Following on from my article on muscle and muscle fibers, we know that we have two types of muscle fibers, slow twitch and fast twitch. The larger, faster-contracting fast-twitch fibers have a greater potential for the development of tension. Individuals who have a higher percentage of fast-twitch fibers have a greater potential for force development. Studies of human muscle tissue reveal that weight lifters have twice the area of fast twitch fibers as non lifters. This size can be attributed to both genetics and to training. The effect of strength training on muscle fiber types has yet to be completely resolved; but current evidence indicates that both types grow larger with training, but growth of the fast fibers is more pronounced. Strength training improves the capabilities of both types but doesn’t seem to change one type to another.
Types of Strength.
Strength can be measured and developed in several ways, each of which is highly specific. How the strength will be used should dictate the type of training and testing.
Also called isotonic, dynamic strength is defined as the maximum weight that can be lifted once with strict form (1RM). This is actually a measure of strength at the hardest part of the lift, usually at the beginning. Because the mechanical advantage of your muscle lever system changes, a lift such as a Bicep curl becomes easier after you overcome the initial resistance and angle of the pull. Dynamic strength measurements are related to performance and work. Weight lifting with machines or free weights is the most common forms of isotonic training. (“Isotonic” means “same tension”)
The measure of static strength is achieved when you exert maximal force against an immovable object. Also called isometric strength, it is specific to the angle at which it was trained. It doesn’t necessarily reflect dynamic strength or strength throughout the range of motion. You train by exerting near maximum force against an immovable object. The muscle doesn’t change length appreciably during the contraction. (Isometric means “same length”)
Isokinetic strength is measured with an expensive electronic or hydraulic apparatus. It allows the exertion of maximal force throughout the range of motion, as well as the control of speed of contraction. Through such devices have become popular testing aids, it is not yet clear to what extent strength throughout the range of motion is related to performance. (Isokinetic means “same length”) Sports physiotherapists use isokinetic devices in rehabilitation exercises.
Muscular endurance means the ability to persist. It is defined and measured as the repetition of sub maximal contractions or sub maximal holding time (isometric endurance). Muscular endurance is essential for success in many work and sport activities. Once you have the strength to perform a repetitive task, additional improvement in performance will depend on your muscular endurance, the ability to persist. As mentioned earlier, stronger fast twitch fibers fatigue more readily. So endurance and strength are not highly related, except when a very heavy load is used in an endurance test.
Endurance and Strength.
Endurance and strength are different in physiologic terms. Endurance is achieved by repetitive contractions of muscle fibers. Repetitive contractions require a continuous supply of energy, and muscle fibers with aerobic (oxidative) capabilities (slow oxidative, fast oxidative glycolytic) are suited to the job the repetitive contractions enhance aerobic enzymes, mitochondria, and the fuels needed for repetitive contractions. Strength comes from lifting heavy loads a few times. The effects of strength training are most noticeable in fast-twitch fibers. Training effects include increases in contractile proteins (actins and myosin) and tougher connective tissue. The increased strength comes from greater cross-sectional area, which means more contractile protein to exert force. So the type of training as well as the physiological effects of endurance and strength training is quite different. This should be kept in mind when planning a training programme. Endurance is important for practice, training, and performance. Repetition leads to skill, and repetition requires endurance, so endurance if one of the keys to success in sport or work.
Benefits of Muscular Fitness.
How does training lead to changes in muscle fibers? How does a muscle fibre know the difference between strength and endurance training? Part of the answer to these questions is related to the training stimulus, the characteristic of training that leads to specific adaptations. Strength improves when sufficient tension is applied to the muscle fiber and its contractile proteins. The tension required seems to be above two thirds of the muscles maximal force. If you do contractions that require little tension, you won’t gain much strength. Contraction time, the total number of repetitions, also seems to influence the development of strength (Smith and Rutherford 1995). Do more contractions and you obtain better results, up to a point? The number of contractions depends on your level of training, nutrition, and also your genetic potential. You will receive benefits from any form of strength training, as long as you exert enough tension for a sufficient number of repetitions (or time).
Strength = Tension x Time (number of sets and repetitions)
Muscular Fitness Training.
In training we often hear the term overload principle, which states:
- For improvements to take place, workloads have to impose a demand (overload) on the body system (above two thirds of maximal force for strength)
- As adaptation to loading takes place, more load must be added
- Improvements are related to the intensity (tension for strength), duration (repetitions), and frequency
Overload training lads to adaptations in the muscles according to the type of training. The principle of specificity applies here, as it did with aerobic training, the adaptation to strength training includes increased muscular size due to increases in contractile proteins (actin and myosin) and tougher connective tissue. These and other adaptations allow the muscle to exert more force. The specific adaptations to muscular endurance training include improved aerobic enzyme systems, larger and more numerous mitochondria (increased mitochondrial density), and more capillaries. All these changes promote oxygen delivery and utilisation within the muscle fibre, thereby improving endurance. (Jackson and Dickinson 1988), Fatiguing repetitions somehow stimulate the muscle fibre to become better adapted to use oxygen and aerobic enzymes for the production of energy (adenosine triphosphate [ATP]) to sustain contractions. Perform more repetitions, and you then become better able to use fat as a source of energy.
The table below reviews the effects of each type of training. It shows that high resistance training leads to the development of strength and that the low resistance repetitions lead to muscular endurance, and suggests that there are still questions regarding the effects of training that falls between strength (high resistance and low repetitions) and endurance (low resistance and high repetitions). The table can help identify your training goals.
|Strength||Short term (anaerobic) endurance||Intermediate endurance||Long-term endurance|
|For||Maximum force||Brief (2-3 minute) persistence with heavy load||Persistence with heavy load||Persistence with lighter load|
Over 100 RM
|Improves||Contractile protein (actin and myosin) ATP & CP. Connective tissue||Some strength and anaerobic metabolism (glycolysis)||Some endurance and anaerobic metabolism. Slight improvement in strength for untrained.||
Aerobic enzymes. Mitochondria.
Oxygen and fat usage.
RM = Repetitions max. ATP = Adenosine Triphosphate. CP = Creatine Phosphate
Strength contributes to performance in work and in sport, and strength training puts stresses on the bones, which leads to stronger bones and a lower risk of osteoporosis. Strength training can also be used to tone muscles as well as improve your appearance and, within genetic limits, your shape. In addition, strength training will certainly help you lead an active and vigorous life, well beyond retirement years. So how does this simple mode of exercise get such remarkable results?
Strength training, also called resistance training or weight training, involves high resistance and low repetitions and leads to the following adaptations.
- Increased contractile protein (actin and myosin)
- Tougher connective tissue
- Reduced inhibitions
- Contractile efficiency
- Possible increase in number of muscle fibers
Years ago, Gordon (1967) compared the effects of strength and endurance training on muscle proteins. The results have since been corroborated in labs throughout the world. Strength training adds to the portion of the muscle that generates tension, the contractile proteins. Endurance training, on the other hand, enhances the energy supply system, the aerobic enzymes (all enzymes are constructed of proteins). But the most surprising outcome of his study was the observation that strength training brought about a decline in endurance enzymes, and that endurance training lead to a decline in contractile protein. Thus if you train for only strength or endurance, you could lose a bit of the other. This aspect of specificity shouldn’t be so surprising, the size and strength of the thigh muscles increase during weight training but decline somewhat when you return to distance running.
Connective tissue and tendons grow in size and toughness when they are placed under tension. This increased toughness in tendons may help quiet the inhibitory influence of the muscle receptor known as the tendon organ, a receptor sensitive to stretching. The increase in thickness of connective tissue contributes some to the growth or hypertrophy of the muscle.
Some of the effects of strength training occur in the nervous system. With experience we seem to have fewer inhibitions, both in the central nervous system and from muscle receptors. Practice (repetition) allows us to be more efficient, more skilled in the application of force. Thus practice alone accounts for some of the improvements in the early stages of training. This may explain why involuntary contractions bought on by an electrical stimulator, do not equal the results obtained with voluntary contractions. Involuntary contractions may elicit changes in the muscle, but they don’t teach the nervous system how to contract (Massey et al. 1965)
The ability to look at samples of human muscle before and after training has led to some fascinating questions. Such as; can stretch training lead to the formation of addition muscle fibers?
Studies on human muscle suggest that we may be able to increase the number of muscle fibers when overloaded fibers split to form new fibers. However, this finding is still the subject of some scientific debate. Athletes who spend hours each day lifting weight and also use hormones (anabolic steroids, growth hormone) to promote extra growth, increased fibers may be possible (however, the use of anabolic steroids has been found to lower HDL (good) cholesterol and increase the risk of heart disease). The available evidence does suggest some differences between the high resistance/low volume training of power lifters and the medium resistance/high volume training of bodybuilders. The high resistance training seems to increase the size (hypertrophy) of fast twitch fibers, whereas the medium resistance/high volume training causes selective hypertrophy of slow twitch fibers. (Tech, Thompson, and Kaiser 1984), Here again the response seems to be specific to the type of training.
Muscular Endurance Training.
Endurance training which involves, low resistance and high repetitions, leads to the following adaptations:
- Increased aerobic enzymes
- Increased mitochondrial density
- Increased capillaries
- More efficient contractions
- Possible changes in fiber type (e.g., fast twitch to slow twitch.
Having already mentioned the effects of endurance training on aerobic enzymes, particularly those involved in fat metabolism; on mitochondria; and on capillaries. More efficient aerobic pathways are available to provide more energy from fat, thereby conserving muscle glycogen as well as blood glucose, which is the preferred fuel of the brain and nervous system. As a result, muscles that once fatigued in minutes become able to endure for hours. Some of the effects of endurance training take place in the nervous system. Skilled, more efficient movements conserve energy, thereby contribute to endurance. But the most documented effects of muscular endurance training seem to focus on the muscle.
Methods of Training.
What is the best method to train for strength or endurance: static, dynamic, or isokinetic methods? The answer depends on what you are training to accomplish the goal of your training. If you just want to get stronger, almost any method will work, if you want to gain strength to improve performance in work or sport, your training should be specific to your goal. A study done in which college women trained with weights (isotonic), isokinetic devices, or callisthenics. The isotonic group did the best on lifting tests, and the callisthenics group scored best on the callisthenics tests. The isokinetic training group, which gained strength on the isokinetic devices, came in third on the other two tests. This study showed how important it is to train in the manner in which the strength will eventually be used. (Sharkey ET al.1978).
Static (Isometric) Training.
Static contractions were the rage in the early 1960’s. Professional athletes were using the technique that promised dramatic results in just six seconds a day. (Most unproven techniques resort to the use of celebrity claims to fool some unsuspecting consumers). Based on an early study conducted in Germany (Hettinger and Muller 1953), the technique was popular until studies finally compared isometrics with traditional weight lifting, and static contractions, came in a distant second. Isometric contractions don’t provide a sense of accomplishment through lifting something, they elevate blood pressure, and they are seldom specific to the training goal. Isometrics do have some uses in rehabilitation, when that is all that can be done; for work at the sticking point of a lift; and in activities where static strength or endurance is required (e.g., archery). More recently, isometric contractions have been used in conjunction with weightlifting to produce better results. The weight is lifted and then held against an immovable object for several counts in a technique known as functional isometrics.
Dynamic (isotonic) Training.
Isotonic contractions (weightlifting) gained popularity when DeLorme and Watkins (1951) outlined a formula for success. Simply stated, the formula called for high resistance/low repetition exercise. Variations of the formula; is still used to develop dynamic strength. Because the resistance is high only at one point of the lift (usually the start), there has been some question about the value of the technique. Iso- tonic programs compare well with isokinetic training, especially when participants are tested on isotonic tests. Free weights and weight machines are normally available in most health clubs. And weightlifting with free weights is the normal method of choice for most serious athletes, and bodybuilders. Though fitness buffs usually lift three days a week, various athletes increase the strength training stimulus by doing five or more sets of each exercise and by training five or six days a week.
Isokinetic exercises combine the best features of isometric (near maximal force) and isotonic (full range of motion) training. With the appropriate device it is possible to overload the muscles with a near maximal contraction throughout the range of motion, and to control the speed of contraction. Theoretically, this method should lead to strength throughout the range of motion. The problem if there is one, seems to be the lack of specific devices for many sports skills. But as more devices are developed for specific sports, isokinetic training may become ever more popular.
Which Method is the Best?
There is no best method for strength and endurance training. Free weights are inexpensive and versatile but require more supervision for safety. Weight machines are convenient and require less supervision. Iso kinetic devices are effective but limited in application. Variable and accommodating resistance devices adjust the resistance to the available force. Popular in health clubs, they are useful for fitness and sport and have one special advantage: Unlike weightlifting, isokinetic training doesn’t cause muscle soreness. So it can be done in conjunction with other activities without affecting performance. Be sure the training program you adopt is appropriate to your level of fitness and ability. What is best for beginners doesn’t work for athletes, and vice versa. In sports psychology many theories are based on research based on university studies. In exercise physiology, numerous studies have been conducted on experienced lifters. When various forms of strength training are compared on lifters, they all seem to give similar results; in other words, follow the prescription and anything works with beginners. But doesn’t predict how the method will work on athletes or experienced lifters with higher levels of strength. Also it doesn’t prove that the increased strength will improve performance.
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