David W. Hill

The critical power concept. A review.

SummaryThe basis of the critical power concept is that there is a hyperbolic relationship between power output and the time that the power output can be sustained. The relationship can be described based on the results of a series of 3 to 7 or more timed all-out predicting trials. Theoretically, the power asymptote of the relationship, CP (critical power), can be sustained without fatigue; in fact, exhaustion occurs after about 30 to 60 minutes of exercise at CP. Nevertheless, CP is related to the fatigue threshold, the ventilatory and lactate thresholds, and maximum oxygen uptake (V̇O2max), and it provides a measure of aerobic fitness. The second parameter of the relationship, AWC (anaerobic work capacity), is related to work performed in a 30-second Wingate test, work in intermittent high-intensity exercise, and oxygen deficit, and it provides a measure of anaerobic capacity. The accuracy of the parameter estimates may be enhanced by careful selection of the power outputs for the predicting trials and by performing a greater number of trials. These parameters provide fitness measures which are mode-specific, combine energy production and mechanical efficiency in 1 variable, and do not require the use of expensive equipment or invasive procedures. However, the attractiveness of the critical power concept diminishes if too many predicting trials are required for generation of parameter estimates with a reasonable degree of accuracy.

Muscle hypertrophy in men and women.

It is widely believed that women experience less skeletal muscle hypertrophy consequent to heavy-resistance training than men. The purpose of this study was to test this hypothesis using both traditional indirect indicators as well as a direct measure of muscle size. Seven male experimental (ME), 8 female experimental (FE), and 7 control subjects were studied before and after a 16-wk weight training program, in which ME and FE trained 3 days.wk-1 at 70 to 90% of maximum voluntary contraction using exercise designed to produce hypertrophy of the upper arm and thigh. Strength increased significantly (P less than 0.05) in ME and FE, respectively, on elbow flexion (36.2 and 59.2%), elbow extension (32.6 and 41.7%), knee flexion (12.8 and 24.4%), and knee extension (28.8 and 33.9%) tests. Absolute changes were significantly greater in ME than FE in 2 of the 4 tests, whereas percentage changes were not significantly different. Substantial muscle hypertrophy occurred in the upper arms of both ME and FE as evidenced by significant increases in upper arm circumference (7.9 and 7.9%), bone-plus-muscle (B+M) cross-sectional area (CSA) estimated by anthropometry (17.5 and 20.4%), and muscle CSA determined from computed tomography scanning (15.9 and 22.8%). Changes by ME and FE were not significantly different, except for the absolute increase in estimated B+M CSA, which was significantly greater in ME (11.2 vs 7.4 cm2). No muscle hypertrophy occurred in the thigh of either ME and FE as evidenced by non-significant changes in thigh circumference (1.7 and 2.3%), B+M CSA (4.9 and 6.1%), and muscle CSA (2.9 and 2.9%). Changes by ME and FE in body weight, fat-free weight, and fat weight were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

The relationship between power and the time to achieve .VO(2max).

PURPOSE The severe exercise intensity domain may be defined as that range of work rates over which .VO(2max) can be elicited during constant-load exercise. The purpose of this study was to help characterize the .VO(2) response within this domain. METHODS Eleven participants performed cycle ergometer exercise tests to fatigue at several discrete work rates between 95% and 135% of the maximum power (P(max)) achieved during an incremental exercise test. RESULTS As previously demonstrated, the relationship between power and time to fatigue was hyperbolic. The asymptote of power (critical power, P(critical)) was 198 +/- 44 W. The rapidity of the .VO(2) response increased systematically at higher work rates such that the relationship between power and time to .VO(2max) was also well fit by a hyperbola. The power asymptote of this relationship (196 +/- 42 W) was not different from P(critical)(P > 0.05). The two hyperbolic relationships converged at 342 +/- 70 W (136% P(max)). CONCLUSION These data suggest that, for this population of male and female university students, the upper boundary of the severe exercise intensity domain is approximately 136% P(max). This upper boundary is the highest work rate for which exercise duration is prolonged sufficiently (in this study, 136 +/- 17 s) to allow .VO(2) to rise to its maximal value. The lower boundary for severe exercise is just above P(critical), which is the highest work rate that is sustainable for a prolonged duration and that will not elicit .VO(2max).

A physiological description of critical velocity

Abstract Although critical velocity (CV) provides a valid index of aerobic function, the physiological significance of CV is not known. Twelve individuals performed exhaustive runs at 95% to 110% of the velocity at which V˙O2max was attained in an incremental test. V˙O2max was elicited in each run. Using the time to exhaustion at each velocity, CV was calculated for each participant. Using the time to achieve V˙O2max at each velocity, which was shorter at higher velocities, a parameter we have designated as CV′ was calculated for each participant. During exercise at or below CV′, V˙O2max cannot be elicited. CV (238 ± 24 m · min−1) and CV′ (239 ± 25 m · min−1) were equal (t = 0.60, p = 0.56) and correlated (r = 0.97, p < 0.01). These results demonstrate that CV is the threshold intensity above which exercise of sufficient duration will lead to attainment of V˙O2max.

Relationship of heart rate to oxygen uptake during weight lifting exercise.

To define the relation of heart rate to oxygen uptake during weight lifting (WL), heart rate (HR) and oxygen uptake (VO2) were determined during bouts of WL at four intensities (40, 50, 60, and 70% of one-repetition maximum (1-RM)) in 15 males. The 11.5-min bouts of WL consisted of three circuits using four exercises (bench press, bent-over row, arm curl, and parallel squat), with each performed for ten repetitions over a 30-s period with a 1:1 work/rest ratio. During lifting at the four intensities, mean (+/- SE) VO2 values were 1.31 +/- 0.04, 1.50 +/- 0.07, 1.72 +/- 0.07, and 1.86 +/- 0.08 l.min-1, or 33-47% of treadmill-determined VO2max. Mean (+/- SE) HR values were 124 +/- 4, 134 +/- 4, 148 +/- 5, and 161 +/- 4 beats.min-1, or 63-82% of maximal HR. The slope of the linear regression equation predicting %VO2max from %HRmax (Y = 0.582X - 1.7911, r = 0.86, SEE = 3.4%) was approximately half that reported for dynamic low-resistance exercise such as running or cycling. At a given %HRmax, %VO2max was consistently lower than predicted for dynamic low-resistance exercise. It was concluded that the HR/VO2 relationship during dynamic high-resistance exercise for intensities between 40 and 70% of 1-RM is linear but is different from that reported for dynamic low-resistance exercise. The data are consistent with the conclusion in previous studies that using HR to prescribe the metabolic intensity of WL exercise results in a substantially lower level of aerobic metabolism than during dynamic low-resistance exercise.

Energy system contributions in middle-distance running events

The aim of this study was to estimate the energy contributions in middle-distance running events for male and female university athletes. The oxygen uptake (VO2) response during high-speed running was measured directly during exhaustive treadmill tests. Muscle mass was estimated using anthropometry. Each athlete completed an average of three races over 400 m, 800 m or 1500 m. Five minutes after each race, they provided a blood sample for determination of blood lactate concentration. For each race, energy cost, which was expressed as oxygen equivalents, was calculated as the sum of the aerobic and anaerobic components. The aerobic contribution was calculated as the sum of oxygen stores (2.3 ml O2.kg body mass-1) and total VO2 (based on the VO2 response to treadmill running). The anaerobic contribution was calculated as the sum of the energy available from phosphocreatine stores (37 ml O2.kg muscle mass-1) and the energy from glycolysis (3.0 ml O2.kg body mass-1 per mmol.l-1 increase in blood lactate concentration). For the women, the anaerobic energy contributions for the 400 m, 800 m and 1500 m averaged 62%, 33% and 17%, respectively. For the men, the anaerobic contributions averaged 63%, 39% and 20%, respectively. This information will help coaches and sport scientists to design and implement individualized training programmes.

Responses to exercise at the velocity associated with VO2maX

The purpose of this study was to assess the significance of the velocity at which an individual achieves VO2max in an incremental treadmill test (Vmax) and the time that this velocity can be sustained (Tmax) to evaluate the rationale for using Vmax and Tmax in the prescription of endurance exercise training. Mean (+/- SD) values for VO2max, and Vmax in 13 female track athletes were 52.1 +/- 5.1 ml.kg.min-1 and 271 +/- 18 m.min-1, respectively. Then each athlete performed an exhaustive run at her Vmax. In these runs, VO2max was achieved after 234 +/- 49 s and was maintained for 56 +/- 48 s (range, 10-155 s) which was the last 18 +/- 13% (range, 4-47%) of the total exercise bout. Only one of the 13 subjects reached VO2max in the first 60% of the constant velocity test. Thus, while VO2max was attained during exhaustive exercise at Vmax, the amount of time that it was sustained was quite small (less than 60 s) and highly variable. It was concluded that Vmax is a suitable intensity to elicit VO2max in training. But 60% (or less) of Tmax is not an appropriate duration for training at this intensity because it is too short a time to allow most athletes to reach VO2max.

Running velocity at VO2max.

Several authors have defined velocities which may, as a group, be described as the velocity associated with VO2max. Although several names, definitions, and abbreviations have been introduced, in this paper we shall use vVO2max for them all. These vVO2max have been reported to be an indicator of performance in distance running events. However, protocols for data collection and definitions used in the calculation of vVO2max have differed between studies. The purpose of this investigation was to compare values of vVO2max obtained using five definitions that have been described in the literature. vVO2max was determined in 22 women track athletes as (a) the speed at which VO2max was attained in a speed-incremented 0%-slope treadmill test, (b) the highest speed in the test that could be sustained for 1 min, (c) the ratio of VO2max to the oxygen cost of submaximal running (C), (d) the ratio of (VO2max - VO2 at rest) to (C - VO2 at rest), and (e) the velocity determined by extrapolation of the submaximal velocity:VO2 relationship. Results of ANOVA suggested that there were significant differences among the values derived using the different methods (F4.84 = 7.80, P < 0.001). Correlations among the various pairs of values ranged from 0.68 to 1.00. It is concluded that there are five distinct parameters described by the five definitions. The value of each of these parameters is influenced by VO2max and the energy cost of running. In theory, three of the parameters have an anaerobic component; two do not.

Modeling the relationship between velocity and time to fatigue in rowing.

INTRODUCTION Several mathematical models describe the relationship between velocity and time to fatigue. PURPOSE The purposes of this study were to evaluate different critical velocity (V(critical)) models applied to rowing ergometry and to investigate prediction of performance time in a 2000-m race based on results from shorter trials. METHODS Sixteen men performed seven rowing ergometer tests. Velocity and time to fatigue data from the 200-m (approximately 0.5 min) to 1200-m (approximately 3 min) trials and from the 200-m to 2000-m (approximately 6.5 min) trials were fit to a two-parameter hyperbolic model, a three-parameter hyperbolic model, and a three-parameter exponential model. RESULTS Including data from the 2000-m trial generally resulted in higher R2 and smaller SEE. V(critical) from the three versions of the two-parameter model were 4.71 +/- 0.28 m x s(-1), 4.80 +/- 0.27 m x s(-1), and 5.04 +/- 0.24 m x s(-1) (P < 0.001). The two three-parameter models had high R2 (0.991 and 0.990, respectively) and generated parameter estimates that appeared reasonable. Time for a 2000-m race was predicted better using the two-parameter model (r > 0.974) than using the three-parameter models (r = 0.820-0.870). CONCLUSION It is necessary to include the relatively long 2000-m predicting trial to describe accurately the velocity-time relationship in rowing. The two-parameter model may be useful in predicting time for a 2000-m race but is not otherwise appropriate for modeling when predicting trials of <1 min duration are included. Choice of model and duration of trials must be considered when using mathematical modeling to derive V(critical) and other parameters in rowing.

Significance of time to exhaustion during exercise at the velocity associated with\(\dot VO_{2max}\)

AbstractIn theory, time to exhaustion at the velocity associated with