Chapter 34

• History of athletic training and performance.
• Enhanced exercise ability (V̇o2max > 40 mL/kg/min).
• Increased left ventricular mass by echocardiography.

The concept of the athlete’s heart is one that has been postulated for almost 100 years, promulgating the idea that myocardial hypertrophy could be a purely physiologic phenomenon. Media attention to the sudden deaths of widely known athletes has helped focus attention on the important distinction between pathologic cardiac hypertrophy and physiologic hypertrophy and the upper limits of the latter.

The adaptations of the human body to physical training involve (but are not confined to) the cardiovascular system. The exercise-related changes in other organ systems influence the cardiovascular response to exercise. It is important for the physician to be familiar with the physiologic responses to physical training in order to distinguish them from similar changes that can occur with cardiovascular disease.

Different forms of exercise produce a number of physiologic responses. Also, cardiovascular responses to short-term training and prolonged training differ. Exercise generally takes two basic physiologic forms—dynamic and static, or isometric, exercise—although most athletic activities are a variable combination of both forms of exercise. Dynamic exercise constitutes an alteration in the length of skeletal muscle with comparatively little change in muscle tension. Static exercise is essentially the reverse—that is, a marked alteration in skeletal muscle tension with little or no change in muscle length. Distance running is a classic example of dynamic exercise; weight lifting is a classic example of static exercise.

The morphologic and physiologic consequences of dynamic and isometric exercise are significant and may simulate changes associated with cardiac disease. The normal limits of changes that are due to athletic conditioning require careful identification. Awareness of these limits improves the physician’s ability to determine the end points at which normal anatomy and physiology become clinical disease.

Maron BJ et al. The heart of trained athletes: cardiac remodeling and the risks of sports, including sudden death. Circulation. 2006 Oct 10;114(15):1633–44.  [PubMed: 17030703]

The acute cardiovascular responses to exercise are specific and vary with different forms of exercise (Figure 34–1). There are also specific adaptive responses to exercise, particularly to dynamic exercise. In particular, the adaptive change in heart rate from an alteration in vagal parasympathetic tone defines the normal physiologic range; as noted earlier, this may be initially misinterpreted as representative of cardiovascular disease.

###### Figure 34–1.

Cardiovascular response to exercise. A: Response to dynamic exercise progressively increasing workload to maximal oxygen consumption. B: Response to static handgrip contraction at 30% maximal voluntary contraction. ABP, systolic, mean and diastolic arterial blood pressures; HR, heart rate; Q, cardiac output; SV, stroke volume; TPR, total peripheral resistance; V̇o2, oxygen consumption.

(Reprinted with permission from Mitchell JH, Raven PB. Cardiovascular adaption to physical activity. In: Bouchard ...

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