Exercise is essential to good health.  This is the take-home message from a growing body of scientific evidence. For example, it has been shown that exercise has a beneficial effect on cognitive function (Erickson, K, Hillman, C and Kramer, A., 2015. "Physical activity, brain and cognition", Current Opinion in Behavioral Sciences, 4: 27-32.) and bone health (NIH Osteoporosis Resource Center).
Because our bodies consist of multiple interrelated systems, a change in one system affects all the others. A recent study (Contrepois, K., et al.,2020. "Molecular choreography of acute exercise", Cell, 181: 1112-1130), showed that a single bout of treadmill exercise induced changes in almost 10,000 of the more than 17,000 molecules the researchers studied.  These molecules are involved in energy metabolism, inflammation, immune response, tissue repair and remodeling and nerve growth.  This study confirms again the idea that all systems in the body are connected in some way.
Because each system operates semi-autonomously, there may be disproportionate effects on one system that are not so apparent in others. We know that exercising within a specific range of joint angles will increase strength within that range, but not outside it.  We know that exercising aerobically, with an elevated heart rate, will beneficially affect heart function, lower resting blood pressure and slow resting pulse rate, but may not increase strength.
So, the best exercise plan incorporates an aerobic component (walking, jogging, running, swimming) and a strengthening component (stretchy bands, exercise machines, free weights).  Some functional tasks like mowing the lawn or chopping wood incorporate both aspects of exercise, but most of us don’t do these tasks often enough to keep healthy.  To maintain good health we need to exercise for at least 30 minutes at least twice a week.  To improve health, we need to exercise at least 30 minutes at least 3 times a week.
In general, more exercise leads to better results and a longer life.  The trick is to exercise with minimal or no damage to joints and muscles.  A health professional can provide valuable guidance.

Since 2008, American Physical Activity Guidelines have recommended 75 minutes of vigorous activity per week or 150 minutes of moderate activity to maintain good health. A recent large meta-analysis (Arem et al., 2015) involving 6 studies and over 660,000 people, found that life expectancy was extended by following these guidelines. Although not quantified, more exercise provided a small but significant improvement in life expectancy, but there was a point of diminishing returns, where even more exercise did not change the outcome. The American College of Sports Medicine (ACSM) has some specific recommendations. For older adults, another comprehensive meta-analysis (Hupin et al.) showed that compared to inactivity, even a small increase in the amount of regular activity could boost life expectancy by 22%. For those motivated to increase activity close to the guideline, the increase in life expectancy was 28%. So, there’s hope for the rest of us. All kinds of benefits accrue to the couch potato who takes some steps in the right direction, and gets more active !
*Arem,H. et al., 2015. “Leisure time physical activity and mortality: a detailed pooled analysis of the dose-response relationship.” JAMA Intern Med. 175(6):959-67
*Hupin,D. et al., 2015. “Even a low-dose of moderate-to-vigorous physical activity reduces mortality by 22% in adults aged ≥60 years: a systematic review and meta-analysis.” Br J Sports Med. Oct;49(19):1262-7

There are no hard and fast rules about over-exercising, except for two situations: 1) making a sudden change in your routine, and 2) delayed onset muscle soreness (DOMS). Making a sudden change may include the couch potato who plans to start a new exercise program, or the normally-active person who finds themselves in a situation where excessive force is unavoidable (moving the sofa without help, for example). The general rule is to make changes gradually to give your body time to adapt, thus avoiding injury. If you are too sore to move easily the day after an exercise bout, you have almost certainly overdone it. We need to stress the muscle cells to make them stronger, but overstress will lead to muscle injury, more recovery time and delayed progress toward your goals. One documented effect of too much exercise, to which over-eager beginners are especially prone, is rhabdomyolysis. Rhabdomyolysis occurs when muscle cells are strained beyond their limits, usually by repetitive, aggressive exercise. In this condition, muscle cells break down and release their contents into the bloodstream. These intracellular proteins are toxic to the kidneys and can block kidney function, resulting in renal failure and death, if symptoms are not treated promptly.

Therapeutic exercise is prescribed by a health professional to accomplish a specific goal or set of goals.
For example, your PT might prescribe a specific set of exercises to give you pain relief, better postural control, or movement control, or for neuromuscular re-education after injury or disuse.
Therapeutic exercise is specific to an individual, and designed to address particular problems, such as regaining elbow function after Tommy John surgery, or overcoming low back pain.
You will not find therapeutic exercises on YouTube or in a Xeroxed handout, because these exercises have not been specifically tailored to your individual case, and are therefore of limited therapeutic value.
Therapeutic exercise will typically involve certain carefully-controlled motions and stresses, and will always have a recommended dosage, classified by a number of repetitions per set, number of sets per day, and number of days per week, and usually will come with a set of instructions in case things don't go as planned.
There may be a varying schedule to allow for optimal neural and physiological adaptation.
Evidence shows that targeted therapeutic exercise, as opposed to general exercise like walking, can have profound, specific effects on the body. For example, Tsao and colleagues (see below) showed that two weeks of therapeutic exercise could normalize the brain representation of a specific core stabilizing muscle, but a two week walking program did not make that change.
Therapeutic exercises can be prescribed by your friendly neighborhood physical therapist, who will design a comprehensive program to most effectively address your particular situation and your particular needs. Relying on a customized therapeutic exercise prescription from a trained healthcare professional will speed your improvement, help avoid setbacks, and provide optimal results.


*Tsao, H., et. al. (2010). “Driving plasticity in the motor cortex in recurrent low back pain.“ Eur J Pain 14(8): 832-839.

Exercise is an important component of a healthy lifestyle. Even a little exercise is better than no exercise at all, but too much exercise all at once can be bad.
Both aerobics and strengthening should be part of a comprehensive exercise plan.
Exercise should be done carefully, regularly, and for most of us, in moderation.
If you are just starting an exercise program, or if you have questions about your program, you should consult a healthcare professional.