Dissociation of changes in VO2 max, muscle QO2, and performance with training in rats

Before the start and after 4, 8, and 12 wk of a treadmill training program male rats were randomly selected and tested for running performance, maximum O2 consumption (VO2 max), running economy (VO2 submax), and skeletal muscle oxidative capacity (QO2). Data were compared with values from untrained weight-matched control rats. Maximum running time to exhaustion increased significantly (P less than 0.01) by 4 wk and again at 12 wk (P less than 0.01). Submaximal running endurance increased by 120 (4 wk), 320 (8 wk), and 372% (12 wk) (P less than 0.01). VO2 max was increased only at 12 wk (86.0 +/- 2.7 vs. 75.5 +/- 1.9 ml O2.kg-1.min-1); VO2 submax was decreased at 4 and 8 wk but not at 12 wk. Soleus QO2 was unchanged after 4 wk of training and increased by 50% at 8 wk and by 77% at 12 wk. This study is the first to show a dissociation in both the time course and the magnitude of longitudinal changes in VO2 max, VO2 submax, QO2, and maximal and submaximal running performance. We conclude that factors other than those measured explain the improvement in running performance that resulted from endurance training in these rats.     

Treadmill economy in girls and women matched for height and weight.

We investigated differences in walking (80 m/min) and running (147 m/min) economy [submaximal oxygen consumption (VO(2) (submax))] between adolescent girls (n = 13; age = 13.3 +/- 0.9 yr) and young women (n = 23; age = 21.0 +/- 1.5 yr). Subjects were matched for height (158.7 +/- 2.9 cm) and weight (52.1 +/- 3.0 kg). Anthropometric measures (height, weight, breadths, skinfolds) and preexercise oxygen consumption were obtained on all subjects before submaximal and maximal treadmill exercise. Anthropometric measures were similar between groups, as was maximal oxygen consumption (girls, 47.7 +/- 5.2; women, 47.5 +/- 5.7 ml. kg(-1). min(-1)). VO(2) (submax) was significantly greater (P < 0.0002) in girls compared with women during both walking (16.4 +/- 1.7 vs. 14.4 +/- 1. 1 ml. kg(-1). min(-1)) and running (38.1 +/- 3.7 vs. 33.9 +/- 2.4 ml. kg(-1). min(-1)). Preexercise oxygen consumption (4.4 vs. 3.9 ml. kg(-1). min(-1)) accounted for only a fraction of the differences found in exercise economy. Although heart rate and respiratory frequency were greater in the girls in both walking (118 +/- 11 vs. 104 +/- 12 beats/min and 31 +/- 3 vs. 25 +/- 4 breaths/min, respectively; P < 0.002) and running (180 +/- 15 vs. 163 +/- 17 beats/min and 47 +/- 11 vs. 38 +/- 8 breaths/min; P < 0.005), this did not likely account for a large part of the difference in VO(2) (submax) between groups.     

Significance of the contribution of aerobic and anaerobic components to several distance running performances in female athletes

To assess the most important determinant for successful distance running (800 m, 1500 m and 3000 m events) in female athletes, measurements of several anaerobic indices were made (peak power, mean power) using the Wingate anaerobic test (WAnT), and aerobic indices such as oxygen uptake (VO2) or running velocity (v) at lactate threshold (LT), VO2 or v at onset of blood lactate accumulation (OBLA), running economy (RE), and maximal oxygen uptake were determined using the incremental treadmill test. The RE was represented by a VO2 value measured at 240 m.min-1 of a standard treadmill velocity. A stepwise multiple regression analysis (SAS stepwise procedure) combined the best features of forward inclusion and backward elimination to determine the most important factors in predicting the performance of running these distances as dependent variables. The stepwise procedure showed that the blood lactate variables such as LT and/or OBLA are highly correlated with, and contributed to predicting performance running 800 m-3000 m, whereas the anaerobic component was related only to running 800 m. In conclusion, blood lactate variables account for a large part of the variation in distance running performance in female as in male runners. The component of the anaerobic system which can be measured by the WAnT was shown to contribute to performance in running 800 m, but not in longer distances.     

Kenyan dominance in distance running

Critical physiological factors for performance in running are maximal oxygen consumption (VO(2max)), fractional VO(2max) utilization and running economy. While Kenyan and Caucasian elite runners are able to reach very high, but similar maximal oxygen uptake levels, the VO(2max) of black South African elite runners seems to be slightly lower. Moreover, the studies of black and white South African runners indicate that the former are able to sustain the highest fraction of VO(2max) during long distance running. Results on adolescent Kenyan and Caucasian boys show that these boys are running at a similar percentage of VO(2max) during competition. Kenyan elite runners, however, appear to be able to run at a high % of VO(2max) which must then have been achieved by training. A lower energy cost of running has been demonstrated in Kenyan elite runners and in untrained adolescent Kenyan boys compared to their Caucasian counterparts. In agreement with this are the results from studies on black South African elite runners who have shown similar low energy costs during running as the Kenyan elite runners. The good running economy cannot be explained by differences in muscle fibre type as they are the same in Kenyan and Caucasian runners. The same is true when comparing untrained adolescent Kenyan boys with their Caucasian counterparts. A difference exists in BMI and body shape, and the Kenyans long, slender legs could be advantageous when running as the energy cost when running is a function of leg mass. Studies comparing the response to training of Kenyans and Caucasians have shown similar trainability with respect to VO(2max), running economy and oxidative enzymes. Taken all these data together it appears that running at a high fractional VO(2max) and having a good running economy may be the primary factors favouring the good performance of endurance athletes rather than them having a higher VO(2max) than other elite runners. In addition to having the proper genes to shape their bodies and thereby contributing to a good running economy, the Kenyan elite runners have trained effectively and used their potential to be in the upper range both in regard to VO(2max) and to a high utilization of this capacity during endurance running.     

Prerequisites in distance running performance of female runners

We investigated which attribute or what combination of attributes would best account for distance running performance of female runners. The subjects were 30 well-trained female distance runners, aged 19 to 23 years. Anthropometric and body composition characteristics, pulmonary function characteristics, blood properties, and cardiorespiratory function characteristics were measured at rest or during submaximal and maximal exercise. Analyses of the data showed that the relationship of oxygen uptake corresponding to lactate threshold (VO2T, ml.kg-1.min-1) with each distance running performance was substantially higher as compared with the relationship of other independent variables including maximal oxygen uptake (VO2max). Furthermore, multiple regression analysis indicated that running performances in 3,000m, 5,000m, and 10,000m are best accounted for by a combination of VO2/LT (X1), fat-free weight (X2), and/or mean corpuscular volume (X3). A multiple regression equation for predicting the 5,000m (Y, s) running performance was formulated as Y = -14.75X1-3. 03X2-5.79X3 + 2282.1. We suggest that VO2max would not stand alone as a decisive factor of distance running success in female runners, and that the distance running performance could be better accounted for by a combination of several attributes relating to lactate threshold, body composition, and/or hematological status. The linear regression of the predicted running performance on the actually measured running performance can be accepted in the range of 986-1197s.     

The effect of short-term Swiss ball training on core stability and running economy

The purpose of this study was to investigate the effect of a short-term Swiss ball training on core stability and running economy. Eighteen young male athletes (15.5 +/- 1.4 years; 62.5 +/- 4.7 kg; sigma9 skinfolds 78.9 +/- 28.2 mm; VO2max 55.3 +/- 5.7 ml.kg(-1).min(-1)) were divided into a control (n = 10) and experimental (n = 8) groups. Athletes were assessed before and after the training program for stature, body mass, core stability, electromyographic activity of the abdominal and back muscles, treadmill VO2max, running economy, and running posture. The experimental group performed 2 Swiss ball training sessions per week for 6 weeks. Data analysis revealed a significant effect of Swiss ball training on core stability in the experimental group (p < 0.05). No significant differences were observed for myoelectric activity of the abdominal and back muscles, treadmill VO2max, running economy, or running posture in either group. It appears Swiss ball training may positively affect core stability without concomitant improvements in physical performance in young athletes. Specificity of exercise selection should be considered.     

The effects of static stretching on running economy and endurance performance in female distance runners during treadmill running

Stretching can lead to decreased muscle stiffness and has been associated with decreased force and power production. The purpose of this study was to investigate the acute effects of static stretching (SS) on running economy and endurance performance in trained female distance runners. Twelve long distance female (30 ± 9 years) runners were assessed for height (159.4 ± 7.4 cm), weight (54.8 ± 7.2 kg), % body fat (19.7 ± 2.8%), and maximal oxygen consumption (VO2max: 48.4 ± 5.1 ml·kg(-1)·min(-1)). Participants performed 2 sessions of 60-minute treadmill runs following a randomly assigned SS protocol or quiet sitting (QS). During the first 30 minutes (running economy), expired gases, heart rate (HR), and rating of perceived exertion (RPE) were recorded while the participant ran at 65% VO2max. During the final 30 minutes (endurance performance), distance covered, speed, HR, and RPE were recorded while the participant attempted to cover as much distance as possible. Repeated measures analyses of variance were performed on the data. Significance was accepted at p < 0.05. The SS measured by sit-and-reach increased flexibility (SS: 29.8 ± 8.3 vs. QS: 33.1 ± 8.1 cm) but had no effect on running economy (VO2: 33.7 ± 3.2 vs. 33.8 ± 2.3 ml·kg(-1)·min(-1)), calorie expenditure (270 ± 41 vs. 270 ± 41 kcal), HR (157 ± 10 vs. 160 ± 12 b·min(-1)), or endurance performance (5.5 ± 0.6 vs. 5.5 ± 0.7 km). These findings indicated that stretching did not have an adverse effect on endurance performance in trained women. This suggests that the performance decrements previously associated with stretching may not occur in trained women.     

Use of recovery VO2 to predict running economy

The purpose of this study was to determine whether running economy (RE) could be predicted accurately using recovery VO2 values. Twelve runners (means VO2max = 61.9, SD 4.9 ml.kg-1.min-1) completed three treadmill RE sessions over a 2-week period. During each session, subjects performed three 6-min runs at 69%, 78%, and 87% VO2max. RE was calculated from a single 2-min gas collection during the last 2 min of running. Immediately following each run, recovery VO2 data obtained during randomly assigned 15-s, 20-s, or 25-s gas collections were used to predict exercise VO2. Correlations and mean absolute percentage variation (% VAR) between actual and predicted VO2 at each relative intensity and recovery period are reported. Although the relationship between actual and predicted VO2 was significant and more pronounced at higher exercise intensities, the overall magnitude of the association was low to moderate (r range = 0.50-0.81). The range of % VAR between actual and predicted aerobic demands also obscured marked underprediction (-6.5% to -12.5%) and overprediction (+10.1% to +17.4%) of actual VO2 in some subjects. These data suggest that 15-, 20-, and 25-s recovery VO2 values do not correlate strongly with steady-state VO2, nor do they adequately account for variation in individual economy profiles.     

Effects of a concurrent strength and endurance training on running performance and running economy in recreational marathon runners

The purpose of this study was to investigate the effects of a concurrent strength and endurance training program on running performance and running economy of middle-aged runners during their marathon preparation. Twenty-two (8 women and 14 men) recreational runners (mean ± SD: age 40.0 ± 11.7 years; body mass index 22.6 ± 2.1 kg·m?2) were separated into 2 groups (n = 11; combined endurance running and strength training program [ES]: 9 men, 2 women and endurance running [E]: 7 men, and 4 women). Both completed an 8-week intervention period that consisted of either endurance training (E: 276 ± 108 minute running per week) or a combined endurance and strength training program (ES: 240 ± 121-minute running plus 2 strength training sessions per week [120 minutes]). Strength training was focused on trunk (strength endurance program) and leg muscles (high-intensity program). Before and after the intervention, subjects completed an incremental treadmill run and maximal isometric strength tests. The initial values for VO2peak (ES: 52.0 ± 6.1 vs. E: 51.1 ± 7.5 ml·kg?1·min?1) and anaerobic threshold (ES: 3.5 ± 0.4 vs. E: 3.4 ± 0.5 m·s?1) were identical in both groups. A significant time × intervention effect was found for maximal isometric force of knee extension (ES: from 4.6 ± 1.4 to 6.2 ± 1.0 N·kg?1, p < 0.01), whereas no changes in body mass occurred. No significant differences between the groups and no significant interaction (time × intervention) were found for VO2 (absolute and relative to VO2peak) at defined marathon running velocities (2.4 and 2.8 m·s?1) and submaximal blood lactate thresholds (2.0, 3.0, and 4.0 mmol·L?1). Stride length and stride frequency also remained unchanged. The results suggest no benefits of an 8-week concurrent strength training for running economy and coordination of recreational marathon runners despite a clear improvement in leg strength, maybe because of an insufficient sample size or a short intervention period.     

A lower-extremities kinematic comparison of deep-water running styles and treadmill running

The purpose of this investigation was to identify a deep-water running (DWR) style that most closely approximates terrestrial running, particularly relative to the lower extremities. Twenty intercollegiate distance runners (women, N = 12; men, N = 8) were videotaped from the right sagittal view while running on a treadmill (TR) and in deep water at 55-60% of their TR VO(2)max using 2 DWR styles: cross-country (CC) and high-knee (HK). Variables of interest were horizontal (X) and vertical (Y) displacement of the knee and ankle, stride rate (SR), VO(2), heart rate (HR), and rating of perceived exertion (RPE). Multivariate omnibus tests revealed statistically significant differences for RPE (p < 0.001). The post hoc pairwise comparisons revealed significant differences between TR and both DWR styles (p < 0.001). The kinematic variables multivariate omnibus tests were found to be statistically significant (p < 0.001 to p < 0.019). The post hoc pairwise comparisons revealed significant differences in SR (p < 0.001) between TR (1.25 +/- 0.08 Hz) and both DWR styles and also between the CC (0.81 +/- 0.08 Hz) and HK (1.14 +/- 0.10 Hz) styles of DWR. The CC style of DWR was found to be similar to TR with respect to linear ankle displacement, whereas the HK style was significantly different from TR in all comparisons made for ankle and knee displacement. The CC style of DWR is recommended as an adjunct to distance running training if the goal is to mimic the specificity of the ankle linear horizontal displacement of land-based running, but the SR will be slower at a comparable percentage of VO(2)max.     

Effects of gradual-elastic compression stockings on running economy, kinematics, and performance in runners

We investigated the effect of gradual-elastic compression stockings (GCSs) on running economy (RE), kinematics, and performance in endurance runners. Sixteen endurance trained athletes (age: 34.73 ± 6.27 years; VO2max: 62.83 ± 9.03 ml·kg(-1)·min(-1); 38 minutes in 10 km; 1 hour 24 minutes in half marathon) performed in random order 4 bouts of 6 minutes at a recent half-marathon pace on a treadmill to evaluate RE with or without GCSs. Subsequently, 12 athletes were divided into 2 equal groups matched by their VO2max, and they performed a time limit test (T(lim)) on a treadmill at 105% of a recent 10-km pace with or without GCSs for evaluation of physiological responses and running kinematics. There were no significant differences in the RE test in all of the variables analyzed for the conditions, but a moderate reproducibility for some physiological responses was detected in the condition with GCSs. In the T(lim), the group that wore GCSs reached a lower % of maximum heart rate (HRmax) compared with the control group (96.00 ± 2.94 vs. 99.83 ± 0.40) (p = 0.01). Kinematics did not differ between conditions during the T(lim) (p > 0.05). There were improvement trends for time to fatigue (337 vs. 387 seconds; d = 0.32) and a lower VO2peak (≈53 vs. 62 ml·kg(-1)·min(-1); d = 1.19) that were detected with GCSs during the T(lim). These results indicate that GCSs reduce the % of HRmax reached during a test at competition pace. The lower reproducibility of the condition with GCSs perhaps suggests that athletes may possibly need an accommodation period for systematically experiencing the benefits of this garment, but this hypothesis should be further investigated.     

The influence of weekly training distance on fractional utilization of maximum aerobic capacity in marathon and ultramarathon runners

This study was designed to examine the interrelationships between performance in endurance running events from 10 to 90 km, training volume 3-5 weeks prior to competition, and the fractional utilization of maximal aerobic capacity (%VO2max) during each of the events. Thirty male subjects underwent horizontal treadmill testing to determine their VO2max, and steady-state VO2 at specific speeds to allow for calculation of %VO2max sustained during competition. Runners were divided into groups of ten according to their weekly training distance (group A trained less than 60 km X week-1, group B 60 to 100 km X week-1, and group C more than 100 km X week-1). Runners training more than 100 km X week-1 had significantly faster running times (average 19.2%) in all events than did those training less than 100 km X week-1. VO2max or %VO2max sustained during competition was not different between groups. The faster running speed of the more trained runners, running at the same %VO2max during competition, was due to their superior running economy (19.9%). Thus all of the group differences in running performance could be explained on the basis of their differences in running economy. These findings suggest either that the main effect of training more than 100 km X week-1 may be to increase running economy, or that runners who train more than 100 km X week-1 may have inherited superior running economy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aging and factors related to running economy

The purpose of this study was to investigate the relationship that age has on factors affecting running economy (RE) in competitive distance runners. Fifty-one male and female subelite distance runners (Young [Y]: 18-39 years [n = 18]; Master [M]: 40-59 years [n = 22]; and Older [O]: 60-older [n = 11]) were measured for RE, step rate, lactate threshold (LT), VO2max, muscle strength and endurance, flexibility, power, and body composition. An RE test was conducted at 4 different velocities (161, 188, 215, and 241 m·min(-1)), with subjects running for 5 minutes at each velocity. The steady-state VO2max during the last minute of each stage was recorded and plotted vs. speed, and a regression equation was formulated. A 1 × 3 analysis of variance revealed no differences in the slopes of the RE regression lines among age groups (y = 0.1827x - 0.2974; R2 = 0.9511 [Y]; y = 0.1988x - 1.0416; R2 = 0.9697 [M]; y = 0.1727x + 3.0252; R2 = 0.9618 [O]). The VO2max was significantly lower in the O group compared to in the Y and M groups (Y = 64.1 ± 3.2; M = 56.8 ± 2.7; O = 44.4 ± 1.7 mlO2·kg(-1)·min(-1)). The maximal heart rate and velocity @ LT were significantly different among all age groups (Y = 197 ± 4; M = 183 ± 2; O = 170 ± 6 b·min(-1) and Y = 289.7 ± 27.0; M = 251.5 ± 32.9; O = 212.3 ± 24.6 m·min(-1), respectively). The VO2max @ LT was significantly lower in the O group compared to in the Y and M groups (Y = 50.3 ± 2.0; M = 48.8 ± 2.9; O = 34.9 ± 3.2 mlO2·kg(-1)·min(-1)). The O group was significantly lower than in the Y and M groups in flexibility, power, and upper body strength. Multiple regression analyses showed that strength and power were significantly related to running velocity. The results from this cross-sectional analysis suggest that age-related declines in running performance are associated with declines in maximal and submaximal cardiorespiratory variables and declines in strength and power, not because of declines in running economy.     

Maximal oxygen uptake during treadmill walking and running at various speeds.

Three groups of male subjects, average fitness (AF, N = 12), high fitness (HF, N = 7) and highly fit competitive race walkers (CRW, N = 3) performed maximal treadmill tests walking at 3.5 and 4.5 mph and running at 4.5, 5.5, 7.0, and 8.5 mph. In addition, the HF group performed a running test at 10.0 mph and the CRW group performed a walking test at 5.5 mph. All maximal oxygen uptake (VO2 max) tests with the exception of the 3.5 mph walking test (modified Balke test) were discontinuous in nature. VO2 max obtained from walking tests was similar regardless of speed within each group. Walking VO2 max was significantly lower than running VO2 max which was found to be similar over a speed range of 4.5 to 8.5 mph in the AF group. Running at 4.5 mph (HF group) and 4.5 and 5.5 mph (CRW group) resulted in lower VO2 max levels than running at speeds greater than or equal to 7.0 mph. Associated physiological variables (heart rate, ventilation, and respiratory exchange ratio) did not demonstrate a discernable pattern with reference to mode of locomotion (walking versus running) or speed. It was concluded that VO2 max elicited during walking is independent of speed and less than VO2 max obtained during running. Running VO2 max was interrelated with speed of running and state of training.     

Physiological parameters related to running performance in college trackmen.

Submaximal and maximal oxygen consumption (VO2) and heart rate (HR) were correlated with running performance in events ranging from 100 yards to 2 miles, using as subjects 20 members of a college track team. In the first of two studies (n=11) a multi-stage walking test was used to determine VO2 and HR. Max VO2 expressed in ml/kg/min, was significantly related to 1 mile run performance but not to any of the other runs. Submaximal HR was significantly related to performance in both the 1 mile and 2 mile runs. Correlations between these physiological parameters and performance in the 220, 440, and 880 yard runs were nonsignificant. Multiple R's using max VO2 (ml/kg/min) and submaximal H were .758 and 9671, respectively, for the 1 and 2 mile runs. In study two (n=9) a running test for VO2 and HR was used, which resulted in a mean max VO2 about 7 ml higher than than elicited in the walking test, implying that for trained runners a running test was a more valid test of aerobic power. Marked relationships were found between body weight and performance, positive for the 100 yard dash and negative for the 2 mile run. Submaximal HR was again significantly related to performance in the 1 and 2 mile runs. Max VO2 was positively related to 2 mile performance and negatively related to 100 yard dash performance. Multiple R's using max VO2 and submaximal HR were .799 and .925 for the 1 and 2 mile runs, respectively. Using submaximal HR and weight the multiple R's were .777 and .945, showing that these two can account for a large amount of the variance in distance running performance. In neither study was submaximal VO2 significantly related to running performance.     

Effects of size, sex, and voluntary running speeds on costs of locomotion in lines of laboratory mice selectively bred for high wheel-running activity

Selective breeding for over 35 generations has led to four replicate (S) lines of laboratory house mice (Mus domesticus) that run voluntarily on wheels about 170% more than four random-bred control (C) lines. We tested whether S lines have evolved higher running performance by increasing running economy (i.e., decreasing energy spent per unit of distance) as a correlated response to selection, using a recently developed method that allows for nearly continuous measurements of oxygen consumption (VO2) and running speed in freely behaving animals. We estimated slope (incremental cost of transport [COT]) and intercept for regressions of power (the dependent variable, VO2/min) on speed for 49 males and 47 females, as well as their maximum VO2 and speeds during wheel running, under conditions mimicking those that these lines face during the selection protocol. For comparison, we also measured COT and maximum aerobic capacity (VO2max) during forced exercise on a motorized treadmill. As in previous studies, the increased wheel running of S lines was mainly attributable to increased average speed, with males also showing a tendency for increased time spent running. On a whole-animal basis, combined analysis of males and females indicated that COT during voluntary wheel running was significantly lower in the S lines (one-tailed P=0.015). However, mice from S lines are significantly smaller and attain higher maximum speeds on the wheels; with either body mass or maximum speed (or both) entered as a covariate, the statistical significance of the difference in COT is lost (one-tailed P> or =0.2). Thus, both body size and behavior are key components of the reduction in COT. Several statistically significant sex differences were observed, including lower COT and higher resting metabolic rate in females. In addition, maximum voluntary running speeds were negatively correlated with COT in females but not in males. Moreover, males (but not females) from the S lines exhibited significantly higher treadmill VO2max as compared to those from C lines. The sex-specific responses to selection may in part be consequences of sex differences in body mass and running style. Our results highlight how differences in size and running speed can account for lower COT in S lines and suggest that lower COT may have coadapted in response to selection for higher running distances in these lines.     

Explosive-strength training improves 5-km running time by improving running economy and muscle power.

To investigate the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 wk. The total training volume was kept the same in both groups, but 32% of training in E and 3% in C was replaced by explosive-type strength training. A 5-km time trial (5K), running economy (RE), maximal 20-m speed (V20 m), and 5-jump (5J) tests were measured on a track. Maximal anaerobic (MART) and aerobic treadmill running tests were used to determine maximal velocity in the MART (VMART) and maximal oxygen uptake (VO2 max). The 5K time, RE, and VMART improved (P < 0.05) in E, but no changes were observed in C. V20 m and 5J increased in E (P < 0.01) and decreased in C (P < 0.05). VO2 max increased in C (P < 0.05), but no changes were observed in E. In the pooled data, the changes in the 5K velocity during 9 wk of training correlated (P < 0.05) with the changes in RE [O2 uptake (r = -0.54)] and VMART (r = 0.55). In conclusion, the present simultaneous explosive-strength and endurance training improved the 5K time in well-trained endurance athletes without changes in their VO2 max. This improvement was due to improved neuromuscular characteristics that were transferred into improved VMART and running economy.     

Modeling: optimal marathon performance on the basis of physiological factors

This paper examines current concepts concerning "limiting" factors in human endurance performance by modeling marathon running times on the basis of various combinations of previously reported values of maximal O2 uptake (VO2max), lactate threshold, and running economy in elite distance runners. The current concept is that VO2max sets the upper limit for aerobic metabolism while the blood lactate threshold is related to the fraction of VO2max that can be sustained in competitive events greater than approximately 3,000 m. Running economy then appears to interact with VO2max and blood lactate threshold to determine the actual running speed at lactate threshold, which is generally a speed similar to (or slightly slower than) that sustained by individual runners in the marathon. A variety of combinations of these variables from elite runners results in estimated running times that are significantly faster than the current world record (2:06:50). The fastest time for the marathon predicted by this model is 1:57:58 in a hypothetical subject with a VO2max of 84 ml.kg-1.min-1, a lactate threshold of 85% of VO2max, and exceptional running economy. This analysis suggests that substantial improvements in marathon performance are "physiologically" possible or that current concepts regarding limiting factors in endurance running need additional refinement and empirical testing.     

Improvement in running economy after 6 weeks of plyometric training

This study determined whether a 6-week regimen of plyometric training would improve running economy (i.e., the oxygen cost of submaximal running). Eighteen regular but not highly trained distance runners (age = 29 +/- 7 [mean +/- SD] years) were randomly assigned to experimental and control groups. All subjects continued regular running training for 6 weeks; experimental subjects also did plyometric training. Dependent variables measured before and after the 6-week period were economy of running on a level treadmill at 3 velocities (women: 2.23, 2.68, and 3.13 m.s(-1); men: 2.68, 3.13, and 3.58 m.s(-1)),VO(2)max, and indirect indicators of ability of muscles of lower limbs to store and return elastic energy. The last were measurements during jumping tests on an inclined (20 degrees ) sled: maximal jump height with and without countermovement and efficiencies of series of 40 submaximal countermovement and static jumps. The plyometric training improved economy (p < 0.05). Averaged values (m.ml(-1).kg(-1)) for the 3 running speeds were: (a). experimental subjects-5.14 +/- 0.39 pretraining, 5.26 +/- 0.39 posttraining; and (b). control subjects-5.10 +/- 0.36 pretraining, 5.06 +/- 0.36 posttraining. The VO(2)max did not change with training. Plyometric training did not result in changes in jump height or efficiency variables that would have indicated improved ability to store and return elastic energy. We conclude that 6 weeks of plyometric training improves running economy in regular but not highly trained distance runners; the mechanism must still be determined.