Richard D. Telford

Factors Affecting Running Economy in Trained Distance Runners

Running economy (RE) is typically defined as the energy demand for a given velocity of submaximal running, and is determined by measuring the steady-state consumption of oxygen (V̇O2) and the respiratory exchange ratio. Taking body mass (BM) into consideration, runners with good RE use less energy and therefore less oxygen than runners with poor RE at the same velocity. There is a strong association between RE and distance running performance, with RE being a better predictor of performance than maximal oxygen uptake (V̇O2max) in elite runners who have a similar V̇O2max.RE is traditionally measured by running on a treadmill in standard laboratory conditions, and, although this is not the same as overground running, it gives a good indication of how economical a runner is and how RE changes over time. In order to determine whether changes in RE are real or not, careful standardisation of footwear, time of test and nutritional status are required to limit typical error of measurement. Under controlled conditions, RE is a stable test capable of detecting relatively small changes elicited by training or other interventions. When tracking RE between or within groups it is important to account for BM. As V̇O2 during submaximal exercise does not, in general, increase linearly with BM, reporting RE with respect to the 0.75 power of BM has been recommended.A number of physiological and biomechanical factors appear to influence RE in highly trained or elite runners. These include metabolic adaptations within the muscle such as increased mitochondria and oxidative enzymes, the ability of the muscles to store and release elastic energy by increasing the stiffness of the muscles, and more efficient mechanics leading to less energy wasted on braking forces and excessive vertical oscillation.Interventions to improve RE are constantly sought after by athletes, coaches and sport scientists. Two interventions that have received recent widespread attention are strength training and altitude training. Strength training allows the muscles to utilise more elastic energy and reduce the amount of energy wasted in braking forces. Altitude exposure enhances discrete metabolic aspects of skeletal muscle, which facilitate more efficient use of oxygen.The importance of RE to successful distance running is well established, and future research should focus on identifying methods to improve RE. Interventions that are easily incorporated into an athlete’s training are desirable.

Influence of Adiposity and Physical Activity on Arterial Stiffness in Healthy Children: The Lifestyle of Our Kids Study

Abstract—Childhood obesity is increasingly prevalent in the community and is related to adverse cardiovascular outcomes during adulthood. In this study of healthy children, we evaluated the influence of adiposity and physical activity on carotid-femoral pulse wave velocity (PWV), an index of arterial stiffness and a marker of cardiovascular risk in adults. In 573 community-based children (mean age: 10.1±0.3 years; 51% boys), we measured body mass index and waist circumference. Percentage body fat was quantitated by dual-energy x-ray absorptiometry. Cardiorespiratory fitness (CRF) and physical activity levels were assessed using a 20-m shuttle run and 7-day pedometer count, respectively. PWV was estimated by applanation tonometry. In univariate analysis, PWV was positively correlated with body mass index (r=0.34), waist circumference (r=0.32), and percentage body fat (r=0.32; P<0.001 for all) and negatively correlated with CRF (r=−0.23; P<0.001) and pedometer count (r=−0.08; P=0.046). In separate multivariable linear regression models, body mass index, waist circumference, and percentage of body fat were independently and positively associated with PWV (P<0.01 for all) after adjusting for age, sex, systolic blood pressure, mean arterial pressure, heart rate, and CRF (P<0.01 for all). The influence of CRF on PWV was attenuated after adjusting for adiposity. In conclusion, increased body mass and adiposity and decreased CRF are associated with arterial stiffening in healthy prepubescent children.

Short-term plyometric training improves running economy in highly trained middle and long distance runners.

Fifteen highly trained distance runners (&OV0312;O2max 71.1 ± 6.0 ml·min−1·kg−1, mean ± SD) were randomly assigned to a plyometric training (PLY; n = 7) or control (CON; n = 8) group. In addition to their normal training, the PLY group undertook 3 × 30 minutes PLY sessions per week for 9 weeks. Running economy (RE) was assessed during 3 × 4 minute treadmill runs (14, 16, and 18 km·h−1), followed by an incremental test to measure &OV0312;O2max. Muscle power characteristics were assessed on a portable, unidirectional ground reaction force plate. Compared with CON, PLY improved RE at 18 km·h−1 (4.1%, p = 0.02), but not at 14 or 16 km·h−1. This was accompanied by trends for increased average power during a 5-jump plyometric test (15%, p = 0.11), a shorter time to reach maximal dynamic strength during a strength quality assessment test (14%, p = 0.09), and a lower &OV0312;O2-speed slope (14%, p = 0.12) after 9 weeks of PLY. There were no significant differences in cardiorespiratory measures or &OV0312;O2max as a result of PLY. In a group of highly-trained distance runners, 9 weeks of PLY improved RE, with likely mechanisms residing in the muscle, or alternatively by improving running mechanics.

Effects of an intensive 12-wk training program by elite swimmers on neutrophil oxidative activity

The effects of an intensive 12-wk training program by 12 national-level swimmers on neutrophil oxidative activity were studied. Eleven sedentary (untrained) subjects (6 males and 5 females) served as environmental controls. Blood samples (10 ml) were taken at rest from an antecubital vein and neutrophils isolated by standard separation techniques. The oxidative burst activity of isolated neutrophils was assessed with an in vitro flow cytometric assay that used the fluorescent probe dihydrorhodamine 123. Two-way ANOVA (repeated measures) showed that oxidative activity was lower (P < 0.05) in the elite swimmers compared with the sedentary control group across the 12-wk period. Analysis of cells from swimmers in training was made: repeated measures ANOVA provided evidence of a significant decline (P < 0.05) in the number of cells responding positively ito in vitro challenge. Despite this decline, there was no significant difference in self-reported upper respiratory tract infection rate between the swimmers and sedentary individuals. These data show that: (i) elite swimmers undertaking intensive training have a significantly lower neutrophil oxidative activity at rest than do age- and sex-matched sedentary individuals; (ii) aspects of oxidative activity in swimmers are further suppressed during periods of strenuous training, and (iii) the extent of the suppression does not appear to be of clinical significance.

Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm

BACKGROUND The influence of adiposity on upper-limb bone strength has rarely been studied in children, despite the high incidence of forearm fractures in this population. OBJECTIVE The objective was to compare the influence of muscle and fat tissues on bone strength between the upper and lower limbs in prepubertal children. DESIGN Bone mineral content, total bone cross-sectional area, cortical bone area (CoA), cortical thickness (CoTh) at the radius and tibia (4% and 66%, respectively), trabecular density (TrD), bone strength index (4% sites), cortical density (CoD), stress-strain index, and muscle and fat areas (66% sites) were measured by using peripheral quantitative computed tomography in 427 children (206 boys) aged 7-10 y. RESULTS Overweight children (n = 93) had greater values for bone variables (0.3-1.3 SD; P < 0.0001) than did their normal-weight peers, except for CoD 66% and CoTh 4%. The between-group differences were 21-87% greater at the tibia than at the radius. After adjustment for muscle cross-sectional area, TrD 4%, bone mineral content, CoA, and CoTh 66% at the tibia remained greater in overweight children, whereas at the distal radius total bone cross-sectional area and CoTh were smaller in overweight children (P < 0.05). Overweight children had a greater fat-muscle ratio than did normal-weight children, particularly in the forearm (92 +/- 28% compared with 57 +/- 17%). Fat-muscle ratio correlated negatively with all bone variables, except for TrD and CoD, after adjustment for body weight (r = -0.17 to -0.54; P < 0.0001). CONCLUSIONS Overweight children had stronger bones than did their normal-weight peers, largely because of greater muscle size. However, the overweight children had a high proportion of fat relative to muscle in the forearm, which is associated with reduced bone strength.

Neutrophil oxidative activity is differentially affected by exercise intensity and type

The differential effects of exercise intensity and type on neutrophil activation were assessed in eight well-trained male runners. Each subject undertook, on different days, three separate 40 min interval (8 x 5 min) treadmill bouts: an intense uphill run (90% VO2 max), a moderate-intensity near-level run and an eccentrically-biased downhill run (both at 52% VO2 max). Blood granulocyte count increased (p< 0.05) after all three treadmill bouts (range 25-108%). Chemiluminescence activity of isolated neutrophils decreased (p< 0.05) immediately after (-58%) and 1-h after (-72%) uphill running, but became significantly elevated (p< 0.05) at 6-h after the near-level (+71%) and downhill (+84%) runs. The ability of neutrophils to release the superoxide anion radical was reduced (p< 0.05) immediately after near-level (-29%) and uphill (-21%) running in cells stimulated with opsonized zymosan. Epinephrine concentration increased by 430% (p=0.01) after uphill but not with near-level or downhill running. The plasma concentration of elastase increased (p< 0.05) immediately after uphill and near-level running, and one hour after uphill running. These results suggest that a population of neutrophils mobilised into the circulation became directly activated in response to exercise, and that neutrophil oxidative activity is affected differentially by both the intensity and type of exercise undertaken.

Physical Education, Obesity, and Academic Achievement: A 2-Year Longitudinal Investigation of Australian Elementary School Children

OBJECTIVES We determined whether physical education (PE) taught by specialists contributed to academic development and prevention of obesity in elementary school children. METHODS Our 2-year longitudinal study involved 620 boys and girls initially in grade 3 in Australia, all receiving 150 minutes per week of PE. One group (specialist-taught PE; n = 312) included 90 minutes per week of PE from visiting specialists; the other (common-practice PE; n = 308) received all PE from generalist classroom teachers. Measurements included percentage of body fat (measured by dual-emission x-ray absorptiometry) and writing, numeracy, and reading proficiency (by government tests). RESULTS Compared with common-practice PE, specialist-taught PE was associated with a smaller increase in age-related percentage of body fat (P = .02). Specialist-taught PE was also associated with greater improvements in numeracy (P < .03) and writing (P = .13) scores. There was no evidence of a reading effect. CONCLUSIONS The attenuated age-related increases in percentage of body fat and enhanced numeracy development among elementary school children receiving PE from specialists provides support for the role of PE in both preventive medicine and academic development.

Influence of training loads on patterns of illness in elite distance runners

Objective:To investigate relationships between training mileage and intensity, and the type, incidence, severity, and duration of respiratory illness in distance runners, and the impact of illness on submaximal and maximal running performance. Design:A longitudinal observational study of distance runners with serial monitoring of training loads and clinical patterns of illness. Setting:A 4-month winter training period in the Southern Hemisphere. Participants:A total of 20 highly trained (elite) male middle-distance and distance runners competing at the national and international levels. Main Outcome Measures:Training was quantified by mileage (km), intensity (scale, 1-5), and load (volume × intensity). Symptoms and signs of respiratory illness (type, duration, and severity) were verified by a physician at a weekly review. Performance was monitored by measuring submaximal and maximal oxygen uptake and time to exhaustion on a incremental treadmill test. Results:A majority of subjects (15/20) experienced 1 or more episodes of respiratory illness (mean, 2.5 episodes; range, 1-5), with 79% of symptoms classified as upper respiratory in origin. There were no significant differences in mean weekly mileage (P = 0.43), training intensity (P = 0.85), or training load (P = 0.45) between healthy runners and those affected by illness. Mean weekly (88 ± 46 km) and mean monthly (373 ± 163 km) mileages prior to each episode of illness were similar to the overall study means (95.5 ± 36.4 km and 382 ± 146 km). There were no substantial relationships between mean weekly training mileage, intensity, or training load and the number of illnesses reported (all r < 0.20). Neither submaximal nor maximal running performance was significantly affected by the presence of illness. Conclusions:Differences in training mileage, intensity, and load were not associated with the incidence of respiratory illness in highly trained middle-distance and distance runners. Runners with mild illness can be reassured that symptoms will not necessarily impair submaximal and maximal performance.

Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise.

AbstractRed blood cell (RBC) susceptibility to oxidative and osmotic stress in vitro was investigated in cells from trained and untrained men before and after submaximal exercise. Whilst no significant change in peroxidative haemolysis occurred immediately after 1 h of cycling at 60% of maximal aerobic capacity (