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 me
|Contact: Christine Guilfoy|
American Physiological Society