The Role Of Genetics in Strength Training Your Genetic makeup is the single most important ingredient in determining your potential for improving your muscular size and physical strength. 1. Predominant Muscle Type Fiber types may be grouped into two major categories a. slow twitch (SW) type I contract slower and produce less force, but they have greater endurance. b. fast twitch (FT) type II can contract quickly and generate large amounts of force, but they fatigue rather easily. Each person s muscles are composed of both fiber types, and the different types are intermingled throughout each muscle. However, the distribution of FT and ST fibers within each muscle is genetically determined. Some individuals have inherited a predominantly fiber type that allows them to be successful in certain activities. A high percentage of FT fibers would be found in the musculature of a sprinter, shot putters, football players, competitive weightlifters and any other athlete whose success in predicated upon rapid, powerful movements. A high distribution of ST fibers would be found in a long distance runner or any individual who excels in events that require large amounts of muscular endurance. It should also be noted that an individual s fiber type mixture may differ from one muscle to another and may even vary from one side of the body to the other.
Implications on Strength Training Both FT and ST muscle fibers have the potential for hypertrophy (increase in muscular size). However, FT fibers display a much greater capacity for hypertrophy than ST fibers. This indicates that people who have a high percentage of FT fibers have a greater potential to increase the size of their muscles. Because FT fibers can produce greater force than ST fibers, these individuals also display a higher potential for strength gains. *No conclusive evidence exists to suggest that strength training will change ST fibers to FT or vise-versa. 2. Muscle-to-Tendon Ratio Another factor that determines a person s potential for increasing muscular size and strength is the relationship between the muscle belly length and the tendon length. The muscle organ consists of two parts : the belly (which is predominantly muscle fiber) and the tendon (the fibrous connective tissue) The potential for muscular growth is directly related to muscle length A person with a muscle-to-tendon ratio depicted by A would have a greater genetic potential for achieving muscular size than a person having a muscle-to-tendon ratio shown by B. Taken from Brzycki, M. A Practical Approach to Strength Training
3. Testosterone Levels Although it is a male sex hormone, testosterone is also found in the blood of perfectly normal women Testosterone encourages protein synthesis and influences secondary sexual characteristics (deeper voice, facial hair, broad shoulders, etc) Testosterone stimulates skeletal growth and the development of the male structure. It s major action is to promote growth. Because of this, individuals who inherit above average levels of testosterone have a greater potential for accelerated growth and maturation. Note : The imagined philosophy of more is better (ie steroids), while sounding good, is not applicable to the physiological reality that more will upset balance the body s homeostatic mechanisms sever to keep the body s internal environment in a finely tuned balance. 4. Lever Lengths Some people inherit short levers (ie bones) and other bodily proportions that give them a significant advantage in biomechanical leverage. For example, if you could line up the best bench presser in the world, you would notice thtt they tend to have similar body dimensions relatively short arms and thick chests. People with short arms are at a distinct advantage in most pushing a pulling movements because they don t have to move the weight as far as someone with longer arms. Interestingly, an individual with longer arms may be doing more work than someone with shorter arms even when using less weight. Example : The first person has arms that are 20 inches long and can bench press 200 pounds; The second person has arms that are 24 inches long and can bench press 180 pounds. Because work is defined as Weight x Distance, The 200-pound bench presser has done 4,000 inch-pounds of work
(20 inches x 200 pounds) The 180-pound bench presser has done 4,320 inch-pounds of work (24 inches x 180 pounds) Therefore, even though the second person cannot bench press as much weight as the other, the effort of the second person is actually greater because the weight is moved a greater distance. 5. Somatotypes There are three main terms used to describe a person s body type : endomorph, mesomorph and ectomorph. Endomorph An endomorph is characterized by softness and round features. Endomorphs have a high percentage of body fat and very little muscle tone. A sumo wrestler would be an example of an extreme endomorph. Mesomorph Mesomorphs are typified by a heavily muscle physique. They have athletic builds with broad shoulders, large chests and slender waists. Ectomorphs Ectomorphs are characterized by long limbs, leanness and a slender physique. They have little body fat but also little in the way of muscular development. Sucessful long-distance runners are usually ectomorphs.
Rating System Since almost everyone has some degree of each component, a rating system was developed in which a person is given a score in each of the three areas. The original system used a scale form 1 to 7 to designate the degrees of each of the three components. Numeral 1 represents the least amound of the component, while numeral 7 indicates the greatest. Therefore, a somatotype of : 7-1-1 : would indicate extreme endomorphy (fatness) 1-7-1 : would indicate mesomorphy (muscularity) 1-1-7 : would indicate extreme ectomorphy (leanness) 6. Tendon Insertion points At one time or another, most of us have encountered an individual who was far stronger than he or she appeared to be. In fact, the person may have been incredibly strong despite not being very muscularly developed. How is this possible if strength is directly related to muscle size?
The farther away a tendon inserts from the axis of rotation the greater the biomechanical advantage. (Taken from : Brzycki, M. A Practical Approach to Strength Training) In this example, the force necessary to maintain the resistance in a static position can be calculated using the formula : force x force arm = resistance x resistance arm. The force arm is defined as the distance from the axis of rotation (elbow) to the point where the force is applied (the insertion point of the tendon); the resistance arm is defined as the distance from the axis of rotation to the point where the resistance is applied. 7. Neurological Efficiency This refers to a person s inherited proficiency at innervating muscle fibres. It has been suggested that some people can recruit a higher percentage of their available muscle fibers than other people, which gives them a decided advantage in terms of strength potential. It has been proposed that neurological efficiency is inversely proportional to anaerobic muscular endurance. This means that you have a high level of muscular endurance, you are not very efficient neurologically. Likewise, if you have a low level of muscular endurance, you are more likely to possess an efficient neurological system. If A can recruit more muscle fibers that B, it follows that B will have more muscle fibers in reserve. Everything else being equal, A would exhibit a greater capacity for strength and B would have greater muscular endurance.
Heritability versus Trainability In terms of results from a weight training program, all individuals are not created equal. If you perform the exact strength training program as someone else for a period of time, the odds are that you won t end up looking like physical clones of each other. Each person responds differently because each person is a unique genetic entity with a different genetic potential for achieving muscular size and strength Whether your sets consist of low repetitions, high repetitions or intermediate repetitions you re still going to develop according to your inherited characteristics - provided that the sets are done with similar levels of intensity.