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Bone adapts to the loads it carries. In a 1977 study of professional tennis players, the hard outer wall of the upper-arm bone in the playing arm was about 35 per cent thicker in men, and 28 per cent thicker in women, than in the other arm.

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The 1977 study, by H. H. Jones and colleagues, compared X-rays of both arms in the same players, so each person served as their own comparison. Later scans found the same gap in bone mineral content, a measure of how much bone there is. A 1995 study of 105 Finnish national-level tennis and squash players, all women, found that the gain was about twice as large in those who had started playing by the time of their first period as in those who started later, which suggests bone responds most while the skeleton is still growing. The principle is often called Wolff's law, after the German surgeon Julius Wolff, who argued in the 1890s that bone reshapes itself to match the forces on it. Cells called osteoblasts build new bone where loads are high, while osteoclasts remove it where it is not needed.

Türkçe oku
Kemik, üzerine binen yüke göre biçimlenir. Profesyonel tenisçilerle 1977'de yapılan bir çalışmada, raket tutan koldaki pazı kemiğinin sert dış tabakası öbür koldakine göre erkeklerde yaklaşık yüzde 35, kadınlarda yüzde 28 daha kalın çıktı.

1977'deki çalışmayı H. H. Jones ve ekibi yaptı: Aynı oyuncuların iki kolunun röntgenlerini karşılaştırdılar; böylece her oyuncu kendi kendisiyle kıyaslanmış oldu. Sonraki taramalar aynı farkı, kemik miktarının bir ölçüsü olan kemik mineral içeriğinde de buldu. Finlandiya'da ulusal düzeyde oynayan 105 kadın tenis ve squash oyuncusuyla 1995'te yapılan bir araştırmaya göre, ilk adetlerini görene kadar oynamaya başlamış olanlarda kemikteki kazanç, daha sonra başlayanlarınkinin yaklaşık iki katıydı. Bu da kemiğin, iskelet hâlâ büyürken yüke en güçlü tepkiyi verdiğini düşündürüyor. Bu ilkeye çoğu zaman Wolff yasası denir: Alman cerrah Julius Wolff 1890'larda kemiğin, üzerine binen kuvvetlere göre kendini yeniden biçimlendirdiğini savunmuştu. Yükün yoğun olduğu yerde osteoblast denen hücreler yeni kemik yapar, gerek olmayan yerde ise osteoklastlar kemiği yıkıp ortadan kaldırır.

Sources and further reading

Background reading: Bone remodeling
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