McMaster University: Exercise compensates for mitochondrial DNA damage in mice

The mitochondrial theory of aging postulates that the lifelong accumulation of somatic mitochondrial DNA (mtDNA) mutations leads to progressive decline in tissue function. To what extent can exercise slow that decline?

Using mice that were genetically engineered for elevated mtDNA mutations, researchers at McMaster University found that 45 minutes of treadmill exercise three times a week stopped the expected rapid aging. The genetically modified mice that exercised on a treadmill three times a week, were comparable to healthy mice, while sedentary mice aged rapidly, becoming bald, gray-haired, weak, socially isolated an less fertile.

The abstract of the article reporting on the research is here, but the article is behind a pay-wall. You can, however, see the detailed supporting material without paying. The supporting material includes four movies that show the effect of exercise. Check this one out:

Click to play the movie

Mice on a treadmill -- which one works out?

This study is great news if you are a genetically engineered mouse, and it may offer a partial explanation of aging and the benefits of exercise in some humans.

One in eight people 65 and older exercise "vigorously" at least five days a week

According to a US Department of Health and Human Services report on the
Health Behaviors of Adults: United States, 2002–04 13.8% of people 65 and older exercise vigorously at least five days a week. A breakdown of the data shows that men are more likely to engage in frequent vigorous exercise than women and young people are more likely than old:

Age	Men	Women	Both
18-24	21.6	12	16.8
25-44	14.7	10.9	12.8
45–64	12.3	9.6	10.9
65-74	10.2	7.5	8.7
>=75	7.9	3.3	5.1

The authors of the 85-page report present other interesting data. For example, they found that the rate of vigorous exercise rises with income and education (which are correlated with age). They also observed differences based on race, region of the country, marital status and whether the respondent is from a metropolitan area, central city or smaller town.

The study defines a "vigorous" activity as one lasting at least 10 minutes and causing heavy sweating or large increases in breathing or heart rate.

Experiments

Cycling coach, writer, and masters champion Arnie Baker has surveyed many controlled experiments in this article. Baker gives very short summaries of studies in many areas -- nutrition, equipment, training/racing, medicine, psychology, etc.

Sample conclusions are: pacing paid off in a 20 kilometer bike time trial, clipless pedals do not offer a physiological advantage, a fifty percent taper a week before a race is beneficial. Still, the bottom line is that the experimental differences tend to be marginal -- training is still the key.

Baker has written many other books and articles, available at his Web site.

Could we learn by each of us conducting a one-person experiments and reported our results on the Net?

How much do clipless pedals help?

After riding an old Raleigh Competition road bike for years with sneakers and toe clips, I was curious about clipless pedals. I purchased a set of Look pedals and Shimano shoes, and compared them with my old pedals in two performance tests.

I compared the pedals in two tests on a flat course and two tests on a hill climb. The clipless pedals improved my time by 1.85% on the flat course and 1.9% on a hill climb. The overall difference was 1.88%.

The flat course is a 7.3 kilometer bike path running along a paved creek from West Los Angeles to the beach and the hill climb is 6.9 kilometers, gaining a net of 246 meters between Sunset Boulevard and Mulholland Drive.

The prevailing wind on the flat course is from the beach, and I average of 122 seconds more when going toward the beach than on the return leg. Most of the hill climb course is uphill – one climbs 358 meters – but there are short descents of 112 meters.

I did trials on four days. Each day, I rode one of the courses twice at my top speed, changing the pedals between the rides. The results of the four trials were:

Trial 1: I rode the 14.6 km round trip on the flat course using clipless pedals (1,586 seconds), changed the pedals, and then rode it again using pedals with toe clips (1,649 seconds).

Trial 2: I rode the 14.6 km round trip on the flat course using pedals with toe clips (1,595 seconds), changed the pedals, and then rode it again using clipless pedals (1,598 seconds).

Trial 3: I rode the 7 km hill climb using pedals with toe clips (1,823 seconds), rode quickly back down the hill, changed the pedals, and then rode up again using clipless pedals (1,844 seconds).

Trial 4: I rode the 7 km hill climb using clipless pedals (1,815 seconds), rode quickly back down the hill, changed the pedals, and then rode up again using pedals with toe clips (1,907 seconds).

Changing pedals took around five minutes, and the downhill ride about ten minutes.

This table shows the total number of seconds using both pedals on both courses. The bottom line is that the toe clips improved my times, but by less than two percent.

	Toe clip	Clipless	Percent
Flat	3,244	3,184	1.85
Hill	3,730	3,659	1.90
Total	6,974	6,843	1.88

Of course, you would see different results. I am 67 years old, and riding an old bike -- a Raleigh Competition with steel tubing, Campagnolo derailleurs, and cheesy replacement wheels. There were a few days between each trial. I did not ride those days, but did run or lift weights. One cannot be sure that I rode all-out on every run, though I did my best. (I did not eat or drink between runs, which may have slowed the second leg a bit).

I believe these results are accurate for me. I will compete in a sprint triathlon later this summer. Based upon this experiment, clip on shoes would only save me about 20 seconds on the 10k bike leg, so I will be better off riding in my running shoes using toe clips, and saving the time to change shoes.

This experiment was simple and easy to do, and there could be many variations on the theme. For example, I would like to compare my current bike against a new one. I also pushed my highest gear throughout the flat course – I wonder whether a lower gear would have helped going into the wind.

Are you curious about some variation in your bike or the way you ride? Run an experiment and let us all know how it turns out.