The Development Of Bones
Bones offer much more than simply the frame of the body. In addition, they also are important for protection of vital organs (such as the brain and central nervous system), storage of many nutrients (including calcium and phosphorus), allow the muscles something to pull on for movement, and they are also responsible for red blood cell development. In the human embryo, the skeleton is composed of either fibrous membranes or hyaline cartilage. The ossification process (whereby these fibrous membranes and cartilage gradually evolve into bone), actually starts as early as six weeks after conception. Two types of ossification have been identified:
• Intramembranous ossification: The simpler of the two processes, intramembranous ossification is responsible for the formation of the flat bones of the roof of the skull, the lower jawbone, and most of the collarbones. Intramembranous ossification occurs when osteoblasts (cells that are responsible for bone formation) begin to cluster in the fibrous membrane of the embryonic “skeleton”. This cluster site is called the center of ossification. The osteoblasts next secrete intercellular fibrous substances which form a matrix or framework in which calcium salts are deposited (a process known as calcification). eventually, numerous calcified cluster fuse onto the latticework of spongy bone. The spaces between the clusters (called “trabeculae”) begin to full with red marrow. Eventually, the outer layers of spongy bone will be reconstructed into compact bone. • Intracartilaginous ossification: This process is responsible for most bone growth in the body. Intracartilaginous ossification is most readily apparent in long bones, which are composed of the diaphysis, or long central shaft, and the epiphysis, or ends of the bone. Intracartilaginous ossification begins at the diaphysis, when blood vessels penetrate the perichondrium (a fibrous membrane that covers the cartilage). Upon vascularization, the perichondruim is called the periosteum, and the cartilage forming cells (called chondrocytes) become osteoblasts. The osteoblasts secrete a ring of fibrous substance around the diaphysis, which subsequently becomes bone. As ossification becomes nearly completed in the epiphysis and the diaphysis, a ring of cartilage remains between the tow structures. This ring is called the “growth plate”. This plate serves to allow the long bones to continue to lengthen as your child grows.
A complex process? Yes, it is! But there is one important part you should definitely be familiar with. The epiphyseal growth plates are fully replaced by bone between the ages of 15 and 19, although the process may continue into the mid twenties. Young athletes who engage in repetitious, high - stress activities may experience injury to these growth plates, disrupting later growth. This growth plate is much weaker than the bone which surrounds it as well as the ligaments (up to 2 to 5 times weaker than ligaments and much more so than bones). Excessive trauma in the form of running as well as skills and situations in sports such as basketball, football and baseball involves potential damage to these growth plates. The key to preventing such damage is through proper conditioning. The inclusion of a supplemental resistance program assists in strengthening those joints that will be subject to trauma. the specific “loading” of the stress through resistance training also helps stimulate normal growth and development of the underlying bones. There is evidence that prolonged trauma to the joint may result in injury to the growth plates as well. Long distance runners and little league pitchers are particularly at risk due to repeated trauma to their growth plates. The key is variation and alliterating your child’s activities, which will change the load and stress on their skeletal system.
The Growth And Development Of Muscle Mass
At birth, your child’s muscle mass will make up approximately 25% of their weight. This percentage will nearly double by the time they reach their adult years. Due to increased testosterone production during puberty, boys experience a greater increase of muscle mass during this time as compared to girls. However, muscle mass in girls during and before puberty is still present. The increase in muscle mass appears to be a result of each individual muscle fiber becoming larger rather than an increase in the number of muscle fibers. As bones grow longer, the length of each muscle fiber also increases. Peak muscle mass is seen around the age of 18 to 25 in males and 16 to 20 in females. Continued muscle growth, of course is possible with the aid of resistance exercise and careful dietary practices which are designed to promote muscle growth. Now comes a topic of great debate among exercise scientists, as well as those who practice exercise science without the needed information to do so: “Is strength - training safe and effective for children?” This is a topic in which exercise scientists frequently disagree. Let’s look at the pro and con opinions of some noted exercise scientists (as well as our rebuttal):
Dr. Ken Cooper:
“I don’t recommend the use of weights or other apparatus by a child until at least age 10, and in most cases after age 12.”
Dr. Cooper is known as “The aerobic guru” and his advise is well sought - after. Apparently Dr. Cooper feels that weight - resistance exercise is potentially damaging to the growth plates found in the bones of kids. While this is true, this danger is also present when kids engage in long distance running. As we stated earlier, the key is variation of exercises, as well as proper supervision.
Thomas Kurz, M.Sc. (quoting a study by Sulmitsev, in which arch height was measured during lifts) :
“11 and 12 year olds can safely lift 30% of body weight; 13 and 14 year olds can use up to 50%; and 15 and 16 year olds can use up to 100%. Kurz says that the growth processes of the long bones is complete at age 17.”
Two thoughts on this quote. First, what kinds of lifts? For example, very few if any people can safely perform a biceps curl with 100% of their body weight, while at any age squatting 30, 50 or 100% of their weight is not dangerous. Second, “the growth processes of the long bones is complete at age 17” is a general statement. Bone growth can continue into the child’s twenties.
Charlie Francis (Olympic track and field coach):
“Another myth that comes to mind is that power - related work can not and should not be performed by children and pre - adolescents. The fact is that kids routinely do more power - related work such as throwing stones, climbing ropes and trees, jumping, and so forth. They do so safely. The key is that the child himself determines how much of this activity is safe, not a coach or parent.”
Here is a keen observation by perhaps one of the greatest coaches of all time! We would like to add that weight - resistance training be supervised by a certified fitness trainer or strength coach for any age group, is it is potentially dangerous for adults as well.
Jack Wilmore and David Costill:
“Generally, the youngster will adapt well to the same type of training routine used by the mature athlete. But training programs for children and adolescents should be designed specifically for each age group, keeping in mind the developmental factors associated with that age.”
Amen! But keep in mind that chronological age is not the only determinate of maturity. Furthermore, we would like to extend this advise to adults as well. Your program and that of your child should be specifically designed for the user.
Dr. Paul Ward (From The Encyclopedia of Weight Training):
“The results of the small amount of research that has been completed regarding the utilization of weight training in prepubescent and pubescent children have produced evidence that weight training for these ages is strongly indicated. This research evidence combined with empirical evidence plus the findings in a number of national physical fitness surveys that demonstrate the strong need for strength development in our your boys and girls, is compelling confirmation that weight training programs are not only safe and effective for prepubescent and pubescent children but must be vigorously pursued...”
Again, proper supervision and program design is the key.
Here is our stand on resistance - training for kids: When weight training programs are properly conceived, organized, and implemented and the proper equipment is available there is no reason to believe that injuries will occur or that the child will not benefit. The existing research evidence and empirical observations have shown that weight training is safe and effective at any age. The key to success of any resistance - training activity is the construction of a scientific program along with adequate supervision. With the proper equipment (meaning it is adaptable to their physical dimensions) and supervision, your child can begin to use reasonable resistance work at any age.