By Julia Kirkpatrick and Amanda Russo, Temple University
Plyometric training is a popular exercise modality among bikini competitors. Box jumps, plyometric lunges, squat jumps, and stair bounds are often incorporated with resistance training in the programs of these competitors. Indeed, a common notion held within this demographic is that the use of plyometric exercises in concordance with resistance training helps accentuate hypertrophy of the lower body. To examine this notion further, we conducted a preliminary quantitative analysis of the use of plyometrics and subsequent hypertrophy of the lower body, and compared it to traditional resistance training hypertrophy effects. This exploratory research can be used to generate future hypotheses to be evaluated as more research surfaces.
The research on plyometrics and subsequent hypertrophy as well as resistance training and subsequent hypertrophy effects was found through the following databases: PubMed, SportDiscus, EbscoHost, and Google Scholar. Research that was included in our analysis were individual, peer-reviewed studies, found using the search terms: plyometrics, resistance training, weight training, adaptations, body composition, hypertrophy, cross-sectional area, muscle growth and muscle mass. Exclusion criteria included (i) articles measuring hypertrophy via traditional resistance training with no control group and (ii) plyometric studies examining hypertrophy combined with training modalities (ex: high intensity interval training (HIIT)).
After a careful review of the literature using the aforementioned search terms, we ended up with a total of eight plyometric studies and seventeen resistance-training studies. The plyometric studies measured change of hypertrophy by either a skinfold measurement or dual-energy X-ray absorptiometry (DXA) reading. The resistance training studies measured change in hypertrophy through one of the following methods: magnetic resonance imaging (MRI), MRI and ultrasound, ultrasound, DXA, skinfolds, skinfolds and bioelectrical impedance analysis (BIA), or hydrostatic weighing. The method of hypertrophy measurement, length of the study (measured in weeks), training status of participants, pre-test and post-test hypertrophy measurements, and percentage change in hypertrophy, were derived from each study. The exception to these data findings were the studies done by Souza et al. (2014) and Whiteford et al. (2010), in which pre and post-test measurements were not given; rather, the overall percentage change in hypertrophy was provided. Percentage changes in hypertrophy and overall averages were calculated for both the control group and treatment groups in all studies, and then scaled to time. The percentage change in hypertrophy was found using the following method: ( (post-test – pre-test) / pre-test ) * 100 and was used to standardize changes in hypertrophy by eliminating variation in unit measurement for different hypertrophy measurement techniques. Similarly, calculating a scaled-to-time percentage change was a crucial step to equate for differences in study length, and make meaningful comparisons of hypertrophy change across all studies. We took the original hypertrophy percentage change and divided by the length of the study (in weeks), to yield a scaled hypertrophy percentage change.
In our final step of data analysis, we categorized each study into one of the following classifications: resistance training v. no training (n = 17), plyometrics v. no training (n=2), resistance training and plyometrics v. no training (n=4), and resistance training and plyometrics v. resistance training (n =1). Based on these classifications, we calculated a group average of hypertrophy change from pre and post-test measurements, unscaled and scaled to time. These classifications isolate differences in the magnitude of hypertrophy change specific to training modality.
Listed below in Figure 1 and Figure 2 are the studies included in our analysis, color-coded to their respective classification. Studies highlighted in blue belong to the classification: plyometrics v. no training. Studies highlighted in orange belong to the classification: resistance training and plyometrics v. no training. The study highlighted in green belongs to the classification: resistance training v. plyometric training and resistance training. The studies in purple belong to the classification: resistance training v. no training. Unscaled to time, the entire plyometric control group yielded an 1.24% average change while the treatment group yielded a 4.44% change. As a whole, the resistance training control group and treatment group yielded a 0.18% and 5.78% change in hypertrophy, respectively.
Figure 3 shows the overall percentage change for each classification, unscaled and scaled to time:
Figure 4 shows the overall percentage change for each classification, unscaled and scaled to time:
Figure 5 provides a visual representation of the scaled to time percentage change in hypertrophy – pre-test to post-test – for each group classification:
To our knowledge, there are very limited studies that examine plyometric training and subsequent hypertrophy effects, particularly of the lower body. However, it is quite common for women in the sport of bikini to use plyometric training as a modality to stimulate muscle hypertrophy (gluteal development, in particular). This presents an interesting notion that using plyometric exercises is a good use of training time, as it thought to develop lower body musculature. The primary purpose of our research was to compare the fundamental effects of plyometric training to that of conventional resistance training, on lower body hypertrophy.
The findings from our research reveal that when compared to resistance training, plyometric training yields a higher percentage change in hypertrophy from their respective no training control groups. However, when resistance training is paired with plyometric exercises, results show a decrease in hypertrophy when compared to only traditional resistance training. Furthermore, when resistance training and plyometric training are combined and compared against a no training control group, hypertrophy changes are less than doing only plyometric training or only resistance training. Thus, our overall findings demonstrate a degree of conflicting evidence in support of a superior training method.
However, the limitations of our exploratory research might provide further insight to the inconclusive data findings. The main limitation to consider is the amount of literature available on plyometric training and hypertrophy effects. This is a new topic to be studied and while we did not a perform a comprehensive review of the literature, there are only a limited amount of studies that pertain to plyometrics and lower body hypertrophy. Within the four classifications assigned to each study, the plyometric training and resistance training v. resistance training group had one study to represent the degree of hypertrophy change. And, the resistance training and plyometrics v. no training group had only two studies. With such data and number of studies, it is difficult to extract general averages that are applicable to all populations, especially bikini competitors. Given the low level of external validity our current research provides, we are unable to make recommendations to populations outside of the group demographic used in the studies which is again, quite limited. Additionally, bikini competitors use plyometric exercises with the notion that it will build their lower body musculature; not all of the studies isolated hypertrophy change in the lower body. Consequently, external valid the low degree of external validity should be considered when making general conclusions and hypotheses about the data findings.
On a similar note, while there is a large body of evidence to support resistance training and concomitant muscle growth, there are limited studies that test resistance training against a control group performing no training at all. A no training control group was essential to evaluate the degree of plyometric exercise superiority or equivalency for muscle growth, in comparison to resistance training. The majority of the participants in the resistance training studies were untrained, older (65+), health impaired, or some combination of all three variables. Consequently, there is potential for an underrepresentation of hypertrophy change in the resistance training v. no training group.
The last limitation to consider is the possibility of skewed effects due to several outlying studies. In the plyometric studies, it should be noted that in the study done by Chelly et al. (2014), there was 13.11% hypertrophy change over the course of eight weeks. There was only one other study in the plyos-only group, (Markovic et al. (2005)), and it recorded no net hypertrophy from plyometrics. Thus, one aberrant study in this case may be vastly over-estimating the hypertrophic yield of plyometric-only training. For this reason, especially the plyometric-only pooled data should be evaluated with a high degree of skepticism and critical analysis.
The skepticism about the conclusions of the Chelly study are further expanded when it is noted that plyometrics + resistance training underperforms resistance training only in hypertrophy results. Additionally, plyometrics + resistance training vs. control also doesn’t promote as much hypertrophy as just resistance training vs. control. If plyometrics were really as simulative of muscle growth as only the Chelly study seems to suggest, both of the aforementioned results would be very unexpected. While only further investigation can elucidate this matter, it seems far more likely that Chelly et al. is an erroneous chance outlier rather than a representative insight into the effects of ploymetrics on muscle growth.
While the current data suggests relatively inconclusive results, we can consider a practical training implication from the results. For an individual, or in this scenario, a bikini competitor looking to make the most of out of their training to maximize hypertrophy, it is beneficial to examine the ratio between hypertrophy and fatigue. The fundamental question to be examined further is the contribution of plyometric exercises to hypertrophy growth, and the extent to which they serve as a better, worse, or equal training modality compared to traditional weight training in terms of muscle growth.
Maximum recoverable volume (MRV) is the most training volume an individual can do and still recover. When comparing traditional resistance training to plyometric training, plyometric training is likely to have a lower MRV than resistance training, as it generates higher levels of fatigue. Data from our research demonstrates that plyometric training yields superior hypertrophy benefits to traditional resistance training when comparing each of these training modalities individually. However, when pairing the exercises together and comparing it to only resistance training, there is evidence of a decrease in hypertrophy. This could suggest that when examining the tradeoff of between plyometric exercises, resistance training and fatigue, it could be better to use traditional resistance training to maximize muscle. We hypothesize that by pairing the exercises together, plyometric exercises will account for a large amount of an individual’s MRV (the result of high levels of fatigue production), leaving resistance training to take a back seat, and consequently reducing the amount of net hypertrophy. Nonetheless, it is evident by the limitations our current research on the subject matter that this data should be used with the intent to generate further hypotheses, rather than derive conclusive findings. There remains much needed growth in plyometric and hypertrophy growth research to be able to generate practical training recommendations, but we hope that our exploratory research can provide initial insight, and spark more questions to be answered in the future.
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