R. Hugh Morton

The critical power and related whole-body bioenergetic models

This paper takes a performance-based approach to review the broad expanse of literature relating to whole-body models of human bioenergetics. It begins with an examination of the critical power model and its assumptions. Although remarkably robust, this model has a number of shortcomings. Attention to these has led to the development of more realistic and more detailed derivatives of the critical power model. The mathematical solutions to and associated behaviour of these models when subjected to imposed “exercise” can be applied as a means of gaining a deeper understanding of the bioenergetics of human exercise performance.

The critical power model for intermittent exercise

This paper develops and illustrates the critical power model for intermittent work. Model theoretic development reveals that total endurance time is always a step function of one or more of the four independent variables: work interval power output (Pw), rest interval power output (Pr), work interval duration (tw), and rest interval duration (tr). Six endurance-trained male athletes recorded their best performances during the season in 3-, 5-, and 10-km races, and performed three different intermittent running tests to exhaustion in random order, recording their total endurance times. These data were used to illustrate the model and compare anaerobic distance capacities (α) and critical velocities (β) estimated from each type of exercise. Good fits of the model to data were obtained in all cases: 0.954<R2<0.999. Critical velocity was found to be significantly less when estimated using an intermittent versus continuous running protocol.

Effect of multiple-micronutrient supplementation on maternal nutrient status, infant birth weight and gestational age at birth in a low-income, multi-ethnic population

Poor nutrient intake during pregnancy can adversely affect both infant and maternal health. The aim was to investigate the efficacy of multiple-micronutrient supplementation during pregnancy in a socially deprived population in the developed world. We conducted a randomised, double-blind, placebo-controlled trial of multiple-micronutrient supplementation including 20 mg Fe and 400 microg folic acid, from the first trimester of pregnancy in 402 mothers, in East London, UK. Nutrient status was measured at recruitment, and at 26 and 34 weeks of gestation. Infants were weighed at birth. At recruitment the prevalence of anaemia was 13 %, vitamin D insufficiency 72 %, thiamin deficiency 12 % and folate deficiency 5 %, with no differences between groups. Only 39 % of women completed the study; rates of non-compliance were similar in both groups. Intention-to-treat analysis showed that participants receiving treatment had higher mean Hb at 26 weeks of gestation (110 (sd 10) v.108 (sd 10) g/l; P = 0.041) and 34 weeks of gestation (113 (sd 12) v.109 (sd 10) g/l; P = 0.003) and packed cell volume concentrations at 26 weeks of gestation (0.330 (sd 0.025) v. 0.323 (sd 0.026) l/l; P = 0.011) and 34 weeks of gestation (0.338 (sd 0.029) v. 0.330 (sd 0.028) l/l; P = 0.014) compared with controls. Analysis of compliant women showed supplemented women had higher median concentrations of serum ferritin, erythrocyte folate and 25-hydroxyvitamin D later in gestation than controls. In the compliant subset (n 149), placebo mothers had more small-for-gestational age (SGA) infants (eight SGA v. thirteen; P = 0.042) than treatment mothers. Baseline micronutrient deficiencies were common; the multiple-micronutrient supplement was well-tolerated and improved nutrient status. Multiple-micronutrient supplements from early pregnancy may be beneficial and larger studies are required to assess impact on birth outcomes and infant development.

Time in human endurance models : From empirical models to physiological models

This article traces the study of interrelationships between power output, work done, velocity maintained or distance covered and the endurance time taken to achieve that objective. During the first half of the twentieth century, scientists examined world running records for distances from <100m to >1000km. Such examinations were empirical in nature, involving mainly graphical and crude curve-fitting techniques. These and later studies developed the use of distance/time or power/time models and attempted to use the parameters of these models to characterise the endurance capabilities of athletes. More recently, physiologists have proposed theoretical models based on the bioenergetic characteristics of humans (i.e. maximal power, maximal aerobic and anaerobic capacity and the control dynamics of the system). These models have become increasingly complex but they do not provide sound physiological and mathematical descriptions of the human bioenergetic system and its observed performance ability. Finally, we are able to propose new parameters that can be integrated into the modelling of the power/time relationship to explain the variability in endurance time limit at the same relative exercise power (e.g. 100% maximal oxygen uptake).

Differential modeling of anaerobic and aerobic metabolism in the 800-m and 1,500-m run

This study examined the hypothesis that running speed over 800- and 1,500-m races is regulated by the prevailing anaerobic (oxygen independent) store (ANS) at each instant of the race up until the all-out phase of the race over the last several meters. Therefore, we hypothesized that the anaerobic power that allows running above the speed at maximal oxygen uptake (VO2max) is regulated by ANS, and as a consequence the time limit at the anaerobic power (tlim PAN=ANS/PAN) is constant until the final sprint. Eight 800-m and seven 1,500-m male runners performed an incremental test to measure VO2max and the minimal velocity associated with the attainment of VO2max (vVO2max), referred to as maximal aerobic power, and ran the 800-m or 1,500-m race with the intent of achieving the lowest time possible. Anaerobic power (PAN) was measured as the difference between total power and aerobic power, and instantaneous ANS as the difference between end-race and instantaneous accumulated oxygen deficits. In 800 m and 1,500 m, tlim PAN was constant during the first 70% of race time in both races. Furthermore, the 1,500-m performance was significantly correlated with tlim PAN during this period (r=-0.92, P<0.01), but the 800-m performance was not (r=-0.05, P=0.89), although it was correlated with the end-race oxygen deficit (r=-0.70, P=0.05). In conclusion, this study shows that in middle-distance races over both 800 m and 1,500 m, the speed variations during the first 70% of the race time serve to maintain constant the time to exhaustion at the instantaneous anaerobic power. This observation is consistent with the hypothesis that at any instant running speed is controlled by the ANS remaining.

Deception by manipulating the clock calibration influences cycle ergometer endurance time in males

It is common for athletes striving to achieve maximal effort to exercise in the presence of a visible clock. It is implicitly assumed that calibration of the clock is normal (i.e. accurate). This study was designed to test the effect of secretly manipulating the clock calibration on maximal effort as measured by endurance times in cycle ergometry. Twelve subjects (6 male and 6 female) each undertook three identical rides to exhaustion on a cycle ergometer. In one the clock was normally calibrated, in another it was calibrated 10% faster, and in the third 10% slower. Tests were conducted double blind and in fully counterbalanced orders within gender. Clocked endurance times were recorded, and later converted to real times. Analysis of clocked times revealed no significant effects. Over all subjects, real endurance times showed a significant calibration effect, being on average 18.3% (73.4s) longer when the clock ran slow, compared to normal, and 20.5% (80.8s) longer when compared to fast. Because males exercised significantly longer than females, separate analyses reveal that the calibration effect was only significant in males, 27.7% (143.2s) and 29.7% (151.2s), respectively, and present but not significant in females, 1.3% (3.6s) and 3.8% (10.5s), respectively. These results suggest that, when deceived by a visible clock running slower than normal, times to exhaustion on the cycle ergometer were significantly longer in male subjects.

Maximal endurance time at VO2max.

INTRODUCTION There has been significant recent interest in the minimal running velocity which elicits VO2max. There also exists a maximal velocity, beyond which the subject becomes exhausted before VO2max is reached. Between these limits, there must be some velocity that permits maximum endurance at VO2max, and this parameter has also been of recent interest. This study was undertaken to model the system and investigate these parameters. METHODS We model the bioenergetic process based on a two-component (aerobic and anaerobic) energy system, a two-component (fast and slow) oxygen uptake system, and a linear control system for maximal attainable velocity resulting from declining anaerobic reserves as exercise proceeds. Ten male subjects each undertook four trials in random order, running until exhaustion at velocities corresponding to 90, 100, 120, and 140% of the minimum velocity estimated as being required to elicit their individual VO2max. RESULTS The model development produces a skewed curve for endurance time at VO2max, with a single maximum. This curve has been successfully fitted to endurance data collected from all 10 subjects (R2 = 0.821, P < 0.001). For this group of subjects, the maximal endurance time at VO2max can be achieved running at a pace corresponding to 88% of the minimal velocity, which elicits VO2max as measured in an incremental running test. Average maximal endurance at VO2max is predicted to be 603 s in a total endurance time of 1024 s at this velocity. CONCLUSION Endurance time at VO2max can be realistically modeled by a curve, which permits estimation of several parameters of interest; such as the minimal running velocity sufficient to elicit VO2max, and that velocity for which endurance at VO2max is the longest.

Why peak power is higher at the end of steeper ramps: An explanation based on the “critical power” concept

Abstract Experimental studies have consistently reported higher peak power outputs at the termination of steeper ramp exercises. One explanation can be deduced from oxygen uptake kinetics. This short communication offers an alternative explanation based on the “critical power” concept of human bioenergetics. Algebraic, calculus, and geometric aspects of this explanation are all detailed, and it is illustrated with data from a previous study.

Low reproducibility of many lactate markers during incremental cycle exercise

Reports on reproducibility of lactate markers usually considered only two trials. The authors assessed reproducibility of power output at seven markers in 11 fit subjects over at least six trials under tightly controlled conditions. Subjects undertook incremental exercises (50 W start, +50 W every 3 min to exhaustion) on a cycle ergometer. At each trial blood lactate concentration was determined at rest and within the final 30 s of each stage. The Rest+1, 2.0 and 4.0 mmol/l markers were determined by interpolation, the D-max and nadir using a quadratic model and the lactate slope index using an exponential plus constant model, and a visual turnpoint was determined empirically. Intraclass correlations and coefficients of variation assessed reproducibility. Power output at all markers differed significantly between subjects, but not between trials. Intraclass correlation coefficients were respectively 0.799, 0.794, 0.807, 0.903, 0.677, 0.769 and 0.648, and corresponding standard errors of measurement 11.9, 9.2, 9.1, 2.5, 9.2, 10.8 and 24.7 W. Statistical powers of detecting a 30 W increment at these markers were 0.30, 0.43, 0.42, 0.98, 0.58, 0.38 and 0.18 respectively. These results indicate that only the D-max marker has good reproducibility and that it alone can identify small but meaningful changes in training status with sufficient statistical power.

The quantitative periodization of athletic training: A model study

A systems model that quantifies the effects of training on athletic performance has been subjected to a detailed simulation study. Four performance‐related variables were considered: (1) predicted peak performance, (2) the date of its occurrence, (3) an index of overtraining stress, and (4) the robustness of predicted performances around the peak. The study suggests that physiologic attributes of an athletes fitness and fatigue responses to training are as relevant in optimizing performance as are parameters of training management. For any given athlete, training intensity, the spacing of training bouts, and the shape of the seasonal training profile are the most relevant parameters. In particular, in order to achieve maximum performance yet avoid overtraining stress, intensive training on alternate days distributed in a triangular shape over a short (150 day) season is preferable to moderate daily training distributed in triangular (or any other shape) over a long season.