Method Article

A Rapidly Incremented Tethered-Swimming Maximal Protocol for Cardiorespiratory Assessment of Swimmers

DOI:

10.3791/60630

⸱

January 28th, 2020

 ,  ,  ,  ,  ,  ,  ,  ,  , 
1Department of Physical Education, São Paulo State University (UNESP) at Bauru, 2Institute of Bioscience, Graduate Program in Human Development and Technology, São Paulo State University (UNESP) at Rio Claro, 3Ciper, Faculdade de Motricidade Humana, Universidade de Lisboa, 4Department of Science and Technology, School of Education, Polytechnic Institute of Setúbal, 5Quality of Life Research Center, Polytechnic Institute of Santarem, 6Universidade Europeia at Lisbon, 7Division of Endocrinology, Diabetes and Bone Disease, Icahn School of Medicine at Mount Sinai, 8Department of Biobehavioral Sciences, Teachers College, Columbia University

* These authors contributed equally

In This Article

Summary

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As opposed to measurement during free swimming, which presents inherent challenges and limitations, determination of important parameters of cardiorespiratory function for swimmers can be made using a more feasible and easier to administer tethered-swimming rapidly incremented protocol with gas exchange and ventilatory data collection.

Abstract

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Incremental exercise testing is the standard means of assessing cardiorespiratory capacity of endurance athletes. While the maximal rate of oxygen consumption is typically used as the criterion measurement in this regard, two metabolic breakpoints that reflect changes in the dynamics of lactate production/consumption as the work rate is increased are perhaps more relevant for endurance athletes from a functional standpoint. Exercise economy, which represents the rate of oxygen consumption relative to performance of submaximal work, is also an important parameter to measure for endurance-athlete assessment. Ramp incremental tests comprising a gradual but rapid increase in work rate until the limit of exercise tolerance is reached are useful for determining these parameters. This type of test is typically performed on a cycle ergometer or treadmill because there is a need for precision with respect to work-rate incrementation. However, athletes should be tested while performing the mode of exercise required for their sport. Consequently, swimmers are typically assessed during free-swimming incremental tests where such precision is difficult to achieve. We have recently suggested that stationary swimming against a load that is progressively increased (incremental tethered swimming) can serve as a "swim ergometer" by allowing sufficient precision to accommodate a gradual but rapid loading pattern that reveals the aforementioned metabolic breakpoints and exercise economy. However, the degree to which the peak rate of oxygen consumption achieved during such a protocol approximates the maximal rate that is measured during free swimming remains to be determined. In the present article, we explain how this rapidly incremented tethered-swimming protocol can be employed to assess the cardiorespiratory capacity of a swimmer. Specifically, we explain how assessment of a short-distance competitive swimmer using this protocol revealed that his rate of oxygen uptake was 30.3 and 34.8 mL∙min-1∙kg-1BM at his gas-exchange threshold and respiratory compensation point, respectively.

Introduction

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An exercise test that involves an incremental increase in work rate (WR) from low to maximal (i.e., incremental exercise test; INC) provides the gold standard method of cardiorespiratory assessment for endurance athletes. In addition to the highest WR that the athlete can achieve (WRpeak), INC also allows for determination of the highest rate at which the individual can consume oxygen (O2) for that form of exercise (V̇O2peak) if gas exchange and ventilatory data are collected during the test1. The V̇O2peak represents the criterion measure of cardiorespiratory fitness. Moreover, analysis of gas exchange and ventilatory data collected as WR is increased provides a non-invasive way to identify the point at which blood-lactate concentration (blood [lactate]) increases above the baseline value (lactate threshold) and the point at which it begins to accumulate at an accelerated rate (lactate turnpoint)2. These metabolic breakpoints are estimated by determining the gas-exchange threshold (GET) and respiratory-compensation point (RCP), respectively3. Importantly, the GET provides a robust estimate of the point at which blood [lactate] initially increases whereas the "hyperventilation" that characterizes RCP is a more complex phenomenon that can be initiated by afferent input other than chemoreception per se. Consequently, conclusions based on identification of RCP should be made with caution.

When exercise is maintained at a constant rate of work (CWR), there are markedly different physiological response profiles based on the "exercise-intensity domain" within which the WR falls4,5. Specifically, achievement of a V̇O2 and blood [lactate] "steady state" is rapid in the moderate domain, delayed in the heavy domain and unattainable in the severe domain4,5. It is well established that the rate at which O2 can be consumed at GET during INC (V̇O2GET) serves as the metabolic rate that separates the moderate from heavy domain during CWR3,6. Although controversial, a number of recent observations indicate similar equivalence between the rate at which O2 can be consumed at RCP (V̇O2RCP) and heavy/severe separation7,8,9,10. Identification of V̇O2GET and V̇O2RCP from data collected during INC might, therefore, be useful for prescribing domain-specific training regimens for endurance athletes via metabolic rate with the caveat that aligning a metabolic rate with a specific work rate is more complex than simply doing so according to the V̇O2-work rate relationship derived from the incremental test8,11.

When the concept of testing to determine V̇O2max was initially explored, researchers had subjects perform bouts of track running to the limit of exercise tolerance (Tlim) at increasing speeds on separate days1. Research followed which confirmed that V̇O2max can also be determined from similar bouts performed to Tlim on the same day with rest periods interspersed12. Eventually, it was shown that a continuous protocol with WR increased in an incremental manner at specific time intervals (e.g., every 3 min) revealed the same V̇O2peak as the discontinuous tests13. Consequently, these "graded exercise tests" became the standard for determining this criterion measure of cardiorespiratory fitness. However, in 1981, Whipp and colleagues published research that indicated that for the purpose of V̇O2max measurement, INC could also be performed entirely in the non-steady state; that is, with WR increasing continuously as a "smooth function of time" (RAMP-INC)14. Unlike INC with extended stages and relatively large WR increases per stage, the gradual increase during RAMP-INC ensures that the "isocapnic buffering region" that separates GET and RCP will be clearly defined15. Furthermore, much like INC with stages, RAMP-INC can be used to assess "exercise economy" (i.e., the V̇O2 required per given WR); however, unlike INC with stages, in this case, it is the inverse of "delta efficiency" (i.e., the slope of the V̇O2-WR relationship) that is used for this purpose11 with consideration given to the fact that due to the complexities of the V̇O2 response to work rates across the intensity spectrum, this parameter will not be an immutable feature of INC per se (e.g., RAMP-INC initiated from different baseline work rates or characterized by different ramp slopes) or CWR exercise16.

For general fitness testing, INC is usually performed on a leg ergometer or treadmill because these modalities are more available and leg cycling and walking/running are familiar to the average person. Moreover, administration of RAMP-INC requires the ability to increase WR continuously in small increments (e.g., 1 W every 2 s); hence, an ergometer (typically leg cycling) is best suited for this type of testing. However, athlete assessment is more complex because athletes must be tested while performing the specific mode of exercise required for their sport. For cyclists and individuals who participate in sports that involve running, this is not problematic because of the accessibility and applicability of the aforementioned testing machines. Conversely, ecologically-valid testing with gas exchange and ventilatory data collection and the gradual WR incrementation required for RAMP-INC is more challenging when assessing aquatic athletes.

Prior to the advent of automated collection systems, gas-exchange assessment of swimmers was often performed using Douglas-bag collection following a maximal swim17. Once automated systems were developed, "real-time" collection took place, but not under "real-swimming" conditions (e.g., while swimmers swam in a flume which controlled WR)17. Unfortunately, the former method has inherent limitations due to the assumptions of "backward extrapolation" while the latter raises concerns regarding the degree to which flume swimming changes technique17. The current state of the art involves the use of portable breath-by-breath collection systems which move with the swimmer alongside the pool during free swimming17. While this type of measurement improves ecological validity, gradual WR incrementation is challenging. Indeed, INC during free swimming typically involves intervals of set distance (e.g., 200 m) at progressively-increasing velocities14,15. This means that a test consists of lengthy stages with large unequal WR increments. It is, therefore, not surprising that only a single metabolic breakpoint (typically called the "anaerobic threshold") is reported by researchers who employ this test18,19. Instead, we have recently shown that both V̇O2GET and V̇O2RCP can be determined from data collected while swimmers performed stationary swimming in a pool against a load that was increased gradually and rapidly (i.e., incremental tethered swimming)20. While the unique breathing pattern that is present during swimming might render the aforementioned breakpoints harder to identify compared to typical modes of assessment (personal observation), we believe that this method of testing might be suitable as a "swim ergometer" that can be used for cardiorespiratory assessment of swimmers in a manner similar to how a stationary cycle is used for cyclists. Indeed, we have shown that V̇O2GET, V̇O2RCP and exercise economy (as indicated by the V̇O2-load slope) can all be determined from the rapidly incremented tethered-swimming protocol that is described below20.

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Protocol

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Participants in the study from which the representative-subject data presented below were extracted20 (n = 11) were required to give their written informed consent prior to initiation of testing after the experimental procedures, associated risks and potential benefits of participation had been explained. The first visit comprised a familiarization session during which the swimmers were introduced to the concept of tethered swimming and the measurement techniques that would be in effect during the actual testing. An all-out tethered-swimming test was performed during the second visit and the rapidly incremented tethered-swimming protocol was performed on the third visit. Both tests were done in a semi-Olympic pool (25 m) with water temperature at 28 °C.

1. Preparation of swimmer

  1. Instruct the swimmer to avoid strenuous exercise for 24 h preceding each testing session.
  2. Instruct the swimmer to arrive at the pool in a rested and fully hydrated state ≥3 h postprandial.
  3. Instruct the swimmer to refrain from ingesting stimulant beverages and alcohol for 24 h prior to each test.

2. All-out tethered-swimming test

  1. Prepare the 500 kg load cell that will be used to measure the highest force that the swimmer can exert during two trials comprising 30 s of all-out swimming21.
    1. Open the N2000PRO Software (Power Din Pro - CEFISE) program on the computer.
    2. Open the Help Menu to verify the communication link between the computer and the load-cell analyzer.
      1. Observe a green signal that indicates that the connection to the RS232 interface is well established.
      2. Set the countdown to start the test depending on circumstances.
      3. Set the sampling duration. Set the rest interval. Set the frames per second at 100 Hz.
      4. Set the unit of force measurement at N or kg depending on personal preference. Set the acquisition time in milliseconds.
    3. Calibrate the load cell22 with 0 and 10 kg loads with the swimmer outside pool.
    4. Attach a load cell to the start block via the L-shaped flattened iron bar that is designed by CEFISE specifically for tethered-swimming measurements.
    5. Attach one end of the inelastic rope to the load cell and the other end to the swimmer by means of the custom-designed belt (CEFISE), which has ropes attached to both hips such that leg kicking will not interfere with the force measurement.
  2. Prepare the swimmer for performance of the two-trial test.
    1. Provide instructions to the swimmer regarding correct performance of all-out front-crawl swimming (e.g., prevent the head and trunk from rising while swimming as rapidly as possible, concentrate on kicking at a maximal rate in addition to maximal stroking, etc.).
    2. Instruct the swimmer to perform stretching and arm/leg swings at poolside in preparation.
    3. Instruct the swimmer to enter the pool and perform a standard warm-up protocol comprised of front-crawl swimming for 800 m at a light intensity with care taken to avoid engendering any lingering effects that could influence the results of the test.
    4. Allow the swimmer to exit the pool and rest at poolside for 10 min.
    5. Secure the belt around swimmer's waist. Attach the free end of the inelastic rope to the belt.
    6. Determine the load required to maintain the swimmer's body horizontally with a minimum amount of tension on the measurement system (loadbase).
    7. Signal the swimmer to begin Trial #1 of the test.
  3. Monitor the swimmer during performance of the test.
    1. Provide verbal encouragement to swimmer throughout 30 s test.
    2. Signal the swimmer to end the test. Detach the swimmer from the inelastic rope.
    3. Instruct the swimmer to perform a standard cool-down protocol comprised of front-crawl swimming at a light intensity.
    4. Allow the swimmer to rest for 30 min at poolside.
    5. Reattach the swimmer to the inelastic rope.
    6. Signal the swimmer to start Trial #2 of the test which is identical to Trial #1 (30 s of all-out swimming).
    7. Signal the swimmer to end the test.
    8. Instruct the swimmer to perform a standard cool-down protocol comprised of front-crawl swimming at a light intensity.
    9. Allow the swimmer to exit pool.
  4. Analyze the data collected during the two-trial test.
    1. Apply the smoothing process to the data using the N2000PRO software package23.
    2. Calculate the peaks of the wave-frequency signal from the force-time sinusoidal curve (range, sine 80°-100°) above loadbase for Trials #1 and 2.
    3. Define the averaged peaks of the force-time wave-frequency signal in the first 5 s and entire 30 s, respectively, as the peak force (Fpeak) and average force (Favg) for each trial.
    4. Use the higher values for Fpeak and Favg for further calculations.

3. Incremental tethered-swimming test

  1. Calculate the loads that will be used to resist the swimmer's forward displacement during the incremental test.
    1. Calculate the starting load as 30% of the Favg above loadbase.
    2. Calculate the increments to be applied per 60-s stage as 5% of Favg above loadbase.
  2. Prepare the automated portable metabolic unit for data collection.
    1. Open the unit's software.
    2. Verify the communication link between the computer and the automated portable metabolic unit.
    3. Power on unit and allow to warm up for 45 min. Ensure that batteries are fully charged.
    4. Perform calibration of unit for environmental air24.
    5. Perform calibration of unit for reference O2 (16%), CO2 (5%) and N (balance) concentrations24.
    6. Perform mask time-delay calibration24.
    7. Perform calibration of turbine with 3 L syringe24.
    8. Enter the subject data, ambient temperature and humidity.
  3. Prepare the swimmer for performance of the incremental test.
    1. Install a facemask and a snorkel on the swimmer.
    2. Instruct the swimmer to rest at poolside for 10 min to collect "baseline" gas exchange and ventilatory data.
    3. Instruct the swimmer to enter the pool and perform a standard warm-up protocol comprised of front-crawl swimming at a light intensity.
    4. Secure a belt around the swimmer's waist. Attach an inelastic rope to the belt with the other end of rope attached to the loading system.
    5. Instruct the swimmer that once the test begins to use the two markers on the bottom of the pool for reference points, which allow them to maintain a relatively-fixed position (e.g., ± 1 m from the desired position).
    6. Signal the swimmer to begin the test.
  4. Monitor the swimmer during performance of the incremental test.
    NOTE: A research assistant who is experienced in monitoring this type of testing should hold the gas-analysis unit at poolside being cognizant to do so without impeding swimmer displacement and/or elevating the swimmer's head.
    1. Increase load while timing the 60 s stages.
    2. Terminate the test and record the time to limit of exercise tolerance when the swimmer is no longer able to maintain the requisite position despite strong verbal encouragement from the testers.
    3. Use the time to limit of exercise tolerance to calculate stages completed.
    4. Record loads for each stage and peak load.
    5. Detach the swimmer from the inelastic rope.
    6. Instruct the swimmer to perform a standard cool-down protocol comprised of front-crawl swimming at a low-to-moderate intensity.
    7. Allow the swimmer to exit the pool.
  5. Analyze the data collected during the incremental test.
    1. Smooth breath-by-breath gas-exchange data that were collected before and during test using the unit's software program.
    2. Export gas-exchange data in consecutive 9 s bin averages.
    3. Perform three-point rolling average on consecutive 9 s bin averages for V̇O2.
    4. Record highest three-point rolling-average value as the V̇O2peak.
    5. Using final three-point rolling-average value for each completed stage, calculate V̇O2-load relationship via linear regression. Exclude data from end stages of test if a V̇O2 plateau appears to be present (visual inspection).
    6. Using consecutive 9 s bin averages, determine V̇O2GET.
      1. Determine the first disproportionate increase in the rate of CO2 production (V̇CO2) compared to V̇O2.
      2. Determine the increase in the ratio of the expired rate of ventilation (V̇E) to V̇O2 with no increase in the ratio of V̇E to V̇CO2.
      3. Determine the increase in end-tidal O2 tension with no fall in end-tidal CO2 tension.
    7. Using consecutive 9-s bin averages, determine V̇O2RCP.
      1. Determine the first disproportionate increase in V̇E compared to V̇CO2.
      2. Determine the decrease in end-tidal CO2.
    8. Express V̇O2peak, V̇O2GET, V̇O2RCP and V̇O2-load slope in both absolute (L∙min-1) and relative (to body mass; mL∙min-1∙kg-1) terms.
    9. Express V̇O2GET and V̇O2RCP in relative terms as a percentage of V̇O2peak.

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Results

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The data presented in Table 1 and depicted in Figures 1-4 represents the response profiles observed for a male swimmer (age, 24 years). At the time of data collection, the swimmer had been training for competitive swimming for 7 years. His specialty was short-distance (i.e., 50 m and 100 m) freestyle events.

The initial load on INC was set at a load that exceeded that which was required for this...

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Discussion

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An exercise challenge that involves enduring an incremental increase in WR until Tlim is reached is a standard testing protocol for assessment of endurance athletes. When such a test is performed with gradual, but rapid incrementation, it is particularly useful because in addition to the V̇O2max, gas exchange and ventilatory data collected during the test can be used to distinguish the region bounded by GET and RCP where acidosis is present, but arterial partial pressure of CO2 (PaCO...

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Disclosures

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The authors have no disclosures to report.

Acknowledgements

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This work was supported by CIPER-Foundation for Science and Technology (FCT), Portugal (UID/DTP/00447/2019) and financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001", and to the São Paulo Research Foundation - FAPESP (PROCESS 2016/04544-3 and 2016/17735-1). Authors would like to thank João Guilherme S. V. de Oliveira to the assistance in data sampling. Mário A. C. Espada acknowledge the financial support from IPDJ – Portuguese Institute of Sports and Youth.

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Materials

List of materials used in this article
NameCompanyCatalog NumberComments
3-L syringeHans RudolphCalibration device
AquatrainerCOSMEDSnorkel system/gas-exchange measurement
K4b2COSMEDPortable CPET unit/gas-exchange measurement
N200PROCefiseSoftware program for analysis of force signal
Pacer 2 SwimKulzer TECSwimming velocity management/underwater LED line
Tether-systemOwn designPulley-Rope system/loading management
Tether attachmentCEFISEBracket for attachment to swimmer

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Tags

Tethered Swimming ProtocolCardiorespiratory AssessmentIncremental Exercise TestGas Exchange ThresholdRespiratory Compensation PointLoad Cell MeasurementOxygen Uptake AnalysisExercise Economy EvaluationSwimmer Performance TestingMetabolic Breakpoint Identification

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