**1. Introduction**

Cardiopulmonary exercise testing (CPET) provides a full assessment of the physiologic responses of the pulmonary, cardiovascular, muscular, and cellular oxidative systems to exercise [1,2]. Sports physicians and physiologists try to identify the effects of exercise on athletes' organs to figure out their conditioning level and plan training programs to develop elite athletes for the team. Although CPET has become a generally well-accepted method to assess organ system adaptations to chronic regular exercise, its useful applications for more comprehensive assessments in the athletic population are not universally widespread yet.

The proposed indications for CPET in apparently healthy athletes are [3–6]:


Athletes mainly recognize CPET assessment just for the measurement of their cardiorespiratory fitness (CRF) that mainly provides aerobic endurance performance expressed as maximal oxygen consumption (VO2max). VO2max measured during a graded maximal exercise is the most significant parameter to assess the cardiopulmonary capacity, especially in endurance sports [7], but it should be validated by completing a short constant work rate phase at higher intensities than the VO2max work rate achieved during the ramp tests [8]. There are additional parameters that extend the number of opportunities to comprehensively study the integrated organ system response to maximal effort. The most remarkable

**Citation:** Mazaheri, R.; Schmied, C.; Niederseer, D.; Guazzi, M. Cardiopulmonary Exercise Test Parameters in Athletic Population: A Review. *J. Clin. Med.* **2021**, *10*, 5073. https://doi.org/10.3390/jcm10215073

Academic Editor: Francesco Giallauria

Received: 24 September 2021 Accepted: 26 October 2021 Published: 29 October 2021

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is likely the ventilatory threshold (VT) that indicates aerobic power and is related to the lactate threshold in endurance and even resistance exercises [9]. Moreover, critical power (CP) is a widely used parameter for training that represents threshold intensities associated with the upper limit for prolonged aerobic exercise and signifies high to severe exercise intensity domain [10].

The series of variables are however consistent, and a careful analysis of each one yields to the best information in the time point assessment of physical performance and response to training programs. Oxygen pulse, defined as the ratio between VO2 and heart rate (HR), indicates stroke volume and peripheral vascular perfusion/extraction response to exercise and reflects the maximal aerobic capacity. Ventilatory efficiency expressed by the relationship between minute ventilation (VE) to carbon dioxide (VCO2) production (VE/VCO2 slope) and/or partial pressure of end-tidal carbon dioxide (PETCO2) at rest and during exercise, represents a match of ventilation and perfusion within the pulmonary system [11]. These quite underused parameters require a specific evaluation and interpretation.

Regular exercise has favourable cardiovascular benefits, but competitive athletes usually perform intense training for prolonged periods which exposes their cardiovascular system to increased levels of strain [12]. Intense exercise may trigger adverse cardiac events in an asymptomatic athlete with latent cardiac disease. Moreover, athletes sometimes experience minor symptoms such as dizziness, palpitation, or chest tightness that might indicate some subclinical cardiovascular or pulmonary disorders. In these instances, CPET analysis may be of additional help in clarifying the underlying causes and abnormalities.

In this review, the applications of CPET in athletes with an emphasis on physiological parameters and their implication in the assessment of athletic performance are discussed. Secondly, the role of CPET in the evaluation of minor nonspecific symptoms to determine and/or distinguish cardiac and pulmonary conditions that might limit sports participation is discussed. Finally, recommendations on exercise prescription for athletes based on the CPET results are summarized at the end of the paper.

#### **2. Cardiorespiratory Fitness**
