In general, it is recommended that the resistance (load) be increased 2% to 10%, depending upon the muscle groups involved, after one to two reps beyond the desired reps can be completed for two consecutive sessions (2). A novice weight trainer will usually start with a load that is equivalent to approximately 65% 1-RM (2, 3). For example, if his or her starting resistance is 100 lbs and the goal reps of 12 have been surpassed for two consecutive sessions, the load should be increased to 102 to 110 lbs. However, some individuals may progress at a faster rate and be able to increase resistance after the first session of achieving the goal reps. Training status of an individual will play a large role in the rate of progression. Novice weight trainers have been shown to increase in strength much faster than intermediates and advanced lifters. For multi-joint exercises such as the bench press or barbell back squat, a 5% to 10% increase may be more feasible. Because the importance of learning proper exercise technique cannot be overemphasized, programs should be designed from simple to complex as one progresses from novice to advanced (2, 3).
Trainable Muscular Characteristics
The primary trainable characteristics of muscular fitness are muscular strength, power, hypertrophy, and endurance. The ACSM 2002 Position Stand on Progression Models in Resistance Training for Healthy Adults thoroughly explains these characteristics and the reader is encouraged to review this position stand for more information (2).
- Muscular strength is defined as the maximal ability of the neuromuscular system to generate force. Increased motor unit recruitment and firing rate, increased muscle cross sectional area, alterations in muscle architecture, and possibly enhanced anaerobic enzymes (ATP-PC system) contribute to increased muscular strength (2, 3).
- Muscular power refers to the rate of muscular work. When the same amount of work (resistance lifted) is completed in less time, more power is generated. Also, if more work (greater resistance lifted) can be accomplished in the same time, power is increased. Factors such as maximal rate of force development, muscular strength at slow and fast speeds, the stretch shortening cycle (fast eccentric muscle/tendon stretching leads to greater concentric contractions), and coordination of movement patterns and skill contribute to enhancing muscular power (2, 3).
- Muscular hypertrophy refers to the enlargement of muscle fibers by the accumulation of proteins through increased synthesis, decreased degradation, or both (2, 3).
- Local muscular endurance is the ability of a muscle or muscle group to contract repeatedly over a period of time. Increased mitochondrial and capillary densities, muscle fiber type transitions, and buffering capacity contribute to enhanced muscular endurance (2).
A number of training variables must be applied appropriately to develop specific musculoskeletal fitness characteristics. These variables include muscle actions, exercise selection and order, loading or intensity, volume (sets/reps/loads), rest intervals, repetition velocity, and frequency of training (2).
Muscular adaptation is quite specific to the type of stimulus applied. Factors involved in specificity include muscle actions, speed of movement, range of motion, specific muscles and muscle fibers used, energy systems involved, intensity used, and volume of training. The adaptations that occur in trained muscles will be specific to the goal and design of the program.
It is important to note that there is a carryover effect with resistance training. While an individual may be training to maximize muscular hypertrophy, he or she also will develop some muscular strength and endurance (2). It's also important to note that novice exercisers will experience strength increases with nearly any beginning resistance training program caused primarily by neural adaptations that occur during the first 2 to 3 months.
Sets, Repetition Speed, and Training Equipment
The optimal number of sets to achieve a muscular fitness goal is an area of particular interest to both health/fitness professionals and researchers. Single-set versus multiple-set programs have been compared. Some studies report that single- and multiple-set programs produce similar strength increases, yet others report that multiple-set programs are superior. No study reports single-set programs being superior to multiple-set programs (2, 4-6).
Untrained individuals respond favorably to single- or multiple-set programs, and this has led to the popularity of single-set resistance training programs for fitness enthusiasts (2, 5). However, multiple-set programs are recommended for long-term muscular characteristic enhancements (2, 5, 7). Novice exercisers can use either single- or multiple-set programs for the first 3 to 4 months. For continued progress in intermediate and advanced weight trainers, data indicate that multiple-set programs should be used (2).
Repetition speed is another training characteristic that needs to be considered. Slow training or "super slow," as it is commonly known, has its origins from an unpublished study on resistance training and osteoporosis. Super slow training calls for intentionally slow rep tempos such as a 10-second concentric and 5- to 10-second eccentric (2, 8). Limited peer reviewed research indicates that super slow may be effective for novice weight trainers (8, 9). However, more traditional rep velocities (2 seconds concentric/4 seconds eccentric) have been shown to be effective for novice, intermediate, and advanced weight trainers (2, 9).
Data suggest that super slow movement speeds limit motor unit activity and may not provide an optimal overload in the muscles. Performing reps in a "super slow" manner necessitates the use of loads that are 30% less than with traditional velocities (2). Intentionally slow speeds are not recommended for most weight trainers. In general, all reps should be performed in a controlled manner, particularly during the eccentric phase, although attempting to accelerate during the concentric phase has some potential advantages (power development).
To summarize, novice weight trainers should use slow to moderate velocities, whereas intermediate and advanced weight trainers should use slow to fast velocities (2). Fast velocities are needed for increasing power output, although novice weightlifters who are training for power should use moderate speeds. Those training for power need to complement the explosive lifting with maximal strength training because muscular strength is the basis for optimal power development (2).
Although many in the fitness profession continually compare and debate the use and applications of free weights and machines, it is important to understand the benefits of each modality. Machines are safer to use and easier to learn. They provide stabilization of the body in a fixed range of motion to focus the stimulus upon the target muscle(s) (10). Sometimes it is beneficial to reduce the need to activate muscles for stabilization and balance (e.g., free weights) and force the targeted muscle to do virtually all the work. Machines also enable the performance of some exercises that would not be possible with free weights (2, 10). Machines provide rotational resistance that enable exercises such as the leg extension and leg curl to be performed effectively. The quadriceps and hamstrings are "under tension" through a full range of motion on a leg extension and leg curl machine, respectively. This also is known as full range resistance. Some body movements (e.g., hip flexion, hip adduction, and abduction) are difficult to work through a full range of motion without machines.
Free weight exercises demand intermuscular coordination that simulates the movement of a specific task (2). More balance, stabilization, and coordination are required for proper execution of free weight exercises (10). Functional resistance training or training that mimics "real life" movements is an area that is becoming increasingly popular in the health/fitness industry. Free weight exercises, particularly multi-joint ones, are functional movements. Both machines and free weights should be used with weight trainers of all training levels. Advanced individuals should focus upon free weights and use machines to complement their program (2).
Recovery time between sets and exercises plays a critical role in dictating how successful a training program is. Short rest periods (e.g., 1 minute) appear to compromise strength performance, thus longer rest periods are recommended to enhance strength gains. Short rest intervals will still enhance muscular strength (carryover effect), just at a slower rate and with a lower absolute potential. Longer recovery times enable greater phosphagen repletion within the muscle, which enables it to produce more subsequent force (3). When training for muscular strength, individuals of all levels should use rest periods of at least 2 to 3 minutes for multi-joint exercises. Recovery periods of 1 to 2 minutes may be sufficient for single-joint movements that don't produce as much fatigue (novices may use 1 to 2 minutes for all exercises) (2, 3). These recommendations also apply to power training.
Rest time for muscular hypertrophy should be less than for muscle strength and power development. Studies have shown that 1- to 2-minute rest intervals between sets and exercises induce the greatest acute hormonal responses (2, 3). In addition to increasing anabolic hormone concentrations, research indicates that shorter rest intervals (1 to 2 minutes) are effective for increasing local blood flow and metabolite accumulation, both of which are linked to muscle hypertrophy (3). Thus 1- to 2-minute recovery periods are recommended for novice and intermediate persons training for muscle hypertrophy. Advanced individuals should use 2- to 3-minute rest intervals for heavy, core movements (squats, bench press) and 1 to 2 minutes for all other exercises (2, 3). It should be noted that the use of heavy loads also are effective for increasing muscle hypertrophy. As a result, a combination of hypertrophy and strength protocols can be used to optimize increases in muscle size (3).
Bodybuilders, who train with shorter rest intervals, demonstrate lower fatigue rates than power lifters who train with longer rest periods, indicating the effects of short rest intervals upon local muscular endurance (2). Shorter recovery times induce the desired metabolic adaptations within the muscle (e.g., increased mitochondria, capillary densities, and fiber type transitions) that enable the muscle to become more fatigue resistant (3). Rest intervals of 1 to 2 minutes are recommended for sets of 15 to 20 reps and less than 1 minute for sets of 10 to 15 reps (2, 3).
Exercise Selection and Order
With the exception of power training, both multi-joint (squat, bench press) and single-joint (leg extension, side lateral raise) exercises should be used for all training levels (2). Advanced weight trainers training for strength should emphasize multi-joint exercises (2, 11). Power training should use predominately multi-joint free weight movements for all training levels (2). However, before progressing to more advanced power movements (e.g., loaded squat jumps), individuals should have established a base level of strength that enables them to perform these exercises safely. Although some experts recommend that trainees be capable of squatting one and one-half times body weight, for example, it appears safe to initiate some basic power movements before the individual has reached this advanced level of strength, provided he or she has been consistently involved in a progressive resistance-training program.
- When performing a total body workout, large muscle groups should be worked before smaller ones and multi-joint exercises before single-joint exercises (2). A rotation of lower body and upper body exercises also can be used. A novice weight trainer may tolerate a workout better with an upper/lower body rotation.
- When training using an upper body/lower body split routine, work the larger muscles before the smaller ones, multi-joint exercises before single-joint exercises, and rotation of agonist-antagonist muscles (2). This is commonly known as push-pull or super sets.
- When training individual muscle groups, perform multi-joint before single-joint movements and higher intensity, greater skill movements before lesser intensity, lesser skill movements (2). Refer to Table 1 for how to manipulate training variables based upon the training goal(s).
Periodization (PER) refers to systematically manipulating training variables (e.g., intensity and volume) to maximize performance (gains) and recovery (12). It can be used with a variety of trainees, from elite athletes to fitness enthusiasts to those in rehabilitation. There are two models of periodization: classic and undulating, also known as linear and nonlinear, respectively (2).
Classic periodization involves initially high-volume training with a low intensity (lighter loads/higher repetitions) and progressing to low-volume training with a high intensity. An entire periodized cycle is known as a macrocycle and can last from several months to a year or longer. The next cycle is known as a mesocycle and may last from a month to a few months. The shortest cycle is the microcycle, which is typically a few weeks to a few workouts in duration. A specific adaptation is usually emphasized during each phase (e.g., strength and power during the low-volume, high-intensity phase). It appears that periods longer than 4 weeks are required to achieve the benefits of periodized training, and a systematic variation of volume and intensity is needed for long-term progress (2). See Table 3 for an example.
The undulating model involves variation in intensity and volume within each 7- to 10-day training cycle, in which different components of the neuromuscular system are emphasized during each workout (2). Following a Monday-Wednesday-Friday program, heavy, moderate, and light resistances can be used to train for strength/power, hypertrophy, and endurance within the same cycle. Undulating has been shown to be comparable to classic periodization (2). See Table 4 for an example.
The recommendations for enhancing motor performance are similar to those for enhancing strength and power. Specific skills can be enhanced with proper resistance training. Vertical jump ability has been correlated with force production (2). Multi-joint exercises using heavy (85% to 100% 1-RM) loads and light loads (30% to 60% 1-RM) with a fast velocity, with moderate- to high-volume (three to six sets/one to six reps), four to six times per week, is recommended for increasing vertical jump ability (2).
Sprint speed also can be enhanced with increased muscular strength (13). Using traditional heavy resistances for strength development, along with other activities such as explosive weightlifting movements and plyometrics can improve sprint ability (2). Other sport specific skills can be enhanced with improved muscular strength and power. Athletes that participate in sports/events that require activities such as kicking, throwing, and distance running can improve these sport-specific skills with proper strength and power training.
There are a number of training variables to consider when designing a resistance training program. Success of any resistance training program will depend upon such factors as the design of the program based upon the training goal(s) and training status of the individual, proper progression, proper exercise technique, and the use of sound knowledge and good judgment from the exercise professional implementing and monitoring the program.
Condensed Version and Bottom Line
Fitness professionals must appropriately set the resistance training variables in a progressive manner to meet an individual's muscular fitness goals.
1. American College of Sports Medicine. Position stand: The recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults. Medicine & Science in Sports & Exercise ®
2. American College of Sports Medicine. Position stand: Progression models in resistance training for healthy adults. Medicine & Science in Sports & Exercise ®
3. Kraemer, W.J., and N.A. Ratamess. Fundamentals of resistance training: Progression and exercise prescription. Medicine & Science in Sports & Exercise ®
4. Wolfe, B.L., L.M. Lemura, and P.J. Cole. Quantitative analysis of single- vs. multiple-set programs in resistance training. Journal of Strength and Conditioning Research
5. Rhea, M.R., B. Alvar, L. Burkett, et al. A meta-analysis to determine the dose-response relationship for strength
. Medicine & Science in Sports & Exercise ®
6. Peterson, M.D., M.R. Rhea, and B.A. Alvar. Maximizing strength
development in athletes: A meta-analysis to determine the dose-response relationship. Journal of Strength and Conditioning Research
7. Kramer, J.B., M.H. Stone, H.S. O'Bryant, et al. Effects of single vs. multiple sets of weight training: Impact of volume, intensity, and variation. Journal of Strength and Conditioning Research
8. Westcott, W.L., R.A. Winett, E.S. Anderson, et al. Effects of regular and super slow speed resistance training on muscle strength
. Journal of Sports Medicine & Physical Fitness
9. Keeler, L.K., L.H. Finkelstein, W. Miller, et al. Early-phase adaptations to traditional speed vs. superslow resistance training on strength
and aerobic capacity in sedentary individuals. Journal of Strength and Conditioning Research
10. Foran, B. Advantages and disadvantages of isokinetics, variable resistance, and free weights. National Strength & Conditioning Association Journal
11. Stone, M.H., S.S. Plisk, M.E. Stone, et al. Athletic performance development: Volume load-1 set vs. multiple sets, training velocity, and training variation. National Strength & Conditioning Association Journal
12. Potteiger, J.A., L.W. Judge, J.A. Cerny, et al. Effects of altering training volume and intensity on body mass, performance, and hormonal concentrations in weight-event athletes. Journal of Strength and Conditioning Research
13. Alexander, M.J.L. The relationship between muscle strength
and sprint kinematics in elite sprinters. Canadian Journal of Sports Science
Keywords:© 2005 American College of Sports Medicine
Strength; Power; Hypertrophy; Local Muscular Endurance; Periodization