Introduction

Competitive rowers perform intensive rowing ergometer tests to measure the effects of their highly demanding training regime on performance. Testing and monitoring performance (i.e., training status) is important to optimize training prescription. As the absolute training intensity is similar for all rowers within the same team, it is challenging to individualize training prescription. Therefore, some rowers may undertrain and some may overtrain. To improve rowing performance, training intensity and recovery should be well-balanced as imbalance can result in stagnation or a decreased performance caused by nonfunctional overreaching or even overtraining syndrome (24,25). In an attempt to optimize performance, it is important to monitor athletes continuously by means of a noninvasive, practical, and reliable test that can predict performance accurately.

Previously, several maximal ergometer tests have been used to assess rowing performance. The most commonly used test to assess rowing performance is the 2,000-m time trial (21), which is usually performed on an indoor rowing ergometer, such as the Concept2 ergometer. Although the 2,000-m time trial is known to be reliable and widely used to assess training status of rowers (32), anecdotal evidence from rowers confirms that this test has an extremely high level of exertion. Therefore, this test is not suitable to be performed on a regular basis. Other tests that are valid to measure rowing performance include peak power (4) and power at maximal oxygen uptake (V[Combining Dot Above]O 2 max) (26) during incremental maximal performance tests and peak power output during a Wingate test (28). However, all of these performance tests require maximal exertion of the rowers, which tends to interfere with normal training and racing habits (15).

In a recent review, it is concluded that lactate power at 4 mmol·L−1 during a maximal incremental exercise test has adequate validity for assessing moderate differences in training status of a rower (32). Although lactate power is a valid method, the reliability of determining blood lactate concentration by ear or finger sampling is associated with a high measurement error (33). Moreover, it is an impractical measure because of the invasiveness of blood sampling and because it is measured during a maximal performance test. Therefore, lactate power cannot be considered optimal for frequent measurements of training status.

In this study, the design of a promising submaximal cycle test, the Lamberts and Lambert (16,20) submaximal cycling test (LSCT), is translated to a submaximal rowing test (SmRT). Within the LSCT, multiple variables are collected such as mean power output, cadence, and ratings of perceived exertion (RPE), whereas 60-second heart rate recovery (HRR 60s ) is also captured after the final stage at the end of the test. Lamberts et al. showed that mean power output during the third stage of the LSCT (cycling at 90% of HR max ) is the strongest predictor of peak power output (r = 0.94), V[Combining Dot Above]O 2 max (r = 0.91), and 40-km time-trial performance (r = −0.92) (20). Even stronger relationships between the LSCT and peak power output (r = 0.98), V[Combining Dot Above]O 2 max (r = 0.96), and 40-km time-trial performance (r = −0.98) are found when multivariate analyses are used (16). In addition, the LSCT changes with a change in training status and is able to reflect a state of nonfunctional overreaching (18,19). Based on these positive results and as the data within a rowing ergometer test can be collected similarly as within a cycle ergometer test, the design of the LSCT was translated to the rowing ergometer.

The aim of this study was to assess the predictive value of the SmRT on 2,000-m ergometer rowing time in competitive rowers. In addition, the reliability of the SmRT was determined.

Methods

Experimental Approach to the Problem

A group of rowers performed an incremental rowing test during the first laboratory visit. The rowers were familiarized to the SmRT on at least 3 occasions. All rowers performed an SmRT followed by a 2,000-m rowing time trial with 1 to 3 days in between to determine predictive value of the SmRT. A subgroup of rowers performed the SmRT 4 times with 2 days in between to determine reliability of the SmRT.

Subjects

Twenty-four competitive male rowers (19–24 years) were recruited to participate in the study. All rowers had experience in competitive rowing of 4 ± 3 years (ranging from 2 to 11 years). The rowers trained 10–12 hours per week on average, including 2–3 hours of strength training, divided over 2 sessions. In addition to outdoor training, the rowers were accustomed to training on an indoor rowing ergometer (Concept2). The coach agreed to plan the tests during a low-intense training period. Nine rowers were classified as “light-weight class rowers” and 15 as “open class rowers.” A rower classified as light weight may not weigh more than 72.5 kg on the racing day according to the rules of racing by FISA (8). Within open class rowing, there are no weight restrictions. Before participation, a sport physician medically cleared all rowers according to the Lausanne recommendations (2) and all rowers signed an informed consent and ethics. This study was approved by the local ethics and research committee. The study has been conducted in line with the requirements of the Declaration of Helsinki.

Procedures

The incremental rowing test started with a 3-minute warm-up at a power output of 150 W for light-weight class rowers and 175 W for open class rowers. Subsequently, rowers were asked to increase their power output by 25 W every minute. When the rowers were not able to elicit the predetermined power output, they were asked to perform a 30-second all-out sprint (22). The rowers were verbally encouraged during the test, and feedback about power, time, distance, and stroke rate was displayed on the screen of the rowing ergometer during the whole test. Heart rate during the test was recorded continuously using a Garmin sport watch (Garmin ForeRunner 310XT, Hampshire, United Kingdom) and calculated as 1 second averages. HR max was determined as the highest heart rate recorded during the test. In addition, gas exchange was measured using an automated breath-by-breath analyzer (Cortex Metalyzer 3b, Leipzig, Germany). V[Combining Dot Above]O 2 max was defined as the highest 30-second V[Combining Dot Above]O 2 interval observed during the test.

All tests were performed on a Concept2 rowing ergometer (Model D; Morrisville, NC, USA) equipped with a PM4 computer (Concept2) in similar environmental conditions (14.6 ± 3.5° C and 49 ± 8% relative humidity). Rowers refrained from strenuous exercise and consuming alcohol 24 hours before each test and the rowers did not consume caffeine 4 hours before all tests. During the tests, the drag factor of the ergometer was set at 120 × 106 kg·m−1 for light-weight class rowers and 130 × 106 kg·m−1 for open class rowers. These drag factors were in line with drag factors of the rower's regular ergometer training.

Submaximal Rowing Test

The SmRT protocol was based on the LSCT in which cyclists were asked to cycle at 60, 80, and 90% of individual HR max (20). After pilot tests and based on feedback from the rowers, the initial stage of the SmRT was changed from 60 to 70% of HR max because it was too difficult for the rowers to keep their heart rate stable at 60%. The total duration of the SmRT was 17 minutes, during which the rowers were asked to row 6 minutes at 70% and 6 minutes at 80% of HR max , followed by 3 minutes at 90% of HR max and 2 minutes of rest (Figure 1). Rowers were asked to row at a heart rate within 2 beats of the predetermined target heart rate. Within the rest stage, rowers sat up straight and did not speak for 2 minutes to capture HRR 60s accurately. Ratings of perceived exertion (3) were asked 30 seconds before the end of each stage (5:30, 11:30, and 14:30 minutes:seconds, respectively). Rowers received continuous feedback on heart rate and elapsed time on the screen of the ergometer. However, they did not receive any feedback on power output during the whole test.

Figure 1: A rower's heart rate and power profile response to an SmRT . *Five-minute period over which the mean SmRT performance parameters were analyzed. #Two-minute period over which the mean SmRT performance parameters were analyzed. SmRT = submaximal rowing test; HRR = heart rate recovery.

Mean power, stroke rate, and the difference between the predetermined target heart rate and actual heart rate during all 3 stages of the SmRT were calculated and used for further analysis. Because of the slow half-life of heart rate (1,20), the first minute of every stage was excluded from analyses. Hence, performance parameters over the last 5 minutes of stage 1 and 2 (1:00–6:00 and 7:00–12:00 minutes) and the last 2 minutes of stage 3 (13:00–15:00 minutes) were analyzed (Figure 1) (20). Although 2 minutes of HRR 60S data were captured within the SmRT, HRR 60s was only calculated over the initial 60 seconds of the recovery period because HRR 60s measurements have been shown to be more reliable and associated with lower day-to-day variations than HRR 120s measurements (17). Heart rate recovery (HRR) was calculated as the difference between mean heart rate in the last 15 seconds of stage 3 (14:45–15:00 minutes:seconds) and mean heart rate in the last 15 seconds during the first minute of rest (15:45–16:00 minutes:seconds) (7,20).

2,000-m Rowing Time Trial

Results of the 2,000-m rowing time trial were also used for selection purposes of the Dutch Rowing Association (KNRB). Therefore, the rowers were highly motivated to perform as well as possible. During the 2,000-m time trial, the rowers were verbally encouraged by their coach. A self-selected warm-up was performed before the start of the 2,000-m time trial. Rowers received continuous feedback about power, time, distance, and stroke rate on the screen of the ergometer. 2,000-m rowing time (i.e., performance) was determined by the time needed (minutes:seconds) to complete the time trial.

Statistical Analyses

All outcome variables were shown to be normally distributed by a Shapiro-Wilk's test (p ≤ 0.05) (27,30) and visual inspection of histograms, normal Q-Q plots, and box plots.

Descriptive statistics for all variables were represented as mean ± SD. Differences in the relationships between light-weight class rowers and open class rowers were analyzed by slope and y-axis intercept analysis (GraphPad Prism version 6.03 for Windows; GraphPad Software, San Diego, CA, USA). No significant differences in slopes and y-axis intercepts between light-weight class and open class rowers were found. Therefore, the analyses were performed for the group as a whole.

The predictive value of the SmRT was assessed by establishing the relationships between mean power output during the 3 stages of the SmRT, HRR 60s , and 2,000-m rowing time (n = 22). The strength of these relationships was analyzed with Pearson's correlations, typical error of the estimate (TEE), and TEE expressed as coefficient of variance (CV TEE% ). In addition, 95% confidence intervals (95% CI) were calculated.

Reliability was determined over the subset of rowers (n = 12) who performed the SmRT on 4 occasions interspaced with 2 days. The repeatability of the SmRT (power output, RPE, and stroke rate during the 3 stages and HRR 60s ) was assessed by calculating intraclass correlation coefficients (ICC), typical errors of measurements (TEM), and the TEM expressed as a coefficient of variation (CV TEM% ).

The thresholds for interpretation of the magnitude of ICC were very small (<0.1), low (0.1–0.3), moderate (0.3–0.5), high (0.5–0.7), very high (0.7–0.9), and nearly perfect (>0.9) (12). CV TEM% and CV TEE% were doubled to interpret the magnitude of differences between tests as being very small (<0.3%), small (0.3–0.9%), moderate (0.9–1.6%), large (1.6–2.5%), very large (2.5–4.0%), and extremely large (>4.0%) (12,31). All measures of validity and reliability were calculated using spreadsheets downloaded from http://sportsci.org (11).

Results

Of the 24 rowers who participated, all test results of 1 rower were excluded for analysis because he was diagnosed with pneumonia a month before the tests, and we could not determine with certainty that he was fully recovered. Of the 23 rowers who were included for analysis (Table 1, for descriptive characteristics), 22 rowers were included in the predictive value study. This was because 1 rower did not complete the 2,000-m rowing time trial because he was not feeling well that day.

A subset of 12 rowers was included in the reliability study, of which 1 rower could not complete the second SmRT because of transportation problems.

Predictive Value of the Submaximal Rowing Test on 2,000-m Rowing Times

Relationships between mean power output during all measures within the SmRT and 2,000-m rowing time are shown in Figures 2A–D (n = 22). The association between parameters of the SmRT and 2,000-m performance increased with stages (intensity) during the SmRT, and CV TEE% decreased with stages. The highest correlation and lowest CV TEE% were shown by power output during stage 3 (r = −0.93; 95% CI: −0.97 to −0.84 and 1.3%; 95% CI: 1.0–1.9%). This indicates that rowers who had a higher mean power output associated with 90% HR max were able to complete the 2,000-m rowing time trial faster. No significant relationship was found between HRR measured within the SmRT and 2,000-m rowing time.

Figure 2: Relationships between mean power output during stage 1 (A), stage 2 (B), stage 3 (C), and heart rate recovery (HRR) (D) of the SmRT and 2,000-m rowing performance (time). Open class rowers (OC) are represented by closed circles (●). Light-weight class rowers (LW) are represented by the open circles (○). Intraclass correlation for OC is −0.94 and for LW is −0.79. Dotted lines represent 95% confidence intervals. SmRT = submaximal rowing test; HRR = heart rate recovery; TEE = typical error of the estimate.

Table 2 shows mean physiological and subjective responses to the SmRT before the 2,000-m rowing test. The mean 2,000-m rowing time was 6:29 ± 0:14 minutes:seconds and ranged from 6:11 to 6:52 minutes:seconds. The average power output over the 2,000-m time trials was 382 ± 39 W, ranging from 331 to 440 W. Power during stages 1, 2, and 3 during the SmRT was 43 ± 6%, 54 ± 4%, and 75 ± 5% of average 2,000-m time-trial power.

Table 2: Mean physiological and subjective responses to the last SmRT before the 2,000-m rowing test.*

Reliability of Submaximal Rowing Test Parameters

Submaximal rowing test parameters of the 4 measurement occasions are shown in Table 3. All rowers adhered well to the predetermined HR during all 3 steps of the test. This was shown by the difference of only 1 b·min−1 on average between predetermined HR and actual HR during the SmRT (Table 3). In addition to the SmRT parameters, ICC, TEM, and CV TEM% of power, stroke rate, RPE, and HRR are shown in Table 2. Power in all 3 stages of the SmRT showed “nearly perfect” ICCs (0.91, 0.92, and 0.90, respectively). CV TEM% was doubled for interpretation of the magnitude, as proposed by Smith and Hopkins (31), which classified CV TEM% of power in stages 1, 2, and 3 (18.4, 11.2, and 15.4%, respectively) as “extremely large.” CV TEM% of power in stage 3 between the first and second test is 6.6%, between the second and third test 5.4%, and between the third and fourth test 6.0%.

Table 3: Mean physiological and subjective responses to the SmRT .*

The ICC of stroke rate increased with intensity of the stages. During stage 3, the ICC of stroke rate was classified as “very high.” However, doubled CV TEM% of stroke rate during all stages was “extremely large” (12.6, 10.4, and 12.8%, respectively).

Intraclass correlation coefficient of RPE during all 3 stages of the SmRT was classified as “high,” whereas doubled CV TEM% of RPE during all stages was “extremely high” (20.8, 18.2, and 15.2%, respectively). Intraclass correlation coefficient of HRR 60s was “nearly perfect,” but CV TEM% was “extremely high” (16.2%).

Discussion

The aim of this study was to determine if the LSCT (20), a submaximal cycle test that is able to predict and monitor cycling performance, could be translated to an SmRT. An important finding of the study was that the design of the LSCT could be well translated to the SmRT. All rowers were able to row close to their predetermined submaximal heart rates (±1 beat) during the 3 different stages of the SmRT. Although the intensity of the first stage of the SmRT was slightly higher (70% of HR max ) compared with the LSCT (60% of HR max ) (20), the mean rating of perceived exertion during the 3 stages were 9, 13, and 16, respectively. These ratings are similar to the 3 stages within the LSCT (8, 12, and 16, respectively) (20).

The main finding of the study was that the SmRT was able to accurately predict 2,000-m rowing time when performed on an indoor rowing ergometer. Significant inverse relationships were found between 2,000-m rowing time mean power during all 3 stages of the SmRT (r = −0.73, −0.85, and −0.93, respectively). The strongest relationship between 2,000-m rowing time and mean power during the third stage of the SmRT (r = −0.93) was associated with a TEE of 5 seconds or 1.3% (Figure 2). These findings are in line with the finding by Lamberts et al. (20) who reported relationships between a 40-km time trial (40-km TT) and the second and third stage of the LSCT of r = −0.84 and r = −0.92, respectively. However, the associated TEEs for 40-km TT time from stage 2 (3.1%) and stage 3 (2.2%) are slightly higher. This can likely be explained by the distance and duration of the performance tests as more variation will be associated with longer tests. The increase in predictive value with exercise intensity within the SmRT is in line with the findings of Lamberts et al. (20).

Cosgrove et al. (6) showed that correlations between submaximal rowing economy during submaximal testing and 2,000-m time trial increase with exercise intensity. The relatively strong correlation between mean power during the SmRT and 2,000-m rowing time can likely be explained by the design of the SmRT. As the rowers row at a similar relative intensity (different absolute intensities) instead of rowing at fixed absolute intensities (different relative intensities), better relationships with rowing performance parameters can be expected. In addition, as the exercise intensity of the third stage of the SmRT was close to the exercise intensity of the 2,000-m rowing time trial, this might explain that the strongest relationship was found between these 2 variables.

In contrast to Lamberts et al. (20), who found a weak relationship between HRR and 40-km TT performance (r = −0.55), we did not find a relationship between HRR and 2,000-m rowing time. The absence of this relationship and therefore poor predictive power of HRR can likely be explained by the duration of the rowing test and the relatively homogenous group of competitive rowers that was tested. Although HRR has shown to be a valuable tool to monitor changes in training status in untrained to elite athletes (7) and is able to predict fitness and health status in the general population (5), the relationship between HRR seems and training status seems become weaker within homogenous groups (7,9,20). This can be explained by genetic polymorphisms in the acetylcholine receptor M2 (CHRM2), which also influences the rate of HRR (9).

Another factor that might have contributed to the absence of a relationship between HRR and 2,000-m rowing time is that in contrast to Lamberts et al. (20), a much shorter time-trial test was used with relatively small time differences between the rowers. Although HRR did not seem to be a good predictor of 2,000-m rowing time, it still potentially can be an important monitoring tool to detect changes in training status of rowers. As HRR within the SmRT varied by about 4 b·min−1 or 8.1%, changes in HRR of ≥5 beats should be interpreted as meaningful. This variation in HRR was slightly higher than within the LSCT (2 beats). An explanation may be that our rowers first detached their feet and only then were able to sit up straight. However, considering this, the variation in HRR (ICC, 0.93) was arguably very low. This can be explained because factors, which influence HRR, such as the mode of exercise (10), the workload intensity (13,23), and duration (14,29) were all standardized and well controlled within the SmRT.

Another finding of the study was that the SmRT is a relatively reliable test. Good ICCs were found for mean power output, which ranged from 0.90 to 0.92. Slightly weaker ICCs were found for stroke rate (ICC range, 0.48–0.73) and RPE (ICC range, 056–0.57) during the 3 stages. These reliability scores were similar to those found within the LSCT (ICC range, 0.91–0.99) (20). Although the CV TEM% of power during the third stage of the SmRT was higher than the 1% yardstick for variation in competitive on-water rowing performance (32), the magnitude of the ICC for the third stage was classified as “nearly perfect” (12). However, the data of each test should always be interpreted within its own capacities.

A limitation of this study was that only well-trained competitive rowers were tested. Therefore, we cannot conclude with certainty that the SmRT will also be able to accurately predict rowing times in less-trained subjects. In addition, this study does not show if the SmRT is able to reflect changes in training status and can be used as a practical monitoring tool. The SmRTs were completed under well-controlled circumstances, and the 2,000-m rowing time trial was completed in real competition conditions. However, this real competition was indoor and not in an on-water rowing competition. Therefore, 2,000-m on-water rowing times are likely to vary more, and measures of predictive value will probably be less precise.

In conclusion, this study showed that the design of the LSCT could be well translated to an SmRT. The SmRT is a relatively reliable test (ICC, 0.90–0.92), which is able to accurately predict 2,000-m rowing time in competitive rowers (within 5 seconds).

Practical Applications

The SmRT is a relatively reliable rowing test, which is able to accurately predict 2,000-m rowing time. As it is a relatively short and submaximal test, it potentially can be used as standardized warm-up on a weekly basis. The SmRT shows potential to be a sport-specific and practical tool to predict and monitor changes in training status of rowers. Future research needs to confirm if the SmRT, in addition to accurately predicting rowing performance, is also able to reflect changes in rowing performance.

Acknowledgments

The authors would like to thank all the rowers and their coaches who took part in this study. In addition, we would also like to thank Steven Edelenbos, Rutger Hoekerd, and Jorrit Kortink for their assistance in the test sessions and Scott Hamilton (Concept 2) for his technical support. This study is part of a larger monitoring study, also known as the “Groningen Monitoring Athletic Performance Study (MAPS),” which was funded by Stichting Innovatie Alliantie RAAK-PRO (PRO-2-018). The authors report no conflicts of interest. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.