Muscular strength is essential for optimal health, well-being, functional ability and enjoyment of life. Research shows we tend to lose muscle mass as we age. Between the ages of 20 and 75, people typically lose as much as 30 percent or more of their muscular strength. However, this tendency to lose lean body mass can be reversed through strength training.

In addition to maintaining lean body mass, the benefits of strength training include improved body composition, glucose metabolism, functional ability for daily activities, body image and self-esteem, a higher metabolism, increased energy, stronger bones, protection against low back pain, reduced stress, better sleep and generally a higher quality of life. The good news is people are becoming aware of these fantastic benefits that go beyond improvements in physical appearance. From young to older adults, people are hitting the weight room.

The American College of Sports Medicine (ACSM) recommends the following guidelines for muscular strength and endurance training:

• one set of 8 to 12 repetitions for healthy adults
• one set of 10 to 15 repetitions for older (ages 50 and above) and frail individuals
• 8 to 10 exercises, for major muscle groups, two to three days per week.

Major muscle groups include the arms, shoulders, chest, abdomen, back, hips and legs. To best complement functional activities, dynamic resistance exercises are recommended. Exercises should be rhythmical and performed through a full range of motion, at a moderate to slow speed, with controlled breathing during lifting movements.

These guidelines, issued in 1998, are based on evidence from numerous research studies. According to ACSM, these guidelines are effective for improving muscular strength and endurance in untrained adults during the first three to four months of training. However, adults who wish to continue improving muscular fitness need additional guidance regarding how to progress their training program.

New Resistance Training Progression Guidelines:
Since the release of the ACSM guidelines, exercise physiologists and scientists continued to evaluate strength training parameters to learn more about how the body responds to resistance exercise. In February 2002, ACSM issued "Progression Models in Resistance Training for Healthy Adults." This position stand extends the 1998 training guidelines with information on how to set appropriate progression goals. It also emphasizes the importance of individualized training programs with trained exercise specialists.

The statement defines progression as "the act of moving forward or advancing toward a specific goal." In resistance training, progression is continued improvement in a specific variable, such as muscular strength, power, hypertrophy or local muscle endurance, over time. Resistance training can enhance speed, balance, coordination, jumping ability, flexibility and other motor performance measures.

To continue improvement, training programs can manipulate variables, such as the amount of resistance (i.e., load or intensity), exercise selection and order, number of sets and repetitions, speed of repetitions, length of rest period and volume (i.e., represented by both the total number of repetitions and amount of resistance). The ACSM statement notes that continued progress over the long term requires variety in volume and intensity of muscular training exercises. To avoid overtraining, volume should not be increased more than 21/2 to 5 percent. Training progression methods affect muscle strength, size, definition, power and endurance.

Periodization:
Linear and non-linear periodization are recommended for effective exercise variety. Linear periodization, also known as the classic model of periodization, features a high initial training volume consisting of a higher number of reps and sets combined with a low intensity or lesser weight. Over time, the training program progresses to a lower volume or fewer reps and sets, with a higher intensity by using more weight. The purpose of this progression is to increase muscle strength, power or both.

Non-linear or undulating periodization provides training variety by rotating different loading schemes for a core exercise program of major muscle groups over a 7- to 10-day cycle. In any single workout, only one characteristic, such as strength, power or local muscle endurance, is trained. This approach attempts to train various components of the neuromuscular system rather than train for strength first and then power?as in the classic linear model.

Program Variables for Beginner to Advanced:
Evidence shows resistance training progression occurs in an orderly manner. Beginning exercisers, who start with an initial basic conditioning program, need to progress to more specific program designs as their conditioning improves and rate of improvement slows. For example, beginners following a basic program are likely to experience an increase in muscle strength, size, power and local endurance. However, a highly trained individual needs specific programs to improve each of these aspects. The guidelines recommend program designs progress from simple to complex during the advancement from novice to intermediate and advanced training.

Muscular Strength:
To improve muscular strength, the guidelines recommend beginning and intermediate exercisers train for 8 to 12 repetitions, at 60 to 70 percent of their maximum capacity, for one lift. They should progress at a 2 to 10 percent increase, depending on the muscle group, when one or two repetitions, more than the desired rep range, can be performed on two consecutive training sessions. To best increase muscle strength, the volume should be low for beginners and increased over time.

Exercises should include both single and multiple-joint movements, with an emphasis on multiple-joint exercises. A squat is an example of a multi-joint exercise that works both the knee and hip joints as well as targets the quadriceps, hamstrings and gluteal muscles. If an exerciser performs a squat using free weights, he also challenges the body?s core stabilizer muscles to maintain neutral postural alignment.

A combination of weight machines and free weights are recommended for beginners, while advanced exercisers should emphasize on using free weights. When training, large muscle groups should be challenged before smaller muscle groups, multiple-joint exercises should precede single-joint exercises and higher intensity exercises should be done before lower intensity. The guidelines also recommend starting with slow to moderate velocities. Moderate velocities are recommended for intermediate exercisers, while advanced exercisers can use a continuum of slow to fast velocities.

Muscle Size and Definition:
To enhance muscle size and definition, training variables should be low to moderate for beginning and intermediate exercisers. For advanced exercisers, variables should be increased to higher levels to continue increase in muscle size.

Muscular Power:
A muscle has more power when it produces the same amount of work in shorter amount of time or more work in the same amount of time. To increase power, the ACSM guidelines recommend multiple-joint exercises, especially those involving the total body. Rest periods and frequency should be the same as those for increasing muscular strength. The progression of training depends on the exerciser?s goals.

Muscular Endurance:
Muscular endurance is the maximum number of repetitions a muscle can perform with a specific training load. Endurance is improved by longer duration sets (e.g., 15 to 20 reps or more) with shorter recovery time between sets. The guidelines recommend short rest periods (i.e., one to two minutes) for high-repetition sets of 15 to 20 reps or more and less than one minute for moderate sets of 10 to 15 reps. To improve muscular endurance, ACSM guidelines recommend performing both single- and multiple-joint exercises targeting specific muscle groups, using varied sequencing, lighter loads and increased repetitions. Slow speed is recommended for a moderate number of repetitions, such as 10 to 15. For high numbers of repetitions in the 15 to 25 range or more, moderate to faster velocities are recommended.

Progression for HEALTHY Older Adults:
To enhance muscle strength and size, healthy older adults should also participate in progressive resistant training. The rate of progression, however, should be gradual with particular attention to recovery. The guidelines recommend that healthy older adults perform multiple and single-joint exercises, at a slow to moderate speed, with a one- to two-minute rest period between sets. To increase power, use a light to moderate load for 6 to 10 repetitions (40 to 60 percent of maximum capacity) at a faster speed. For improvements in muscular endurance, use low to moderate loads for repetitions of 10 to 15 or more with short rest intervals.

Conclusion:
The guidelines conclude by reiterating the importance of qualified trainers, "Trained and competent strength and conditioning specialists should be involved [in] this process to optimize the safety and design of a training program." To keep your clients interested in their fitness programs, emphasize the important benefits of a resistance training program. Through effective resistance training program design, your clients will reap the rewards of a better quality of life as well as experience the continued rewards of their commitment to training. For more information, the ACSM guidelines are available at www.acsm.org.
By Shirley Archer J.D., M.A.

Shirley Archer, J.D., M.A, authored The Everything  Weight Training Book and is an internationally recognized health and wellness educator, an award-winning author and a Master fitness trainer.

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