Progression Models in Resistance Training for Healthy Adults POSITION STAND SUMMARY American College of Sports Medicine Position Stand on Progression Models in Resistance Training for Healthy Adults. Med. Sci. Sports Exerc. Vol. 34, No. 2, 2002, pp. 364���380. In order to stimulate further adaptation toward a specific training goal(s), progression in the type of resistance training protocol used is necessary. The optimal characteristics of strength-specific programs include the use of both concentric and eccentric muscle actions and the performance of both single- and multiple-joint exercises. It is also recommended that the strength program sequence exercises to optimize the quality of the exercise intensity (large before small muscle group exercises, multiple-joint exercises before single-joint exercises, and higher intensity before lower intensity exer- cises). For initial resistances, it is recommended that loads corresponding to 8���12 repetition maximum (RM) be used in novice training. For intermediate to advanced training, it is recommended that individuals use a wider loading range, from 1���12 RM in a periodized fashion, with eventual emphasis on heavy loading (1���6 RM) using at least 3-min rest periods between sets performed at a moderate contraction velocity (1���2 s concentric, 1���2 s eccen- tric). When training at a specific RM load, it is recommended that 2���10% increase in load be applied when the individual can perform the current workload for one to two repetitions over the desired number. The recommen- dation for training frequency is 2���3 d��wk 1 for novice and intermediate training and 4���5 d��wk 1 for advanced training. Similar program designs are recommended for hypertrophy training with respect to exercise selection and frequency. For loading, it is recommended that loads corresponding to 1���12 RM be used in periodized fashion, with emphasis on the 6���12 RM zone using 1- to 2-min rest periods between sets at a moderate velocity. Higher volume, multiple-set programs are recommended for maximizing hypertrophy. Pro- gression in power training entails two general loading strategies: 1) strength training, and 2) use of light loads (30���60% of 1 RM) performed at a fast contraction velocity with 2���3 min of rest between sets for multiple sets per exercise. It is also recommended that emphasis be placed on multiple-joint exercises, especially those involving the total body. For local muscular endur- ance training, it is recommended that light to moderate loads (40���60% of 1 RM) be performed for high repetitions ( 15) using short rest periods ( 90 s). In the interpretation of this position stand, as with prior ones, the recommen- dations should be viewed in context of the individual���s target goals, physical capacity, and training status. INTRODUCTION The ability to generate force has fascinated humankind throughout most of recorded history. Not only have great feats of strength intrigued people���s imagination, but a suf- ficient level of muscular strength was important for survival. Although modern technology has reduced the need for high levels of force production during activities of everyday living, it has been recognized in both the scientific and medical communities that muscular strength is a fundamen- tal physical trait necessary for health, functional ability, and an enhanced quality of life. Resistance exercise using an array of different modalities has become popular over the past 70 years. Although organized lifting events and sports have been in existence since the mid to late 1800s, the scientific investigation of resistance training did not dramat- ically evolve until the work of DeLorme and Watkins (46). Following World War II, DeLorme and Watkins demon- strated the importance of ���progressive resistance exercise��� in increasing muscular strength and hypertrophy for the rehabilitation of military personnel. Since the early 1950s and 1960s, resistance training has been a topic of interest in the scientific, medical, and athletic communities (19 ��� 21,31,32). The common theme of most resistance training studies is that the training program must be ���progressive��� in order to produce substantial and continued increases in muscle strength and size. Progression is defined as ���the act of moving forward or advancing toward a specific goal.��� In resistance training, progression entails the continued improvement in a desired variable over time until the target goal has been achieved. Although it is impossible to continually improve at the same rate with long-term training, the proper manipulation of program variables (choice of resistance, exercise selection and order, number of sets and repetitions, rest period length) can limit natural training plateaus (that point in time where no further improvements takes place) and consequently en- able achievement of higher levels of muscular fitness (236). Trainable fitness characteristics include muscular strength, power, hypertrophy, and local muscular endurance. Other variables such as speed, balance, coordination, jumping ability, flexibility, and other measures of motor performance have also been positively enhanced by resistance training (3,45,216,238,249). Increased physical activity and participation in a compre- hensive exercise program incorporating aerobic endurance 0195-9131/02/3402-0364/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE�� Copyright �� 2002 by the American College of Sports Medicine This pronouncement was written for the American College of Sports Medicine by: William J. Kraemer, Ph.D., FACSM (Chairper- son) Kent Adams, Ph.D. Enzo Cafarelli, Ph.D., FACSM Gary A. Dudley, Ph.D., FACSM Cathryn Dooly, Ph.D., FACSM Matthew S. Feigenbaum, Ph.D., FACSM Steven J. Fleck, Ph.D., FACSM Barry Franklin, Ph.D., FACSM Andrew C. Fry, Ph.D. Jay R. Hoffman, Ph.D., FACSM Robert U. Newton, Ph.D. Jeffrey Potteiger, Ph.D., FACSM Michael H. Stone, Ph.D. Nicholas A. Ratamess, M.S. and Travis Triplett-McBride, Ph.D. 364

activities, resistance training, and flexibility exercises has been shown to reduce the risk of several chronic diseases (e.g., coronary heart disease, obesity, diabetes, osteoporosis, low back pain). Resistance training has been shown to be the most effective method for developing musculoskeletal strength, and it is currently prescribed by many major health organizations for improving health and fitness (7���9,71,206,208). Resistance training, particularly when incorporated into a comprehensive fitness program, reduces the risk factors associated with coronary heart disease (84,86,126,127), non���insulin-dependent diabetes (72,180), and colon cancer (141) prevents osteoporosis (91,158) promotes weight loss and maintenance (56,135,251,259) improves dynamic stability and preserves functional capac- ity (56,79,138,235) and fosters psychological well-being (59,235). These benefits can be safely obtained when an individualized program is prescribed (172). In the American College of Sports Medicine���s position stand, ���The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults,��� the initial standard was set for a resistance training program with the performance of one set of 8���12 repetitions for 8���10 exercises, including one exercise for all major muscle groups and 10���15 repetitions for older and more frail persons (8). This initial starting program has been shown to be effective in previously untrained in- dividuals for improving muscular fitness during the first 3��� 4 months of training (33,38,63,165,178). However, it is important to understand that this recommendation did not include resistance training exercise prescription guidelines for those healthy adults who wish to progress further in various trainable characteristics of muscular fitness. The purpose of this position stand is to extend the initial guide- lines established by the American College of Sports Medi- cine (ACSM) for beginning resistance training programs and provide guidelines for progression models that can be applied to novice, intermediate, and advanced training. FUNDAMENTAL CONCEPTS OF PROGRESSION Progressive overload. Progressive overload is the gradual increase of stress placed upon the body during exercise training. Tolerance of increased stress-related overload is a vital concern for the practitioner and clinician monitoring pro- gram progression. In reality, the adaptive processes of the human body will only respond if continually called upon to exert a greater magnitude of force to meet higher physiological demands. Considering that physiological adaptations to a stan- dard, nonvaried resistance training program may occur in a relatively short period of time, systematically increasing the demands placed upon the body is necessary for further im- provement. There are several ways in which overload may be introduced during resistance training. For strength, hypertro- phy, local muscular endurance, and power improvements, ei- ther 1) load (resistance) may be increased, 2) repetitions may be added to the current load, 3) repetition speed with submaxi- mal loads may be altered according to goals, 4) rest periods may be shortened for endurance improvements or lengthened for strength and power training, 5) volume (i.e., overall total work represented as the product of the total number of repeti- tions performed and the resistance) may be increased within reasonable limits, or 6) any combination of the above. It has been recommended that only small increases in training vol- ume (2.5���5%) be prescribed so as to avoid overtraining (69). Specificity. There is a relatively high degree of task spec- ificity involved in human movement and adaptation (217) that encompasses both movement patterns and force-velocity char- acteristics (95,113,261). All training adaptations are specific to the stimulus applied. The physiological adaptations to training are specific to the 1) muscle actions involved (50,51,115), 2) speed of movement (51), 3) range of motion (15,144), 4) muscle groups trained (69), 5) energy systems involved (153,213,248), and 6) intensity and volume of training (21,109,194,222). Although there is some carryover of training effects, the most effective resistance training programs are those that are designed to target specific training goals. Variation. Variation in training is a fundamental princi- ple that supports the need for alterations in one or more program variables over time to allow for the training stim- ulus to remain optimal. It has been shown that systemati- cally varying volume and intensity is most effective for long-term progression (241). The concept of variation has been rooted in program design universally for many years. The most commonly examined resistance training theory including planned variation is periodization. Periodization. Periodization utilizes variation in resis- tance training program design. This training theory was developed on the basis of the biological studies of general adaptation syndrome by Hans Selye (224). Systematic vari- ation has been used as a means of altering training intensity and volume to optimize both performance and recovery (110,166,209). However, the use of periodization concepts is not limited to elite athletes or advanced training, but has been used successfully as the basis of training for individ- uals with diverse backgrounds and fitness levels. In addition to sport-specific training (112,140,147,154), periodized re- sistance training has been shown to be effective for recre- ational (47,118,238) and rehabilitative (62) training goals. Classic (linear) model of periodization. This model is characterized by high initial training volume and low intensity (239). As training progresses, volume decreases and intensity increases in order to maximize strength, power, or both (68). Typically, each training phase is designed to emphasize a particular physiological adapta- tion. For example, hypertrophy is stimulated during the initial high-volume phase, whereas strength is maximally developed during the later high-intensity phase. Comparisons of classic strength/power periodized models to nonperiodized models have been previously reviewed (68). These studies have shown classic strength/power periodized training superior for increasing maximal strength (e.g., 1 repetition maximum (1 RM) squat), cycling power, motor performance, and jumping ability (192,238,241,256,257). However, a short- term study has shown similar performance improvements between periodized and multiple-set nonperiodized models PROGRESSION MODELS IN RESISTANCE TRAINING Medicine & Science in Sports & Exercise 365

(13). It has been shown that longer training periods (more than 4 wk) are necessary to underscore the benefits of periodized training compared with nonperiodized training (257). The results of these studies demonstrate that both periodized and nonperiodized training are effective during short-term training, whereas variation is necessary for long- term resistance training. Undulating (nonlinear) periodization. The nonlinear program enables variation in intensity and volume within each 7- to 10-day cycle by rotating different protocols over the course of the training program. Nonlinear methods attempt to train the various components of the neuromuscular system within the same 7- to 10-day cycle. During a single workout, only one characteristic is trained in a given day (e.g., strength, power, local muscular endurance). For example, in loading schemes for the core exercises in the workout, the use of heavy, moderate, and lighter resistances may be randomly rotated over a training sequence (Monday, Wednesday, Friday) (e.g., 3���5 RM loads, 8���10 RM loads, and 12���15 RM loads may used in the rotation). This model has compared favorably with the classical periodized and nonperiodized multiple-set models (13). This model has also been shown to have distinct advan- tages in comparison with nonperiodized, low-volume training in women (154,165). IMPACT OF INITIAL TRAINING STATUS Initial training status plays an important role in the rate of progression during resistance training. Training status reflects a continuum of adaptations to resistance training such that level of fitness, training experience, and genetic endowment con- tribute categorically. Untrained individuals (those with no re- sistance training experience or who have not trained for several years) respond favorably to most protocols, thus making it difficult to evaluate the effects of different training programs (68,92). The rate of strength increase differs considerably be- tween untrained and trained individuals (148), as trained indi- viduals have shown much slower rates of improvement (83,107,111,221). A review of the literature reveals that mus- cular strength increases approximately 40% in ���untrained,��� 20% in ���moderately trained,��� 16% in ���trained,��� 10% in ���ad- vanced,��� and 2% in ���elite��� over periods ranging from 4 wk to 2 yr. Individuals who are ���trained��� or ���intermediate��� typically have approximately 6 months of consistent resistance training experience. ���Advanced��� training referred to those individuals with years of resistance training experience who also attained significant improvements in muscular fitness. ���Elite��� individ- uals are those athletes who are highly trained and achieved a high level of competition. Although the training programs, durations, and testing procedures of these studies differed, these data clearly show a specific trend toward slower rates of progression of a trainable characteristic with training experience. The difficulty in continuing gains in strength appears to occur even after several months of training. It is well docu- mented that changes in muscular strength are most prevalent early in training (92,185). Investigations that have examined the time course of strength gains to various training protocols support this concept. Short-term studies (11���16 weeks) have shown that the majority of strength increases take place within the first 4���8 wk (119,192). Similar results have been observed during 1 yr of training (185). These data demonstrate the rapidity of initial strength gains in untrained individuals, but also show slower gains with further training. TRAINABLE CHARACTERISTICS MUSCULAR STRENGTH The ability of the neuromuscular system to generate force is necessary for all types of movement. Muscle fibers, classified according to their contractile and metabolic char- acteristics, show a linear relationship between their cross- sectional area (CSA) and the maximal amount of force they can generate (66). In whole muscle, the arrangement of individual fibers according to their angle of pull (pennation), as well as other factors, such as muscle length, joint angle, and contraction velocity, can alter the expression of mus- cular strength (90,144). Force generation is dependent on motor unit activation (217). Motor units are recruited ac- cording to their size (from small to large, i.e., size principle) (117). Adaptations with resistance training enable greater force generation. These adaptations include enhanced neural function (e.g., greater recruitment, rate of discharge (159,181,217)), increased muscle CSA (6,170,232), changes in muscle architecture (136), and possibly a role of metabolites (215,226,230) for increased strength. The magnitude of strength enhancement is dependent on the muscle actions used, intensity, volume, exercise selection and order, rest periods between sets, and frequency (245). Muscle action. Most resistance training programs in- clude primarily dynamic repetitions with both concentric (muscle shortening) and eccentric (muscle lengthening) muscle actions, whereas isometric muscle actions play a secondary role. Greater force per unit of muscle size is produced during eccentric actions (142). Eccentric actions are also more neuromuscularly efficient (55,142), less met- abolically demanding (58), and more conducive to hyper- trophy (115), yet result in more delayed onset muscle sore- ness (52) as compared with concentric actions. Dynamic muscular strength improvements are greatest when eccentric actions are included in the repetition movement (50). The role of muscle action manipulation during resistance train- ing is minimal with respect to progression. Considering that most programs include concentric and eccentric muscle actions in a given repetition, there is not much potential for variation in this variable. However, some advanced pro- grams use different forms of isometric training (e.g., func- tional isometrics (128)), in addition to use of supramaximal eccentric muscle actions in order to maximize gains in strength and hypertrophy (139). These techniques have not been extensively investigated but appear to provide a novel stimulus conducive to increasing muscular strength. For progression during strength training for novice, intermedi- ate, and advanced individuals, it is recommended that both concentric and eccentric muscle actions be included. 366 Official Journal of the American College of Sports Medicine http://www.acsm-msse.org