The principle of progression states that if an exercise program is to produce the desired outcome, the intensity should gradually become more challenging to apply an effective overload. This tells us that an individual needs to work harder, but that the changes to a program should be incremental and not occur all at once. Progression and overload are closely related—the intensity of the overload should increase gradually, 5 percent or less at a time, to allow the body to receive and adapt to the new stimulus.

A set is defined as a group of repetitions before taking a rest interval to allow recovery. According to the American College of Sports Medicine (ACSM) Guidelines for Resistance Training, one set of 10 to 12 repetitions to momentary muscle fatigue is sufficient to create initial strength improvements in clients with little-to-no training experience. However, once a client experiences initial strength gains as a result of improved recruitment of involved muscle fibers, the number of sets needs to be progressed to apply an overload and create the desired training effect. This is why clients can seem to make strength gains relatively quickly when they are consistently training—the nervous system becomes more effective at recruiting and using the involved muscle fibers to generate the necessary force.

Weight lifting tempo is the program design variable referencing the speed of movement for an exercise. A different consideration of tempo is the time under tension (TUT), which is the length of time that muscle fibers are under mechanical tension from a resistance-training exercise. Along with intensity, TUT is critical for creating the desired stimulus for increasing muscle definition or size. Mechanical strain on muscle fibers signal the mechanisms responsible for repairing structural damage to existing fibers and laying down the foundation for new muscle cells.

To review, a repetition is compromised of three distinct phases of muscle action: 

• Eccentric: The muscle is lengthening, yielding to the force of the applied resistance while storing mechanical (potential) energy, which is then released during the concentric phase of muscle action. Depending on the skill level and training goal of a client, this phase can last from a very brief instant to a number of seconds.

• Isometric: The muscle is developing tension and contracting, but no joint movement occurs. During an exercise, this is the transition from lengthening (storing potential energy) to shortening (the release of kinetic energy). The technical term for this action is the amortization phase, and it can last from milliseconds during an explosive exercise to an extended period of time for an isometric exercise.

• Concentric: The muscle is shortening, releasing the mechanical (kinetic) energy to generate the force required to overcome an applied resistance. This phase can last from a brief instant during an explosive exercise to a period of 15 seconds or longer during a slow-tempo exercise.

In most strength training programs, weight lifting tempo is expressed as eccentric-to-isometric-to-concentric, which means that a 3:1:1 tempo = 3 sec. eccentric : 1 sec. isometric : 1 sec. concentric. While TUT in the eccentric phase provides a strong stimulus for muscle growth, the overall goal of the training program, the amount of intensity used and the client's experience dictate the tempo of an exercise.

• Maximum strength training with heavier loads (85-100% 1-RM) generally requires a faster, more explosive tempo to create a mechanical stimulus and recruit all available muscle motor units. Even though the weight might not be traveling that fast, the lifter is pushing as hard as possible to generate momentum, which is defined as the product of a mass and its velocity.

• Training for hypertrophy (muscle volume) and strength endurance requires keeping a muscle under tension for an extended period of time to create the metabolic stimulus necessary for growth.

Recommended Exercise Tempos Based Upon Resistance Training Goals 

Reference:  NSCA Essentials of Strength and Conditioning, 3rd edition (2008)

Sets and tempo are closely related and both are an effective way to apply the principle of progression. The initial gains from resistance training are the result of improved neural activation of muscle contractions. A client new to resistance training should start with one to two sets per exercise using a slow-to-moderate tempo (3:1:2 to 4:2:3) to recruit the motor units to activate their attached muscle fibers. Delayed onset muscle soreness (DOMS) can be attributed to extended eccentric phases; thus, slower tempos coupled with higher rep ranges increases the quantity of eccentric work performed. Keep in mind that, for a new client just starting a strength-training program, muscle soreness can negatively affect participation.

Probably the worst feedback I ever received came from a client who e-mailed to let me know her legs were so sore that she couldn't get out of bed. This is not a good thing. While a little muscle soreness is good, as it’s an indication the training session was at an appropriate level of intensity, too much muscle damage can be dangerous because it could create toxicity in the blood stream (known as rhabdomyolisis), which could send a client to the hospital or even be fatal. A client might seem like he or she is not affected by the workout, but be sure to monitor the quantity of sets and pace of the exercise tempo, especially for new clients, to reduce the risk of DOMS. Also, be sure to inform them that they might experience some muscle soreness, but that it is simply an indication the training program is having the desired effect.

Once a client has experienced the initial strength gains and adjusted to the physical demands of resistance training, tempo can be sped up to a 2:1:1 or 1:1:1 pace and the number of sets can be increased to progressively increase the training stimulus enough to create the necessary overload to continue making adaptions. Three to four sets is generally considered effective for younger, healthy adults seeking aesthetic results from strength training, while one to three sets can be considered optimal for older adults seeking health benefits.

Progressively applying an overload by simply increasing the number of sets per workout requires additional time that might not be available during the allotted appointment with a client. An exercise program can be organized in a variety of ways to progress the level of difficulty and increase the amount of training stimulus without having to extend the length of the training session. The table below identifies a variety of examples of how sets can be organized to create different workout programs, each one with a distinctly unique physiological challenge. Just as sets can be manipulated to create a different training effect, the tempo can be increased to create explosive movements for power exercises or slowed down to increase the metabolic demand on a muscle for an extended period of time.

There is an almost limitless number of ways to organize sets in a workout. The table below contains some examples to give you a few ideas, but the sky is the limit with your creativity. Exercising to stimulate physical adaptations requires placing metabolic or mechanical stresses on the body, both of which trigger the mechanisms responsible for a number of desired adaptations, such as weight loss, muscle growth or enhancing definition.

Once I learned how to play around with sets and tempo, I found that I could keep the exercises relatively consistent, but increase or decrease the level of difficulty by having clients do circuits or compound sets with minimal rest. Or I could have them use an explosive tempo to increase the speed of motor unit recruitment and change the metabolic work-rate. The next time you find that you or your clients are getting a little stale, simply reorganize the sets or tempo and see if it can make a difference. I'm betting that it does.

Part 1: How to Select the Right Exercises for Your Clients

Part 2: how to Select the Right Intensity and Repitions for Your Clients