The Wolff’s Law

I’ve been studying biomechanics these few days, and learned another interesting topic about the bone response to stress.

Wolff’s Law, a widely known bone adaptation theory in the orthopedics, was developed by the German anatomist Julius Wolff in 1892:

The form of a bone being given, the bone elements place or displace themselves in the direction of functional forces and increase or decrease their mass to reflect the amount of the functional forces.

According to Wolff’s Law, bone grows in proportion to mechanical stress. A healthy living bone models and remodels in response to the mechanical stress it experiences so as to produce a minimal weight structure that is adapted to the stresses acted on it.

The changes in bone density, size and shape are the work of two specialized bone cells called osteoblasts and osteoclasts, which respectively form and resorb bone tissue. The bone remodeling occurs throughout life. During the process, resorption precedes formation, so as old bone tissue is replaced by new bone tissue. Remodeling can be in either “conservation mode” with no change in bone mass, or “disuse mode” with a net loss of bone mass characterized by an enlarged marrow cavity and thin cortex. The latter leads to osteoporosis, results from either excessive resorption or inadequate formation. The bone modeling occurs during growth and healing. Unlike remodeling, the osteoblasts predominate the activity (formation) with a net gain in bone mass.

Dynamic mechanical loading causes bones to deform or strain; the larger the loads, the greater the strain. When strain exceeds the remodeling threshold, bone remodeling occurs in conservation mode with balanced resorption and formation. When strain exceeds the higher modeling threshold, the bone modeling occurs, with bone density and mass increased. Disuse mode remodeling is triggered when strain stays below the remodeling threshold, induces a slow loss of bone.

A physically active individual tends to develop denser and more mineralized bones, particularly at the stressed sites. For example, a tennis player has a stronger and denser radius at the racquet-holding arm than the other arm due to the repetitive high stresses exerted on it. Likewise, a trained runner has an increased bone density at the lower extremity due to the high-impact of the running motion. Interesting to note that a competitive swimmer who spends a lot of time in the water however may have less dense bones than a sedentary individual as the buoyant force exerted on the body has counteracted the body weight (gravity).

The law also explains why astronauts suffer from a kind of bone-loss similar to osteoporosis after a long stay in space. Due to the microgravity, the floating human body undergoes a weightless and almost immobile condition. Since no weight is acted on the skeleton and the body do not have to fight the gravity to move about, the bone mass diminishes, hence the strength and the bone mineral density decrease. Bedridden patients and individuals who lead a sedentary or inactive lifestyle tend to have a decrease in bone mass too as a result of reduced mechanical stress and weightbearing activity. The bones become more susceptible to fractures.

In many traditional Okinawan karate-do and Chinese martial arts, body conditioning is crucial as part of the training routine to strengthen muscles and bones, as well as to elevate the pain threshold. Uechi-ryu karate-do emphasizes conditioning on knuckles, forearms, abdomen, tips of toes, dorsal feet, shins, thighs and calves by repetitively blocking and striking the areas to produce slight trauma to them. Other practices like rubbing, knuckle push-ups, rolling a stick on the shin are formulated for conditioning purpose as well. The principle founded by the ancient Chinese masters is the same as the Wolff’s law theory: the bones become denser and stronger after bearing a long period of dynamic mechanical loadings provided by the body conditioning, thus minimize the possible injuries caused by training and sparring.

However, if the applied mechanical loadings are beyond the power of (re)modeling, it leads to fatigue or stress fractures. This problem is very common to athletes who run and jump on the hard surfaces such as distance runners, basketball players, and ballet dancers. The most common affected bones are femur, tibia, navicular and metatarsals. Similarly, martial artists who overtrain themselves may encounter the same problem, when the stresses applied to the bone exceed the bone’s ability to adapt. Therefore it is important for martial artists to ensure the training is done within safe bounds.

Corpus Luteum

While responding to a sparring injuries topic in a martial art forum, I learn about this corpus luteum and I find it an interesting knowledge, so I decide to blog it for better memory, and maybe can share with some readers?

In the menstrual cycle of humans and great apes, the corpus luteum (yellow body in Latin), a temporary endocrine structure, is formed by the remainder of the follicle after the ovulation. Its main function is to secrete the progesterone to maintain the pregnancy if fertilization occurs.

Basically a menstrual cycle of a female human (estrous cycle of animals) can be divided into 4 main phases, which are the menstruation, the follicular phase, the ovulation and the luteal phase. During the follicular phase (preovulation), the secretion of FSH (follicle-stimulating hormone) stimulates the development of several follicles in the ovary. Each follicle contains a oocyte or ovum but normally only one ovum is mature enough to be released during the ovulation. The luteal phase is the second phase of the menstrual cycle and is also known as the post-ovulation. Averagely it starts on the 14th day of a normal 28-days menstrual cycle and lasts for 10 to 14 days. During this phase, the progesterone produced helps to thicken the lining of the uterus or endometrium for implantation and is essential to support a healthy pregnancy.

When the egg is not fertilized, the corpus luteum starts to decay and eventually the production of progesterone stops. The lining of the uterus is then shed off the uterus wall due to the drop of the progesterone level and expelled through vagina during the menstruation.

When the egg is fertilized, the embryo secretes the HCG (human chorionic gonadotropin) to signal the corpus luteum to continue producing the progesterone for maintaining the thick lining of the uterus. The progesterone production by corpus luteum lasts for 10 weeks after ovulation, and eventually the placenta takes over the job to produce progesterone through the end of the pregnancy.

The decay of the corpus luteum leads to the formation of corpus albicans (white body in Latin), which remain as the fibrous scar tissues in the ovary.

Most females know the harms caused by the intense exercise during menstruation but only a little of them are aware of this luteal phase. During the luteal phase, intense exercises such as running, weight-lifting, and other abdominal exercises should be avoided as they instantly rise the abdominal pressure. High abdominal pressure is likely to cause the rupture of the mature corpus luteum. Occasionally, the ruptured site may bleed, resulting in abdominal pain or some signs of hemorrhage. If the ruptured site is capillary-rich, it may lead to massive internal hemorrhage, and cause the hemorrhagic shock or even death; anyway, this kind of case rarely happens.

In my opinion, this is also a potential injury for the female karate-do practitioners, who train for jiyu kumite (free sparring) but so many of them are not aware of it. The impact of a forceful punch or kick in the abdomen instantly rises the abdominal pressure, leading to the rupture of the corpus luteum.

I hope more female sports and martial art enthusiasts will realize the fact and take necessary precautions. After all, prevention is better than cure.

You may find out more here about other potential injuries obtained from the karate kumite training.

Going Back Home

In another 2 hours I’m leaving Malacca for my home sweet home – Penang! Oh I miss home so much! It’d been 8 months since my last return, wonder how things change over there, I just can’t wait to step on my homeland soon.

Anyway, I am really sick of the long and boring journey to Penang. The so-called “express” bus but actually wastes a long time waiting at the Pudu Bus Terminal just to fill the bus to capacity. That’s one thing I hate the most. There are many bus companies claim to offer non-stop journey from Malacca directly to Penang, but most of the time when they don’t meet the targeted quantity, they will stop at the PBT, looking for passengers for more gain, sometimes it takes more than an hour to do so! So a 6-hour journey actually takes 8 hours or more to complete, pretty frustrating when you’re so eager to reach the destination.

I expect to spend even longer time on the bus later, there are most likely traffic jams along the journey the day before Raya celebration, sigh… I’m taking a book to read, hopefully I can concentrate on it. I do pray for a safe journey, as the accident rate on highway is pretty high during the Raya celebration, when many people are driving back their kampung (home) for reunion and celebration.

Here Comes to The End

Finally, the exams come to the end, that’s the moment I’ve been longing for the past few weeks, but… Why don’t I feel any excitement?

When everyone was laughing and chit-chatting outside the hall, I quickly grabbed my belongings and wanted to reach my room as soon as possible. My room seems to have some kind of attraction; it’s not well-decorated, nothing much in the room except the mess, but probably it’s the only corner where my true self reveals. It remains silent even with my presence, the street noise outside the room contrasts with the silence even more. At this moment, I just hope to hear the sound I want, when will it come?

Take a deep breath, calm the mind…

Back to the exams topic. What a relief after much of last-minute effort paid, after nights of midnight oil burnt. I have confidence to score in 3 papers, (another one is totally screwed up ) and they are really answered based on my understanding of them, not memorizing (maybe just a little part).

I am going to take a shower and have a rest, I hope it can be a good one.