Gary S. Krahenbuhl

Running economy and distance running performance of highly trained athletes.

The purpose of the study was to determine the relationship between running economy and distance running performance in highly trained and experienced distance runners of comparable ability. Oxygen uptake (Vo2) during steady-state and maximal aerobic power (Vo2max) were measured during treadmill running using the open-circuit method. Distance running performance was determined in a nationally prominent 10 km race; all subjects (12 males) placed among the top 19 finishers. The subjects averaged 32.1 min on the 10 km run, 71.7 ml.kg-1.min-1 for Vo2max, and 44.7, 50.3, and 55.9 ml.kg-1.min-1 for steady-state Vo2 at three running paces (241, 268, and 295 m.min-1). The relationship between Vo2max and distance running performance was r = -0.12 (p = 0.35). The relationship between steady-state Vo2 at 241, 268 and 295 m.min-1 and 10 km time were r = 0.83, 0.82, and 0.79 (p < 0.01), respectively. Within this elite cluster of finishers, 65.4% of the variation observed in race performance time on the 10 km run could be explained by variation in running economy. It was concluded that among highly trained and experienced runners of comparable ability and similar Vo2max, running economy accounts for a large and significant amount of the variation observed in performance on a 10 km race.

Factors Affecting Running Economy

SummaryRunning economy, defined as the steady-state V̇O2 for a given running velocity, has been shown to account for a large and significant proportion of variation in distance-running performance among runners roughly comparable in V̇O2 max. Despite this recognition, relatively little is known regarding the potpourri of physiological, environmental, structural and mechanical factors potentially associated with a lower aerobic demand of running.Early attempts at quantifying the energy expenditure of exhaustive runs incorporated measurements of oxygen consumption before, during, and after exercise. The validity of this approach has been questioned, however, since recent evidence has demonstrated that only a moderate relationship exists between postexercise V̇O2 and anaerobic metabolism. The energy demands for submaximal running (i.e. running economy) can be quantified by calculating the steady-state V̇O2, expressed with respect to body mass and time, for a standardised, submaximal running speed. Since this variable represents the aerobic demand of running, the generation of energy must derive wholly from cell respiration and not from substantial protein catabolism. Research has indicated that at low to moderate work rates, the steady-state energy condition is attained in about 3 minutes. Trained individuals reach steady-state sooner that unfit subjects. While limited by methodological constraints, the existence of a steady-state has also been verified by the lack of blood lactate accumulation and the presence of a respiratory exchange ratio of less than 1.00.The ability of economy, either singly or in combination with V̇O2 max, to account for a substantial portion of performance variation among trained distance runners and untrained subjects of comparable ability and fitness level has been demonstrated in recent cross-sectional studies. Limited data from short and long term longitudinal research also suggests that endurance running success is linked to training and growth-related improvements in economy.Intraindividual variation in economy has been shown to vary between 2% and 11% for a given speed. Most of this variation can probably be attributed to biological error. While the majority of evidence does not support a gender difference in running economy, data from some studies suggest that males may be more economical than women. Prepubescent children are less economical than older children and adults, whereas older adults exhibit the same trend when compared to younger counterparts. Because of air and wind resistance, the aerobic demands of indoor treadmill running significantly underestimate the cost of overground running, especially at higher speeds. As body temperature rises during exercise, V̇O2 increases as a result of the ‘Q10 effect.’ While conflicting data exist with respect to the effect of fatigue on the aerobic demand of running, recent work incorporating physiological and biomechanical measures demonstrated that a 30-minute maximal run produced little or no change in the metabolic and biomechanical profiles of trained runners. No consensus exists regarding the effects of different types and intensities of training on running economy. Substantial variation in economy among long distance runners who compete in the same event suggests non-training factors may also influence economy.A number of anthropometric and biomechanical factors have been considered for their ability to account for some of the interindividual variability in running economy commonly observed. Despite assumptions to the contrary, it seems appropriate to conclude that when the confounding influence of speed is negated, few biomechanical variables have been shown consistently to account for a substantial portion of variation in economy. It has been suggested that at present it is not possible to distinguish whether mechanical variables describing the running pattern of an uneconomical runner contribute to making the runner uneconomical, or whether the pattern reflects the means by which the individual has optimised his or her own anatomical and physiological features.

Variation in the aerobic demand of running among trained and untrained subjects.

Variation in the aerobic demand (VO2) of submaximal running was quantified among trained and untrained subjects stratified by performance capability. Based on a retrospective analysis of seven published studies, maximal aerobic power (VO2max), and submaximal VO2 values were analyzed in three groups of trained distance runners (Category 1 (C1) (elite runners; N = 22), Category 2 (C2) (sub-elite runners; N = 41), and Category 3 (C3) (good runners; N = 16), and one group (N = 10) of untrained subjects (Category 4; C4). Results indicated that VO2max differed significantly (P < 0.05) across groups, such that C1 > C2 > C3 > C4. Analysis of submaximal VO2 data also revealed that C4 was more uneconomical than C1, C2, and C3 and that C2 and C3 were less economical than C1. Average within-group variability in submaximal VO2 was similar across categories and a marked overlap of minimum, mean and maximal economy values existed across categories. These data suggest that 1) trained subjects are more economical than untrained subjects, 2) elite runners display better economy compared to less-talented counterparts, and 3) economical and uneconomical runners can be found in all performance categories.

Variability in running economy and mechanics among trained male runners.

Data from two studies were analyzed to quantify intraindividual variability and reliability in running economy (RE) and mechanics. Following 30-60 min of treadmill accommodation, stride-to-stride and day-to-day biomechanical stability were assessed in 31 male runners (studies 1 and 2) who performed two level treadmill runs (3.33 m.s-1) at the same time of day, in the same footwear, and in a nonfatigued state. Under the same testing conditions, daily stability in RE was determined in 17 of the 31 subjects (study 2). RE demonstrated high day-to-day reliability (r = 0.95), and the mean coefficient of variation in RE was 1.32% (range = 0.30-4.40%). Stride-to-stride reliability for temporal (T), kinematic (KNM), and kinetic (KIN) measures was very high (mean r = 0.96; range = 0.91-0.99), but day-to-day reliability was lower for KIN (mean r = 0.67; range = 0.28-0.88) compared with T and KNM (mean r = 0.91; range = 0.68-0.98). Further analyses revealed no significant (P less than or equal to 0.05) mean stride-to-stride differences for any biomechanical variable, and only three of 22 variables (peak resultant velocity of the ankle joint, step length, and swing time) demonstrated statistically significant day-to-day differences. Viewed in concert, these results suggest that, if the testing environment is controlled, multiple trials are not required to obtain stable measures of running economy and basic mechanical characteristics in trained male runners if group data from adequate sample sizes are considered. However, if individual records are scrutinized or if small sample sizes cannot be avoided, at least two measures of individual performances should be secured.

Following Steve Scott: Physiological Changes Accompanying Training

In brief: American mile record holder Steve Scott was tested for maximal aerobic capacity and running economy on three occasions over nine months, a period that included off-season, preseason, the indoor season, and the early part of the outdoor season. The laboratory results demonstrated that Scotts training raised his maximal aerobic capacity approximately 8% and improved his running economy 5%. In comparing Scotts data with that of former American record holder Jim Ryun, it appears that Scotts better economy, which allowed him to perform at a lower percentage of his maximal aerobic capacity, was the essential difference between the two runners.

Menstrual cycle phase and running economy

To further elucidate the relationship between RE and menstrual cycle phase, eight eumenorrheic moderately-trained female runners were studied throughout their menstrual cycles, which were divided into five phases: early follicular (EF), late follicular (LF), early luteal (EL), mid-luteal (ML), and late luteal (LL). Subjects were studied at rest and while running at speeds initially corresponding to 55% and 80% maximal oxygen consumption (VO2max). Ventilation (L x min-1) was significantly (P < 0.05) higher in ML compared with EF during all three conditions (mean +/- SE) (rest: 12.4 +/- 0.7 vs 10.3 +/- 0.8; 55% VO2max: 46.2 +/- 0.9 vs 42.2 +/- 1.4; and 80% VO2max: 68.8 +/- 3.0 vs 63.3 +/- 2.0 L x min-1, respectively). Resting VO2 (mL x kg-1 x min-1) was significantly (P < 0.05) hi gher in ML (4.8 +/- 0.1) compared with EF (3.9 +/- 0.2). Profile of Mood States (POMS) total mood disturbance (TMD) and three subscale (depression, fatigue, and confusion) scores were also significantly higher during ML compared with EF; TMD: 127 +/- 6.0 vs 104 +/- 6.0; depression: 6 +/- 1.4 vs 3 +/- 1.4; fatigue: 9 +/- 1.0 vs 4 +/- 0.9; and confusion: 7 +/- 0.9 vs 5 +/- 1.2, respectively. The POMS vigor subscale score was significantly lower during ML (11 +/- 1.5) when compared with EF (19 +/- 0.7). RE at speeds corresponding to 55% VO2max was not significantly different between phases of the menstrual cycle. RE at speeds corresponding to 80% VO2max was, however, significantly less (higher VO2) during ML (41.4 +/- 0.8 mL x kg-1 x min-1) than EF (40.2 +/- 0.5 mL x kg-1 x min-1). It was concluded that RE at speeds corresponding to 80% VO2max in moderately-trained female runners covaries independently with ventilatory drive changes and with fluctuations in mood state which occur throughout the menstrual cycle.

Running economy: changes with age during childhood and adolescence.

The purpose of this study was to synthesize work directed at describing and understanding changes in running economy (the steady-state demand for oxygen at a set running speed) that occur with increased age during childhood and adolescence. Although the data are limited, a number of tentative conclusions were drawn. Children are less economical than adults. Running economy improves steadily with age in normally active children and adolescents, even in the absence of formal running training. Running economy in later childhood fails to respond to either short-term instruction on the techniques of running or short-term participation in running training. Long-term participation in running training may augment improvements in running economy that occur naturally with age. In a group of heterogeneous subjects of the same age, running economy is not strongly related to performance. Within a subject over a period of years, running economy is strongly related to performance. Children are less economical than adults because when compared with adults, children exhibit (a) higher resting metabolic rates, (b) greater ventilatory equivalents for oxygen, and (c) disadvantageous stride rates and stride lengths.

Training for Aerobic Capacity and Running Economy.

In brief: Successful long-distance running is often attributed to a high VO2 max, but running economy-the steady-state oxygen consumption at a given speed-may be more important. The physiological changes in a 31-year-old elite runner were studied during an 18-week training program using both interval and endurance running. Most improvements in running economy were noted during or immediately after weeks of increased interval training. Among runners of similar ability, a small difference in economy can make a large difference in finishing time in races longer than 10,000 meters.

Characteristics associated with running performance in young boys.

The purpose of the study was to replicate and extend the investigation of characteristics associated with running performance in young boys. Two groups of 10-year-old males were studied. One group (A runners) consisted of subjects who placed above the 55th percentile on a 1.6-km run; a second group (B runners) included children who placed below the 45th percentile. No significant (P greater than 0.05) between-group mean differences were noted for leg length, skeletal age, body coordination, or running economy (the aerobic demands at steady-state submaximal speeds). Significant (P less than 0.05) between-group mean differences were found for maximal aerobic power (A, 55.1; B, 48.6 ml X min-1 X kg-1), two-site skinfold sum (A, 15.2; B, 22.7 mm), and maximal sprinting speed (A, 359.7; B, 341.1 m X min-1). When compared with A runners, B runners performed 9-min runs at a higher percentage of their maximal speed (A, 58.0; B, 51.6%), required a higher VO2 to maintain this pace (A, 48.5; B, 40.8 ml X min-1 X kg-1), and exhibited higher 4.5-min post-run blood lactate levels (A, 9.1; B, 6.7 mM X 1(-1). It was concluded that post-exercise blood lactate levels are associated, and maturity and body composition are not associated with differences in distance-running performance in boys of this age.

Effects of a prolonged maximal run on running economy and running mechanics

The purpose of this study was to document the effects of a prolonged (30 min) maximal run (PMR) on running economy (RE) and running mechanics in 16 male runners (mean VO2max = 59.0 +/- 4.5 ml.kg-1.min-1). After completing 60 min of treadmill accommodation, each subject performed two 10 min economy runs at 200 m.min-1. Subjects were also filmed at 100 fps during the last 30 s of each run in order to quantify 20 temporal, kinematic, and kinetic gait descriptors previously associated with RE variation. Following the second run, each subject completed the PMR at 85% of his predicted velocity at VO2max (89% VO2max). One, two, and four days after the PMR, subjects repeated the 10 min economy run. No significant difference (P greater than or equal to 0.05) in RE (range = 42.3-42.6 ml.kg-1.min-1) was observed following the PMR. Biomechanical analyses also indicated that, with the exception of one variable (plantar flexion angle at toe-off), gait characteristics remained unaltered after the PMR. When considered from a cross-disciplinary perspective, these data suggest that a 30 min maximal run does not increase the aerobic demand of running or disrupt the running mechanics of moderately trained male subjects who perform subsequent submaximal runs over the short term.