In the current study, we sought to determine if 4 weeks of plyometric training would increase rowing economy, peak power, or performance in experienced youth rowers when combined with on-the-water training. After the 4-week intervention, rowing economy for both groups was significantly improved, but no group differences were found. Peak rowing power was moderately changed as there was a tendency for difference between groups post-training with higher peak power in the plyometric group in response to this relatively short intervention. However, the main finding of this study is that the rowers who performed plyometric training significantly improved their 500-m TT, while this did not change for the endurance group. This study provides the first instance in which plyometric training significantly improved rowing sprint performance.
Plyometric Training and Rowing Economy
In the current study, rowing economy across work rate was significantly improved in both groups (Fig. 1), possibly indicating that plyometric and aerobic training had a similar effect on rowing economy. Previously, running economy has been shown to improve after plyometric training [21, 24, 28], and the reason for this improvement has been suggested to be increased musculotendinous stiffness (MTS) in the legs of runners . A high MTS increases an individual’s ability to absorb, harness, and recoil force during the stretch-shortening cycle, such as in running . An increase in MTS is thus beneficial for a sport such as running, which involves an eccentric contraction when the runner’s foot makes contact with the ground, where after plyometric training, the increased MTS results in more stored energy in the series elastic elements and reduces eccentric muscle demand. However, the beginning of the rowing stroke (known as the catch), is an anticipated motion in which the athlete is actually pulling themselves towards their feet, followed by a rapid press of the legs to apply power . As there is not so much of a reactive movement, or ground reaction force in rowing when compared with running, increased MTS is likely less beneficial in rowing. Although, plyometric training has also been shown to increase muscle activation  and muscle force  and decrease ground reaction times  suggesting plyometrics might alter the work to rest ratio of rowing, through improved drive speed, allowing more time of the stroke cycle to be spent in recovery for a given stroke rate. Such a change, perhaps independent of economy, might correspond to improved boat speed, allowing for greater maintenance of the forward propulsion or “run” of the rowing shell in the water from each stroke. It is worth noting that these hypotheses warrant further investigation to confirm if this is, in fact, the case.
Plyometric Training and Rowing Power
Plyometric training has been suggested to improve power  in adults and in youth . Results from the current study indicate that plyometric training in this athlete cohort (youth rowers), for this length of time (4 weeks), may elicit a moderate increase in rowing power (Fig. 4). This is in agreement with previous research as plyometrics are typically used to improve power [2, 11, 12]. It has been suggested by rowing biomechanics experts that elasticity stored in the tendons of rowers could be beneficial or initiating the drive sequence of the stroke . The fact that the moderate improvement in rowing power did not reach statistical significance may be attributed to a number of potential factors. The training period was relatively short compared to other studies in the field of plyometrics, so with further training, there could have been a greater and/or significant change in rowing power. The sample size was also relatively small, possibly lacking the statistical power necessary to observe an increase in rowing power. Changes in RP also varied within the groups, suggesting that some individuals may have been better at performing the 15-s peak power ergometer test or possess the innate physiological traits or training acumen to achieve high rowing powers. Also, the motor coordination trained using plyometrics (jumping) is vastly different to the patterns used during the maximal peak power test, with a high rowing resistance. Furthermore, muscle coordination could have differed greatly between individuals due to the athletes being at varying stages of athletic maturity. However, it should be noted that with a greater sample size, and/or a longer training period, a significant difference in peak rowing power could be observed.
The peak rowing power test is a valuable test and predictor of rowing performance, as suggested by Ingham et al. . However, the athletes whom Ingham et al. used were all elite rowers (current or former World Championship Finalists), who have a significantly higher athletic maturity and training history  when compared with the athletes in the current study. Therefore, the younger age and relatively lower training history (i.e., coordination and technical mastery) of the athletes utilized in the current study could explain the moderate improvement in rowing power. Specifically, these athletes may not have completed the physical and technical development to truly achieve maximum power, thus perhaps underestimating the possible changes with the training. However, we did find a significant inverse correlation between rowing power and rowing economy, that is, a greater rowing power was associated with lower energy expenditure for a given power output. This is suggestive that rowers with greater power may be more technically masterful and thus expend less energy during rowing.
Plyometric Training and Rowing Sprint Performance
Plyometric training has been shown to improve short running sprint performance , and results from the current study indicate that plyometric training is able to improve rowing sprint performance (Fig. 3). These findings are in contrast to a study performed by Kramer et al. in , in which 20 min of simple double leg plyometric exercises were added at the end of the strength training sessions completed by female collegiate rowers. Their rowing measures were a 2.5-km ergometer test, and the distance in meters achieved in 90 s. As a comparison with the current investigation, the 90-s rowing test is very similar to the 500-m TT. The average time for the plyometric group to perform the 500-m TT after training was ~95 s. Kramer et al. found no changes in the 90-s test after 9 weeks of training, whereas we observed a significant improvement in 500-m performance . There are several potential reasons for this discrepancy.
The plyometric exercises used in the earlier study of Kramer et al.  were more simplistic than in the current investigation (e.g., no rotation or multiple jumps or upper body involvement). Indeed, the authors did indicate that the exercises they selected may not have been the best for improving rowing performance  and were performed following strength training, likely in a semi-fatigued state, suboptimal conditions for plyometric training. Additionally, in comparison to the study by Kramer et al., the current study contained more foot contacts (Table 2.) and focused on plyometric training versus steady-state training, matched for training volume (time) between groups. Kramer et al. did not match training volume . To avoid this, training times were matched for volume of the dry-land training in the present investigation. All on the water rowing training was also matched as all participants were members of the same team. Finally, Kramer et al.  recruited collegiate female rowers who were older than the high school male participants in the current study (mean age of 21 compared with a mean age of 16 years). As such, when prescribing plyometric training, it is important to consider factors such as performing these exercises in a non-fatigued state, foot contacts, and load in order to optimize any potential performance improvements.
Nonetheless, the current investigation was able to demonstrate that plyometric training improved 500-m rowing performance (Fig. 3). However, it remains to be seen if plyometric training is capable of improving rowing performance of a more gold standard distance, such as 2- or 6-km TT. As peak power was only moderately increased for the plyometric group, but rowing economy did not differ between pre- and post-training, the improvement in rowing performance could be due to increased rowing power but also to other mechanisms not measured in the current study (e.g., muscle coordination, activation, and rate of force development). Alternatively, the rating of perceived exertion, while not different prior to the intervention, was significantly reduced post-training in the PLYO group only (Fig. 2), which suggests a possible shift in maximal work rate, or the plyometric training may have increased the tolerance for work, thereby reducing perceived effort, and either phenomena might have contributed to the increased performance.
The current study is not provided without limitation or further consideration. While the 500-m TT was shown to improve as a result of the plyometric training, the training program (three 30-min sessions/week) might be considered time consuming for coaches that are usually working under stringent time constraints. Although, the results from the current study indicate that plyometric training does not impair rowing economy; thus, if on-the-water or ergometer training is not available (e.g., weather or time constraints), plyometric training might serve as an effective substitute or adjunct.
As the purpose of the study was to highlight the effects of plyometric training, we cannot ascertain whether inclusion of strength training or strength training alone would provide additional or superior benefit. Plyometrics are often performed in conjunction with weight training (also known as complex training) and have been shown to cause greater improvements in power than either modality alone . Whether or not complex training is beneficial for rowing performance has yet to be evaluated.
The 500-m TT measure used here is not the gold standard rowing performance test used by rowing coaches. The 2-km ergometer time trial is the most common rowing performance measure . This test not only measures rowing ability, fitness, and technique but also mental fortitude. For this last reason, the 2-km test was not used to evaluate rowing performance of the young athletes in the current study. In young rowers, 2-km performances can vary greatly due to it being mentally challenging so the much shorter 500-m test was used to provide a more objective measure of whether the plyometric program improved rowing performance. Although it is worth mentioning that the reliability of the 500-m TT was not tested, the athletes were very accustomed to the test distance as it is included in training and assessment. Additionally, the athletes were not periodized for the 2-km test, which typically occurs in the spring season. As the 2-km test was not performed in the current study, further research is needed to definitively demonstrate whether improvements in 500-m performance due to plyometrics can be translated into the full 2-km test. The results of the current study can only be applied to youth males, and it remains to be seen if such training responses would be seen in older and/or more developed athletes. Although the 500-m test is not a gold standard measure for rowing, the fact that the athletes were able to significantly improve performance with plyometric training is important. First, because the athletes were able to improve their rowing sprint performance during a time in which no rowing sprint training was being undertaken, this might be a way to preserve anaerobic performance without detriment to aerobic performance (i.e., rowing economy). Second, coaches can also use the 500-m performance to estimate the 2000-m performance, as some coaches consider the wattage produced over 500 m to be 138% of 2000-m watts. Finally, more detailed exploration of the possible changes in muscle will provide greater insight into the training responses to plyometrics in rowers (e.g., hop test and vertical jump).