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Resistance Exercise: How Much Is Enough?

Loveless, Melinda S. MD; Ihm, Joseph M. MD

Current Sports Medicine Reports: May/June 2015 - Volume 14 - Issue 3 - p 221–226
doi: 10.1249/JSR.0000000000000149
Training, Prevention, and Rehabilitation: Section Articles
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Multiple organizations recommend that resistance exercise be part of an adult health and fitness regimen. Extensive research has been done over the years on how to appropriately use a resistance exercise program to increase strength and power for general health and improve athletic performance. This article will review the literature on the components of a resistance exercise program and the recommendations for increasing strength and power in healthy adults.

Rehabilitation Institute of Chicago, Chicago, IL

Address for correspondence: Joseph M. Ihm, MD, Rehabilitation Institute of Chicago, 1030 North Clark Street, Suite 500, Chicago, IL 60610; E-mail: jihm1@ric.org.

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Introduction

Modern resistance exercise has its origins in the 19th century; it began in Europe and soon spread to the United States (73). In the early years, there was widespread belief that weight training was detrimental to health and athletic performance, although no research had been done at that time. Charles Atlas began popularizing resistance exercise for increasing strength and muscle size in the 1920s. Use of resistance exercise for improving athletic performance was promoted by Bob Hoffman of York Barbell Company in the 1930s, Joe and Ben Weider in the 1940s, and Walt Marcyan in the 1950s. In the 1950s, the first scientific articles on the benefits of resistance exercise for athletic performance were published (68). In 1955, Alvin Roy’s addition of a resistance exercise program to a high school football team’s training regimen was thought to be what helped them become a winning team (69). From there, resistance exercise became a regular part of training to improve athletic and sports performance.

Resistance exercise is now part of recommended activities for maintaining overall health in adults. It has been shown to reduce mortality, cardiovascular disease, cholesterol, depression, and fatigue and improve bone density and insulin sensitivity (28). With the multitude of potential benefits, individuals view resistance exercise with different goals. Some want to improve sports performance, while others want to increase muscle size and others just want to improve their health and ability to perform daily activities. All of these affect the trainee’s ability to perform with appropriate intensity and meet the recommended guidelines.

There are many factors involved in developing a resistance exercise program including frequency and intensity of training. Frequency is the number of times per week a muscle group is exercised. Intensity is affected by a combination of the amount of resistance, number of repetitions, and number of sets of repetitions performed per muscle group. Intensity is also affected by the trainee’s ability to fatigue the muscle group being exercised. A repetition is one full movement of an exercise, and the number of times that movement is done without stopping is the number of repetitions per set. A set refers to how many times you will repeat an exercise for a set number of repetitions. For example, if you do 12 repetitions of an exercise and rest, then do another 12 repetitions and rest, and then another 12 repetitions, you have completed 3 sets of 12 repetitions of that exercise.

Resistance can be in the form of resistance bands, body weight, or weights such as dumbbells, barbells, machines, or kettlebells. With weights, the amount lifted is often defined with respect to a repetition maximum (RM). For example, 1RM is the amount of weight that can be lifted with proper form only once. The amount of resistance also can be defined as the maximum resistance that can be lifted a specified number of repetitions; for example, a 6RM would be the maximum resistance that an individual could lift six times but not a seventh. Often, these numbers correlate to a percentage of the 1RM. The 12RM often matches 60% of the 1RM, and the 8RM, 80% of 1RM (64). In this review, we will discuss recommendations for frequency and intensity of resistance exercise in the healthy adult population for improving strength, power, and athletic performance.

The focus of this article is to review the evidence that seeks to determine the minimum or adequate amount of resistance exercise that can provide the exerciser or athlete with strength and performance gains. The current evidence does not allow us to easily determine the optimal amount of resistance exercise, but it does suggest that many different types of resistance exercise protocols can provide meaningful results. Reviewing all types of exercise that provide strength and performance gains is beyond the scope of this article. The bulk of the literature on resistance exercise involves using resistance that is measurable (e.g., as a percentage of 1RM). As a result, this article will not cover popular exercise regimens that focus on use of body weight for resistance, even though many of these types of exercise regimens are effective in promoting strength and functional gains. Also, while high-intensity workouts such as CrossFit can be effective in promoting strength and fitness, those workouts have not been studied extensively enough to allow for direct comparison with other resistance exercise programs. This article will not cover specialized areas within resistance training such as Olympic weightlifting, powerlifting, or bodybuilding. Olympic weightlifting involves obtaining a maximum single repetition of the snatch and clean and jerk. Similarly, powerlifting involves obtaining a maximum single repetition of the squat, bench press, and deadlift. Thus, the focus of training for an Olympic weightlifter or powerlifter is to maximize performance of these specific exercises.

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Components of Resistance Exercise

Frequency

Studies evaluating the effect of frequency generally follow one of two protocols: equal number of sets per muscle group per week or per exercise session. Those studies that maintained the same total number of sets per muscle group per week in each group have shown variable results. The study of McLester et al. (48) evaluating equal weekly volumes demonstrated greater increases in upper and lower body 1RM when training was spread over 3 d·wk−1 compared with 1 d·wk−1. Candow and Burke (14) compared 2 d·wk−1 with 3 d·wk−1 of resistance exercise and demonstrated no significant difference between groups in 1RM gains in bench press and squat. A study by DiBrezzo et al. (22) comparing 2 d·wk−1 with 3 d·wk−1 demonstrated greater strength gains in 3 of 8 muscle groups tested in the 3 d·wk−1 group compared with those in the 2 d·wk−1 group. The remaining five muscle groups tested had similar gains between groups (22). Lastly, Hunter (38) compared four consecutive days of a seven-exercise whole body routine with three alternating days of the same whole body exercise routine and demonstrated greater increase in maximum bench press strength in the group training four consecutive days after a 7-wk training period. However, this is an unusual frequency of performing resistance exercise, as studies have shown that most individuals require at least 48 h for recovery between bouts of resistance exercise (7).

Studies that maintained equal daily volumes, but unequal total sets per muscle group per week in each group, also demonstrated mixed results. For untrained individuals, Gillam (30) found greater improvement in strength in those who performed a bench press exercise 3 to 5 d·wk−1 compared with 1 or 2 d·wk−1. Again, like Hunter’s (38), this study included consecutive days of resistance exercise, which is not usually recommended for those trying to increase strength and power. In two studies comparing 1 d·wk−1 with 2 d·wk−1, no differences in strength gains were noted (12,29). A study by Braith et al. (10) of untrained individuals found 3 d·wk−1 to be superior to 2 d·wk−1. However, in another study of untrained individuals, Carroll et al. (16) found 2 and 3 d·wk−1 to be equivalent for gains in 1RM strength. In studies of cervical extension, torso rotation, and lumbar extension strengthening, one study concluded 1, 2, or 3 d·wk−1 to be equivalent while the other two concluded 2 d·wk−1 to be superior to 1 d·wk−1 for resistance exercise (21,34,58).

Most of the mentioned studies focus on the untrained individual and support 2 to 4 d·wk−1 for each muscle group. Meta-analyses by Peterson et al. (56) and Rhea et al. (64) recommend 3 d·wk−1 for untrained individuals and 2 d·wk−1 for trained individuals, with higher volumes and intensities for those who are more experienced. However, in these studies, training one or more days per week all produced positive results, which suggests that the resistance exercise program can be tailored to meet an individual’s needs.

An additional consideration is performance of a whole body resistance exercise routine versus a split routine. A split routine involves exercising different muscle groups on consecutive days one or more times per week compared with a total body workout completed in 1 d. Benton et al. (5) demonstrated no difference in 1RM bench press and leg press gains, comparing 3 d·wk−1 of whole body training and a split routine over 4 d·wk−1 with the total number of sets per muscle group the same. Calder et al. (13) also demonstrated no significant difference in 1RM gains when performing a split routine over 4 d versus a whole body routine twice per week. This study also maintained equal number of repetitions and sets per muscle group for the week (13). Ultimately, the use of a split or whole body routine will be determined by the individual’s goals and training history.

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Volume

One of the primary components of a strength training program is the number of sets performed per muscle group. This has been one of the most controversial aspects of resistance exercise research (27), which started with a 1962 study by Berger (6). In his study, 9 groups performed either 1, 2, or 3 sets of 2, 6, or 10 repetitions of the bench press 3 times per week for 12 wk. The results demonstrated that 3 sets of 6 repetitions produced the greatest increase in 1RM; however, this was not statistically significant when compared with the 1 set of 6 repetitions group. Additionally, all but the 2 sets of 2 repetitions group demonstrated at least 20% increase in 1RM, with the greatest increase being 29.6% in the 3 sets of 6 repetitions group (6).

Studies that compare a single set with multiple sets per muscle group have variable results; however, no studies demonstrate superiority of a single set over multiple sets for gaining strength. Of the studies comparing one set with three sets per muscle group, three studies found no significant difference in strength gains between groups of individuals performing exercises 3 d·wk−1 over 8, 14, or 25 wk (36,70,71). Other similarly designed studies comparing one with three sets per muscle group found greater strength gains in three-set regimens compared with those in one-set regimens when exercises were performed 2 d·wk−1 for 6 or 8 wk or 3 d·wk−1 for 7 or 14 wk (42,44,67,72). Additional studies of one versus three sets per muscle group specifically evaluated upper versus lower body strength improvements. Three of these studies found greater strength gains with three sets for lower body exercises and equivalent strength gains with one and three sets for upper body exercises (55,62,65), while one study found the opposite — greater upper body strength gains with three sets but no difference in lower body strength gains (37).

Other studies that have tried to determine the optimal number of sets per muscle group included multiple exercises per muscle group. While they may have been described as comparing a single-set regimen with multiple sets, both groups studied actually performed multiple sets for the given muscle group. These studies tend to show no significant difference in strength gains between the “single-set” and “multiple-set” groups (4,35,50,52).

Given the controversy surrounding the topic, multiple reviews and meta-analyses have been performed. A 1998 review article by Carpinelli and Otto (15) reviewed 35 comparative studies and concluded that there is no difference in strength gains or hypertrophy in comparing single versus multiple sets per muscle group (15). As a follow-up to the review of Carpinelli and Otto (15), Galvão and Taaffe (27) provided an updated review in 2004. Most of the new articles supported multiple sets over a single set per muscle group for maximizing strength gains. However, they summarized that for the general goal of increasing strength and fitness, one set per muscle group may be sufficient (27). The same year, a quantitative analysis by Wolfe et al. (76) concluded that trained individuals have greater strength gains when performing multiple sets per muscle group, and in studies of longer duration, multiple sets also demonstrate greater strength gains. Other meta-analyses also support multiple sets over single sets for increased strength (26,45,46,63,76). In the end, either one or multiple sets per muscle group produce positive strength gains, so the workout can be tailored to meet individual needs based on the goals of the fitness enthusiast.

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Intensity

Intensity is often based on one’s maximal effort, either a multiple RM or a percentage of the individual’s 1RM for that exercise. The goal of training, whether that is improving strength, endurance, or power, will direct the number of repetitions and load used.

Chestnut and Docherty (17) studied 24 untrained men performing exercises with either six sets of 4RM or three sets of 10RM. Exercises were performed three times per week for 10 wk. There were no differences between the two groups in strength or cross-sectional muscle area gains over 10 wk (17). A study by Weiss et al. (74) of 38 untrained men compared four sets of squats at either 3RM to 5RM, 13RM to 15RM, or 23RM to 25RM for 7 wk and found significant improvement in squat strength in all groups compared with that in a group that did not exercise. However, there was significantly greater improvement in the 3RM-to-5RM group than that in the 23RM-to-25RM group, with average 1RM squat increase of 75.0 and 34.1 kg, respectively (74). Another study of 30 resistance-trained collegiate baseball players evaluating low-resistance exercise (40% to 60% 1RM) versus high-resistance exercise (70% to 90% 1RM) revealed greater gains in 1RM squat in the high-resistance group (39).

With regard to the type of resistance exercise, there have been no significant differences noted between strength gains with use of machines versus free weights with comparable loads (9,70). For increasing power, studies have shown that lighter loads between 30% and 60% of 1RM or periodized programs with variable loads are more beneficial (41,43). Periodized resistance exercise programs include planned changes at different intervals (days or weeks, in-season versus off-season) in the volume or intensity of the exercises performed (61). Resistance bands, plyometric exercises, and kettlebell exercises can be incorporated into the exercise routine as a form of lighter resistance for increasing power (40,53).

The 2003 meta-analysis by Rhea et al. (64) recommends 60% of 1RM (approximately 12RM) load for untrained individuals and 80% of 1RM (approximately 8RM) in trained individuals to maximize strength gains. Meta-analyses of Peterson et al. (56,57) drew similar conclusions, recommending training at 60% of 1RM for untrained individuals, 80% of 1RM for recreationally trained individuals, and 85% of 1RM for competitive athletes to maximize strength. All studies demonstrated positive strength gains at every level of intensity evaluated, so the resistance exercise program may be tailored to meet the individual’s goals.

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Velocity

The velocity of an exercise is the rate at which the concentric (i.e., resistance during muscle shortening) and eccentric (i.e., resistance during muscle lengthening) phases are completed. Studies have been performed to evaluate the speed that produces the largest strength and power gains. The study of Farthing and Chilibeck (24) on elbow flexion in 36 untrained college-aged men and women found that fast eccentric exercise (180° per second) produced the greatest strength gains when compared with fast concentric and slow eccentric or concentric exercise (30° per second). The study of Morrissey et al. (49) on squat training in 21 untrained college-aged women demonstrated greater power gains using fast repetition speed (2 s) and equal strength gains at fast and slow repetition speeds (4 s). The ACSM Position Statement recommends performing the exercise movement over 2 to 6 s depending on the individual’s level of training. Maximum strength and power gains are obtained with faster velocities (60).

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Athletic Performance

Sprinting

Studies on the effects of resistance exercise using weights and plyometric training on sprinting performance demonstrate faster times with resistance exercise. Ozbar et al. (54) demonstrated an average 0.3-s (8.1%) improvement in 20-m sprint time with the addition of plyometric exercises (a variety of explosive jumping exercises) to the training regimen for soccer players with at least 4 years training experience. Similar results were demonstrated in the study of Brito et al. (11) on college-aged soccer players involved in a resistance, plyometric, or combined training program. The plyometric exercises included high skipping, vertical jumps, and drop jumps, while the resistance exercise group performed squat, leg extension, and calf extension exercises at 80% to 90% of 1RM. The combined group performed both programs. Training was completed twice weekly for 9 wk. The three groups had comparable improvements in 20-m sprint time of 4.6% to 6.2% (11). Additionally, Deane et al. (19) demonstrated that hip flexor strengthening in untrained physically active individuals led to a 0.233-s decrease in 40 yd and a 0.646-s decrease in 4 × 5.8-m shuttle run times. Hip flexor strengthening with resistance tubing was performed three times per week for 8 wk with two sets of 10 followed by one set to failure (19). Ross et al. (66) compared a periodized split body resistance training program performed 4 d·wk−1 with treadmill sprint training and with a group that performed both resistance and sprint training over 7 wk. The sprint and combined training groups had significant improvements in 30-m sprint time of 0.08 to 0.10 s. Participants were current or former competitive athletes (66). Delecluse et al. (20) demonstrated 0.21-s improvement in 100-m sprint time using plyometric training 2 d·wk−1 over 9 wk (jumps, sit-ups, push-ups, skipping, hopping, and squat throwing) and a 0.26 m·s−1 improvement in initial 10-m acceleration time. In those who performed lower body resistance exercise over the same training period, there was no improvement in 100-m sprint time and only minimal improvement in acceleration. Participants were nonresistance-trained college physical education students (20). While the changes noted previously are relatively small, they can produce a noticeable difference for competitive athletes.

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Vertical Jump

Resistance exercise has been shown to lead to improvements in vertical jump height as well. Closed kinetic chain exercises (e.g., squat or lunge) are proven to be superior to open kinetic chain exercises (e.g., leg extensions) for improving vertical jump height (2,8). Augustsson et al. (2) showed a 5-cm (10%) improvement in vertical jump height in a group performing closed kinetic chain exercise (squats) compared with no change in the open kinetic chain group (knee extension, hip adduction) during a 6-wk resistance exercise program. A study comparing one set, three sets, and a periodized program performed 3 d·wk−1 showed significantly greater improvement in vertical jump height (∼5 cm) in the periodized training group at the end of 7 wk, with no improvement in the one set and three set groups (72).

Plyometric exercises, such as varied jumps and hops, have been shown to increase vertical jump as well, especially when combined with a resistance exercise program (54). A study by Adams et al. (1) demonstrated a 10.67-cm increase in vertical jump height after a 6-wk combined squat and plyometric training program while the groups performing squats or plyometric exercises alone improved by 3 to 4 cm. Another study of 64 resistance-trained athletes compared training twice weekly with 6RM to 10RM squats, depth jumps without weight, or weighted jump squats at 30% maximum isometric force over 10 wk. The weighted jump squat group demonstrated greatest improvement in jump height followed by the plyometric group (75). Similarly, a study of 16 male collegiate volleyball players found jump squat training to produce greater percent increase in vertical jump height than training with 6RM squat and leg press over 8 wk (51).

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Maintenance

Little research has been done on the maintenance of strength using a resistance exercise program. The study of DeLorme in 1945 describes using 15 to 30 min of exercise once or twice weekly to maintain muscle size and power. A study by Graves et al. (33) evaluated 50 trained individuals and found that reducing training to 1 or 2 d·wk−1 for 12 wk maintained strength while those who stopped training lost 68% of the strength gains made with prior training of 10 or 18 wk. Baker’s (3) study proved that two whole body sessions per week in a periodized program was sufficient in maintaining preseason levels of strength and power during the rugby season in athletes that also participated in conditioning and skill training. The 2004 review of Kraemer and Ratamess (43) of resistance training recommends 1 to 2 d·wk−1 as a maintenance frequency in those previously trained. Naclerio et al. (50) agree that a low-volume (three sets per muscle group) program may be sufficient to maintain strength and optimize power during a competitive season. Overall, strength maintenance requires a lower volume of training than increasing strength, although the optimal maintenance program has yet to be determined.

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Recommendations

Beginner

For those who are not resistance trained, the recommendation is to begin with 2 to 3 d·wk−1 of resistance exercise. Each exercise session should involve whole body training with one to three sets per muscle group at an intensity of at least 60% of 1RM (approximately 8 to 12 repetitions) to build strength. The velocity of the repetition should be about 2 to 4 s each for the concentric and eccentric portions of the lift.

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Advanced

For individuals with more than 6 months of resistance exercise experience who want to continue gaining strength, the recommended frequency is the same as that for beginners (two times per week per muscle group). However, these individuals may benefit from split routines if lifting at higher intensities given the greater demand on the body. For strength gains, resistance should be higher than that for beginners, generally 70% to 90% of 1RM. Additionally, multiple sets may provide more benefit than one set for each muscle group. The velocity of repetitions can be slightly faster at 1 to 2 s for each portion of the exercise. For individuals who have been performing resistance exercise regularly, they also may benefit from incorporating regular changes into their volume and/or intensity through a periodized training program (60,61).

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Athletic Performance

To add improvements in power such as vertical jump and sprinting performance, it is recommended that body weight plyometric exercises or low-resistance exercises such as jump squats be added to the individual’s resistance exercise program (60). Also, performing repetitions with faster velocity can facilitate power gains in the upper or lower body.

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Other Considerations

Many studies show that individuals often self-select the recommended moderate-level intensity for aerobic fitness activity (31); however, they select an intensity lower than the recommended level for resistance exercise (25,32). This relates to an individual’s lack of knowledge of recommended intensity and inability to determine the appropriate intensity without assistance or guidance. Furthermore, studies comparing strength gains in supervised versus unsupervised groups demonstrate greater strength gains in the supervised groups (18,47). This can be accomplished with group resistance exercise programs or with a personal trainer. Ratamess et al. (59) demonstrated that individuals who have worked with a trainer also are more likely to self-select a higher intensity for training.

When it comes to adhering to a program, studies have demonstrated a more favorable response to lower levels of perceived exertion. Therefore, prescribing resistance exercise at an appropriately high level of intensity may lead to dissatisfaction and negative affective response (23). For practitioners who prescribe resistance exercise, understanding the details of resistance exercise can help one counsel more thoroughly, which will assist individuals in training at an optimal intensity and adhering to the recommended training program (43).

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How to Counsel

The main consideration when counseling an individual on a resistance exercise program is understanding the individual’s goals. For example, if the individual wants to increase strength and power for athletic performance, the program would be different from that for someone simply wanting to improve overall health and fitness. It is important that an individual be educated both on expected results and on the required level of training needed to meet his or her goals. The utilization of a personal trainer or other qualified individual, especially when beginning, may improve safety, technique, motivation, and adherence to a resistance exercise program while ensuring that an adequate intensity of exercise is performed. Lastly, as with aerobic exercise, it is generally better to do something than nothing.

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Conclusions

For beginners starting a resistance exercise program, the recommendations are to train each muscle group 2 to 3 d·wk−1 with a moderate level of resistance (∼60% of 1RM) utilizing one to three sets per muscle group. Exercises should be performed at a slow-to-moderate velocity (2 to 6 s). When advancing to more intermediate or advanced levels of resistance exercise, the changes required to continue increasing strength are to increase the resistance to 70% to 90% of 1RM and potentially utilize split routines and/or a periodized training program. The use of a personal trainer or other qualified individual may be especially beneficial for a beginner for the purposes of teaching proper form and for motivation to train at adequate intensity. For increasing athletic performance, adding low-resistance exercises including explosive moves, such as jump squats, may further increase gains made with a standard resistance exercise program.

The authors declare no conflicts of interest and do not have any financial disclosures.

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