As Good As It Gets: Octogenarian Muscles Don't Get Stronger With Exercise

Main Category: Sports Medicine / Fitness
Also Included In: Seniors / Aging
Article Date: 02 Apr 2009 - 3:00 PDT

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Octogenarian women were unable to increase muscle mass after a 3-month weight lifting program targeted at strengthening the thigh muscle, according to a new study from the Journal of Applied Physiology. The results are surprising because previous studies have found resistance training capable of increasing muscle mass, even for people who are into their 70s. An increase in muscle size translates to an increase in strength.

Still, the Ball State University study contained some good news: The octogenarians were able to lift more weight after the training program, likely because the nervous system became more efficient at activating and synchronizing muscles.

The American Physiological Society published the study, "Improvements in whole muscle and myocellular function are limited with high-intensity resistance training in octogenarian women." The researchers are Ulrika Raue, Dustin Slivka, Kiril Minchev and Scott Trappe.

Aim: Strengthen Octogenarian Thigh Muscle

The experiment involved six women, all in their 80s, all of whom lived independently and came to the laboratory three times a week for three months. The women exercised on a machine designed to strengthen the thigh (quadriceps) muscle. They did three sets of 10 lifts, with a 2-minute rest period between sets.

The researchers measured the size of the women's thigh muscle using an MRI, before the exercise program began and after it ended. They also took biopsies from the thigh muscles, which they used to track muscle changes at the cellular level.

The biopsies included both fast-twitch and slow-twitch muscle fibers. Fast-twitch muscles are high powered and explosive and are associated with anaerobic exercise. Slow-twitch are associated with aerobic tasks, including endurance exercise such as marathons.

Fast-twitch muscles are important in posture and balance and so may be of particular importance for the elderly, who are more prone to falls. When people do not use their muscles during a period of convalescence or with a sedentary lifestyle, the fast twitch muscles lose functionality and atrophy more quickly than slow-twitch.

From the muscle biopsies, the researchers isolated single muscle strands, both fast-twitch and slow-twitch. They measured the strength, speed and power of each fiber and examined the genetic profile of these strands.

No change in muscle strength

As a result of the exercise program, the octogenarians were able to increase the amount they could lift with their quadriceps by 26%. That was the good news. The bad news was that the pre- and post-training MRIs showed that the training did not change their muscle size. This was surprising because an earlier study had found that 70-year-old women gained 5% muscle mass with resistance training.

The biopsy results confirmed the MRI results: there was no change in the size of the individual muscle strands, pre-training versus post-training. This confirms that the increase in the amount the women could lift with the quadriceps was unrelated to improvement in muscle strength. Instead, the results were probably due to improvements in how efficiently the nervous system was able to activate and synchronize the muscles.

In an earlier study, the researchers found that the muscles of octogenarian men also failed to gain strength with the exercise program. Together, the studies show that the muscles of octogenarian men and women are far less responsive to improving with exercise, even compared to people only 10 years younger.

"The message of the study is that exercise is good for octogenarians, just not as good as we thought it would be," Dr. Trappe said. The study also suggests that it is better to build as much muscle mass as possible earlier in life to ensure more muscle strength in later life. "We should do all we can to educate people to build up the muscle before 80," he said.

Next steps

Muscle atrophy relates not only to aging, but to people whose muscles are immobilized for a period and even for astronauts who spend long periods of time in space. Dr. Trappe, who also does research on astronauts, next wants to begin to uncover the physiological basis for why the muscles of octogenarians do not gain strength with resistance exercise.

His team may be able to build on two intriguing findings from the current study:

* while the octogenarian women had many fewer muscle fibers, the fibers they did have were large and healthy looking

* the genes involved in muscle growth are present in the resting muscle of the octogenarians at much higher levels compared to young people.

These results suggest that the octogenarian muscle is already operating at peak capacity and may not have the potential for better performance, Dr. Trappe said. If these mechanisms can be understood, it may be possible to find ways to strengthen older muscles.

Notes:

Full study.

Physiology is the study of how molecules, cells, tissues and organs function to create health or disease. The American Physiological Society (APS) has been an integral part of this scientific discovery process since it was established in 1887.

Source:
Christine Guilfoy
American Physiological Society