Speaking for myself, and I’d guess the same would go for many others, when talking about lifting weights, I tend to focus on the changes taking place in the musculature. However, there are other changes occurring in the body as well that are directly due to weightlifting. For instance, as I stated in the most recent post, weightlifting can cause up to 70 genes to be re-coded.
One major non-musculature area affected by working out with weights is the skeleton– and thank God, too, or else we’d soon snap ourselves in two.
When a bone experiences, on a regular basis, strains exceeding about one-tenth of the maximum amount of force that it can take before fracturing, bone augmentation will commence. Our authors tell us that in response to weight bearing exercise, osteoblasts “migrate to the bone surface [the periosteum] and begin bone modeling” by synthesizing proteins, mostly of the collagen variety. These collagen molecules are deposited in the spaces between the bone cells already present to increase the bone’s strength. The collagen deposits collectively form a “bone matrix” which will eventually become mineralized as calcium phosphate crystals. In this way, the bone thickens, increasing its sturdiness by allowing forces to be distributed over a larger surface area.
Besides the stain of bearing weights, bigger muscles can also put more stress on bone since they will be able to contract all the more forcefully. Thus, “exercise that stimulates muscle hypertrophy [growth] and strength gains appears to stimulate bone growth.”
Again, as with muscle growth, it is important in forming strong bones not to do the same few exercises over and over. This is because the collagen fibers of the bone matrix will orient so as to “conform to the lines of stress experienced.” That’s why it’s vital to vary both the distribution and the direction of forces.
Bone growth is stimulated not just by load size but also by… the speed of the lift, the number of reps attempted, and the direction of the forces.
Besides muscle and bone growth, weightlifting also stimulates the strengthening of connective tissue such as tendons.
The main component of connective tissue is collagen. In tendons and ligaments, collagen-bundles form together longitudinally. In cartilage and bone, collagen arranges itself in layers of differently oriented sheets. The true strength of collagen, our authors state, comes from its ability to form crosslinks between adjacent collagen molecules within a collagen bundle.
Concerns have been expressed by some people that vigorous or heavy exercise which puts repeated stress on joints could cause joint decay. However, our authors state that research indicates that “strenuous exercise does NOT appear to cause degenerative joint disease.”
One of the interesting facts about cartilage is that cartilage has no blood supply. Thus, to get the oxygen and other nutrients that it needs (to keep from dying), it must depend on diffusion of these things from the synovial fluid encapsulated in joints. Our authors point-out that this is why torn cartilage is such a bitch to heal (I think they may have worded that differently).