Deterioration of muscles occurs in old age. This is due to the decreased synthesis of new muscle proteins and increased loss of stored proteins. The current study used a radioactive tracer, namely heavy water, to estimate new DNA and protein synthesis. It was found that DNA synthesis, associated with new cell division, was higher in muscle cells of older people who exercised on treadmills than younger participants who did not exercise. The exercise capacity improved in participants who drank protein drinks after exercise compared to participants who drank a mixture of proteins and carbohydrates.
Aging is a major public health concern as the percentage of older people is increasing in the overall population. People older than 50 years lose about 1-2% of their skeletal muscle mass every year. Muscle mass is determined by the synthesis of new proteins and degradation of existing proteins. Aerobic exercise could potentially address muscle wasting by stimulating the synthesis of new muscle proteins and increasing the numbers of mitochondria, the storehouses of energy in cells. This may be beneficial for aging the population. Similarly, protein consumption after exercise is found to increase the whole body protein turnover. This study used heavy water, containing an isotope of hydrogen, to study long-term protein synthesis in muscles. It studied the effects in older people and compared them with those in young non-exercising people.
- The researchers recruited 16 sedentary participants between 37 and 64 years as the experimental group. The control group consisted of four participants who did not perform exercise.
- Participants in the experimental group completed a progressive aerobic exercise protocol of three sessions per week for six weeks. Some participants received a carbohydrate drink and others received a drink containing protein and carbohydrate after each exercise session.
- They also drank deuterium (heavy water) every day, which when absorbed by the body could be detected in newly synthesized proteins.
- Blood sample collection, muscle biopsy, and tests for maximum oxygen consumption (an indicator of exercise capacity) were done for all participants, at the beginning and end of the study.
- The exercise capacity (maximum oxygen consumption) improved in the participants who drank protein drinks, but not in participants who drank drinks with proteins and carbohydrates. The increase from the baseline with protein supplementation was 12.2%, while it was 3.3% for the other group.
- The ratio of mitochondrial DNA to nuclear DNA did not differ between the groups at the baseline or following six weeks of endurance exercise.
- The older exercise group had a higher percentage (7.4%) of newly synthesized muscle proteins than the younger sedentary group (5.54%).
- DNA synthesis indicates cell division. Newly synthesized DNA over six weeks for the older exercising group was about 0.5-1% per week. In contrast, the calculated percentage of newly synthesized DNA was nearly zero in the young sedentary group.
This study used young sedentary participants as the control group rather than old sedentary participants. Direct comparison is therefore not possible, as the groups are not matched. Treadmill training was used as an exercise. Walking on a treadmill involves both shortening and lengthening contractions of muscles. Thus, new muscle protein synthesis could be attributed to repair of muscle fibers after the higher force applied in lengthening contractions.
This study used heavy water (a tracer) to measure new protein synthesis in muscles after exercise and protein consumption after exercise. Consuming protein after exercise was not found to increase DNA or protein synthesis in the long term, but did increase the exercise performance. As skeletal muscle cells do not divide under normal conditions, it was thought that the rate of new DNA synthesis would be zero. Contrary to this hypothesis, the new DNA synthesis in older participants doing aerobic exercise was about 0.5 to 1% per week. This value was near zero for young participants who did not exercise. This indicates that aerobic exercise can stimulate skeletal muscle adaptations. Aerobic exercise also improves exercise capacity. Therefore, older people can do aerobic exercises to avoid the wasting of muscles and prevent the resultant weakness and decline in health.
For More Information:
Synthesis Rates of Skeletal Muscle DNA and Protein with Aerobic Training and Protein Supplementation in Older and in Sedentary Young Subjects
Publication Journal: The FASEB Journal, June 2011
By Matthew M Robinson; Scott M Turner
From the Colorado State University, Fort Collins, Colorado and KineMed Inc., Emeryville, California
*FYI Living Lab Reports Are Summaries of the Original Research.