OTHER FACTORS INFLUENCING THE OXYGEN COST OF RUNNING
If running economy is so important, can it be altered? It seems that persons beginning exercise definitely become more efficient with training (Robinson & Harmon, 1941), as do persons who are already trained but who continue heavy training. Conley et al. (1981b) followed a single runner during 6 months of interval training and found that the subject’s running efficiency improved by between 9 and 16% at three different speeds. However, his body weight also fell about 6%, which could have been the more important factor explaining the improved running efficiency. Subsequently these authors (Conley et al, 1984) showed that the running efficiency of Steve Scott, America’s premier 1,500-m runner of the early 1980s, improved with interval training. Svedenhag and Sjodin (1985) showed that the running efficiencies of a group of elite Swedish distance runners improved between 1 and 4% during the course of 1 year, changes that were in the range (up to 4%) of those measured in the adolescent runners studied by J. Daniels and Oldridge (1971). Svedenhag and Sjodin (1985) speculated that the continual improvements in the running performances of these Swedish athletes were due to slowly progressive improvements in their running efficiencies rather than to increases in V02max values, which were relatively fixed, increasing only during that phase of the season when the athletes were performing high-intensity interval-type training. This has indeed been shown in a group of elite Czechoslovakian runners (Bunc et al, 1989).
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Athletes appear to choose stride lengths at which they are most efficient, that is, at which oxygen uptake is the least (Cavanagh & Williams, 1982). When forced to take either shorter or longer strides but to maintain the same running pace, athletes become less efficient and require an increased oxygen uptake. As Arthur Newton said, “Don’t draw the line too fine about the length of your stride . Just make a habit of acquiring a reasonable length and Nature will attend to the rest” (1935, p. 71). With training, runners increase the length of their strides and reduce their stride frequency (R.C. Nelson & Gregor, 1976). Some researchers believe that this optimizes running efficiency because increasing stride length is more economical than increasing stride frequency.
Children are less efficient runners than are adults (see Exercises 2.4; Krahenbuhl & Pangrazi, 1983) but become more efficient as they age (J. Daniels & Oldridge, 1971), partly due to training (J. Daniels et al, 1978b) but also because of weight gain (MacDougall et al, 1983). Improvements in running performance in adolescents appear to be due to changes in running economy, not in V02max (Krahenbuhl et al, 1989). Researchers found that instruction in running technique did not improve the running economies of 10-year-old boys (Petray & Krahenbuhl, 1985). Other researchers have suggested that children may be less able to store and utilize elastic energy during running (Thorstensson, 1986).
Although V02max values do differ between the sexes, gender has no effect on running efficiency; trained men and women are equally efficient (J. Daniels et al, 1977; C.T.M. Davies & Thompson, 1979; P. Hopkins & Powers, 1982; Maughan & Leiper, 1983). Race may influence running efficiency; researchers have found that Asians and Africans utilize 17% less energy than Europeans when lying, sitting, or standing, but no studies have compared energy uses of these groups during exercise (Geissler & Aldouri, 1985). In a study of elite runners of different racial groups, researchers found no race-related differences in running economies (Noakes et al, 1990b).