How Muscles Work & Respond to Resistance Exercise (cont.)

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Movement requires the whole system to work.

  • When you think about moving, your brain decides which muscles are necessary to make that movement happen.
  • Electrical impulses are sent via the spinal cord and nerves to the appropriate muscles.
  • Adequate supplies of neurotransmitters need to be present to stimulate the muscle to contract.
  • Once the movement has started, there are feedback mechanisms to allow the brain to monitor the movement. This is called proprioception: the sense of where one body part is located in relation to others and in relation to gravity.


Strength is both a function of mass and the amount of neurological patterning of the muscle fiber. We've all known someone who isn't huge in terms of mass or body size but who has lots of strength. While there is a relationship between mass and strength, the power to move also comes from recruitment patterns in the nervous system that connect to muscle fibers. People generate more strength in their biceps if they can recruit and fire 50,000 muscle fibers than if they can only recruit 25,000 fibers. Muscle recruitment allows people to get so much stronger in the first few weeks of a new strength training program without increasing the mass of muscle. Routinely lifting weights recruits new patterns of communication between the brain, nerves, neuromuscular junction, and muscle fibers. Every time someone lift weights and engage up those muscles, he or she lays down new neuromuscular patterns and gets stronger.

Motor neurons in the muscle and nervous system die as people get older and do not regenerate, and as a result, people lose strength. Exercise can reverse that process. Geriatric patients can increase motor neuron firing by as much as 20% and increase stretch by more than one-third in just six weeks of weight training.


Muscle hypertrophy (increase in cell size) is a separate mechanism that increases muscle strength. While the nervous system and neuromuscular junctions are needed to fire muscles to contract, hypertrophy works differently. When people lift weights, microscopic damage (microtears) occurs to the myofibrils within the muscle fiber. These microtears stimulate the body's repair response. The body delivers nutrients that flow to the muscle cells to repair the damage and to stimulate more myofibrils to grow. The increased number of myofibrils causes muscle fibers to enlarge, increasing their volume and size. It is important to remember that no new muscle fibers are created; they just swell as the number of myofibrils increases.

Molecular biology and microscopic technologies allow scientists to look into the lives of cells, hundreds of times smaller than the head of a pin. They can see how the muscle fiber contractions stimulated immature cells to grow into mature myofibrils, thus causing muscle fiber hypertrophy. These images were of muscles in men and women 65 to75 years of age who were weight lifting. In addition, the researchers were able to "tag" these satellite cells with special tracer molecules that can be seen under a microscope. The tags clearly show increases in activity of the satellite cells by as much as 30%, proving that activities like weight lifting have a profound effect on growth and development no matter what the age of the individual.

Go for It

Weight lifting and other resistance exercises are effective at any age and are beneficial for a lifetime. Everybody has the right stuff to get stronger no matter how old or how sedentary. Muscle-building exercises have their benefit beginning with the first workout. Sticking with it will add not only strength but also quality of life. Enjoy your workouts!


Buford, T.W., et al. "Optimizing the Benefits of Exercise on Physical Function in Older Adults." PM&R. Available online 19 December 2013. Elsevier Press.

Krist, L., et al. "Can progressive resistance training twice a week improve mobility, muscle strength, and quality of life in very elderly nursing-home residents with impaired mobility? A pilot study." Clin Interv Aging 8 (2013): 443-448.

Last Editorial Review: 2/28/2014