1. Introduction

Rowing ergometer is a commonly used tool for land training and simulating on-water to evaluate the performance of rowers [1]. It was reported that the results of the rowing ergometer test were highly correlated with performance in a 2000 m competition [2]. To analyze pacing strategies and metabolic responses, the 2000 m trial is often divided into four 500 m stages [3, 4]. Previous literature on 2000 m rowing ergometer tests mainly focused on power output, maximal oxygen uptake, heart rate, blood lactate, and body morphology [5, 6, 7], while the performance of local muscles during the test has not be thoroughly examined.

Electromyography (EMG) technology has frequently been used to obtain vast information about electrical muscle activities [8]. It is a useful tool to study muscle contraction properties, muscle fatigue, muscle fiber types and muscle-force sequences during cyclic locomotive exercises such as running, cycling and rowing [9]. EMG has the advantages of non-invasiveness and real-time monitoring, which is suitable for simulating actual competition scenarios and analyzing specific muscles [10].

Additionally, EMG technology is useful for analyzing rowing techniques, reducing the risk of injury and designing training programs [11, 12]. Daireaux et al. [13] used EMG to investigate rowing performance and discovered that experienced athletes produced greater integrated EMG (iEMG) than novice athletes, while the novice demonstrated higher variability in EMG activity during the recovery phase. Nowicky [14] employed EMG to investigate the differences in the lower limb and trunk muscle strength across various types of rowing ergometers and demonstrated that EMG is an effective tool to further reveal underlying issues.

Although EMG has been commonly used to study muscle activity during rowing, there is no study on the EMG changes at different distance points in a simulated racing state. It was previously shown that the performance of well-trained rowers during a 2000 m rowing ergometer test was reliable [3, 15]. Gee et al. [16] assessed the reliability of EMG measurements in seven muscles during three repeated 2000 m rowing ergometer sessions and found that although the EMG values could be generally considered “acceptable”, EMG did not appear to be sensitive enough to detect potential changes between sessions. The results calculated by mean rectified EMG from each 500 m segment could eliminate the changes during the 2000 m trial process. Thus, we hypothesized that EMG could change in EMG may still occur between different distance points and that different EMG indexes could be more sensitive to these changes.

In regard to limitations in existing literature, we designed this present study to investigate seven EMG index changes of three muscles divided into four segments during a 2000 m all-out rowing ergometer test. We hypothesized that the EMG indexes would change according to different phases of the 2000 m test and different muscles, while not all EMG indexes would be sensitive to these changes.

2. Materials and methods

3. Results

The results showed that the mean velocity and power were greater during the first and last phases (0–500 m and 1500–2000 m) than the middle two phases (500–1000 m and 1000–1500 m) (p < 0.01). The iEMG of the VAM muscles was significantly higher at the start and at the 2000 m compared to the other distance points (p < 0.05). The pRMS of the ERS muscles was significantly higher at the start and 2000 m compared to consecutive points (p < 0.05). The frequency domain indexes MNF and MDF of the three muscles were significantly reduced at 1500 m compared to 1000 m (p < 0.05). However, no significant changes were observed in EMG time domain indexes of LD muscles for any distance points (p > 0.05).

4. Discussion

In this study, we examined the performance of professional rowers in a 2000 m all-out ergometer test. The main finding of this study was that the mean velocity and power were greater during the 0–500 m and 1500–2000 m phases than the 500–1000 m and 1000–1500 m phases (p < 0.01). Analysis of the 2000 m ergometer test of different phases revealed that subjects completed the test using a fast start strategy, whereby the speed was stable during the cruise phase and increased during the sprint phase. The results were in line with a previous research on rowing strategy reporting that most athletes used a sprint start strategy during the first 500 m in a competition [20] and that the maximum speed in the start and sprint phases played a key role in the final result. According to a previous study, observing the position of opponents behind was beneficial in controlling the speed of the boat and avoiding waves from other boats [4].

The iEMG of VAM muscles was significantly higher at the start and 2000 m compared to consecutive points (p < 0.05) and the pRMS of ERS muscles was significantly higher at the start and 2000 m compared to consecutive points (p < 0.05), while there were no significant changes in EMG time domain indexes of LD muscles at any distance points (p > 0.05). The MNF and MDF of the three muscles’ EMG frequency domain indexes were significantly reduced at the 1500 m phase compared to the 1000 m phase (p < 0.05). Our study is the first to analyze the changes in EMG activity using multiple indicators from different distance points during a 2000 m rowing ergometer test. Gee et al. [16] investigated the reliability of EMS assessed in seven muscles during three repeated 2000 m rowing ergometer tests and reported that the reliability of EMG values over repeated 2000 m was generally “acceptable” although EMG seemed not sensitive enough to detect potential changes concerning changes in pacing strategy. We hypothesized that the lack of sensitivity of EMG could be related to the results calculated by mean 500 m raw EMG signals. In this present study, we selected EMG data from three strokes at each distance point, whereby significant changes were observed. However, not all the indicators were consistent. In previous studies, the normalization of EMG signals has been highlighted [21, 22, 23], and there is no consensus on the optimal normalization process. It was previously described that when EMG is used in rowing training, it might be unreliable to use MVC as the EMG normalization results because most rowers’ EMG peaks appear during rowing [14]. MNF and MDF are considered the “gold standard” for evaluating muscle fatigue [24, 25], especially during maximal-intensity exercise [26]. In this experiment, it was speculated that 1500 m might be a critical distance point for fatigue during 2000 m rowing. Our results showed that the frequency domain indicators of the three muscles changed significantly simultaneously, which was not only related to a decline in endurance but might also be related to central fatigue. Airaksinen et al. [27] found that changes in EMG activities were not related to peripheral fatigue and were mainly affected by changes in motor center activity. Lepers et al. [28] found that during prolonged exercise, the decrease in muscle output power was related to the decrease in nerve impulse firing. Based on these data, we suggest that focus should not only be placed on peripheral fatigue caused by energy metabolism but also on central fatigue due to decreased neuromuscular control during the monitoring of endurance training programs to improve the sports performance of athletes from the perspective of central fatigue.

VAM muscles play a major role in the initial phase of knee extension [29]. Previously, Secher et al. [30] found knee and hip extension important for rowing power generation. Yoshiga et al. [31] and Shimoda et al. [32] reported that knee extension strength was related to ergometer rowing results and that VAM muscles are critical for rowing acceleration. According to the results presented in Table 2, iEMG, MNF and MDF of VAM muscles were significantly higher during the start phase than during the 500 m phase, it means VAM recruited more motor units to power the ergometer’s accelerate from rest to motion. Guével [33] proved that VAM muscles played a major role in improving the power of the ergometer through changes in the MVC level of VAM muscles during rowing, which was concordant with our present study as similar conclusions were obtained through different EMG indicators.

According to the results presented in Table 3, the pRMS of ERS muscles was significantly higher in the start phase and sprint phase than in the cruise phase. pRMS represents the peak value of EMG amplitude, which can reflect the maximum electrical activity of the exercising muscles. During the start phase and the sprint phase, the ergometer speed increased, and the maximum electrical activity of ERS muscles increased significantly. During rowing, ERS muscles stabilize and support the spine in the early stage of leg press and to contract and exert force in the later stage of body swing. The spine is known to be the most injured part of rowers [34]. Koopmann et al. [35] found that low back pain might be related to spinal stability and recommended that the degree of spinal curvature should be controlled during training by improving muscle strength around the spine. Therefore, paying attention to the exercise state and fatigue levels of ERS muscles can reflect on the core strength level of athletes, prevent the occurrence of sports injuries, and identify the presence of wrongly implemented techniques by athletes.

The correct rowing technique is defined by a long drive phase and relaxed and controlled recovery. The drive phase is initiated with a push from the legs. The energy generated by leg presses during rowing is transferred through the arm to the handle, during which LD muscles play the role of connection and suspension [36]. Rodriguez et al. [37] found that sustained production of propulsion was associated with trunk extension and upper extremity activity during rowing. According to the results presented in Table 4, there was no significant change in the EMG time domain index of LD muscles throughout the whole rowing task. It can be surmised that LD muscles generated a consistent and stable force during the varying ergometer velocities, serving as a strong connection between them.

5. Conclusions

In conclusion, this study sheds light on the pacing pattern of the 2000 m all-out rowing ergometer test, which includes a “fast start-speed maintain-final sprint”. The higher EMG activation rates of VAM and ERS at the start and final phases indicate a higher contribution to the increase in power output. The decline in MNF and MDF of all three muscles at the 1500 m point reflects increased muscle fatigue. The study also highlights the importance of using multiple EMG indexes for comprehensive analysis, as the sensitivity varies with the length of the test. This study’s contribution lies in its analysis of multiple EMG indexes of the three main force-generating muscles of professional rowers during rowing-specific technology, providing insights into the dynamic changes of EMG indexes in different stages of the commonly used 2000 m rowing ergometer test.

Availability of Data and Materials

The data presented in this study are available on reasonable request from the corresponding author.

Author contributions

XHZ and JLL—designed the research study. JLL and FR—performed the research; wrote the manuscript. XHZ—provided help and advice on the rowing ergometer test design. JLL—analyzed the data. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript.

Ethics approval and consent to participate

This study was performed with the approval of the Institutional Review Board of Capital University of Physical Education and Sports (2020A63). All the study participants signed an informed consent form.

Acknowledgment

Not applicable.

Funding

This research received no external funding.

Conflict of interest

The authors declare no conflict of interest.