Six-minute rowing test: a valid and reliable method for assessing power output in amateur male rowers

Participants

Twelve male amateur rowers from the Naval Academy “Arturo Prat” participated voluntarily in this study. The main inclusion criterion was the VO_2max assessed in the initial test (IT). This initial evaluation made verifying the fitness level of the male amateur rowers possible. In this regard, all participants in the study presented a VO_2max ≤ 65 mLO₂·kg⁻¹·min⁻¹. Also, it was found that the rowers trained less than 6 h per week. All these antecedents allowed defining the participants as amateur rowers. In contrast, those who could not perform the IT and the 6-min_RT correctly were eliminated during the study. Statistical software (G*Power, v3.1.9.7; Heinrich-Heine-Universität, Düsseldorf, Germany) was used to calculate the sample (Faul, 2020). The combination of tests used in the statistical software to calculate the sample size was as follows: (a) t-test, (b) Linear bivariate regression: One group, size of the slope, and (c) A priori: Compute required size – given α, power, and effect size. Tests considered two tails, slope H1 = 0.67, α-error < 0.05 and a desired power (1-β error) = 0.8, slope H0 = 0.00, standard deviation (SD) σ_x = 0, and SD σ_y = 0, the total sample size was 12 participants. All participants were informed of the study’s objective and the possible risks of the experiment. Before applying the protocols, all amateur rowers signed the informed consent form in person. The study and the informed consent were approved by the Scientific Ethical Committee of the Universidad Mayor, Santiago, Chile (registration number: 197_2020) and developed under the ethical standards for exercise and sports sciences (Harriss, Macsween & Atkinson, 2019).

Design

A repeated measures design was used to compare test-retest inter-day reliability for different PO, speed, VO₂, and Heart Rate (HR) variables collected during the 6-min_RT exercises. All study participants attended the laboratory for 3 days at 72-h intervals. Also, participants did not exercise between assessment days. This time between races ensured the physical recovery of the rowers.

During the first visit, basic anthropometric assessments and the IT were performed. The 6-min_RT test and retest were performed on the second and third, respectively. All the tests were performed with a rowing machine (Concept2 Model D, monitor PM5, Morrisville, VT, USA) using a drag factor of 111–114 (Fig. 1A).

Anthropometric measurements

For the characterization of the sample, weight, height, body mass index (BMI), and body fat percentage were evaluated. These evaluations were performed on the day, 30 min after snack intake. This ensured that the participants were evaluated in a euhydrated condition. The body fat percentage was assessed using an impedance meter (Tanita Inner Scan, BC-554® digital scale, Tokyo, Japan).

Snack

The snack is intended to prevent athletes from starting evaluations with a low blood glucose level (Ojeda et al., 2019). It was a carbohydrate load before the IT and 6-min_RT test and retest. All participants were available 2 h before the tests in a fasting condition. The snack consisted of 2 g of rapidly absorbed carbohydrates per kg of body weight (Fig. 1B).

Standardized warm-up

The warm-up consisted of 10 min on a bicycle (Airbike Xebex® resistance, ABMG-3, USA). The warm-up intensity was between 60–70% of the theoretical maximum HR, calculated through the formula: 208-(0.7 * age) (Tanaka, Monahan & Seals, 2001). Five minutes of upper and lower extremity ballistic movements were then included. After, athletes rowed for 5 min between 60–70% of the theoretical maximum HR (Tanaka, Monahan & Seals, 2001), and finally, there was a 10-min rest (this time was used to install the mask and HR sensors) (Fig. 1B).

Oxygen uptake

VO₂ and other ventilatory parameters were evaluated for all tests with an automatic gas analyzer system (model Quark CPET; Cosmed, Rome, Italy). The analyzer was calibrated strictly according to the manufacturer’s recommendations before testing. The data were processed through a laptop computer that calculated the results using software developed by the manufacturer. All ventilatory parameters were averaged at 15 s intervals. Absolute and relative VO_2max (VO_2max abs and VO_2max rel, respectively) and other ventilatory parameters at VO_2max (pulmonary ventilation at VO_2max (VE at VO_2max) and respiratory exchange ratio (RER) at VO_2max (RER at VO_2max)) were considered when VO₂ kinetics generated a variation of less than 150 mLO₂·min⁻¹ between 15 s intervals (Howley, Bassett & Welch, 1995).

Incremental test

This test aims to progressively reach the highest oxygen consumption with an equivalent PO or MAP. During the test, the participants received verbal encouragement from the research team (Neto et al., 2015). VO_2max, RER, VE, and carbon dioxide production/oxygen consumption (VCO₂/VO₂) was performed with an IT in a rower-ergometer. Each step lasted 1 min in this IT, starting with 100 watts (W) and increasing 50 W in each step until exhaustion or the impossibility of maintaining the requested power (Mekhdieva, Zakharova & Timokhina, 2019). The IT was performed on a rowing machine (Concept2 Model D, monitor PM5; Concept2, Morrisville, VT, USA) using a drag factor of 111–114. The latter intensity was also considered as the MAP of each subject. Power data were recorded in the ErgData V1.4.4® app, USA, and downloaded from an account created at https://log.concept2.com/.

6-minute rowing test

This test aims to row for 6 min on a rowing machine and achieve the greatest possible distance. The final distance of the 6-min_RT is recorded in meters (m). During the test, the participants received verbal encouragement from the research team (Neto et al., 2015). In this way, it was sought that the participants would achieve the greatest possible distance during the study in both the test and retest. The variables evaluated in this test are described in the following sections. This test aimed to generate a new tool for assessing and programming training loads according to fitness and technical development in amateur rowers.

Power output

The evaluation of the PO for all the tests was performed with a rowing machine (Concept2 Model D, monitor PM5, Morrisville, VT, USA) using a drag factor of 111–114. The PO was recorded stroke to stroke; however, for analysis and synchronization with the VO₂ y HR, the PO was averaged at 15-s intervals. Subsequently, the P_mean for both IT and 6-min_RT in test and retest was determined. Also, the PO at VO_2max was observed. The power data were recorded in the application developed by the manufacturer (ErgData, V1.4.4® app; Concept2 Morrisville, VT, USA) and downloaded from an account created at https://log.concept2.com/.

Heart rate

In the IT and 6-min_RT in test and retest, HR was evaluated with a heart rate monitor (model H10®; Polar, Kempele, Finland). This device was synchronized via Bluetooth with the rowing machine. HR was recorded by rowing stroke by stroke. However, for analysis and synchronization with VO₂ and PO, HR was averaged at 15 s intervals. Subsequently, the HR mean (HR_mean) was determined. Also, HR at VO_2max was observed. The HR data were recorded in the application developed by the manufacturer (ErgData, V1.4.4® app, Morrisville, VT, USA) and downloaded from an account created at https://log.concept2.com/.

Data analysis

For all the tests, ventilatory, mechanical, and HR parameters were sorted on a spreadsheet designed for the study. Descriptive data are presented as means and standard deviation (SD). The Shapiro-Wilk test confirmed the normal distribution of the data (p > 0.05). The validity of the 6-min_RT was determined by comparing ventilatory, mechanical, and HR parameters between the IT and 6-min_RT. Reliability of the 6-min_RT was assessed through the coefficient of variation (CV), intra-class correlation coefficient (ICC), standard error of the mean (SEM), and corresponding 95% confidence interval between the 6-min_RT test and retest. Acceptable reliability was determined as a CV < 10% and ICC > 0.85 (Cormack et al., 2008). The criteria for interpreting the strength of the r coefficients were as follows: trivial (0.00–0.09), small (0.10–0.29), moderate (0.30–0.49), large (0.50–0.69), very large (0.70–0.89), almost perfect (0.90–0.99) and perfect (1.00) (Hopkins et al., 2009). The t-tests for related samples and the Bland-Altman technique were used to assess concordance between the 6-min_RT test and retest (Hopkins et al., 2009). Reliability assessments were performed using a customized spreadsheet (Hopkins, 2000). All other statistical analyses were performed with Prism version 7.00 for Windows® software. The significance level for all statistical analyses was p < 0.05.

Oxygen uptake

Concerning VO₂ values during the 6-min_RT in amateur rowers, our findings showed that the present study participants showed an “excellent” VO_2max (52.91 ± 3.38 mLO₂·kg⁻¹·min⁻¹) when compared to healthy and physically active individuals (Herdy & Caixeta, 2016). Although these VO₂ values are qualified as “excellent,” they are lower than those observed in elite rowers (Hagerman et al., 1978; Huntsman et al., 2011). Despite this, the evidence of amateur rowers is scarce (Kendall et al., 2011; Huerta Ojeda et al., 2022). In this sense, Huerta Ojeda et al. (2022) showed that amateur rowers reach 55.9 ± 3.4 mlO₂·kg⁻¹·min⁻¹ during the 2,000m_TT. Specifically, the researchers reported that VO_2max was reached 345 s after the start of the 2,000m_TT, after which time VO₂ began to decline (Huerta Ojeda et al., 2022), possibly due to low fitness and technical development of the amateur rowers (Huntsman, Drury & Miller, 2011). Likewise, Kendall et al. (2011) showed that, during the 2,000m_TT, amateur female rowers reached a VO_2max equivalent to 2.88 LO₂·min⁻¹, while they took 485.8 ± 10.3 s to complete the test. The same researchers reported an r = −0.55 between el VO_2max value and time in the 2,000m_TT (Kendall et al., 2011). Likewise, there is evidence that the 2,000m_TT induces a high blood oxidative stress in rowers with high training status (Kyparos et al., 2009), which allows inferring higher blood oxidative stress in amateur rowers. However, this issue needs further exploration.

Concerning VO_2max and rowing performance, there is a big difference between elite and amateur rowers. While elite rowers can complete the 2,000m_TT in less than 360 s (Silva, 2016), reaching VO_2max (Hagerman et al., 1978; Mahler, Andrea & Andresen, 1984), amateur rowers can only cover 1,696.3 ± 46.8 m in the 6-min_RT (360 s). Consequently, the 6-min_RT is a test that allows amateur rowers to reach VO_2max without experiencing a decrease in this parameter at the end of the race. However, this last issue also requires further exploration.

Power output

A significantly lower value was observed when comparing the MAP in the IT and P_mean performed in the 6-min_RT by amateur rowers (p = 0.004). However, this CV was only 8.04% between both tests (91.96% of the MAP generated in the TI). Indeed, this is the most relevant background to affirm that shorter tests in amateur rowers (6-min_RT) allow for measuring P_mean close to the PO at VO_2max (Huerta Ojeda et al., 2022). On the other hand, the PO kinetics observed in the present study is similar to those described by Mahler, Andrea & Andresen (1984). Specifically, higher PO is observed in the first minutes of the test and a gradual decrease until the last minute. However, it should be noted that the PO generated by amateur rowers is lower than that generated by elite rowers in the 6-min_RT. The latter far exceeds the 289.8 ± 20.9 generated by amateur rowers in this study (Mahler, Andrea & Andresen, 1984). These differences between categories are conditioned by amateur rowers’ low fitness and technical development compared to higher-level rowers (Huntsman, Drury & Miller, 2011). In this sense, it has been observed that the PO (P_mean and P_max) presents the advantage of being obtained with a simple ergometer test without biological measurements (Bourdin et al., 2017). In this context, based on the results of the present study, the 6-min_RT is performed with a P_mean close to VO_2max and, therefore, allows establishing the MAP in amateur rowers. In fact, it has been shown that those rowers who can maintain a MAP for a longer time have a higher performance; the MAP was the most important predictor of performance in rowers (Turnes et al., 2020). Consequently, the measurement and PO use have an additional advantage since most existing rowing meters provide this information in the field (Bourdin et al., 2017). Only tests according to each rower’s physical and technical level should be applied (in the case of amateur rowers, the 6-min_RT).

Reliability of 6-min_RT

Finally, the results show that the 6-min_RT has a high degree of reliability for distance (CV = 0.50%; ICC = 0.97), P_mean (CV = 1.85%; ICC = 0.96) and HR_mean (CV = 0.85%; ICC = 1.15). In this regard, other reliable tests evaluate physical parameters in rowers (Ingham et al., 2002; Otter et al., 2015; Cheng et al., 2012). However, none of the consulted studies allows the evaluation of P_mean in amateur male rowers.

Limitations

The lack of descriptive information on ventilatory kinetics, PO (P_mean and P_max), and HR in amateur rowers made it challenging to compare our findings. Also, the non-inclusion of women in the study limits the conclusions only to study participants and male amateur rowers. We also believe that future research with amateur rowers should analyze in-depth the kinetics of VO₂, both the slow and fast components. Finally, future studies should include randomization of participants between tests, thus eliminating any cumulative physiological effects affecting the reliability of the results.