During stationary swimming against an increasing load, the gas-exchange threshold and respiratory compensation point can be readily discerned, two important parameters to measure during free swimming at increasing velocity. Intensity progression via load increases during incremental exercise can be symmetrical, gradual, and rapid during tethered swimming, which is not the case during incremental free swimming at an increasing velocity. Administering the procedure will be Leandro Oliveira, Luiz Gustavo Santos, and Camila Vasconcelos, graduate students from my laboratory.

The swimmer will be Julia Kato who has been in involved in competitive swim training for five years. To prepare the 500-kilogram load cell that will be used to measure the highest force that the swimmer can exert during two trials comprising 30 seconds of all-out swimming, open the N2000PRO software program, and open the Help menu to verify the communication link between the computer and the load-cell analyzer. When the connection to the RS232 interface is established, a green signal will appear.

Set the countdown to start the test, the sampling duration, and the rest interval. Then set the frames per second at 100 hertz. Set the unit of force measurement, then set the acquisition time in milliseconds.

Then calibrate the load cell with zero-and 10-kilogram loads with the swimmer outside of the pool. Before beginning the two-trial test, provide instructions regarding the correct performance of all-out front-crawl swimming, and have the swimmer practice the stretching and arm and leg swings at poolside. Next, have the swimmer enter the pool and perform a standard warm-up protocol comprised of front-crawl swimming for 800 meters at a light intensity.

At the end of the warm-up, allow the swimmer to rest at poolside for 10 minutes. At the end of the rest period, attach a load cell to the start block via the L-shaped flattened iron bar for the tethered swimming measurements, and attach one end of the inelastic rope to the load cell. Use a custom-designed belt that has ropes attached to both hips such that leg kicking will not interfere with the force measurement, and attach the other end of the rope to the swimmer.

Then determine the load required to maintain the swimmer's body horizontally with a minimum amount of tension on the measurement system. When the swimmer is ready, signal the swimmer to begin the trial in the water, monitoring the swimmer and providing verbal encouragement throughout the 30-second test. At the end of the trial, signal the swimmer to end the test, and detach the swimmer from the inelastic rope.

Instruct the swimmer to perform a standard cool-down protocol comprised of front-crawl swimming at a light intensity, and let the swimmer rest for 30 minutes at poolside. At the end of the rest period, reattach the swimmer to the inelastic rope, and signal the swimmer to begin the second trial of all-out tethered swimming. At the end of the trial, signal the swimmer to stop the test and to perform a second standard cool-down protocol comprised of front-crawl swimming at a light intensity.

At the end of the cool-down, allow the swimmer to exit the pool. For an incremental tethered swimming test, after calculating the loads to resist the swimmer's forward displacement during the test, verify the communication link between the computer and the automated portable metabolic unit within the unit's software. Power on the unit to allow the unit to warm up for 45 minutes, and confirm that the batteries are fully charged.

Then enter the subject data, ambient temperature, and humidity. To prepare the swimmer for the incremental test, install a face mask and a snorkel on the swimmer. Instruct the swimmer to rest at poolside to collect the baseline gas exchange and ventilatory data.

After 10 minutes, instruct the swimmer to perform a standard warm-up protocol comprised of front-crawl swimming at a light intensity wearing the snorkel system to ensure familiarization. At the end of the warm-up, detach an inelastic rope to the belt with the other end of the rope attached to the loading system. Secure the belt around the swimmer's waist.

Instruct the swimmer to enter the pool and to use the two markers from the bottom of the pool for reference points to allow them to maintain a relatively fixed position within the pool. When the swimmer is ready, signal to begin the test, and monitor the swimming during the trial. A research assistant experienced in monitoring this type of testing should hold the gas analysis unit at poolside without impeding the swimmer's displacement or elevating the swimmer's head.

This test requires a synchronized effort that includes changing the load, encouraging the swimmer, monitoring the position in the water, and the data that are being collected. During the trial, increase the load while timing the 60-second stages. When the swimmer is no longer able to maintain the requisite position despite strong verbal encouragement, terminate the test, and record the time to limit of exercise tolerance.

Use the time to the limit of exercise tolerance to calculate the stages completed and record the loads for each stage and the peak load. Then detach the swimmer from the inelastic rope, and instruct the swimmer to perform a standard cool-down protocol comprised of front-crawl swimming at a low-to-moderate intensity before exiting the pool. The initial load on the incremental exercise test was set at a load that exceeded that which was required for the swimmer to maintain body alignment prior to initiation of the all-out swim by 30%of the difference between the average force measured during the all-out swim and the initial all-out swim.

The load was then increased by 0.7 kilograms for every 60-second stage. The limit of exercise tolerance for the swimmer occurred at stage 10 after 576 seconds. When the breath-by-breath oxygen uptake data collected during the baseline and exercise portions of the incremental exercise test were averaged into consecutive nine-second bins, the highest three-point rolling average was 3.44 liters per minute, and the oxygen uptake load slope was 261 milliliters per minute per kilogram.

During the rapid incremental exercise test, the decline in arterial blood carbon dioxide and end-tidal carbon dioxide that characterizes respiratory compensation and response to metabolic acidosis does not occur for at least two or more minutes, during which the work and metabolic rates continue to increase. For this swimmer, the metabolic rates characterizing these distinct changes in gas exchange and ventilatory response driven by the increased contribution of the anaerobic pathway to energy demand occurred at 75%and 86%of the peak oxygen uptake, respectively. The technicians administering the test must be coordinated as precise timing is required, and swimmer must be highly motivated and familiar with the novel aspects of tethered swimming.

As the metabolic response to a linear increase in work is not linear, this type of test allows identification of the breakpoints that defines an athlete's nonlinearity.