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10. 6. 2012.

Training economy

Economy of effort

As people become more skillful at performing an exercise, the energy demands during exercise at a given pace are  reduced. In a sense, people become more economical. ( It is not called “efficiency” cause it has deeper economical meaning).  Compare the data from two imaginative distance runners. At all running speeds faster than 11.3 km/h(7.0 mph), runner B used significantly less oxygen than runner A. These men had similar VO2max values(64-65 ml x kg-1 x min-1), so runner B’s lower submaximal energy use would be a decided advantage during competition.
These two runners competed on numerous occasions. During marathon races, they ran at paces requiring them to use 85% of their VO2max values were so similar but their energy needs so different during these events, much of runner B’s competitive advantage could be attributed to his greater running economy. Unfortunately, there is no specific explanation for the underlying causes of these differences in economy.
Various studies with sprint, middle-distance, and marathon runners have shown that marathon runners are generally the most economical. In general, these ultra-long-distance runners use 5% to 10% less energy than middle-distance and sprint runners at a given pace. However, this economy of effort has been studied at only relatively slow speeds(paces of 10-19km/h, or 6-12 mph). We can reasonably assume that distance runners are less economical at sprinting than runners who train specifically for short, faster races.
Variations in running form and the specificity of training for sprint and distance running may account for at least part of these differences in running economy. Film analysis reveal that middle-distance and sprint runners have significantly more vertical movement when running at 11 to 19 km/h(7-12 mph) than marathoners do. But such speeds are well below those required during middle-distance races and probably do not accurately reflect the running economy of competitors in shorter events of 1500m(1 mi) or less.
Performance in other athletic events might be even more affected by economy of movement than is running. Part of the energy expended during swimming, for example, is used to support the body to the surface of water and to generate enough force to overcome the water’s resistance to motion. Although the energy needed for swimming depends on body size and buoyancy, the efficient application of force against the water is the major determinant of swimming economy.
In untrained people, lactate threshold typically occurs at around 50% to 60% of their VO2max. Elite endurance athletes may not reach lactate threshold until closer to 70% to 80% of VO2max.

Energy cost of various activities

The amount of energy expended for different activities varies with the intensity and type of exercise. Despite subtle differences in economy, the average energy costs of many activities have been determined, usually through monitoring of oxygen consumption during the activity to determine an average oxygen uptake per unit of time. Kilocalories of energy used per minute(kcal/min) then can be calculated from this value.
These values typically ignore the anaerobic aspects of exercise and then the EPOC. This omission is important because an activity that costs a total of 300 kcal during the actual exercise period may cost an additional 100 kcal during the recovery period. Thus, the total cost of that activity would be 400, not 300, kcal.
An average body requires 0.16 to 0.35L of oxygen per minute to satisfy its resting energy requirements. This would amount to 0.80 to 1.75 kcal/min, 48 to 105 kcal/h, or 1,152 to 2,520 kcal/day. Obviously, any activity above resting levels will add to the projected daily expenditure. The range for total daily caloric expenditure is highly variable. It depends on many factors, including:
  • Activity level(by far the largest influence)
  • Age
  • Sex
  • Size
  • Weight
  • Body composition.

The energy costs of sport activities also differ. Some, such as archery or bowling, require only slightly more energy than when one is at rest. Others, such as sprinting, require such a high rate of energy delivery that they can be maintained for only seconds. In addition to exercise intensity, the duration of the activity must be considered. For example, approximately 29 kcal/min are expended during running at 25 km/h(15.5 mph), but this pace can be endured for only brief periods. Jogging at 11 km/h(7 mph), on the other hand, expends only 14.5 kcal/min, half that of running at 25 km/h(15.5 mph). But jogging can be maintained for considerably longer, resulting in a greater total energy expenditure.
Table below provides an estimate of energy expenditure during various activities for average men and women. Remember that these values are merely averages. Most activities involve moving the body mass, so these figures may vary considerably with individual differences such as those previously listed and with individual skill(economy of movement).

Energy expenditure during various physical activities
Relative to body mass ( kcal x kg-1 x min-1)
Cycling(16.1 km/h – 10.0 mph)
Running(12.1 km/h – 7.5 mph)
Running(16.1 km/h – 10.0 mph)
Walking (5.6 km/h – 3.5 mph)

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