The design of a resistance training program requires the appropriate manipulation of a variety of variables, all of which can affect the adaptations to a resistance training program. These variables include but are not limited to frequency, intensity, and volume. A primary way that training volume can be manipulated is through the number of sets performed per exercise and per muscle group. Thus, the number of sets can have a strong impact on the morphological and performance-based outcomes of a resistance training program. The response of the body to changes in set volume can be viewed as a dose-response relationship. For example, as the dose of a drug is increased, the body's response to that drug increases, until a plateau is reached. If the drug dose continues to increase, there is no further increase in the body's response to the drug, but an increase in side effects can occur. Similarly, as the number of sets of a resistance exercise increases, the body's response (the increase in strength and muscle mass) may increase. However, at some point, this response will plateau, and too many sets may increase the risk of injury.
The personal trainer should take an evidence-based approach when it comes to program design for a client. However, the evidence regarding the appropriate number of sets has not been straightforward. Review articles on this topic have come to different conclusions as to whether multiple sets can produce superior strength gains (1,3,4,23). Most studies published over the past decade have shown multiple sets to result in significantly greater strength gains than single sets (2,5-9,12-14,17,20,21). Some published meta-analyses indicate multiple sets to be superior (18,19,24); however, these articles have a number of methodological limitations, which has resulted in criticism of their conclusions (10,16). Also, the results of these articles have not been consistent. For example, Rhea et al. (19) reported multiple sets to be superior in both trained and untrained subjects, but Wolfe et al. (24) reported multiple sets to be superior in trained subjects only.
Another problem is that the majority of resistance training studies compare 1 set with 3 sets per exercise (1,4). However, there are many other variations in set volume that can be prescribed. There has been very little research done regarding the dose-response effects of the number of sets on strength gains. Ostrowski et al. (15) compared 1, 2, and 4 sets per exercise and reported no significant differences between groups. However, the variability of the responses and the small number of subjects per group limit the statistical power to detect differences between groups. Rhea et al. (19) looked at dose-response effects with a meta-analysis, reporting 4 sets per muscle group to be the optimal number for both trained and untrained subjects. However, as mentioned earlier, the limitations of the study design indicate that the results should be interpreted with caution. Also, since Rhea et al. reported the data as sets per muscle group, the sets-per-exercise problem is not adequately addressed. Given the lack of convincing scientific data regarding the dose-response effects of the number of sets, it can be difficult for the personal trainer to decide what number is appropriate for a client.
A recent meta-analysis was published in the Journal of Strength and Conditioning Research to try to shed more light on the dose-response effects of the number of sets per exercise (10). This meta-analysis had 2 purposes: to address the criticisms of previous meta-analyses in this area and to establish a dose-response relationship of set volume on strength. The main finding was that a single set per exercise resulted in strength gains, but multiple sets were superior. Specifically, 2-3 sets per exercise was associated with 46% greater strength gains than 1 set, and no further benefit was observed for more than 3 sets. These findings applied to both trained and untrained subjects, upper- and lower-body exercises, and a variety of training frequencies. These findings were also true whether or not multiple exercises were performed per muscle group.
The main limitation of this recent analysis is that there were only 2 studies included that incorporated 4 or more sets per exercise. This limits the statistical power to detect significant differences. It is still possible that 4 or more sets could result in greater strength gains than 2-3 sets, but more research in this area will be needed to answer this question. What is apparent is that there is a plateau in strength gains once you get to 4-6 sets per exercise; 2-3 sets resulted in 46% greater gains than 1 set, whereas 4-6 sets only resulted in 13% greater gains than 2-3 sets. The reason for this plateau is not currently known. It is known that mechanical loading stimulates protein synthesis in skeletal muscle (22), and increasing loads result in greater responses until a plateau is reached (11). It is likely that protein synthesis responds in a similar manner to the number of sets (i.e., an increasing response as the number of sets are increased, until a plateau is reached), although there is no research examining this.
The findings of this analysis allow for a number of practical applications that personal trainers can use in their program designs:
- If a client is only interested in general fitness and does not need maximal gains in strength, then 1 set per exercise is a sufficient stimulus to improve strength. Also, clients who are lacking time can still experience strength gains by doing only 1 set to failure or near-failure per exercise.
- If a client is interested in maximal strength gains, then multiple sets per exercise are necessary. Because the majority of studies in this meta-analysis compared 1 set with 3 sets per exercise, than 3 sets per exercise is an appropriate starting point for a client. Because these numbers are based on averages, individual client responses may vary. Thus, set volume can be adjusted up or down from this starting point based on client response and tolerance.
- The point of diminishing returns appears to be above 3 sets per exercise. In this meta-analysis, 4-6 sets per exercise was not significantly different from 2-3 sets. Thus, there is little additional benefit to doing more than 3 sets per exercise, although individual responses may vary.
- There is no need to differentiate between trained and untrained subjects in regards to set volume; both are equally likely to benefit from multiple sets. However, for clients with little resistance training experience, it is probably prudent to keep initial volume to 1-2 sets per exercise to help prevent the delayed-onset muscle soreness that usually accompanies unaccustomed exercise. Set volume can then be progressed.
- These set volumes are considered work sets and do not include warm-up sets.
There are still questions that science needs to answer regarding program design. For example, is it beneficial to incorporate multiple exercises targeting the same muscle group? The recent meta-analysis found no benefit to doing multiple exercises, although it was not specifically designed to answer this question. Also, more research is needed looking at dose-response relationships in regards to the number of sets; there are very few studies that use volumes of more than 3 sets per exercise (13,15). Another question that needs to be answered is the relationship between the number of sets and intensity. The studies in the recent meta-analysis involved an average of 7-10 repetition maximum (RM) per set. The optimal set volume for higher training intensities (1-5 RM) has not been adequately investigated.
Although scientists have more to investigate regarding other topics, the evidence in the single versus multiple set debate overwhelmingly favors multiple sets. It is also clear that there is a dose-response relationship in regards to set volume and strength, with an apparent plateau in the response beyond 3 sets per exercise. Clients who want maximal strength gains are best off doing 2-3 sets per exercise, whereas clients who just want to stay fit or lack time can achieve moderate strength improvements with a single set. It should also be noted that these conclusions are limited to general fitness and maximal strength and that the appropriate set volume may be different for other goals such as hypertrophy, power, and endurance. As always, a personal trainer should tailor a client's program to his/her individual needs, goals, and limitations.
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