Bishop D, Jenkins D G, Howard A
Department of Human Movement Studies, The University of Queensland, Brisbane, Australia.
Int J Sports Med. 1998 Feb;19(2):125-9. doi: 10.1055/s-2007-971894.
The linear relationship between work accomplished (W(lim)) and time to exhaustion (t(lim)) can be described by the equation: W(lim) = a + CP x t(lim). Critical power (CP) is the slope of this line and is thought to represent a maximum rate of ATP synthesis without exhaustion, presumably an inherent characteristic of the aerobic energy system. The present investigation determined whether the choice of predictive tests would elicit significant differences in the estimated CP. Ten female physical education students completed, in random order and on consecutive days, five all-out predictive tests at preselected constant-power outputs. Predictive tests were performed on an electrically-braked cycle ergometer and power loadings were individually chosen so as to induce fatigue within approximately 1-10 mins. CP was derived by fitting the linear W(lim)-t(lim) regression and calculated three ways: 1) using the first, third and fifth W(lim)-t(lim) coordinates (I135), 2) using coordinates from the three highest power outputs (I123; mean t(lim) = 68-193 s) and 3) using coordinates from the lowest power outputs (I345; mean t(lim) = 193-485 s). Repeated measures ANOVA revealed that CPI123 (201.0+/-37.9W) > CPI135 (176.1+/-27.6W) > CPI345 (164.0+/-22.8W) (P<0.05). When the three sets of data were used to fit the hyperbolic Power-t(lim) regression, statistically significant differences between each CP were also found (P<0.05). The shorter the predictive trials, the greater the slope of the W(lim)-t(lim) regression; possibly because of the greater influence of 'aerobic inertia' on these trials. This may explain why CP has failed to represent a maximal, sustainable work rate. The present findings suggest that if CP is to represent the highest power output that an individual can maintain "for a very long time without fatigue" then CP should be calculated over a range of predictive tests in which the influence of aerobic inertia is minimised.
完成的功（W(lim)）与力竭时间（t(lim)）之间的线性关系可用以下方程描述：W(lim) = a + CP × t(lim)。临界功率（CP）是这条线的斜率，被认为代表了无疲劳状态下ATP合成的最大速率，大概是有氧能量系统的一个固有特征。本研究确定了预测测试的选择是否会在估计的CP上产生显著差异。十名女性体育专业学生以随机顺序并在连续几天内，在预先选定的恒定功率输出下完成了五项全力预测测试。预测测试在电动刹车的自行车测力计上进行，功率负荷是根据个人情况选择的，以便在大约1 - 10分钟内引起疲劳。通过拟合线性W(lim)-t(lim)回归来推导CP，并通过三种方式计算：1）使用第一个、第三个和第五个W(lim)-t(lim)坐标（I135），2）使用来自三个最高功率输出的坐标（I123；平均t(lim) = 68 - 193秒），3）使用来自最低功率输出的坐标（I345；平均t(lim) = 193 - 485秒）。重复测量方差分析显示CPI123（201.0±37.9W）> CPI135（176.1±27.6W）> CPI345（164.0±22.8W）（P<0.05）。当使用这三组数据来拟合双曲线功率 - t(lim)回归时，在每个CP之间也发现了统计学上的显著差异（P<0.05）。预测试验越短，W(lim)-t(lim)回归的斜率就越大；这可能是因为“有氧惯性”对这些试验的影响更大。这也许可以解释为什么CP未能代表最大的可持续工作速率。目前的研究结果表明，如果CP要代表一个人能够“长时间无疲劳地维持”的最高功率输出，那么CP应该在一系列预测测试中计算，在这些测试中，有氧惯性的影响被最小化。
