This graphical review highlights a focused application of a key principle (‘Krogh Principle’) identified by Nobel-prize winning physiologist Professor August Krogh (1874–1949) that states “for many problems there is an animal on which it can be most conveniently studied”. We apply the Krogh Principle to human physiology by proposing that “for many problems there is a unique group of humans on which it can be most conveniently studied”. As such, we present 5 unique human case studies. Case 1 discusses whether signals from exercising muscles cause blood pressure to rise using a patient with a spinal cord lesion. Case 2 investigates the role of the sympathetic nervous system in the blood pressure response to exercise using patients who have undergone sympathectomy for hypertension. Case 3 asks whether increases in blood lactate are necessary for the non-linear increase in breathing with heavy exercise using patients with McArdle's disease. Case 4 applies fundamental scaling principles from comparative physiology to elite athletes to investigate the role of body size on maximal aerobic capacity. Finally, Case 5 describes our recent work that investigates whether a left shift in the oxygen hemoglobin dissociation curve can facilitate hypoxic exercise using patients with left-shifted hemoglobinopathies. In summary, we have expanded the inter-species message of the August Krogh Principle and highlighted the need to search for odd examples and experiments of nature. In this context, observations from unusual humans are a source of insights into physiology, which may be translated into therapeutic approaches for disease.

这篇图解评论突出了诺贝尔奖获得者生理学家奥古斯特·克罗格教授 (August Krogh, 1874-1949) 确定的关键原理（“克罗原理”）的重点应用，该原理指出“对于许多问题，有一种动物可以最方便地对其进行研究”。我们将克罗原理应用于人类生理学，提出“对于许多问题，有一组独特的人类可以最方便地研究它”。因此，我们提出了 5 个独特的人类案例研究。案例 1 讨论了来自运动肌肉的信号是否会导致患有脊髓损伤的患者血压升高。案例 2 使用因高血压接受交感神经切除术的患者调查交感神经系统在对运动的血压反应中的作用。案例 3 询问血液乳酸的增加是否对于使用麦卡德尔病患者进行剧烈运动时呼吸的非线性增加是必要的。案例 4 将来自比较生理学的基本比例原则应用于精英运动员，以研究体型对最大有氧能力的作用。最后，案例 5 描述了我们最近的工作，该工作调查了氧血红蛋白解离曲线的左移是否可以促进左移血红蛋白病患者的缺氧运动。总之，我们扩展了 August Krogh 原则的物种间信息，并强调了寻找奇怪的例子和自然实验的必要性。在这种情况下，来自不同寻常的人类的观察是洞察生理学的一个来源，这可能会转化为疾病的治疗方法。