A FEW WEEKS ago, I wrote about some research showing that cycling efficiency declines with age – that is, it takes more energy to produce the same power on the bike. Is the same thing true in running? The evidence is far from definitive, but a couple of studies have investigated the question and found that running economy (an efficiency measure analogous to the petrol mileage of a car) doesn’t decline with age if you keep training consistently. Now a new study in PLoS ONE, from researchers at Humboldt State and the University of Colorado led by Justus Ortega and Owen Beck, offers some interesting new wrinkles by looking at the effect of running training on walking economy.
Why are we interested in walking economy? Well, for one thing, decreases in walking economy are a pretty reliable indicator and predictor of declining health: as walking gets worse, day-to-day life gets more difficult and other problems are quick to follow. The researchers measured walking economy in two groups with an average age of 69: walkers, who reported walking for at least 30 minutes at least three times a week; and runners, who reported running a similar amount. They compared the results with previous data from younger and older sedentary subjects. Here’s how they stacked up:
The open circles are young adults (average age 25) – they have the best economy, meaning that they consume the least power and energy at whatever speed they’re walking. The next best group (diamonds) is the runners. The walkers (triangles) and sedentary older adults are pretty much same, with about 7-10% worse walking economy than the runners.
The real question that we’re all interested in, of course, is how to prevent declines in economy. In cycling, there’s a bit of data suggesting that the problem is declining muscle mass, so resistance training might offset the decline. The picture is murkier in walking and running. As the paper notes:
Recent studies by Thomas et al.  and Malatesta et al.  show that vigorous walking interval training effectively reduces the metabolic cost of walking in older adults by as much as 20% … Conversely, a generalized year-long training program that included resistance, aerobic and balance exercises had no effect on post-training walking economy in older adults .
The fact that running and “vigorous” walking seem to help walking economy but resistance training doesn’t suggests there’s something going on in the muscles themselves. The researchers point the finger (speculatively) at “mitochondrial dysfunction,” which effectively means you get less energy per molecule of oxygen you send to your muscle cells. One way to combat mitochondrial dysfunction? Vigorous aerobic exercise.
When we look at efficiency in different sports and different age groups, it’s likely that there are several different factors at play – hence the seemingly contradictory results in walking, running, and cycling. After looking at the cycling literature, I had the impression that it was all about muscle mass and strength. This study is a good counterbalance – a reminder that aerobic exercise may also play a pretty important in keeping your muscles functioning efficiently at a cellular level.