Stress tests

Stress tests are used to assess the fitness in athletes or to diagnose physical activities. An athlete will usually undergo these tests in a specialized stress measuring laboratories. Field tests which are equally important are usually conducted under specific conditions for a sport discipline in question.

Equipment of a stress measuring laboratory

• ergometers (treadmill, bicycle ergometer, rowing ergometer, etc.)
• devices to measure circulation parameters (sport-testers, ECG, pressure metres)
• devices to measure ventilation parameters (spirometers, gas analyzers)
• dynamometers
• biochemical blood analyzers
• other (e.g. calorimeters)

Examples of stress protocols

Before a stress test is taken it is necessary to choose the right stress protocol (Fig. 34) which will further specify the intensity of workload, its duration, etc.

• single-grade stress test
• graded stress test
• graded test with pauses
• ramp
• continual
• combined

Figure 34 Basic protocols of ergometry

Anaerobic tests

Using anaerobic tests the level of anaerobic predispositions, i.e. speed-strength abilities is assessed. The most frequently used tests include:

Nejčastěji využívané anaerobní testy:

• Wingate tests
• jump ergometry (Bosco test)
• dynamometry

Wingate test

The test is conducted on the isokinetic cycle ergometer. The test duration is 30s (Fig. 35) during which an individual makes an absolute effort to push the pedals as fast as possible on a bicycle ergometer. The values assessed include: maximum performance achieved, total work and fatigue index. The test focuses on the ATP-AC system assessment and the LA system-speed-assessment.

Figure 35 Wingate test

Jump ergometry (Bosco test)

The test is carried out on the jump ergometer (a board acting as an electrical switch). The test duration is 10-60 s. Depending on the duration both explosive and endurance strength of the lower limbs may be measured. In the test speed of the active stage of take-off, the height of the jump, etc. are assessed.

Dynamometry

Muscle dynamometry is used to test strength predispositions. Isometric dynamometers test muscles in isometric contraction (muscle length does not change) and isokinetic dynamometers test muscles during a movement within a joint range. In addition to maximum power we may also watch the dynamographic curve showing power progression in time. On the dynamographic curve a moment of turning may be observed, etc.

Aerobic tests

Using aerobic tests the level of aerobic predispositions, i.e. endurance abilities are assessed. The most frequently used tests are:

• maximum oxygen uptake (VO2max)
• evaluation of anaerobic threshold (ANT)
• running (movement) economy
• The test of physical working capacity 170 (PWC 170)

The basic physiological factors constraining endurance performance include: maximum oxygen uptake (VO₂max), the 'anaerobic threshold' value (ANT) and economy of movement (e.g. economy of

VO₂max – maximum oxygen uptake

Average values of the population and average values for selected athletes shows Fig. 36.

Figure 36 Maximum oxygen uptake

ANT – anaerobic threshold

The issue of the anaerobic threshold is widely discussed nowadays. The previously used definition of the ANT read as follows: 'The anaerobic threshold is a divide between predominantly anaerobic and aerobic ways of energy production. It is a period of time characterized by the commencement of anaerobic glycolysis accompanied by the release of lactate into blood.'

The value of the 'anaerobic threshold' may be expressed in a number of ways, in training most commonly in % from HRmax. The ANT value may also be expressed in % derived from the VO2max detected in the maximum stress test. As it is not always easy to detect the ANT value, following are the examples of the threshold value assessment using the basic methods:

1. Lactate threshold – detection using the lactate curve (Fig. 37). Under the workload of rising intensity blood samples are taken to determine the lactate concentration in the blood. Based on these values a curve is drawn including a breakpoint when the volume of lactate in the body rises dramatically. The lactate threshold may be found between 2-8 mmol/l.

Figure 37 Lactate threshold


2. Ventilation threshold (ventilatory breakpoint) – threshold determined using ventilation parameters (most frequently minute ventilation). During a run of a rising intensity the values of ventilation parameters are recorded using the air analyzer (VE, VE/VO2, RER) – Fig. 38, 39). Based on the gathered data a graph is drawn and the breakpoint, in which an increase has been observed, is determined. The breakpoint may denote an increase on the ventilation curve or in oxygen equivalent.

Figure 38 Ventilation threshold



Figure 39 “Anaerobic threshold” determined from oxygen equivalent



Threshold determination using the ratio of the respiratory exchange ratio is carried out in a moment when the carbon dioxide output (VCO2) equals oxygen intake (VO2), RER = 1.

3. Circulatory threshold – determination of the anaerobic threshold using the Conconi test (Fig. 40). This is an indirect method through which we estimate the heart frequency curve. A tested person takes the Conconi test on a treadmill or outdoors. Every 200m is increased the running speed by 1 km/h. The initial speed is set in accordance with the person's fitness. The 'circulatory threshold' is determined in the moment of deflection, i.e. when the HR curve diverges from the linear curve.

Figure 40 Example of circulatory threshold determination (Novotný et al., 2006)

Economy of movement (running)

Using the Saltin test and the air analyzer we may determine the value of oxygen intake at various running speeds. Modification of the test shows Fig. 41.

Figure 41 Modification of the Saltin test to determine the economy of running

The PWC 170

Widely used in the Czech Republic the W170 test assesses the overall fitness of an individual. The test is conducted on the cycle ergometer. It aims to determine the workload in watts (W/kg) which a human is able to pedal at the HR value of 170 beats/min. The average values assessed in Czech women are approximately 1.8 W/kg (Placheta et al., 1999). The best male endurance athletes, especially road cyclists show values of up to 4 W/kg while women show 3.2 W/kg (Lipková, 2006).