special subjects
Overview of Exercise
Strength Training
Strength (resistance) training involves forceful muscular contraction against a load—typically provided by free or machine weights, cable weights, or sometimes body weight (eg, push-ups, abdominal crunches, chin-ups, deep knee bends). Such training increases muscle strength, muscle endurance, and muscle size. Strength training also improves functional ability and, depending on the pace of the program, aerobic performance. Cardiovascular endurance and flexibility increase concurrently. Also, strengthened muscles around an injury (eg, thigh muscles with an injured knee) decrease pain, because strengthened muscles are more functional, and more functional muscles have less pain as they develop and restructure. Thus, a strength training program may help in injury rehabilitation. Volumetypically is categorized in terms of amount of weight lifted, the number of sets, and the number of repetitions per set. However, an equally important parameter is tension time, which is the total duration of lifting and lowering the weight during one set. To achieve moderate conditioning (developing both muscle mass and strength), appropriate tension time may be about 60 seconds. A tension time of 90 to 120 seconds is appropriate for injury rehabilitation and improving muscular endurance. When the goal is increasing strength, tension time is more important than number of repetitions, because the number of repetitions can vary within tension time due to differences in technique, set duration, and how slowly each repetition is performed. When a person can achieve at least a 60-second tension time with good technique, resistance (weight) can be increased with the aim of a tension time of at least 60 seconds at the next weight level. Number of sets is determined by intensity of the training; more intense training may necessitate fewer sets. Intensityis essentially a subjective measure of perceived effort and how close a person comes to muscular fatigue in a given set (or exhaustion in a workout). Intensity may also be characterized objectively by the amount of weight lifted expressed as a percentage of the person’s maximum for one repetition (1 RM) of a given exercise; ie, for a person who can deadlift at most 100 kg one time, 75 kg is 75% RM. A general guideline is to exercise with a load at 70 to 85% RM. Heavier loads increase risk of injury and are usually appropriate only for competitive strength athletes. Lifting<30 to 40% RM provides minimal strength gain, although aerobic conditioning and muscular endurance may occur with sufficient tension time and effort. During strength training, the stimulus of tissue change is governed primarily by the quality, effort, and volume of training. For example, a person lifting 85% RM once (where 6 repetitions could be done with maximal effort) would have less stimulus for tissue change than if lifting 75% to 80% RM multiple times (close to or at muscular fatigue). Intensity is limited by motivation and tolerance. For many patients undergoing rehabilitation, discomfort, pain, exercise inexperience, and/or limitation in range-of-motion (due to discomfort or pain) result in less effort than may be possible or tolerated. As a result, more sets are required to derive desired benefit (although the extent of adding more sets must take into consideration that doing too much activity can increase irritation and soreness to an injury). People should vary the intensity of workouts regularly to provide both a mental and a physical break. Exercise should be done at the highest intensity level during no more than half of the sets in a given workout. People should incorporate breaks or layoffs from high-intensity training (eg, 1 week every 3 months, perhaps coordinated with holidays or vacations) into their fitness planning to allow for sufficient recovery. More frequent layoffs may be required for those who train with very high intensity frequently. Continual high-intensity training is counterproductive, even for trained athletes. In such people, symptoms such as fatigue or muscle heaviness when not exercising, lack of motivation to exercise, reduced exercise performance, joint and tendon pain (caused by inflammation), and increased resting heart rate suggest that exercise has been too intense for too long. Some people are conditioned mentally or physically to train very hard regularly (eg, athletes training at high-intensity), and so, in such people recovery breaks may be required (eg, 3 weeks on and 1 week off) to recover from such strenuous and regular activity. Maximizing muscle hypertrophyrequires good effort. However. exercising until the muscle can no longer do the repetition (muscle failure) is unnecessary and may be difficult to tolerate. The number of sets needed to maximize muscle hypertrophy varies based on a person's genetics—some people increase muscle hypertrophy with more sets, and others have better results with fewer sets. Regardless of the number of sets or exercises, the amount of improvement diminishes with each additional repetition or exercise. Doing too much exercise does not produce any better results and can result in loss of muscle and strength from overstimulation. Beginners should start with 1 set or exercise per muscle or muscle group and then slowly increase repetitions or exercises until reaching 3 to 5 sets of 1 exercise or 1 set each of 3 to 5 exercises, particularly if they do not train to muscle failure. Variationhelps by providing different stimuli; use of the same stimulus (eg, exercises in the same plane of movement) repeatedly eventually fails to elicit the desired effects because muscles adapt to the stimulus. Variation also helps prevent minor injuries caused by repetitive actions. Proper body mechanicsare important for personal safety and effective strength training. People should strive for proper body mechanics (eg, chest high, shoulders square and back, and stomach pulled in tight, while refraining from locking the joints) and exercise with smooth and continuous motions without jerking or lowering weights too quickly. It is equally important to encourage controlled breathing, which prevents dizziness (and in extreme cases, fainting) that can occur with the Valsalva maneuver. People should exhale while lifting a weight and inhale while lowering a weight. If a movement is slow, such as lowering a weight for≥5 seconds, people may need to breathe in and out more than once, but breathing should still be coordinated so that a final breath is taken in just before the lifting phase and released when the lift begins. Blood pressure increases during resistance training (unrelated to atherosclerosis) and tends to be highest when gripping excessively (common during the leg press exercise when working the large lower body muscles and clenching the machine's hand grips very tightly). However, blood pressure returns to normal quickly after exercise; the increase is minimal when breathing technique is correct, regardless of exertion. 