or fibromyalgia (Cochrane Database Syst Rev, 2013; 20(12): CD010884).

Elastic Bands Are Less Likely to Lead to Injuries
Just exercising will not make you stronger. If it did, marathon runners would have the largest and strongest muscles. If you want to make your muscles stronger, you need to exercise them against resistance strong enough to damage the muscle fibers. Then the muscles will be stronger when they heal.

When middle-aged and older people start a weight-lifting program, they often are injured because they try to train like younger people who pick the heaviest weight they can lift ten times in a row and then do three sets of ten lifts. They feel sore for the next few days and when the soreness goes away, they lift heavy weights again, usually two or three times a week. This type of training frequently injures older people and novice weight lifters, which ends their training program. The best way for middle-aged and older people to prevent injuries is to lift lighter weights.

As you age, you lose muscle fibers and lifting heavy weights markedly increases risk for injuries. So you are less likely to injure yourself when you lift lighter weights with more repetitions or use elastic stretch bands instead of heavy weights or strength training machines. A review of 22 studies on how to grow larger and stronger muscles found that the best way for older and untrained people to grow larger muscles is to use lighter weights with more repetitions, even though most trained athletes gained more strength by using heavier weights with fewer repetitions (Human Movement, July 23, 2020;21(4):18-29).

Why You Need Strength Training As You Age
Muscles are made up of hundreds of thousands of individual fibers, just as a rope is made up of many strands. Each muscle fiber is innervated by a single motor nerve. With aging, you lose motor nerves, and with each loss of a nerve, you also lose the corresponding muscle fiber that it innervates. For example, the vastus medialis muscle in the front of your thigh contains about 800,000 muscle fibers when you are 20, but by age 60, it probably has only about 250,000 fibers. However, after a muscle fiber loses its primary nerve, other nerves covering other fibers can move over to stimulate that fiber in addition to stimulating their own primary muscle fibers. Lifelong competitive athletes over 50 who train four to five times per week did not lose as many of the nerves that innervate muscles and therefore retained more muscle size and strength with aging than their non-athlete peers (The Physician and Sportsmedicine, October 2011;39(3):172-8).

How Muscles Become Stronger
Each muscle fiber is made of a series of blocks called sarcomeres that are lined up end to end. Each sarcomere is attached to the one next to it at a “Z line.” Muscle fibers do not contract equally along their lengths; they contract only at each “Z line”.

To strengthen a muscle, you have to put enough force on the muscle to damage the Z-lines, as evidenced by bleeding and swelling into the Z-lines. You can tell you have damaged the Z-lines by the feeling of muscle soreness that begins 4-24 hours after you have lifted weights or done any form of resistance exercise. That is the time it takes for the swelling to occur in the Z-lines. This is called Delayed Onset Muscle Soreness (DOMS). Exercising your muscles intensely enough to damage them makes muscles stronger so they can withstand higher loads and be more resistant to injury.

When a muscle is damaged, your immune system sends to the damaged tissue large amounts of the same cells (lymphocytes) and chemicals (cytokines) that are used to kill germs when you have an infection. This causes inflammation, characterized by soreness (pain), increased blood flow to the injured fibers (redness), and increased flow of fluid into the damaged area (swelling). The immune cells release tissue growth factors to heal the damaged muscle fibers, and you should allow the muscle soreness to decrease or disappear before exercising intensely again. If you do not wait until the soreness goes away before exercising intensely again, the fibers can be torn, the muscles weaken and you can become injured.

How to Start Your Resistance Training Program
I recommend that older people who want to become stronger and also to help prevent osteoporosis, start a program of pulling on elastic stretch bands. Find a gym with a good program, or hire a personal trainer for a few sessions to help you select the equipment and learn how to use it. Dr. Richard Winett of Virginia Tech and an expert on strength training has written a detailed introduction to Basic Resistance Band Training to help you get started. Dr. Winett recommends the inexpensive Theraband Resistance Bands sets that are available on Amazon